Title of Invention

METHOD AND APPARATUS FOR ENCODING AND DECODING AN AUDIO SIGNAL

Abstract

A method and apparatus for encoding and decoding an audio signal are provided. The present invention includes receiving an audio signal including a downmix signal and a spatial information signal, if a header is included in the spatial information signal, extracting configuration information from the header, extracting spatial information included in the spatial information signal, and converting the downmix signal to a multi-channel signal using the configuration information and the spatial information. Accordingly, the header can be selectively included in the spatial information signal, thereby if the header is plurally included in the spatial information signal, it is able to decode spatial information in case of reproducing the audio signal from a random point.

Full Text

METHOD AND APPARATUS FOR ENCODING AND DECODING AN AUDIO SIGNAL TECHNICAL FIELD The present invention relates to an audio signal processing, and more particularly, to an apparatus for encoding and decoding an audio signal and method thereof. BACKGROUND ART Generally, an audio signal encoding apparatus compresses an audio signal into a mono or stereo type downmix signal instead of compressing each channels of a multi-channel audio signal. The audio signal encoding apparatus transfers the compressed downmix signal to a decoding apparatus together with a spatial information signal (or, ancillary data signal) or stores the compressed downmix signal and the spatial information signal in a storage medium. In this case, the spatial information signal, which is extracted in downmixing a multi-channel audio signal, is used in restoring an original multi-channel audio signal from a compressed downmix signal. The spatial information signal includes a header and 1 spatial information. And, configuration information is included in the header. The header is the information for interpreting the spatial information. An audio signal decoding apparatus decodes the spatial information using the configuration information included in the header. The configuration information, which is included in the header, is transferred to a decoding apparatus or stored in a storage medium together with the spatial information. An audio signal encoding apparatus multiplexes an encoded downmix signal and the spatial information signal together into a bitstream form and then transfers the multiplexed signal to a decoding apparatus. Since configuration information is invariable in general, a header including configuration information is inserted in a bitstream once. Since configuration information is transmitted with being initially inserted in an audio signal once, an audio signal decoding apparatus has a problem in decoding spatial information due to non- existence of configuration information in case of reproducing the audio signal from a random timing point. Namely, since an audio signal is reproduced from a specific tirring point requested by a user instead of being reproduced from an initial part in case of a broadcast, VOD 2 (video on demand) or the like, it is unable to use configuration information transferred by being included in an audio signal. So, it may be unable to decode spatial information. DISCLOSURE OF THE INVENTION An object of the present invention is to provide a method and apparatus for encoding and decoding an audio signal which enables the audio signal to be decoded by making header selectively included in a frame in the spatial information signal. Another object of the present invention is to provide a method and apparatus for encoding and decoding an audio signal which enables the audio signal to be decoded even if the audio signal is reproduced from a random point by the audio signal decoding apparatus by making a plurality of headers included in a spatial information signal. To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of decoding an audio signal according to the present invention includes receiving the audio signal including a downmix signal and a spatial information signal, if a header is included in the spatial information signal, extracting configuration 3 information from the header, extracting spatial information included in the spatial information signal, and converting the downmix signal to a multi-channel signal using the configuration information and the spatial information. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configurational diagram of an audio signal according to one embodiment of the present invention. FIG. 2 is a configurational diagram of an audio signal according to another embodiment of the present invention. FIG. 3 is a block diagram of an apparatus for decoding an audio signal according to one embodiment of the present invention. FIG. 4 is a block diagram of an apparatus for decoding an audio signal according to another embodiment of the present invention. FIG. 5 is a flowchart of a method of decoding an audio signal according to one embodiment of the present invention. FIG. 6 is a flowchart of a method of decoding an audio signal according to another embodiment of the present invention. 4 FIG. 7 is a flowchart of a method of decoding an audio signal according to a further embodiment of the present invention. FIG. 8 is a flowchart of a method of obtaining a position information representing quantity according to one embodiment of the present invention. FIG. 9 is a flowchart of a method of decoding an audio signal according to another further embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. For understanding of the present invention, an apparatus and method of encoding an audio signal is explained prior to an apparatus and method of decoding an audio signal. Yet, the decoding apparatus and method according to the present invention are not limited to the following encoding apparatus and method. And, the present invention is applicable to an audio coding scheme for generating a multi-channel using spatial information as well as MP3 (MPEG 1/2-layer III) and AAC (advanced audio coding). 5 FIG. 1 is a configurational diagram of an audio signal transferred to an audio signal decoding apparatus from an audio signal encoding apparatus according to one embodiment of the present invention. Referring to FIG. 1, an audio signal includes an audio descriptor 101, a downmix signal 103 and a spatial information signal 105. In case of using a coding scheme for reproducing an audio signal for broadcasting or the like, the audio signal may include ancillary data as well as the audio descriptor 101 and the downmix signal 103. The present invention may include the spatial information signal 105 as ancillary data. In order for an audio signal decoding apparatus to know basic information of audio codec without analyzing an audio signal, the audio signal may selectively include the audio descriptor 101. The audio descriptor 101 is comprised of small number of basic informations necessary for audio decoding such as a transmission rate of a transmitted audio signal, a number of channels, a sampling frequency of compressed data, an identifier indicating a currently used codec and the like. An audio signal decoding apparatus is able to know a type of a codec used by an audio signal using the audio descriptor 101. In particular, using the audio descriptor 6 101, the audio signal decoding apparatus is able to know whether a received audio signal is the signal restoring a multi-channel using the spatial information signal 105 and the downmix signal 103. In this case, the multi-channel may include a virtual 3-dimensional surround as well as an actual multi-channel. By the virtual 3-dimensional surround technology, an audio signal having the spatial information signal 105 and the downmix signal 103 combined together is made audible through one or two channels. The audio descriptor 101 is located independent from the downmix or the spatial information signal 103 or 105 included in the audio signal. For instance, the audio descriptor 101 is located within a separate field indicating an audio signal. In case that a header is not provided to the downmix signal 103, the audio signal decoding apparatus is able to decode the downmix signal 103 using the audio descriptor 101. The downmix signal 103 is a signal generated from downmixing a multi-channel. The downmix signal 103 can be generated from a downmixing unit (not shown in the drawing) included in an audio signal encoding apparatus (not shown in the drawing) or generated artificially. The downmix signal 103 can be categorized into a case 7 of including the spatial information signal 105 and a case of not including the header. In case that the downmix signal 103 includes the header, the header is included in each frame by a frame unit. In case that the downmix signal 103 does not include the header, as mentioned in the foregoing description, the downmix signal 103 can be decoded using the audio descriptor 101 by an audio signal decoding apparatus. The downmix signal 103 takes either a form of including the header for each frame or a form of not including the header. And, the downmix signal 103 is included in an audio signal in a same manner until contents end. The spatial information signal 105 is also categorized into a case of including the header and spatial information and a case of including the spatial information only without including the header. The header of the spatial information signal 105 differs from that of the downmix signal 103 in that it is unnecessary to be inserted in each frame identically. In particular, the spatial information signal 105 is able to use a frame including the header and a frame not including the header together. Most of information included in the header of the spatial information signal 105 is configuration information that decodes the spatial information by interpreting the spatial 8 information. FIG. 2 is a configurational diagram of an audio signal transferred to an audio signal decoding apparatus from an audio signal encoding apparatus according to another embodiment of the present invention. Referring to FIG. 2, an audio signal includes the downmix signal 103 and the spatial information signal 105. And, the audio signal exists in an ES (elementary stream) form that frames are arranged. Each of the downmix signal 103 and the spatial information signal 105 is occasionally transferred as a separate ES form to an audio signal decoding apparatus. And the downmix signal 103 and the spatial information signal 105, as shown in FIG. 2, can be combined into one ES form to be transferred to the audio signal decoding apparatus. In case that the downmix signal 103 and the spatial information signal 105, which are combined into one ES form, are transferred to the audio signal decoding apparatus, the spatial information signal 105 can be included in a position of ancillary data (ancillary data) or additional data (extension data) of the downmix signal 103. And, the audio signal may include signal identification information indicating whether the spatial informatic: n signal 105 is combined with the downmix signal 9 103. A frame of the spatial information signal 105 can be categorized into a case of including the header 201 and the spatial information 203 and a case of including the spatial information 203 only. In particular, the spatial information signal 105 is able to use a frame including the header 201 and a frame not including the header 201 together. In the present invention, the header 201 is inserted in the spatial information signal 105 at least once. In particular, an audio signal encoding apparatus may insert the header 201 into each frame in the spatial information signal 105, periodically insert the header 201 into each fixed interval of frames in the spatial information signal 105 or non-periodically insert the header 201 into each random interval of frames in the spatial information signal 105. The audio signal may include information (hereinafter named header identification information') indicating whether the header 201 is included in a frame 201. In case that the header 201 is included in the spatial information signal 105, the audio signal decoding apparatus extracts the configuration information 205 from the header 201 and then decodes the spatial informatior 203 10 transferred after (behind) the header 201 according to the configuration information 205. Since the header 201 is information for decoding by interpreting the spatial information 203, the header 201 is transferred in the early stage of transferring the audio signal. In case that the header 201 is not included in the spatial information signal 105, the audio signal decoding apparatus decodes the spatial information 203 using the header 201 transferred in the early stage. In case that the header 201 is lost while the audio signal is transferred to the audio signal decoding apparatus from the audio signal encoding apparatus or in case that the audio signal transferred in a streaming format is decoded from its middle part to be used for broadcasting or the like, it is unable to use the header 201 that was previously transferred. In this case, the audio signal decoding apparatus extracts the configuration information 205 from the header 201 different from the former header 201 firstly inserted in the audio signal and is then able to decode the audio signal using the extracted configuration information 205. In this case, the configuration information 205 extracted from the header 201 inserted in the audio s Lgnal may be identical to the former configuration information 205 extracted from the header 201 11 which had been transferred in the early stage or may not. If the header 201 is variable, the configuration information 205 is extracted from a new header 201, the extracted configuration information 205 is decoded and the spatial information 203 transmitted behind the header 201 is then decoded. If the header 201 is invariable, it is decided whether the new header 201 is identical to the old header 201 that was previously transferred. If theses two headers 201 are different from each other, it can be detected that an error occurs in an audio signal on an audio signal transfer path. The configuration information 205 extracted from the header 201 of the spatial information signal 105 is the information to interpret the spatial information 203. The spatial information signal 105 is able to include information (hereinafter named xtime align information' ) for discriminating a time delay difference between two signals in generating a multi-channel using the downmix signal 103 and the spatial information signal 105 by the audio signal decoding apparatus. An audio signal transferred to the audio signal decoding apparatus from the audio signal encoding apparatus is parsed by a demultiplexing unit (not shown in the drawing) and is then separated into the downmix signal 103 12 and the spatial information signal 105. The downmix signal 103 separated by the demultiplexing unit is decoded. A decoded downmix signal 103 generates a multi-channel using the spatial information signal 105. In generating the multi-channel by combining the downmix signal 103 and the spatial information signal 105, the audio signal decoding apparatus is able to adjust synchronization between two signals, a position of a start point of combining two signals and the like using the time align information (not shown in the drawing) included in the configuration information 205 extracted from the header 201 of the spatial information signal 105. Position information 207 of a time slot to which a parameter will be applied is included in the spatial information 203 included in the spatial information signal 105. As a spatial parameter (spatial cue), there is CLDs (channel level differences) indicating an energy difference between audio signals, ICCs (interchannel correlations) indicating closeness or similarity between audio signals, CPCs (channel prediction coefficients) indicating a coefficient predicting an audio signal value using other signals. Hereinafter, each spatial cue or a bundle of spatial cues will be called 'parameter' . In case N parameters exist in i frame included in the 13 spatial information signal 105, the N parameters are applied to specific time slot positions of frames, respectively. If information indicating a parameter will be applied to which one of time slots included in a frame is named the position information 207 of the time slot, the audio signal decoding apparatus decodes the spatial information 203 using the position information 207 of the time slot to which the parameter will be applied. In this case, the parameter is included in the spatial information 203. FIG. 3 is a schematic block diagram of an apparatus for decoding an audio signal according to one embodiment of the present invention. Referring to FIG. 3, an apparatus for decoding an audio signal according to one embodiment of the present invention includes a receiving unit 301 and an extracting unit 303. The receiving unit 301 of the audio signal decoding apparatus receives an audio signal transferred in an ES form by an audio signal encoding apparatus via an input terminal INI. The audio signal received by the audio signal decoding apparatus includes an audio descriptor 101 and the downmix signal 103 and may further include the spatial 14 information signal 105 as ancillary data (ancillary data) or additional data (extension data). The extracting unit 303 of the audio signal decoding apparatus extracts the configuration information 205 from the header 201 included in the received audio signal and then outputs the extracted configuration information 205 via an output terminal OUT1. The audio signal may include the header identification information for identifying whether the header 201 is included in a frame. The audio signal decoding apparatus identifies whether the header 201 is included in the frame using the header identification information included in the audio signal. If the header 201 is included, the audio signal decoding apparatus extracts the configuration information 205 from the header 201. In the present invention, at least one header 201 is included in the spatial information signal 105. FIG. 4 is a block diagram of an apparatus for decoding an audio signal according to another embodiment of the present invention. Referring to FIG. 4, an apparatus for decoding an audio signal according to another embodiment of the present invention includes the receiving unit .301, the 15 demultiplexing unit 401, a core decoding unit 403, a multi- channel generating unit 405, a spatial information decoding unit 407 and the extracting unit 303. The receiving unit 301 of the audio signal decoding apparatus receives an audio signal transferred in a bitstream form from an audio signal encoding apparatus via an input terminal IN2. And, the receiving unit 301 sends the received audio signal to the demultiplexing unit 401. The demultiplexing unit 401 separates the audio signal sent by the receiving unit 301 into an encoded downmix signal 103 and an encoded spatial information signal 105. The demultiplexing unit 401 transfers the encoded downmix signal 103 separated from a bitstream to the core decoding unit 403 and transfers the encoded spatial information signal 105 separated from the bitstream to the extracting unit 303. The encoded downmix signal 103 is decoded by the core decoding unit 403 and is then transferred to the multi- channel generating unit 405. The encoded spatial information signal 105 includes the header 201 and the spatial information 203. If the header 201 is included in the encoded spatial information signjil 105, the extracting unit 303 extracts the configuratior information 205 from the header 201. The 16 extracting unit 303 is able to discriminate a presence of the header 201 using the header identification information included in the audio signal. In particular, the header identification information may represent whether the header 201 is included in a frame included in the spatial information signal 105. The header identification information may indicate an order of a frame or a bit sequence of the audio signal, in which the configuration information 205 extracted from the header 201 is included if the header 201 is included in the frame. In case of deciding that the header 201 is included in the frame via the header identification information, the extracting unit 303 extracts the configuration information 205 from the header 201 included in the frame. The extracted configuration information 205 is then decoded. The spatial information decoding unit 407 decodes the spatial information 2 03 included in the frame according to decoded configuration information 205. And, the multi-channel generating unit 4 05 generates a multi-channel signal using the decoded downmix signal 103 and decoded spatial information 203 and then outputs the generated multi-channel signal via an output terminal OUT2. FIG. 5 is a flowchart of a method of decoding an audio signal according to one embodiment of the present 17 invention. Referring to FIG. 5, an audio signal decoding apparatus receives the spatial information signal 105 transferred in a bitstream form by an audio signal encoding apparatus (S501). As mentioned in the foregoing description, the spatial information signal 105 can be categorized into a case of being transferred as an ES separated from the downmix signal 103 and a case of being transferred by being combined with the downmix signal 103. The demultiplexing unit 401 of an audio signal separates the received audio signal into the encoded downmix signal 103 and the encoded spatial information signal 105. The encoded spatial information signal 105 includes the header 201 and the spatial information 203. If the header 201 is included in a frame of the spatial information signal 105, the audio signal decoding apparatus identifies the header 201 (S503). The audio signal decoding apparatus extracts the configuration information 205 from the header 201 (S505) . And, the audio signal decoding apparatus decodes the spatial information 203 using the extracted configuration information 205 (S507). FIG. 6 is a flowchart of a method of decoding an 18 audio signal according to another embodiment of the present invention. Referring to FIG. 6, an audio signal decoding apparatus receives the spatial information signal 105 transferred in a bitstream form by an audio signal encoding apparatus (S501) . As mentioned in the foregoing description, the spatial information signal 105 can be categorized into a case of being transferred as an ES separated from the downmix signal 103 and a case of being transferred by being included in ancillary data or extension data of the downmix signal 103. The demultiplexing unit 401 of an audio signal separates the received audio signal into the encoded downmix signal 103 and the encoded spatial information signal 105. The encoded spatial information signal 105 includes the header 201 and the spatial information 203. The audio signal decoding apparatus decides whether the header 201 is included in a frame (S601). If the header 201 is included in the frame, the audio signal decoding apparatus identifies the header 201 (S503). The audio signal decoding apparatus then extracts the configuration information 205 from the header 201 (S505)'. The audio signal decoding apparatus decides whether 19 the configuration information 205 extracted from the header 201 is the configuration information 205 extracted from a first header 201 included in the spatial information signal 105 (S603) . If the configuration information 205 is extracted from the header 201 extracted first from the audio signal, the audio signal decoding apparatus decodes the configuration information 205 (S611) and decodes the spatial information 203 transferred behind the configuration information 205 according to the decoded configuration information 205. If the header 201 extracted from the audio signal is not the header 201 extracted first from the spatial information signal 105, the audio signal decoding apparatus decides whether the configuration information 205 extracted from the header 201 is identical to the configuration information 205 extracted from the first header 201 (S605). If the configuration information 205 is identical to the configuration information 205 extracted from the first header 201, the audio signal decoding apparatus decodes the spatial information 203 using the decoded configuration information 205 extracted from the first header 201. If the extracted configuration inform ition 205 is not identical to the configuration information 205 extracted 20 from the first header 201, the audio signal decoding apparatus decides whether an error occurs in the audio signal on a transfer path from the audio signal encoding apparatus to the audio signal decoding apparatus (S607). If the configuration information 205 is variable, the error does not occur even if the configuration information 205 is not identical to the configuration information 205 extracted from the first header 201. Hence, the audio signal decoding apparatus updates the header 201 into the new header 201 (S609). The audio signal decoding apparatus then decodes the configuration information 205 extracted from the updated header 201 (S611). The audio signal decoding apparatus decodes the spatial information 203 transferred behind the configuration information 205 according to the decoded configuration information 205. If the configuration information 205, which is invariable, is not identical to the configuration information 2 05 extracted from the first header 201, it means that the error occurs on the audio signal transfer path. Hence, the audio signal decoding apparatus removes the spatial information 203 included in the frame including the erroneous configuration information 205 or corrects the error of the spatial information 203 (S613) . 21 FIG. 7 is a flowchart of a method of decoding an audio signal according to a further embodiment of the present invention. Referring to FIG. 7, an audio signal decoding apparatus receives the spatial information signal 105 transferred in a bitstream form by an audio signal encoding apparatus (S501). The demultiplexing unit 401 of an audio signal separates the received audio signal into the encoded downmix signal 103 and the encoded spatial information signal 105. In this case, the position information 207 of the time slot to which a parameter will be applied is included in the spatial information signal 105. The audio signal decoding apparatus extracts the position information 207 of the time slot from the spatial information 203 (S701). The audio signal decoding apparatus applies a parameter to the corresponding time slot by adjusting a position of the time slot, to which the parameter will be applied, using the extracted position information of the time slot (S703). FIG. 8 is a flowchart of a method of obtaining a position information representing quantity according to :>ne embodiment of the present invention. A position information 22 representing quantity of a time slot is the number of bits allocated to represent the position information 207 of the time slot. The position information representing quantity of the time slot, to which a first parameter is applied, can be found by subtracting the number of parameters from the number of time slots, adding 1 to the subtraction result, taking a 2-base logarithm on the added value and applying a ceil function to the logarithm value. In particular, the position information representing quantity of the time slot, to which the first parameter will be applied, can be found by ceil (log2 (k-i+1) ) , where k' and *i' are the number of time slots and the number of parameters, respectively. Assuming that XN' is a natural number, the position information representing quantity of the time slot, to which an (N+l)th parameter will be applied, is represented as the position information 207 of the time slot to which an Nth parameter is applied. In this case, the position information 207 of the time slot, to which an Nth parameter is applied, can be found by adding the number of time slots existing between the time slot to which the Nth parameter is applied and a time slot to which an (N-l)th parameter is applied to the position information of the time slot to which the (N-l)th parameter is applied and adding 1 to the 23 added value (S801). In particular, the position information of the time slot to which the (N+l)th parameter will be applied can be found by j(N)+r(N+l)+1, where r(N+l) indicates the number of time slots existing between the time slot to which the (N+l)th parameter is applied and the time slot to which the Nth parameter is applied. If the position information 207 of the time slot to which the Nth parameter is applied is found, the time slot position information representing quantity representing the position of the time slot to which the (N+l)th parameter is applied can be obtained. In particular, the time slot position information representing quantity representing the position of the time slot to which the (N+l)th parameter is applied can be found by subtracting the number of parameters applied to a frame and the position information of the time slot to which the Nth parameter is applied from the number of time slots and adding (N+l) to the subtraction value (S803). In particular, the position information representing quantity of the time slot to which the (N+l)th parameter is applied can be found by ceil(log2(k-i+N+l-j (N) ) ) , where *k', *i' and Aj (N) ' are the number of time slots, the number of parameters and the position information 205 of the time slot to which an Nth parameter is applied, respectively. 24 In case of obtaining the position information representing quantity of the time slot in the above- explained manner, the position information representing quantity of the time slot to which the (N+l)th parameter is applied has the number of allocated bits inverse- proportional to *N'. Namely, the position information representing quantity of the time slot to which the parameter is applied is a variable value depending on *N'. FIG. 9 is a flowchart of a method of decoding an audio signal according to further embodiment of the present invention. An audio signal decoding apparatus receives an audio signal from an audio signal encoding apparatus (S901). The audio signal includes the audio descriptor 101, the downmix signal 103 and the spatial information signal 105. The audio signal decoding apparatus extracts the audio descriptor 101 included in the audio signal (S903). An identifier indicating an audio codec is included in the audio descriptor 101. The audio signal decoding apparatus recognizes that the audio signal includes the downmix signal 103 and the spatial information signal 105 using the audio descriptor 101. In particular, the audio signal decoding apparatus is able to discriminate that the transferred audio signal is a 25 signal for generating a multi-channel, using the spatial information signal 105(S905). And, the audio signal decoding apparatus converts the downmix signal 103 to a multi-channel signal using the spatial information signal 105. As mentioned in the foregoing description, the header 201 can be included in the spatial information signal 105 each predetermined interval. INDUSTRIAL APPLICABILITY As mentioned in the foregoing description, a method and apparatus for encoding and decoding an audio signal according to the present invention can make a header selectively included in a spatial information signal. And, in case that a plurality of headers are included in the spatial information signal, a method and apparatus for encoding and decoding an audio signal according to the present invention can decode spatial information even if the audio signal is reproduced from a random point by the audio signal decoding apparatus. While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled 26 in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents. WHAT IS CLAIMED IS: 1. An audio signal decoding method comprising: receiving an audio signal including a downmix signal and a spatial information signal; if a header is included in the spatial information signal, extracting configuration information from the header; extracting spatial information included in the spatial information signal; and converting the downmix signal to a multi-channel signal using the configuration information and the spatial information. 2. The audio signal decoding method of claim 1, wherein the converting of the downmix signal comprising: adjusting start points of the downmix signaA and the 27 spatial information signal using time align information included in the configuration information; and applying a parameter included in the spatial information to a corresponding time slot using position information of the corresponding time slot included in the spatial information. 3. The audio signal decoding method of claim 2, wherein a position information representing quantity of the time slot is variable. 4. The audio signal decoding method of claim 2, wherein the position information representing quantity of the time slot to which an Nth parameter is applied is obtained using at least one selected from the group composing of a number of the time slots, a number of the parameters, N and position information of a time slot to which an (N-l)th the parameter is applied. 5. The audio signal decoding method of claim 4, wherein the position information representing quantity of the time slot to which the parameter after the second is applied is obtained by ceil(log2 (k-i+N-j(N-l))) wherein 'k', 'i' and 'j(N-1)' are the number of time slots, the number 28 of the parameters and the position information of the time slot to which the (N-l)th parameter is applied, respectively. 6. The audio signal decoding method of claim 4, wherein the position information representing quantity of the time slot to which a first parameter is applied is obtained by ceil (log2 (k-i+1) ) wherein *k' and Ai' are the number of the time slots and the number of the parameters, respectively. 7. The audio signal decoding method of claim 5, wherein the position information of the time slot to which an Nth parameter is applied is found by j (N-l)+r(N)+1 wherein 'r(N)' is a number of the time slots existing between the time slot to which the Nth parameter is applied and the time slot to which (N-l)th parameter is applied. 8. The audio signal decoding method of claim 1, wherein the audio signal includes at least one selected from the group composing of signal identification information indicating whether the spatial information signal is combined with the downmix signal and header identification information indicating whether the header is 29 included in the spatial information signal. 30 A method and apparatus for encoding and decoding an audio signal are provided. The present invention includes receiving an audio signal including a downmix signal and a spatial information signal, if a header is included in the spatial information signal, extracting configuration information from the header, extracting spatial information included in the spatial information signal, and converting the downmix signal to a multi-channel signal using the configuration information and the spatial information. Accordingly, the header can be selectively included in the spatial information signal, thereby if the header is plurally included in the spatial information signal, it is able to decode spatial information in case of reproducing the audio signal from a random point.

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