| Full Text |
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
"ENCODING DEVICE, DECODING DEVICE, AND METHOD
THEREOF"
MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD a Japanese company of 1006, Oaza Kadoma, Kadoma-shi, Osaka 571-8501, Japan
The following specification particularly describes the invention and the manner in which it is to be performed.
2F05047-PCT
2
DESCRIPTION
ENCODING DEVICE, DECODING DEVICE, AND METHOD THEREOF
5 Technical Field
[0001] The present invention relates to a coding apparatus and decoding apparatus that codes/decodes a speech signal, audio signal and the like, and methods thereof.
10 Background Art
[0002] A speech coding technology that compresses a speech signal at a low bit rate is important for efficiently using a radio wave etc . in mobile communication . Further, in recent years, expectation for improvement of quality
15 of communication speech has been increased, and it is desired to implement communication services with high realistic quality. Here, realistic quality means the sound environment surrounding the speaker (for example, BGM) , and it is preferable that signals other than a speech
20 signal such as audio can be coded with high quality. [0003] There are schemes such as G726 and G729 defined in ITU-T (International Telecommunication Union Telecommunication Standardization Sector) for speech coding of coding speech signals . In these schemes , coding
25 is carried out at 8kbit/s to 32kbit/s targeting a narrow band signal (300Hz to 3.4kHz). Though these schemes are capable of coding at a low bit rate, since the targeted
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narrow band signal is narrow up to a maximum of 3.4kHz, this quality tends to lack realistic quality.
[0004] Further, in ITU-T and 3GPP (The 3rd Generation Partnership Project) , there are standard schemes of speech
5 coding with signal band of 50Hz to 7kHz (G.722, G. 722.1, AMR-WB, and the like). Though these schemes are capable of coding a wideband speech signal at a bit rate of 6 . 6kbit/s to 64kbit/s, it is necessary to increase bit rates relatively for coding wideband speech with high quality.
10 From the viewpoint of speech quality, wideband speech is high quality compared to narrow band speech, but it is difficult to say that this is sufficient for services requiring high realistic quality.
[0005] Typically, when maximum frequency of a signal
15 is 10 to 15kHz, realistic quality equivalent to FM radio quality can be obtained, and, when maximum frequency is 20kHz, quality equivalent to CD can be obtained. Audio coding such as a layer 3 scheme or AAC scheme defined by MPEG (Moving Picture Expert Group) is suitable for
20 a signal having such band. However, when these audio coding schemes are applied as a coding scheme for speech communication, it is necessary to set a high bit rate in order to code speech with good quality. There are also other problems such as a problem that a coding delay
25 becomes substantial.
[0.006] As a method of coding a signal with wide frequency band at a low bitrate with high quality, there is a technology
2F05047-PCT 4
for reducing overall bit rate by dividing the spectrum of an input signal into low frequency band and high frequency band to obtain two spectrums, duplicating the low frequency band spectrum and substituting the low frequency band
5 spectrum for the high frequency band spectrum (using the low frequency band spectrum in place of the high frequency band spectrum) (for example, refer to Patent Document 1). In this technology, a large number of bits are allocated for coding of the low frequency band spectrum, and coding
10 is performed with high quality, while on the other hand, the high frequency band spectrum duplicates the coded low frequency band spectrum as basic processing, and coding is performed with a small number of bits.
[0007] Further, as a technology similar to this technology,
15 there are a technology of improving quality by performing approximation on band where coded bits cannot be sufficiently allocated using other predetermined partial band spectrum information (for example, refer to Patent Document2), and a technology of duplicating a low frequency
20 band spectrum of a narrow band signal as a high frequency band spectrum as basic processing .in order to extend band of a narrow band signal to a wideband signal without additional information (for example, refer to Patent Document 3).
25 [0008] In either technology, another band spectrum is duplicated for band where it is wished to compensate a spectrum, and after gain is adjusted to smooth the spectrum
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envelope, this duplicated spectrum is inserted.
Patent Document 1: Japanese Patent Publication Laid-open
No.2001-521648.
5 Patent Document 2 : Japanese Patent Application Laid- open
No.HEI9-153811.
Patent Document 3 : Japanese Patent Application Laid- open
No.HEI9-90992.
10 Disclosure of Invention
Problems to be Solved by the Invention
[0009] However, in a spectrum of a speech signal or audio signal, the phenomena can be often seen where the dynamic range (ratio between the maximum value and minimum value
15 of the absolute value of the spectral amplitude (absolute amplitude)) of the low frequency band spectrum is larger than the dynamic range of the high frequency band spectrum. FIG.l illustrates this phenomena and shows an example of a spectrum for an audio signal. This spectrum is a
20 log spectrum in the case where an audio signal with sampling frequency of 32kHz is subjected to frequency analysis for 30ms.
[0010] As shown in this drawing, a low frequency band spectrum with frequency of 0 to 8000Hz has strong peak 25 performance (a large number of sharp peaks exist) , and the dynamic range of the spectrum at this band becomes large. On the other hand, the dynamic range of the high
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frequency band spectrum with frequency of 8000 to 15000Hz becomes small. With the conventional method of duplicating the low frequency band spectrum as a high frequency band spectrum, even if gain adjustment of the
5 high frequency band spectrum is performed on a signal
having such a spectrum characteristic, unnecessary peak
shapes appear in the high frequency band spectrum as shown
below.
[0011] FIG.2 shows the entire band spectrum in the case
10 where a high frequency band spectrum (10000 to 16000Hz) is obtained by duplicating a low frequency band spectrum (1000to7000Hz) of the spectrum shown in FIG.l and adjusting energy.
[0012] When the above - described processing is carried
15 out, as shown in this drawing, unnecessary peak shapes appear in band Rl of 10000Hz or above. These peaks are not found in the original high frequency band spectrum. In a decoded signal obtained by converting this spectrum to a time domain, a problem arises that noise that sounds
20 like a bell ringing occurs and the subjective quality therefore deteriorates. In this way, with technology where a. spectrum of another band is substituted for a spectrum of given band, it is necessary to appropriately adjust the dynamic range of the inserted spectrum.
25 [0013] It is therefore an object of the present invention to provide a coding apparatus, decoding apparatus, and methods for these apparatuses capable of appropriately
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adjusting dynamic range of an inserted spectrum and increasing the subjective quality of the decoded signal in a technology for substituting (replacing) a spectrum of another band for a spectrum of given band.
5
Means for Solving the Problem
[0014] A coding apparatus of the present invention adopts a configuration having: a coding section that codes a high frequency band spectrum of an input signal; and a
10 limiting section that generates a second low frequency band spectrum in which amplitude of a first low frequency band spectrum that is a decoded signal of a coded low frequency band spectrum of the inputted signal is uniformly limited, wherein the coding section codes the high
15 frequency band spectrum based on the second low frequency band spectrum.
[0015] A decoding apparatus of the present invention adopts a configuration having: a converting section that generates a first low frequency band spectrum in which
20 a decoded signal of code of a low frequency band spectrum included in code generated in the coding apparatus is converted to a signal of a frequency domain; a decoding section that decodes code of a high frequency band spectrum included in the code generated in the coding apparatus;
25 and a limiting section that generates a second low frequency band spectrum in which amplitude of the first low frequency band spectrum is uniformly limited according to spectrum
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modification information included in the code generated in the coding apparatus, wherein, the decoding section decodes the high frequency band spectrum based on the second low frequency band spectrum.
5 [0016] Further, the decoding apparatus of the present invention adopts a configuration having: a converting section th at generates a first low frequency band spectrum in which a decoded signal of code of a low frequency band spectrum generated in the coding apparatus is converted
10 to a signal of a frequency domain; a decoding section that decodes code of a high frequency band spectrum included in the code generated in the coding apparatus, and a limiting section that generates a second low frequency band spectrum in which amplitude of the first low frequency band spectrum
15 is uniformly limited, wherein: the limiting section estimates information about the way of limiting based on the first low frequency band spectrum and generates the second low frequency band spectrum using the estimated information; and the decoding section decodes the high
20 frequency band spectrum based on the second low frequency band spectrum.
Advantageous Effect of the Invention
[0017] According to the present invention,in a technology
25 of substituting a spectrum of another band for a spectrum of given band, it is possible to appropriately adjust the dynamic range of the inserted spectrum and improve
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the subjective quality of the decoded signal.
Brief Description of the Drawings
[0018]
5 FIG.l shows an example of an audio signal spectrum; FIG.2 shows the entire band spectrum in the case of obtaining a high frequency band spectrum by duplicating a low frequency band spectrum and adjusting energy;
FIG.3 is a block diagram showing the main
10 configuration of the coding apparatus according to Embodiment 1;
FIG.4 is a block diagram showing the main configuration of the internal part of a spectrum coding section according to Embodiment 1;
15 FIG.5 is a block diagram showing the main configuration of the internal part of a spectrum modification section according to Embodiment 1;
FIG.6 is a block diagram showing the main configuration of the internal part of a modification
20 section according to Embodiment 1;
FIG.7 shows an example of a modified spectrum obtained by the modification section according to Embodiment 1.
FIG.8 is a block diagram showing a configuration
of another variation of the modification sect ion according
25 to Embodiment 1 ;
FIG.9 is a block diagram showing the main configuration of a hierarchical decoding apparatus
2F05047-PCT 10
according to Embodiment 1 ;
FIG.10 is a block diagram showing the main configuration of the internal part of a spectrum decoding section according to Embodiment 1;
5 FIG.11 is a block diagram illustrating a spectrum coding section according to Embodiment 2;
FIG.12 is a block diagram showing a configuration of another variation of the spectrum coding section according to Embodiment 2 ,-
10 FIG.13 is a block diagram showing the main configuration of a spectrum decoding section according to Embodiment 2 ;
FIG. 14 is a block diagram showing the main
configuration of a spectrum coding section according to
15 Embodiment 3;
FIG.15 illustrates a modification information estimating section according to Embodiment 3;
FIG.16 is a block diagram showing the main configuration of the modification section according to
20 Embodiment 3;
FIG.17 is a block diagram showing the main configuration of a spectrum decoding section according to Embodiment 3;
FIG.18 is a block diagram showing the main
25 configuration of a hierarchical coding apparatus according to Embodiment 4;
FIG.19 is a block diagram showing the main
2F05047-PCT 11
configuration of a spectrum coding section according to Embodiment 4;
FIG.20 is a block diagram showing the main configuration of a hierarchical decoding apparatus
5 according to Embodiment 4 ;
FIG.21 is a block diagram showing the main configuration of a spectrum decoding section according to Embodiment 4;
FIG.22 is a block diagram showing the main
10 configuration of a spectrum coding section according to Embodiment 5;
FIG.23 is a block diagram showing the main configuration of a modification information estimating section according to Embodiment 5;
15 FIG.24 is a block diagram showing the main configuration of a spectrum decoding section according to Embodiment 5;
FIG.25 illustrates a spectrum modification method according to Embodiment 6;
20 FIG.26 is a block diagram showing the main configuration of internal part of a spectrum modification section according to Embodiment 6;
FIG.27 illustrates a method for generating a modified spectrum;
25 FIG.28 illustrates a method for generating a modified spectrum; and
FIG.29 is a block diagram showing the main
2F05047-PCT 12
configuration of the internal part of a spectrum modification section according to Embodiment 6.
Best Mode for Carrying Out the Invention
5 [0019] Embodiments of the present invention explained below in detail with reference accompanying drawings.
[0020] (Embodiment 1)
10 FIG.3 is a block diagram showing the main configuration of hierarchical coding apparatus 100 according to Embodiment 1 of the present invention. Here , a case will be explained as an example where coding information has a hierarchical structure made up of a
15 plurality of layers, that is, hierarchical coding (scalable coding) is performed.
[0021] Each part of hierarchical coding apparatus 100 carries out the following operation in accordance with input of the signal.
20 [0022] Down-sampling section 10 1 generates a signal with a low sampling rate from the input signal and supplies this signal to first layer coding section 102. First layer coding section 102 codes the signal outputted from down-sampling section 101. Coded code obtained at first
25 layer coding section 102 is supplied to multiplex section 103 and to first layer decoding section 104. First layer decoding section 104 then generates first layer decoding
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signal SI from the coded code outputted from first layer coding section 102.
[0023] On the other hand, delay section 105 gives a delay of a predetermined length to the input signal. This delay
5 is for correcting a time delay occurring at down-sampling section 101, first layer coding section 102 and first layer decoding section 104. Spectrum coding section 106 performs spectrum coding on input signal S2 delayed by a predetermined time and outputted from delay section
10 105, using first layer decoding signal SI generated at first layer decoding section 104, and outputs the generated coded code to multiplex section 103.
[0024] Multiplex section 103 then multiplexes the coded code obtained at first layer coding section 102 with the
15 coded code obtained at spectrum coding section 106 and outputs the result to outside of coding apparatus 100 as output coded code.
[0025] FIG.4 is a block diagram showing the main configuration of the internal part of the above-de scribed
20 spectrum coding section 106.
[0026] This spectrum coding section 106 is mainly configured with frequency domain converting section 111, spectrum modification section 112, frequency domain converting section 113, extension frequency band spectrum
25 coding section 114 and multiplex section 115.
[0027] Spectrum coding section 106 receives first, signal Sl with valid signal band of O
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from first layer decoding section 104, and second signal S2 with valid signal band of 0
5 a spectrum with band of 0
[0028] Frequency domain converting section 111 performs frequency conversion on inputted first signal SI and calculates first spectrum S1 (k) that is a low frequency
10 band spectrum. On the other hand, frequency domain converting section 113 performs frequency conversion on inputted second signal S2 , and calculates wideband second spectrum S2 (k) . Here, Discrete Fourier Transform (DFT) , Discrete Cosine Transform (DCT) , Modified Discrete Cosine
15 Transform (MDCT) , or the like, is applied as the method of frequency conversion. Further, Sl(k) is a spectrum with frequency k of the first spectrum, and S2(k) is a spectrum with frequency k of the second spectrum.
[0029] Spectrum modification section 112 investigates
20 a way of modifying so as to obtain an appropriate dynamic range by changing the dynamic range of the first spectrum by variously modifying first spectrum S1(k). Information about this modification (modification information) is coded and supplied to multiplex section 115. This spectrum
25 modification processing is described in detail later. Further, spectrum modification section 112 outputs first spectrum S1(k) having an appropriate dynamic range to
2F05047-PCT 15
extension frequency band spectrum coding section 114. [0030] Extension frequency band spectrum coding section 114 estimates a spectrum (extension frequency, band spectrum) which should be included in high frequency band
5 (FL
10 spectrum after modification SI' (k) .
[0031] Multiplex section 115 then multiplexes and outputs coded code of the modification information outputted from spectrum modification section 112 and coded code of estimation information about the extension frequency band
15 spectrum outputted from extension frequency band spectrum coding section 114.
[0032] FIG.5 is a block diagram showing the main configuration of internal part of the above-described spectrum modification section 112.
20 [0033] Spectrum modification section 112 applies the modification so that the dynamic range of first spectrum Sl(k) becomes the closest to the dynamic range of the high frequency band spectrum FL
25 coded and outputted.
[0034] Buffer 121 temporarily stores the inputted first spectrum S1(k), and supplies first spectrum S1(k) to
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modification section 122 as necessary. [0 03 5] Modification section 12 2 then variously modifies first spectrum S1(k) in accordance with the procedure described below so as to generate modified first spectrum
5 S1’ (j , k) , and this is supplied to subband energy calculating section 123. Here, j is an index for identifying each modification processing.
[0036] Subband energy calculating section 123 then divides the frequency band of modified first spectrum
10 S ‘ (j, k) into a plurality of subbands , and obtains subband energy (subband energy) of a predetermined range. For example, when a range for obtaining subband energy is determined as FlL
15 by the following (equation 1).
BWS=(F1H-F1L+1)/N (Equation 1)
As a result, minimum frequency FlL(n) of the nth
20 subband and maximum frequency FlH(n) are expressed respectively by (equation 2) and (equation 3).
F1L(n) =FlL + n BWS (Equation 2)
25 F1H(n)=F1L+(n+1)BWS-1 (Equation 3)
where n is a value from 0 to N-l.
2F05047-PCT 17
At this time, subband energy P1 ( j, n) is calculated as shown in the following (Equation 4) .
Further, this may also be obtained as an average value of a spectrum included in the subband as shown in (Equation 5) below.
Subband energy PI (j , n) obtained in this way is then supplied to variance calculating section 124.
[0037] Variance calculating section 124 calculates
15 variance al2(j) in accordance with (equation 6) below in order to indicate the degree of variation of subband energy P1(j , n) .
Here, Plmean(j)indicates the average value of subband energy Pl(j, n) and is calculated from (Equation
5 Variance ol2(j ) indicating the degree of variation of subband energy in the modification information j calculated in this way is then supplied to search section 125 .
[0038] As with a series of processing carried out at
10 subband energy calculating section 123 and variance calculating section 124, subband energy calculating section 126 and variance calculating section 12 7 calculate variance o22 indicating the degree of variation of subband energy for the inputted second spectrum S2(k). However,
15 the processing of subband energy calculating section 126 and variance calculating section 12 7 differ from the above processing with regard to the following points. Namely, the predetermined range for calculating subband energy of second spectrum S2(k)is determined as F2L
20 since it is necessary for the dynamic range of the first spectrum to be close to the dynamic range of the-high frequency band spectrum of the second spectrum, F2L is set so as to satisfy the conditions of FL
25 second spectrum to correspond to the number of subbands
2F05047-PCT 19
N of the first spectrum. However, the number of subbands of the second spectrum is set so that the subband width of the first spectrum substantially corresponds to the subband width of the second spectrum.
5 [0039] Search section 125 determines variance ol2(j) of the subband of the first spectrum for the case where variance al2(j) of the subband of the first spectrum is the closet to variance a22 of the subband of the second spectrum, by searching. Specifically, search section 125
10 calculates variance ol2(j) of the subband of the first spectrum for all the modification candidates of 0
15 modification information jopt), and outputs jopt to outside of spectrum modification section 112 and modification section 128.
[0040] Modification section 128 generates a modified first spectrum S' (jopt, k) corresponding to this optimum
20 modification information j opt, and outputs this to outside of spectrum modification section 112. Optimum modification information j opt is transmitted to multiplex section 115, and modified first spectrum S1' (jopt, k) is transmitted to extension frequency band spectrum coding
25 section 114.
[0041] FIG.6 is a block diagram showing the main configuration of the internal part of the above-described
2F05047-PCT 20
modification section 122. The configuration of the internal part of modification section 128 is basically the same as modification section 122.
0042] Positive/negative sign extracting section 131
5 obtains coding information sign(k) for each subband of
the first spectrum, and outputs the result to
positive/negative sign assigning section 134.
[0043] Absolute value calculating section 13 2 calculates
an absolute value of amplitude for each subband of the
10 first spectrum and supplies this value to exponent value calculating section 133.
[0044] Exponent variable table 135 records exponent variable a(0) to be used in modification of the first spectrum. A value corresponding to j out of the variables
15 included in this table is outputted from exponent variable
table 135. Specifically, in exponent variable table 135 ,
candidates for exponent variables, for example, four
exponent variables a(j)={l.0, 0.8, 0.6, 0.4}are recorded,
and one exponent variable α ( j ) is selected based on index
20 indicated by search section 12 5 , and supplied to exponent value calculating section 133.
[0045] Exponent value calculating section 13 3 calculates
an exponent value of a spectrum (absolute value) outputted
from absolute value calculating section 132, that is,
25 a value in which an absolute value of amplitude for each subband is raised to the power of α( . ) using the exponent variable outputted from exponent variable table 135.
2F05047-PCT 21
[0046] Positive/negative sign assigning section 134 assigns coded information sign (k) obtained in advance at positive/negative sign extracting section 131 to the exponent value outputted from exponent value calculating
5 section 133, and outputs the result as modified first spectrum SI'(j, k).
[0047] Modified first spectrum SI' ( j , k) outputted from modification sect ion 12 2 is expressed as shown in ( Equation 8) below.
ST(j,k) = sign(k).\S1(k)\a(j) (Equation 8)
[0048] FIG.7 shows an example of a modified spectrum obtained by the modification section 12 2 (or modification
15 section 128).
[0049] Here, a case of exponent variable a(j) ={l.0, 0.6, 0.2} is explained as an example. Further, here, in order to simplify comparison of each spectrum, spectrum S71 for the case of a(j) = 1.0 is shifted up by 40dB,
20 and spectrum S72 for the case of a(j) = 0.6 is shifted up by just 20dB. From this drawing, it can be understood that it is possible to change the dynamic range of the spectrum according to exponent variable α(j).
[0050] As described above, according to the coding
25 apparatus (spectrum coding section 106) of this embodiment, the high frequency band FL
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obtained from a second signal 0
5 modification to the first spectrum without using the first spectrum as is. At this time, information (modification information) indicating how the modification has been performed is coded together and transmitted to the decoding side.
10 [0051] The specific method of applying modification to the first spectrum is to divide the first spectrum into subbands, obtain average of absolute amplitude of the spectrum (subband average amplitude) included in each subband, and modify the first spectrum so that variance
15 obtained by performing statistical processing on these subband average amplitudes becomes the closet to variance of average amplitude of the subband obtained in the similar way from the spectrum of the high frequency band of the second spectrum. Namely, the first spectrum is modified
20 so that the average deviation of the absolute amplitude of the first spectrum and the average deviation of the absolute amplitude of the high frequency band spectrum of the second spectrum have the similar value. Further, modification information indicating this specific
25 modification method is coded. It is also possible to use energy of the spectrum included in each subband instead of the average amplitude of the subband.
2F05047-PCT 23
[0052] Further detail of the specific modification method is to raise the spectrum of the first spectrum to the power of a (α
5 Information about used a is transmitted to the decoding side .
[0053] By adopting the above - described configuration, even in the case where the dynamic range of the first spectrum is substantially different from the dynamic range of the high frequency band of the second spectrum, it is possible to appropriately adjust the dynamic range
10 of the estimated spectrum and improve the subjective quality of the decoded signal.
[0054] Further, in the above configuration, by raising
15 the entire first spectrum to the power of a (α
20 of a predetermined value or more, the spectrum may be discontinuous and generate a strange noise. However, by adopting the above - described configuration, it is possible to keep the spectrum smooth and prevent the occurrence of a strange noise.
25 [0055] In this embodiment, a case has been described as an example where variance is used as an index indicating the degree of variation (deviation) of the absolute
2F05047-PCT 24
amplitude of the spectrum, but this is by no means limiting, and, another index such as standard deviation, for example, may be also applied.
[0056] In this embodiment, a case has been described
5 as an example where an exponential function is used in modification section 122 (or modification section 128) within coding apparatus 100, but it is also possible to use the method shown below.
[0057] FIG.8 is a block diagram showing a configuration
10 of another variation (modification section 122a) of the modification section. Components that are identical with modification section 122 (or modification section 128) will be assigned the same reference numerals without further explanations.
15 [0058] At the above - described modification section 122 (or modification section 128) , the amount of calculation tends to increase since the exponential function is used. Therefore, increase of the amount of calculation is avoided by changing the dynamic range of the spectrum without
20 using the exponential function.
[0059] Absolute value calculating section 132 calculates an absolute value for each spectrum of inputted first spectrum Sl(k) and outputs the result to average value calculating section 142 and modified spectrum calculating
25 section 143. Average value calculating section 142 calculates average value S1 mean of the absolute value of the spectrum in accordance with the following (Equation
2F05047-PCT
25
9).
(Equation 9)
5 [0060] Candidates for multipliers for use at modified spectrum calculating section 143 are recorded in multiplier table 144, and one multiplier is selected based on the index indicated by search section 125 and is outputted to modified spectrum calculating section 143. Here, it
10 is assumed that four candidates for multipliers g(j) 1.0 , 0.9, 0.8, 0.7 are recorded in the multiplier table . [0061] Modified spectrum calculating section 143 calculates the absolute value of modified spectrum S1' (k) in accordance with the following (Equation 10) using the
15 absolute value of the first spectrum outputted from absolute value calculating section 132 and multiplier g(j) outputted from multiplier table 144, and outputs the result to positive/negative sign assigning section 134 .
(Equation 10)
[0062] Positive/negative sign assigning section 134 assigns coded information sign(k) obtained at
25 positive/negative sign extracting section 131 to the absolute value of modified spectrum S1' (k) outputted from
2F05047-PCT 26
modified spectrum calculating section 14 3, and generates and outputs final modified spectrum SI' (k) expressed by the following (Equation 11).
5 (Equation 11)
[0063] Further, in this embodiment, a case has been described as an example where a modification section is provided with positive/negative sign extracting section,
10 absolute value calculating section, and positive/negative sign assigning section, but these configurations are not necessary when the inputted spectrum is always positive. [0064] Next, the configuration of hierarchical decoding apparatus 150 capable of decoding the coded code generated
15 at coding apparatus 100 will be described in detail. [0065] FIG.9 is a block diagram showing the main configuration of hierarchical decoding apparatus 150 according to this embodiment.
[0066] Separating section 151 implements separating
20 processing on the inputted coded code and generates coded code S51 for first layer decoding section 152 and coded code S52 for spectrum decoding section 153 . First layer decoding section 152 decodes a decoded signal with signal band of 0
25 section 151, and this decoded signal S53 is supplied to spectrum decoding section 153. Further, the output of first layer decoding section 152 is also connected to
2F05047-PCT 27
an output terminal of decoding apparatus 150. By this means, when it is necessary to output the first layer decoded signal generated at first layer decoding section 152, the signal can be outputted via this output terminal .
5 [0067] Spectrum decoding section 153 is provided with coded code S52 separated at separating section 151 and first layer decoding signal S53 outputted from first layer decoding section 152. Spectrum decoding section 153 carries out the following spectrum decoding, and generates
10 and outputs a wideband decoding signal with signal band of 0
15 [0068] FIG.10 is a block diagram showing the main configuration of the internal part of spectrum decoding section 153.
[0069] Coded code S52 and first layer decoded signal S53 (a first signal with valid frequency band of 0
20 are inputted to spectrum decoding section 153.
[0070] Separating section 161 then separates modification information and extension frequency band spectrum coded information generated at spectrum modification section 112 of the above-described coding
25 side, from inputted coded code S52, and outputs modification information to modification section 162 and extension frequency band spectrum coded information to
2F05047-PCT 28
extension frequency band spectrum generating section 16 3. [0071] Frequency domain converting section 164 carries out frequency conversion on first layer decoding signal S53 that is an inputted time domain signal and calculates
5 first spectrum S1 (k) . Discrete Fourier Transform (DFT) , Discrete Cosine Transform (DCT) , Modified Discrete Cosine Transform (MDCT), or the like is used as the method of frequency conversion.
[0072] Modification section 162 applies modification
10 to first spectrum Sl(k) supplied from frequency domain converting section 164 based on the modification information supplied from separating section 161 and generates modified first spectrum S1' (k) . The internal configuration of modification section 162 is the same
15 as modification section 122 (refer to FIG . 6 ) of the coding side already described, and explanations will be therefore omitted.
[0073] Extension frequency band spectrum generating section 163 generates estimationvalueS2' ' (k) for a second
20 spectrum which should be included in extension frequency band of FL
25 [0074] Spectrum configuration section 165 then integrates first spectrum Sl(k) supplied from frequency domain converting section 164 and estimation value S2 ' ' (k)
2F05047-PCT 29
of the second spectrum supplied from extension frequency band spectrum generating section 163, and generates decoded spectrum S3 (k) . This decoded spectrum S3 (k) is expressed by the following (Equation 12).
This decodedspectrumS3 (k) is supplied to time domain converting section 166.
10 [0075] After decoded spectrum S3(k) is converted to a signal of the time domain, time domain converting section 166 carries out appropriate processing such as windowing and overlapped addition as necessary so as to avoid discontinuities occurring between frames, and outputs
15 a final decoding signal.
[0076] In this way, according to the decoding apparatus (spectrum decoding section 153) of this embodiment, it is possible to decode a signal coded in the coding apparatus of this embodiment.
20
[0077] (Embodiment 2)
In Embodiment 2 of the present invention, a second spectrum is estimated using a pitch filter having a first spectrum as an internal state, and the characteristics
25 of this pitch filter are coded.
0078] The configuration of the hierarchical coding
2F05047-PCT 30
apparatus according to this embodiment is the same as the hierarchical coding apparatus shown in Embodiment 1, and therefore spectrum coding section 201 which has a different configuration will be explained using the
5 block diagram of FIG.11. Components that are identical with spectrum coding section 106 (refer to FIG.4) shown in Embodiment 1 will be assigned the same reference numerals without further explanations.
[0079] Internal state setting section 203 sets internal
10 state S(k) of a filter used at filtering section 2 04 using modified first spectrum SI'(k) generated at spectrum modification section 112.
[0080] Filtering section 2 04 carries out filtering based on internal state S (k) of the filter set at internal state
15 setting section 203 and lag coefficient T supplied from lag coefficient setting section 206, and calculates estimation value S2' ' (k) of the second spectrum. In this embodiment, a case of using a filter expressed by the following (Equation 13) will be described.
Here, T expresses a coefficient supplied from lag
coefficient setting section 206, and it is assumed that
25 M=l. As shown in the following (Equation 14 ) , filtering
2F05047-PCT 31
processing at filtering section 204 calculates an estimation value by multiplying corresponding coefficient β using the spectrums with frequency lower by frequency T as a center and performing addition in ascending order
5 of the frequencies.
Processing in accordance with this equation is
10 carried out between FL
internal state of the filter. S(k) calculated at this
time (where FL
of the second spectrum.
[0081] Search section 205 then calculates a degree of
15 similarity of second spectrum S2(k) supplied from
frequency domain converting section 113 and estimation
value S2'(k) of the second spectrum supplied from
filtering section 204.
[0082] Various definitions exist for this degree of
20 similarity, but in this embodiment, a degree of similarity calculated in accordance with the following (Equation 15) defined based on a minimum square error assuming filter coefficients β and β to be 0 is used.
In this method, filter coefficient β is determined after optimum lag coefficient T is calculated. Here,
5 E indicates the square error between S2 (k) and S2' ' (k) . Further, the first term on the right side of (Equation 15) is a fixed value regardless of lag coefficient T. Therefore, lag coefficient T generating S2'(k) which makes the second term on the right side of (Equation 15)
10 a maximum is searched. In this embodiment, the second term on the right side of (Equation 15) is referred to as the degree of similarity.
[0083] Lag coefficient setting section 206 then sequentially outputs lag coefficient T included in a
15 predetermined search range of TMIN to TMAX to filtering section 204. Therefore, at filtering section 204, every time lag coefficient T is supplied from lag coefficient setting section 206, filtering is carried out after S(k) with a range of FL
20 section 205 calculates the degree of similarity every time. Search section 205 then determines coefficient Tmax for the case where the calculated degree of similarity is a maximum, from between TMIN to TMAX, and supplies this coefficient Tmax to filter coefficient calculating
2F05047-PCT 33
section 207, spectrum outline coding section 208 and multiplex section 115.
[0084] Filter coefficient calculating section 207
obtains filter coefficient 3 using coefficient Tmax
5 supplied from search section 205. Here, filter
coefficient (3; is obtained so that square error E in
accordance with the following (Equation 16) is a minimum.
Filter coefficient calculating section 207 has a combination of a plurality of Pi.- as a table in advance, determines a combination of (3.-. so that square error E of the above-described (Equation 16) is a minimum, outputs
15 the code to multiplex section 115, and supplies filter coefficients (J.-: to spectrum outline coding section 208. [0085] Spectrum outline coding section 208 then carries out filtering using internal state S(k) supplied from internal state setting section 203, lag coefficient Tmax
20 supplied from search section 205 and filter coefficients P: supplied from filter coefficient calculating section 207, and obtains estimation value S2' ' (k) of the second spectrum with band of FL
25 spectrum outline using second spectrum estimation value S2'(k) and second spectrum S2(k).
2F05047-PCT 34
[0086] In this embodiment, a case will be described where
this spectrum outline information is expressed with
spectral power for each subband. At this time, spectral
power of the jth subband is expressed by the following
5 (Equation 17) .
Here, BL(j) indicates the minimum frequency of the
10 jth subband, and BH (j) indicates the maximum frequency
of the jth subband. Spectral power of the subband of
the second spectrum obtained in this way is then regarded
as spectrum outline information of the second spectrum.
[0087] Similarly, spectrum outline coding section 208
15 calculates spectral power B' (j) of the subband of
estimation value S2' (k) of the second spectrum in
accordance with the following (Equation 18), and
calculates the amount of fluctuation V(j) for each subband in accordance with the following (Equation 19).
20
2F05047--PCT 35
Next, spectrum outline coding section 208 codes the amount of fluctuation V(j) and transmits this code to multiplex section 115.
[0088 ] Multiplex section 115 then multiplexes
5 modification information obtained from spectrum modification section 112, information of optimum lag coefficient Tmax obtained from search section 205, information of the filter coefficient obtained from filter coefficient calculating section 207, and information of
10 the spectrum out line adjustment coefficient obtained-from spectrum out line coding section 2 08 and outputs the result. [0089] According to this embodiment, the second spectrum is estimated using a pitch filter having the first spectrum as an internal state, and therefore it is only necessary
15 to code only the characteristic of this pitch filter, so that a low bit rate can be realized. [0090] In this embodiment, a case has been described where a frequency domain converting section is provided, but this is a component necessary when a time domain signal
20 is used as input, and the frequency domain converting section is not necessary when the spectrum is directly inputted.
[0091] Further, in this embodiment, a case has been described as an example where M = l in the above-described
25 (Equation 13), but the value of M is not limited to 1, and it is possible to use integers of 0 or more. [0092] Moreover, in this embodiment, a case has been
2F05047-PCT 36
described as an example where the pitch filter uses a filter function(transfer function)in the above described (Equation 13) , but the pitch filter may also be a first order pitch filter.
5 [0093] FIG.12 is a block diagram showing a configuration of another variation (spectrum coding section 201a) of spectrum coding section 201 according to this embodiment . Components that are identical with spectrum coding section 201 will be assigned the same reference numerals without
10 further explanations.
[0094] The filter used at filtering section 204 may be simplified as shown in the following (Equation 20).
This equation is a filter function for the case where M=0 and β in the above-described (Equation 13). EstimationvalueS2' ' (k) of the second spectrum generated by this filter can be obtained by sequentially copying
20 a low frequency band spectrum with internal state S(k) separated by just T using the following (Equation 21).
25 [0095] Further search section 205 determines optimum coefficient Tmax by searching lag coefficient T that makes
2P05047-PCT 37
the above-described (Equationl5) a minimum. Coefficient Tmax obtained in this way is then supplied to multiplex section 115.
[0096] By adopting the above - described configuration,
5 the configuration of the filter used at filtering section 2 04 is simple, and filter coefficient calculating section 207 is unnecessary, so that it is possible to estimate the second spectrum with a small amount of calculation. According to this configuration, the configuration of
10 the coding apparatus is simplified, and the amount of calculation in coding processing can be reduced. [0097] Next, a configuration of spectrum decoding section 251 on the decoding side capable of decoding coded code generated at the above-described spectrum coding section
15 201 (or spectrum coding section 201a) will be described in detail.
[0098] FIG.13 is a block diagram showing the main configuration of spectrum decoding section 251 according to this embodiment. This spectrum decoding section 251
20 has the same basic configuration as spectrum decoding section 153 (refer to FIG.10) shown in Embodiment 1, and therefore components that are identical will be assigned the same reference numerals without further explanations. The difference is in the internal configuration of
25 extension frequency band spectrum generating sectionl6 3a. [0099] Internal state setting section 252 sets internal state S(k) of the filter used at filtering section 253
2F05047-PCT 38
using modified first spectrum SI' (k) outputted from modification section 162.
[0100] Filtering section 253 obtains information relating to the filter via separating section 161 from
5 the coded code generated at spectrum coding section 201
(201a) on the coding side. Specifically, in the case of spectrum coding section 201, lag coefficient Tmax and filter coefficient (J,-! are obtained, and in the case of spectrum coding section 201a, only lag coefficient Tmax
10 is obtained. Filtering section 253 then carries out filtering based on obtained filter information using modified first spectrum SI' (k) generated at modification section 162 as internal state S(k) of the filter, and calculates decoded spectrum S' ' (k) . This filtering
15 method depends on the filter function used in spectrum coding section 201(201a) on the coding side, and in the case of spectrum coding section 201, filtering is also carried out on the decoding side in accordance with the above-described (Equation 13) , while in the case of
20 spectrum coding section 201a, filtering is also carried out on the decoding side in accordance with the above - described (Equation 20) .
[0101] Spectrum outline decoding section 254 decodes spectrum out line information based on the spectrum out line 25information supplied from separating section 161. In this embodiment, a case will be described as an example where quantizing value Vq (j ) of the amount of fluctuation
2F05047--PCT 39
for each subband is used.
[0102] Spectrum adjusting section 255 adjusts the shape of the spectrum with frequency band of FL
5 filtering section 253 by quantizing value Vq(j) of the amount of fluctuation for each subband obtained from spectrum outline decoding section 254 in accordance with the following (Equation 22), and generates estimation value S2'(k) of the second spectrum.
10
(Equation
Here, BL(j) and BH(j) indicate the minimum frequency
15 and maximum frequency of the jth subband respectively.
Estimation value S2' ' (k) calculated in accordance with the above-described (Equation 22) is supplied to spectrum configuration section 165.
[0103] As described above in Embodiment 1, spectrum
20 configuration section 16 5 integrates first spectrum SI (k)and estimation value S2'(k) of the second spectrum,
generates decoded spectrum S3(k) and supplies this to
time domain converting section 166.
[0104] In this way, according to the decoding apparatus 25 (spectrum decoding section 251) according to this
embodiment, it is possible to decode a signal coded in
the coding apparatus according to this embodiment.
2F05047-PCT
40
[0105] (Embodiment 3)
FIG.14 is a block diagram showing the main configuration of a spectrum coding section according to
5 Embodiment 3 of the present invention. In FIG. 14 , blocks assigned with the same names and same reference numerals as in FIG.4 have the same functions, and therefore explanations will be omitted. In Embodiment3, the dynamic range of the spectrum is adjusted based on common
10 information between the coding side and the decoding side . By this means, it is not necessary to output coded code indicating a dynamic range adjustment coefficient for adjusting the dynamic range of the spectrum. It is not necessary to output coded code indicating the dynamic
15 range adjustment coefficient, so that a bit rate can be reduced.
[0106] Spectrum coding section 301 in FIG.14 has dynamic range calculating section 302, modification information estimating section 303 and modification section 304
20 between frequency domain converting section 111 and extension frequency band spectrum coding section 114 instead of spectrum modification section 112 in FIG.4. Spectrum modification section 112 in Embodiment 1 investigates away of modifying(modification information)
25 so as to obtain an appropriate dynamic range by changing the dynamic range of the first spectrum by variously modifying the first spectrum SI (k) , and codes and outputs
2F05047-PCT 41
this modification information. On the other hand, in Embodiment 3, this modification information is estimated based on common information between the coding side and the decoding side, and modification of first spectrum
5 Sl(k) is carried out in accordance with estimated modification information.
[0107] Therefore, in the Embodiment 3, instead of spectrum modification section 112, dynamic range calculating section 3 02, modification information estimating section
10 303 , and modification section 3 04 that modifies the first spectrum based on this estimated modification information are provided. In addition, since modification information can be obtained by estimation inside the spectrum coding section and spectrum decoding section
15 described later, it is not necessary to output modification information as coded code from spectrum coding section 301, and therefore multiplex section 115 provided at spectrum coding section 106 inFIG.4 is no longer necessary. [0108] First spectrum Sl(k) is then outputted from
20 frequency domain converting section 111 and is supplied to dynamic range calculating section 3 02 and modification section 304. Dynamic range calculating section 302 quantizes the dynamic range of first spectrum Sl(k) and outputs the result as dynamic range information. As with
25 Embodiment 1, the method for quantizing the dynamic range is to divide the frequency band of the first spectrum into a plurality of subbands, obtain energy for a
2F05047-PCT 42
predetermined range of subbands (subband energy), calculate an appropriate subband energy variance value, and output the variance value as. dynamic information. [0109] Next, modification information estimating
5 section 303 will be described using FIG.15. At modification information estimating section 303 , dynamic range information is inputted from dynamic range calculating section 302 and supplied to switching section 305. Switching section 305 then selects and outputs one
10 estimated modification information from candidates for estimated modification information recorded- in modification information table 306 based on the dynamic range information. A plurality of candidates for estimated modification information taking values between
15 0 and 1 are recorded in modification information table 3 06 , and these candidates are determined in advance through study so as to correspond to the dynamic range information . [0110] FIG.16 is a block diagram showing the main configuration of modification section 304. Blocks
20 assigned with the same names and same reference numerals as in FIG. 6 have the same functions, and therefore explanations will be omitted. Exponent value calculating section 30 7 of modification section 304 in FIG.16 outputs an exponent value of absolute amplitude of a spectrum
25 outputted from absolute value calculating section 13 2--a value that is raised to the power of estimated modification information—to positive/negative sign assigning section
2F05047-PCT 43
134 in accordance with estimated modification information (taking values between 0 and 1) supplied from modification information estimating section 303. Positive/negative sign assigning section 134 assigns coded information
5 obtained in advance at positive/negative sign extracting
section 131 to the exponent value outputted from exponent
value calculating section 307 and outputs the result as
modified first spectrum.
[0111] As described above, according to the coding
10 apparatus ( spectrum coding section 301) of this embodiment, by estimating the high frequency band (FL
15 applying modification to the first spectrum without using the first spectrum as is in the case where estimation information is coded, it is possible to appropriately adjust the dynamic range of the estimated spectrum and improve the subjective quality of the decoded signal.
20 At this time, information indicating how the modification has been performed (modification information) is defined based on common information between the coding side and the decoding side (the first spectrum in Embodiment 3) , so that it is not necessary to transmit coded code relating
25 to modification information to the decoding section, and the bit rate can be reduced.
[0112] At modification information estimating section
2F05047-PCT 44
303, it is also possible to use a mapping function, faking dynamic range information of a first spectrum as an input value and estimated modification information as an output value, instead of making dynamic range information of
5 the first spectrum correspond to the estimated modification information using modification information table 306. In this case, estimated modification information that is an output value of a function is limited so as to take values between 0 and 1.
10 [0113] FIG.17 is a block diagram showing the main configuration of spectrum decoding section 353 according to Embodiment 3 . In this configuration, blocks assigned with the same names and same reference numerals as in FIG . 10 have the same functions, and therefore explanations
15 will be omitted. Dynamic range calculating section 361, modification information estimating section 362 and modification section 363 are provided between frequency domain converting section 164 and extension frequency band spectrum generating section 163. Modification
20 section 162 in FIG.10 receives modification information generated at spectrum modification section 112 on the coding side and performs modification on first spectrum Sl(k) supplied from frequency domain converting section 164 based on this modification information. On the other
25 hand, inEmbodiment3, as with the above-described spectrum coding section 301, modification information is estimated based on common information between the coding side and
2F05047-PCT 45
the decoding side, and modification of first spectrum Sl(k) is carried out in accordance with the estimated modification information.
[0114] Therefore, in Embodiment 3, dynamic range
5 calculating section 361, modification information estimating section 362 and modification section 363 are provided. As with spectrum coding section 301, since modification information can be obtained by estimation inside the spectrum decoding section, modification
10 information is not included in the inputted coded code. Therefore, separating section 161 provided at spectrum decoding section 153 in FIG.10 is no longer necessary. [0115] First spectrum Sl(k) is then outputted from frequency domain converting section 164 and supplied to
15 dynamic range calculating section 361 and modification section 363 . In the following, the operation of dynamic range calculating section 361, modification information estimating section 362'and modification section 363 is the same as dynamic range calculating section 302,
20 modification information estimating section 303 and modification section 304 inside spectrum coding section 301 on the coding side described previously, and therefore explanations will be omitted. In modification information table inside modification information
25 estimating section 362, the same candidates for estimated modification information as in modification information table 306 inside modification information estimating
2F05047-PCT 46
section 303 of spectrum coding section 301 are recorded. [0116] Further, the operation of extension frequency band spectrum generating section 163, spectrum configuration section 165 and time domain converting
5 sectionl66 is the same as described in FIG.lO of Embodiment 1, and therefore explanations will be omitted. [0117] According to the decoding apparatus (spectrum decoding section 353) of this embodiment, by decoding a signal coded at the coding apparatus according to this
10 embodiment, it is possible to appropriately adjust the dynamic range of the estimated spectrum and improve subjective quality of the decoded signal. [0118] In this embodiment, estimated modification information can be obtained at modification information
15 estimating section 303, and this estimated modification information is applied to spectrum coding section 106 shown in FIG.4 of Embodiment 1 to supply the estimated modi fi cat ion information to spec trummodi.fi cat ion sect ion 112 . At spectrum modification section 112, the adjacent
20 modification information is selected from exponent variable table 135 using the estimated modification information supplied from modification information estimating section 303 as a reference, and the optimum modification information is determined from the limited
25 modification information at search section 125. In this configuration, coded code of the finally selected modification information is indicated as a relative value
2F05047-PCT 47
from estimated modification information used as the reference. In this way, accurate modification information is coded and transmitted to the decoding section, so that it is possible to obtain the advantage
5 of reducing the number of bits indicating the modification information while maintaining subjective quality of the decoded signal.
[0119] (Embodiment 4)
10 In Embodiment 4 of the present invention, estimated modification information outputted to the modification section inside the spectrum coding section is determined based on pitch gain supplied from the first layer coding section.
15 [0120] FIG.18 is a block diagram showing the main configuration of hierarchical coding apparatus 400 according to this embodiment. In FIG.18, blocks assigned with the same names and same reference numerals as in FIG. 3 have the same functions, and therefore explanations
20 will be omitted.
[0121] Athierarchicalcodingapparatus400of Embodiment 4, pitch gain obtained at first layer coding section 402 is supplied to spectrum coding section 406. Specifically, at first layer coding section 402, adaptive code vector
25 gain multiplied with adaptive code vectors outputted from an adaptive codebook (not shown) within first layer coding section 402 is outputted as pitch gain and inputted to
2F05047--PCT 48
spectrum coding section 406. This adaptive code vector gain has a feature of taking a large value when periodicity of the input signal is strong, and a small value when periodicity of the input signal is weak.
5 [0122] FIG.19 is a block diagram showing the main configuration of spectrum coding section 406 according to Embodiment 4. In FIG.19, blocks assigned with the same names and same reference numerals as in'FIG.14 have the same functions, and therefore explanations- will be
10 omitted. Modification information estimating section 411 outputes estimated modification information using pitch gain supplied from first layer coding section 402. Modification information estimating section 411 adopts the same configuration as the above-described modification
15 information estimating section 303 in FIG.15. However, a modification information table designed for pitch gain is applied. In this embodiment also, it is possible to adopt a configuration using a mapping coefficient instead of the configuration using the modification information
20 table.
[0123] According to the coding apparatus ( spectrum coding section 406) of this embodiment, it is possible to appropriately adjust the dynamic range of the estimated spectrum with periodicity of an input signal taken into
25 consideration, and improve subjective quality of the decoded signal. [0124] Next, a configuration of hierarchical decoding
2F05047-PCT 49
apparatus 450 capable of decoding the coded code generated in the above-described hierarchical coding apparatus 400 will be described.
[0125] FIG.20 is a block diagram showing the main
5 configuration of hierarchical decoding apparatus 450 according to this embodiment. In FIG.20, pitch gain outputted from first layer decoding sect ion 4 52 is supplied to spectrum decoding section 4 53 . At first layer decoding section 452, adaptive code vector gain multiplied by the
10 adaptive code vector outputted from the adaptive code book (not shown) within first layer decoding section 452 is outputted a spitch gain and inputted to spectrum decoding section 453.
[0126] FIG.21 is a block diagram showing the main
15 configuration of spectrum decoding section 453 according to Embodiment 4. Modification information estimating section 461 outputs estimated modification information using pitch gain supplied from first layer decoding section 452. Modification information estimating section 461
20 adopts the same configuration as the above-described modification information estimating section 303 inFIG.15.However, a modification information table is applied that is the same as that within modification information estimating section 411 and is designed for pitch gain. 25In this embodiment also, it is possible to adopt a configuration using the mapping coefficient instead of the configuration using the modification information
2F05047-PCT 50
table.
[0127] According to the decoding apparatus (spectrum decoding section 453) of this embodiment, by decoding a signal coded at the coding apparatus of this embodiment,
5 it is possible to appropriately adjust the dynamic range of the estimated spectrum with periodicity of an input signal taken into consideration, and improve subjective quality of the decoded signal.
[0128] It is also possible to adopt a configuration of
10 estimating modification information using pitch gain and pitch period (lag obtained as a result of searching the adaptive code book within first layer coding section 402). In this case, by using pitch period, it is possible to perform estimation of modification information suitable
15 for each of speech with a short pitch period (for example, a female voice) and speech with a long pitch period (for example, a male voice) and thereby improve estimation accuracy.
[0129] Further, in this embodiment, estimated
20 modification information can be obtained at modification information estimating section 411, and, as with in Embodiment 3, this estimated modification information is applied to spectrum coding section 106 shown in FIG. 4 of Embodiment 1, and the estimated modification
25 information is supplied to spectrum modification section 112. At spectrum modification section 112 , the adjacent modification information is selected from exponent
2F05047-PCT 51
variable table 135 using the estimated modification information supplied from modification information estimating section 411 as a reference, and the optimum modification information is determined from the limited
5 modification information at search section 125. In this configuration, coded code of the finally selected modification information is indicated as a relative value from estimated modification information used as the reference. In this way, accurate modification
10 information is coded and transmitted to the decoding section, so that it is possible to obtain an advantage of reducing the number of bits indicating the modification information while maintaining subjective quality of the decoded signal.
15
[0130] (Embodiment 5)
In Embodiment 5 of the present invention, estimated modification information outputted to the modification section within the spectrum coding section is determined
20 based on LPC coefficients supplied from the first layer coding section.
[0131] The configuration of the hierarchical coding apparatus according to Embodiment 5 is the same as the above-described FIG.18. However, a parameter outputted
25 from first layer coding section 402 to spectrum coding section 406 is not pitch gain but LPC coefficients. [0132] The main configuration of spectrum coding section
2F05047-PCT 52
406 according to this embodiment is as shown in FIG.22. The difference from the above-described FIG.19 is that the parameter supplied to modification information estimating section 511 is not pitch gain but LPC
5 coefficients, and it is the internal configuration of modification information estimating section 511. [0133] FIG.23 is a block diagram showing the main configuration of modification information estimating section 511 according to this embodiment. Modification
10 information estimating section 511 is configured with determination table 512, similarity degree determining section 513, modification information table 514 and switching section 515 . As with modification information table306 in FIG.15, candidates for estimated modification
15 information are recorded in modification information table 514. However, candidates for estimated modification information designed for LPC coefficients are applied. Candidates for the LPC coefficients are stored in determination table 512, and determination table 512
20 corresponds to modification information table 514. Namely, when a jth candidate for the LPC coefficients is selected from determination table 512, estimated modification information suitable for this candidate for LPC coefficients is stored in jth of modification
25 information table 514. The LPC coefficient shave a feature of capable of accurately expressing the spectrum outline ( spectrum envelope) with few parameters , and it is possible
2F05047-PCT 54
taken into consideration, and improve subjective quality of the .decoded signal.
[0137] Next, the configuration of the hierarchical decoding apparatus capable of decoding the coded code
5 generated in the coding apparatus according to Embodiment 5 will be described.
[0138] The configuration of the hierarchical decoding apparatus according to Embodiment 5 is the same as the above-described FIG.20 . However, a parameter outputted
10 from first layer decoding section 4 52 to spectrum decoding section 453 is not pitch gain but LPC coefficients.
[0139] The main configuration of spectrum decoding section 453 according to this embodiment is as shown in FIG.24. The difference from the above-described FIG.21
15 is that the parameter supplied to modification information estimating section 561 is not pitch gain but LPC coefficients, and it is the internal configuration of modification information estimating section 561.
[0140] The internal configuration of modification
20 information estimating section 561 is the same as modification information estimating section 511 within spectrum coding section 406 in FIG.22, that is, the same as shown in FIG. 23, and information recorded in determination table 512 and modification information table
25 514 is common between the coding side and decoding side.
[0141] According to the decoding apparatus (spectrum decoding section 453) of this embodiment, by decoding
2F05047-PCT 55
a signal coded at the coding apparatus of this embodiment, it is possible to appropriately adjust the dynamic' range of the estimated spectrum with the spectrum outline of the input signal also taken into consideration, and improve
5 subjective quality of the decoded signal. [0142] Further, in this embodiment, estimated modification information is obtained at modification information estimating section 511, and, as with in Embodiment 4, this estimated modification information
10 is applied to spectrum coding section 106 shown in FIG.4 of Embodiment 1, and the estimated modification information is supplied to spec t rum modification section 112 . At spectrum modification section 112, the adjacent modification information is selected from exponent
15 variable table 135 using the estimated modification information supplied from modification information estimating section 511 as a reference, and the optimum modification information is determined from the limited modification information at search section 125. In this
20 configuration, coded code of the finally selected modification information is indicated as a relative value from the estimated modification information used as the reference. In this way, accurate modification information can be coded and transmitted to the decoding
25 section, so that it is possible to obtain an advantage of reducing the number of bits indicating the modification information while maintaining subjective quality of the
2F05047-PCT 56
decoded signal.
[0143] (Embodiment 6)
The basic configuration of the hierarchical coding
5 apparatus according to Embodiment 6 of the present invention is the same as the hierarchical coding apparatus shown in Embodiment 1, and therefore explanations will be omitted, and just spectrum modification section 612 with a different configuration from spectrum modification
10 section 112 will be described below.
[0144] Spectrum modification section 612 applies the following modification to first spectrum Sl(k) so that the dynamic range of first spectrum SI (k) [0
15 second spectrum S2(k) [FL
[0145] FIG.25 illustrates a spectrum modification method according to this embodiment.
20 [0146] This drawing shows amplitude distribution of first spectrum SI (k). First spectrum SI (k) indicates amplitude differing according to values of frequency k [0
25 this amplitude, a distribution similar to normal distribution shown in the drawing appears centered on average value ml of the amplitude.
2F05047-PCT 57
[0147] In this embodiment, first, this distribution can be roughly divided into a group (region B in the drawing) close to average value ml and a group (region A in the drawing) far from average value ml. Next, typical values
5 of amplitude of these two groups, specifically, an average value of spectral amplitude included in region A and an average value of spectral amplitude included in region B, are obtained. Here, the absolute value of amplitude for the case where average value ml is re-converted to
10 zero (average value ml is subtracted from each value) is used. For example, region A is made up of two regions of a region where amplitude is greater than average value ml and a region where amplitude is smaller than average value ml, but by re-converting average value ml to zero,
15 the absolute values of spectral amplitude included in the two regions have the same value. Accordingly, in the case of the average value of region A, for example, this corresponds to obtaining a typical value of amplitude of this group with a spectrum in which converted amplitude
20 (absolute value) is relatively large out of the first spectrum taken as one group, and in the case of the average value of region B, this corresponds to obtaining a typical value of amplitude of this group with a spectrum in which converted amplitude is relatively small out of the first
25 spectrum taken as one group. As a result, these two typical values are parameters expressing an outline of the dynamic range of the first spectrum.
2F05047-PCT 58
[0148] Next, in this embodiment, the same processing as carried out on the first spectrum is carried out on the second spectrum, and typical values corresponding to the respective groups of the second spectrum are obtained
5 A ratio between the typical value of the first spectrum and the typical value of the second spectrum in region A (specifically, a ratio of the typical value of the first spectrum to the typical value of the second spectrum) and a ratio between the typical value of the first spectrum
10 and the typical value of the second spectrum in region B, are obtained. It is therefore possible to approximately obtain the ratio between the dynamic range of the first spectrum and the dynamic range of the second spectrum. The spectrum modification section according to this
15 embodiment codes this ratio as spectrum modification information and outputs this information.
[0149] FIG.26 is a block diagram showing the main configuration of the internal part or spectrum modification section 612.
20 [0150] Spectrum modification section 612 can be roughly classified into: a system that calculates typical values of the above-described respective groups of the first spectrum; a system that calculates typical values of the above-described respective groups of the second spectrum;
25 modification information determining section 626 that determines modification information based on the typical values calculated by these two systems; and modified
2F05047-PCT 59
spectrum generating section 62 7 that generates a modified spectrum based on this modification information. [0151] Specifically, the system that calculates, the typical values of the first spectrum is made up of :'variation
5 degree calculating section 621-1; first threshold value setting section 622-1; second threshold value setting section 623 - 1; first average spectrum calculating section 624-1; and second average spectrum calculating section 625-1. The system that calculates the typical values
10 of the second spectrum has also basically the same configuration as the system that calculates the typical values of the first spectrum. The same components in the drawings will be assigned the same reference numerals , and differences of the processing system are indicated
15 with branch numbers after the reference numerals. Explanations about the same components will be omitted. [0152] Variation degree calculating section 621-1 calculates "variation degree" from average value ml of the first spectrum from amplitude distribution of inputted
20 first spectrum SI (k), and outputs this to first threshold value setting section 622-1 and second threshold value setting sect-ion 6.23 - 1. Specifically, "variation degree" is standard deviation a of the amplitude distribution of the first spectrum.
25 [0153] First threshold value setting section 622-1 obtains first threshold value TH1 using first spectrum standard "deviation a obtained at variation degree
2F05047-PCT 60
calculating section 621-1. Here, first threshold value TH1 is a threshold value for specifying a spectrum with relatively large absolute amplitude included in the above-described region A out of the first spectrum, and
5 a value where a predetermined constant a is multiplied by standard deviation or is used.
[0154] The operation of second threshold value setting section 623-1 is also the same as the operation of first threshold value setting section 622-1, but obtained second
10 threshold value TH2 is a threshold value for specifying a -spectrum with relatively small absolute amplitude included in region B out of the first spectrum, and a value where predetermined constant b (
15 [0155] First average spectrum calculating sect ion 624 - 1 obtains a spectrum positioned on the outside of first threshold value THl--an average value of amplitude of a spectrum included in region A (hereinafter referred to as a first average value)--and outputs the result to
20 modification information determining section 626.
[0156] Specifically, first average spectrum calculating sect ion 624 - 1 compares the amplitude (here, a value before conversion) of the first spectrum with a value (ml + TH1) where first threshold value TH1 is added to average value
25 ml of the first spectrum, and specifies a spectrum, having larger amplitude than this value (step 1). Next,, first average spectrum calculating section 624-1 compares the
2F05047-PCT 61
amplitude of the first spectrum with a value (ml - TH1) where first threshold value TH1 is subtracted from average value ml of the first spectrum, and specifies a spectrum having, smaller amplitude than this value (step 2) . The
5 amplitudes of the spectrums obtained in both step 1 and step 2 are converted so that the above-described average value ml becomes zero, and the average values of the absolute values of the obtained converted values are calculated, and outputted to modification information determining
10 section 626.
[0157] The second average spectrum calculating section obtains a spectrum positioned on the inside of second threshold value TH2--an average value of amplitude of the spectrum included in region B (hereinafter referred
15 to as second average value)--and outputs the result to modification information determining section 626. The specific operation is the same as first average spectrum
calculating section 624-1.
[0158] First average value and second average value
20 obtained in the above-described processing are typical values for region A and region B of the first spectrum. [0159] Processing for obtaining typical values of the second spectrum is basically the same as described above. However, the first spectrum and the second spectrum are
25 different spectrums. A value where standard deviation a of the second spectrum is multiplied by predetermined constant c is then used as third threshold value TH3
2F05047-PCT 62
corresponding to first threshold value TH1, and a value where standard deviation o\ ■ of the second spectrum is multiplied by predetermined constant d (
5 threshold value TH2.
[0160] Modification information determining section 626 determines modification information as below using the first average value obtained at first average spectrum calculating section 624-1, the second average value
10 obtained at second average spectrum calculating section 625-1, the third average value obtained at third average spectrum calculating section 624-2 and the fourth average value obtained at fourth average spectrum calculating section 625-2 .
15 [0161] Namely, modification information determining section 626 calculates a ratio between the first average value and the third average value (hereinafter referred to as first gain), and a ratio between the second average value and the fourth average value (hereinafter referred
20 to as second gain). Modification information determining section 626 is internally provided with a data table in which a plurality of coding candidates for modification information are stored. Modification information determining section 626 then compares the first gain and
25 second gain with these coding candidates, selects the most similar coding candidate, and outputs an index indicating this coding candidate as modification
2F05047-PCT 63
information. This index is also transmitted to modified spectrum generating section 627.
[0162] Modified spectrum generating section 627 carries out modification of the first spectrum using the first
5 spectrum that is the input signal, first threshold value TH1 obtained at first threshold value setting section 622-1, second threshold value TH2 obtained at second threshold value setting section 623-1, and modification information outputted from modification information
10 determining section 626.
[0163] FIG.27 and FIG.28 illustrate a method of generating a modified spectrum.
[0164] Modified spectrum generating section 627 generates a decoded value of a ratio between the first
15 average value and the third average value (hereinafter referred to as decoded first gain) and a decoded value of a ratio between the second average value and the fourth average value (hereinafter referred to as decoded second gain) using modification information. These
20 corresponding relationships are as shown in FIG.27.
[0165] Next, modified spectrum generating section 627 specifies spectrums belonging to region A by comparing the first spectral amplitude value with first threshold value TH1, and multiplies the decoded first gain by these
25 spectrums. Similarly, modified spectrum generating section 627 specifies spectrums belonging to region B by comparing the first spectrum amplitude value with second
2F05047-PCT 64
threshold value TH2 , and multiplies the decoded second gain by these spectrums,
[0166] On the other hand, as shown in FIG.28, coding information does not exist for spectrums belonging to
5 a region (hereinafter, region C) between first threshold value THl and second threshold value TH2 , out of the first spectrum . Modified spectrum generating section 62 7 uses gain having a value midway between the decoded first gain and the decoded second gain. For example, decoded gain
10 y corresponding to given amplitude x may be obtained from a characteristic curve based on the decoded first gain, decoded second gain, first threshold value THl and second threshold value TH2, and the amplitude of the first spectrum may be multiplied by this gain. Namely, decoded gain
15 y is a linear interpolation value for the decoded first gain and decoded second gain.
[0167] FIG.29 is a block diagram showing the main configuration of the internal part of spectrum modification section 662 used in the decoding apparatus.
20 This spectrum modification section 662 corresponds to modification section 162 shown in Embodiment 1. [0168] The basic operation is the same as the above-described spectrum modification section 612, and therefore detailed explanations will be omitted, but this
25 spectrum modification section 662 only takes the first spectrum as a processing target, and therefore there is only one processing system.
2F05047--PCT 65
[0169] According to this embodiment, amplitude distribution of the first spectrum and amplitude distribution of the second spectrum are respectively obtained, and divided into a group of relatively large
5 absolute amplitude and a group of relatively small absolute amplitude. Then, typical values of the amplitudes for respective groups are obtained. The ratio of the dynamic range between the first spectrum and the second spectrum--modification information of the spectrum—is
10 obtained and coded using the ratio of the typical values of amplitudes for the respective groups of the first spectrum and the second spectrum. As a result, it is possible to obtain modification information without using a function with a large amount of calculation such as
15 an exponential function.
[0170] According to this embodiment, standard deviation is obtained from amplitude distribution of the first spectrum and second spectrum, and the first threshold value to the fourth threshold value are obtained based
20 on this standard deviation. A threshold value is set based on the actual spectrum, so that it is possible to improve coding accuracy of modification information. [0171] ' Further, according to this embodiment, the dynamic range of the first spectrum is controlled by adjusting
25 the gain of the first spectrum using the decoded first gain and decoded second gain. The decoded first gain and decoded second gain are determined so that the first
2F05047-PCT 66
spectrum is close to the high frequency band of the second spectrum. The dynamic range of the first spectrum is then close to the dynamic range of the high frequency band of the second spectrum. Further, it is not necessary
5 to use a function with a large amount of calculation such as an exponential function for calculation of the decoded first gain and decoded second gain.
[0172] In this embodiment, a case has been described as an example where the decoded first gain is larger than
10 the decoded second gain, but there are cases where the decoded second gain is larger than the decoded first gain depending on the quality of the speech signal. Namely, there are cases where the dynamic range of the high frequency band of the second spectrum is larger than the dynamic
15 range of the first spectrum. This kind of phenomena frequently occurs in the cases where the inputted speech signal is a sound such as a fricative. In this case also, it is possible to apply the spectrum modification method according to this embodiment.
20 [0173] Further, in this embodiment, a case has been described as an example where spectrums are divided into two groups , a group of relatively large absolute amplitude and a group of relatively small absolute amplitude. However, it is also possible to divide into larger numbers
25 of groups so as to increase reproducibility of the dynamic range.
[0174] In addition, in this embodiment, a case has been
2F05047-PCT 67
described as an example where amplitude is converted using an average value as a reference and spectrums are divided into a group of relatively large amplitude and a group of relatively small amplitude based on the amplitude after
5 conversion, but it is also possible to use the original amplitude value as is and carry out grouping of the spectrums based on the amplitude.
[0175] Moreover, in this embodiment, a case has been described as an example where standard deviation is used
10 for calculating the variation degree of the absolute amplitude of the spectrum, but this is by no means limiting, and, for example, it is possible to use variance as the same statistical parameter as standard deviation.
[0176] Further, in this embodiment, a case has been
15 described as an example where an average value of absolute amplitude of the spectrum for each group is used as a typical value of spectral amplitude of each group, but this is by no means limiting, and, for example, it is possible to use a central value of the absolute amplitude
20 of the spectrum for each group.
[0177] Moreover, in this embodiment, a case has been described as an example where an amplitude value of each spectrum is used for adjustment of the dynamic range, but it is also possible to use a spectral energy value 25instead of the amplitude value.
[0178] Further, when a typical value corresponding to each group is obtained, in the case where amplitude of
2F05047-PCT 68
the spectrum originally has a positive or negative sign as with, for example, an MDCT coefficient, it is not necessary to convert the average value to zero, and a typical value corresponding to each group may be obtained
5 simply using an absolute value of amplitude of the spectrum. [0179] The above is a description of each of the embodiments of the present invention.
[0180] The coding apparatus and decoding apparatus of the present invention are by no means limited to each
10 of the above-described embodiments, and various modifications thereof are possible.
[0181] The coding apparatus and decoding apparatus of the present invention can be loaded on a communication terminal apparatus and base station apparatus of a mobile
15 communication system so as to make it possible to provide a communication terminal apparatus and base station apparatus having the same operation effects as described above. [0182] Here, a case has been described as an example
20 where the present invention is applied to a scaleable coding scheme, but the present invention may also be applied to other coding schemes.
[0183] Moreover, a case has been described as an example where the present invention is configured using hardware,
25 but it is also possible to implement the present invention using software. For example, by describing the coding method (decoding method) algorithm according to the
2F05047-PCT 69
present invention in a programming language, storing this program in a memory and making an information processing section execute this program, it is possible to implement the same function as the coding apparatus (decoding
5 apparatus) of the present invention.
[0184] Furthermore, each function block used to explain the above- described embodiments is typically implemented as an LSI constituted by an integrated circuit. These may be individual chips or may partially or totally
10 contained on a single chip.
[0185] Furthermore, here, each function block is described as an LSI, but this may also be referred to as "IC", "system LSI", "super LSI", "ultra LSI" depending on differing extents of integration.
15 [0186] Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible . After LSI manufacture , utilization of a programmable FPGA (Field Programmable Gate Array) or a re configurable
20 processor in which connections and settings of circuit
cells within an LSI can be reconfigured is also possible.
[0187] Further, if integrated circuit technology comes out to replace LSI's as a result of the development of
semi conduct or technology or a derivative other technology,
25 it is naturally also possible to carry out function block integration using this technology. Application in biotechnology is also possible.
2F05047-PCT 70
[0188] The present application is based on Japanese Patent Application No. 2004 - 145425 filed on May 14th,. 2004, Japanese Patent Application No.2004 - 322953 filed on November 5th, 2004, and Japanese Patent Application
5 No.2005-133729 filed on April 28th, 2005, the entire content of which is expressly incorporated by reference herein.
Industrial Applicability
10 [0189] The coding apparatus, decoding apparatus, and methods thereof according to the present invention can be applied to scaleable coding/decoding, and the like.
2F05047-PCT 71
CLAIMS
1. A coding apparatus comprising:
a coding section that codes a high frequency band
5 spectrum of an input signal; and
a limiting section that acquires a first low frequency band spectrum in which a coded signal of a low frequency band spectrum of the input signal is decoded, and generates a second low frequency band spectrum in which amplitude
10 of the first low frequency band spectrum is uniformly 1imited,
wherein the coding section codes the high frequency band spectrum based on the second low frequency band spectrum.
15
2. The coding apparatus according to claim 1 further comprises a transmission section that transmits information about a way of limiting used at the limiting section together with coded information obtained by the
20 coding section.
3. The coding apparatus according to claim 1, wherein the limiting section limits amplitude of the first low frequency band spectrum so that average deviation of the
25 second low frequency band spectrum amplitude is equivalent to average deviation of amplitude of the high frequency band spectrum.
2F05047-PCT 72
4. The coding apparatus according to claim 1, wherein
the limiting section generates the second low frequency
band spectrum by uniformly raising the amplitude of the
5 first low frequency band spectrum to the power of a predetermined value within a range from 0 to 1.
5. The coding apparatus according to claim 1, wherein
the coding section comprises:
10 a pitch filter that has the second low frequency band spectrum as an internal state; and
an estimating section that estimates the high frequency band spectrum using the pitch filter,
wherein characteristics of the pitch filter are coded
15 so as to correspond to an estimation result of the estimating section.
6. The coding apparatus according to claim 5, wherein
the pitch filter characteristics are indicated by the
20 following transfer function.
where
25 P(z): pitch filter transfer function,
z: z conversion coefficient,
2F05047-PCT
73
T: lag coefficient.
7. The coding apparatus according to claim 1, wherein
the limiting section estimates information about the way
5 of limiting based on the first low frequency band spectrum and generates the second low frequency band spectrum using the estimated information.
8. The coding apparatus according to claim 1, wherein
10 the limiting section comprises:
a dynamic range calculating section that calculates dynamic range information using the first low frequency band spectrum;
a modification information estimating section that
15 estimates modification information for uniformly limiting amplitude of the first low frequency band spectrum using the dynamic range information; and
a modification section that uniformly limits amplitude of the first low frequency band spectrum using
20 the estimated modification information.
9. The coding apparatus according to claim 7, wherein
the limiting section comprises:
a modification information estimating section that
25 estimates modification information for uniformly limiting amplitude of the first low frequency band spectrum using pitch information indicating periodicity of the input
2F05047.-PCT 74
signal; and
a modification section that uniformly limits amplitude of the first low frequency band spectrum using the estimated modification information.
5
10. The coding apparatus according to claim 9, wherein the pitch information is configured using at least one of pitch gain and pitch period.
10 11. The coding apparatus according to claim 7, wherein the limiting section comprises:
a modification information estimating section that estimates modification information for uniformly limiting amplitude of the first low frequency band spectrum using
15 spectrum outline information of the input signal; and a modification section that uniformly limits amplitude of the first low frequency band spectrum using the estimated modification information.
20 12. The coding apparatus according to claim 11, wherein the modification information estimating section comprises:
a spectrum outline information storage section that stores a plurality of candidates for spectrum outline
25 information; and
a dynamic range information storage section that stores a plurality of candidates for dynamic range
2F05047-PCT 75
information, wherein:
a candidate for spectrum outline information corresponding to spectrum out line information of the input signal is selected from the spectrum outline information
5 storage section; and
the modification information is estimated by selecting a candidate for dynamic range information corresponding to the selected candidate for spectrum outline information from the dynamic range information
10 storage section.
13. The coding apparatus according to claim 1, further comprising:
a first classifying section that classifies the first
15 low frequency band spectrum into a plurality of groups according to differences in amplitude;
a first typical value acquiring sect ion that acquires a typical value for amplitude for each group of the first low frequency band spectrum;
20 a second classifying section that classifies the high frequency band spectrum into a plurality of groups according to differences in amplitude; and
a second typical value acquiring section that acquires a typical value for amplitude for each group
25 of the high frequency band spectrum,
wherein the limiting section uniformly limits the amplitude of the first low frequency band spectrum based
2F05047-PCT 76
on the typical value for each group of the first low frequency band spectrum and the typical value for each group of the high frequency band spectrum.
5 14. The coding apparatus according to claim 13 , wherein the limiting section obtains amplitude between the typical values by carrying out linear interpolation on the typical values.
10 15. The coding apparatus according to claim 13 , wherein the limiting section uniformly limits the amplitude of the first low frequency band spectrum based on a ratio between the typical value for each group of the first low frequency band spectrum and the typical value for
15 each group of the high frequency band spectrum.
16. The coding apparatus according to claim 13 , wherein the first and second typical value acquiring sections acquire an average value or central value of the amplitude
20 for each group.
17. A decoding apparatus comprising:
a converting section that generates a first low
frequency band spectrum in which a decoded signal of code
25 of a low frequency band spectrum included in code generated in a coding apparatus is converted to a frequency domain signal;
2F05047-PCT 77
a decoding section that decodes code of a' high frequency band spectrum included in the code generated in the coding apparatus; and
a limiting section that generates a second low
5 frequency band spectrum in which amplitude of the first
low frequency band spectrum is uniformly limited according
to spectrum modification information included in the code generated in the coding apparatus,
wherein the decoding section decodes the code of
10 the high frequency band spectrum based on the second low frequency band spectrum.
18. A decoding apparatus comprising:
a converting section that generates a first low
15 frequency band spectrum in which a decoded signal of code of a low frequency band spectrum included in code generated in a coding apparatus is converted to a frequency domain signal;
a decoding section that decodes code of a high
20 frequency band spectrum included in the code generated in the coding apparatus; and
a limiting section that generates a second low frequency band spectrum in which amplitude of the first low frequency band spectrum is uniformly limited,
25 wherein the limiting section estimates information about a way of limiting based on the first low frequency band spectrum and generates the second low frequency band
2F05047-PCT 78
spectrum using the estimated information; and
the decoding section decodes the code of the high frequency band spectrum based on the second low frequency band spectrum.
5
19. A communication terminal apparatus comprising the
coding apparatus according to claim 1.
20. A base station apparatus comprising the coding
10 apparatus according to claim 1.
21. A communication terminal apparatus comprising the
decoding apparatus according to claim 17.
15 22. A base station apparatus comprising the decoding apparatus according to claim 17.
23. A communication terminal apparatus comprising the
decoding apparatus according to claim 18.
20
24. A base station apparatus comprising' the decoding apparatus of claim 18.
25. A coding method comprising:
25 a coding step of coding a high frequency band spectrum of an input signal;
an acquiring step of acquiring a first low frequency
2F05047-PCT 79
band spectrum in which a coded signal of the low frequency, band spectrum of the input signal is decoded; and
a limiting step of generating a second low frequency band spectrum in which amplitude of the first low frequency
5 band spectrum is uniformly limited,
wherein the coding step codes the high frequency band spectrum based on the second low frequency band spectrum.
10 26. A decoding method comprising:
a conversion step of generating a first low frequency band spectrum in which a decoded signal of code of a low frequency band spectrum included in code generated in a coding apparatus is converted to a frequency domain
15 signal;
a decoding step of decoding code of a high frequency band spectrum included in the code generated in the coding apparatus;
an acquisition step of acquiring spectrum
20 modification information included in the code generated in the coding apparatus; and
a limiting step of generating a second low frequency band spectrum in which amplitude of the first low frequency band spectrum is uniformly limited according to the
25 spectrum modification information,
wherein the decoding step decodes the high frequency band spectrum based on the second low frequency band
2F05047-PCT 80
spectrum.
27. A decoding method comprising:
a conversion step of generating a first low frequency
5 band spectrum in which a decoded signal of code of a low frequency band spectrum included in code generated in a coding apparatus is converted to a frequency domain signal;
a decoding step of decoding code of a high frequency
10 band spectrum included in the code generated in the coding apparatus; and
a limiting step of generating a second low frequency band spectrum in which amplitude of the first low frequency band spectrum is uniformly limited, wherein:
15 the limiting step estimates information about a way of limiting based on the first low frequency band spectrum and generates the second low frequency band spectrum using the estimated information; and
the decoding step decodes the code of the high
20 frequency band spectrum based on the second low frequency band spectrum.
Dated this 12th day of November, 2006
2F05047-PCT 81
ABSTRACT
There is disclosed an encoding device capable of
appropriately adjusting the dynamic range of spectrum
inserted according to the technique for replacing a
5 spectrum of a certain band with a spectrum of another
band. The device includes a spectrum modification unit
(112) which modifies a first spectrum Sl(k) of the band
0
so that a way of modification for obtaining an
10 appropriate dynamic range is checked. The information
concerning the modification is encoded and given to a
multiplexing unit (115) . By using a second spectrum
S2(k) having a valid signal band 0
|