Patent Publication Number: US-2012033819-A1

Title: Signal processing method, encoding apparatus therefor, decoding apparatus therefor, and information storage medium

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims priority from U.S. Provisional Application No. 61/371,294 filed on Aug. 6, 2010, and Korean Patent Application No. 10-2011-0056342, filed on Jun. 10, 2011 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference. 
    
    
     BACKGROUND 
     1. Field 
     Method and apparatuses consistent with exemplary embodiments relate to a signal processing method, an encoding apparatus therefor, a decoding apparatus therefor, and an information storage medium, and more particularly, to a signal processing method for inserting additional information into a bitstream, an encoding apparatus therefor, a decoding apparatus therefor, and an information storage medium. 
     2. Description of the Related Art 
     To compress and transmit an audio signal, and receive the compressed audio signal and restore the original audio signal, a decoder is used in a transmission end, and an encoder is used in a reception end. The transmission end and the reception end respectively compress and restore an audio signal according to a predetermined standard. 
     One standard for transmitting an audio signal is Audio Coding-3 (AC-3). AC-3 is a third format of an audio coding scheme developed by Dolby Laboratories, Inc. in the United States of America and an audio standard for Digital Video Discs (DVDs). AC-3 uses 5.1 channels to represent sound. In particular, AC-3 uses 5.1 channels for separately outputting audio signals through 6 corresponding speakers, i.e., a left speaker, a right speaker, a center speaker, a left surround speaker, a right surround speaker, and a sub-woofer speaker for a low frequency effect. 
     Recently, to implement a more stereoscopic sound system, methods and apparatuses for generating an audio signal by increasing the number of audio channels more than the 5.1 channels have been developed. For example, a 10.2-channel audio system capable of outputting separate audio signals to 12 corresponding speakers has been developed. 
     The AC-3 standard limits the number of compressible audio channels to 5+1=6. Thus, according to the AC-3 standard, only bitstreams conforming to 5.1 channels can be generated and transmitted, but bitstreams beyond 5.1 channels cannot be generated or transmitted. 
     The Enhanced AC-3 standard obtained by enhancing the AC-3 standard limits the number of compressible audio channels to maximum 13.1 channels. Thus, bitstreams beyond 13.1 channels cannot be generated or transmitted under the Enhanced AC-3 standard. 
     Accordingly, a method and apparatus for generating and transmitting an audio signal beyond 5.1 channels under the AC-3 standard are required. 
     In addition, a method and apparatus for generating and transmitting an audio signal beyond 13.1 channels under the Enhanced AC-3 standard are required. 
     SUMMARY OF THE INVENTION 
     One or more exemplary embodiments may overcome the above disadvantages and other disadvantages not described above. However, it is understood that one or more exemplary embodiment are not required to overcome the disadvantages described above, and may not overcome any of the problems described above. 
     According to an aspect of an exemplary embodiment, there is provided a signal processing, the method including: extracting additional information which is for performing at least one of a channel number expansion of an audio signal in an encoding apparatus and a three-dimensional (3D) reproduction of the audio signal in the encoding apparatus; encoding the audio signal according to a predetermined standard; formatting the encoded audio signal into a bitstream including bitstream information, at least one audio block and an auxiliary data field; and inserting the additional information into at least one of additional bitstream information included in the bitstream information, a skip field included in the audio block and auxiliary data bits included in the auxiliary data field. 
     The additional information may include at least one of multi-channel restoration information for expanding a number of channels to be greater than a number of audio channels included in the bitstream, and 3D information of the audio signal. 
     The multi-channel restoration information may include at least one of information regarding the audio channels, information for down-mixing the audio signal according to a number of channels defined in the predetermined standard and parameter information for up-mixing the down-mixed audio signal. 
     The bitstream information may include: additional bitstream existence information indicating whether the additional bitstream information exists; and length information of the additional bitstream information, wherein the additional bitstream information includes the additional information. 
     The audio block may include: skip field existence information indicating whether the skip field exists; and length information of the skip field, wherein the skip field includes the additional information. 
     The auxiliary data field may include: the auxiliary data bits including the additional information; length information of the auxiliary data; and auxiliary data existence information which indicates whether the auxiliary data exists. 
     The signal processing method may further include determining whether to perform at least one of the channel number expansion and the 3D reproduction of the audio signal. 
     If a number of channels included in the audio signal input to the encoding apparatus is greater than a number of channels allowed in the predetermined standard, the encoding may include down-mixing the audio signal according to a number of channels allowed in the predetermined standard. 
     If the additional information is inserted into the bitstream, the method further include transmitting the bitstream from the encoding apparatus to the decoding apparatus. 
     The signal processing method may further include: deformatting the bitstream in the decoding apparatus; and extracting the additional information from at least one of the additional bitstream information, the skip field and the auxiliary data bits of the deformatted bitstream. 
     The signal processing method may further include: determining whether an expanded channel exists, based on the extracted additional information; and if an expanded channel exists, decoding the deformatted bitstream according to the expanded number of channels, wherein the decoding the deformatted bitstream is based on the extracted additional information. 
     The signal processing method may further include: determining whether the decoding apparatus can perform the channel number expansion. 
     If the decoding apparatus cannot perform the channel number expansion, the method may further include decoding the deformatted bitstream without extracting the additional information. 
     According to an aspect of another exemplary embodiment, there is provided an encoding apparatus including: a controller which extracts additional information that is information for performing at least one of a channel number expansion of an audio signal and a three-dimensional (3D) reproduction of the audio signal; an encoder which encodes the audio signal according to a predetermined standard under a control of the controller; and a formatter which formats the encoded audio signal into a bitstream including bitstream information, at least one audio block and an auxiliary data field, wherein the controller which controls to insert the additional information into at least one of additional bitstream information included in the bitstream information, a skip field included in the audio block and auxiliary data bits included in the auxiliary data field. 
     The additional information may include at least one of multi-channel restoration information, which is for expanding the number of channels to be greater than a number of audio channels included in the bitstream, and 3D information of the audio signal. 
     If the additional information is inserted into the bitstream, the controller may transmit the bitstream from the encoding apparatus to a decoding apparatus. 
     According to an aspect of another exemplary embodiment, there is provided a decoding apparatus including: a deformatter which deformats a bitstream including bitstream information, at least one audio block and an auxiliary data field; a controller which extracts additional information, which is for performing at least one of a channel number expansion and a three-dimensional (3D) reproduction of the bitstream from at least one of additional bitstream information included in the bitstream information, a skip field included in the audio block and auxiliary data bits included in the auxiliary data field; and a decoder which decodes the deformatted bitstream. 
     Based on the extracted additional information, the controller may determine whether an expanded channel exists, and if an expanded channel exists, the decoder decodes the deformatted bitstream according to meet the expanded number of channels. 
     The additional information may include at least one of multi-channel restoration information, which is for expanding the number of channels to a number greater than a number of audio channels included in the bitstream, and 3D information of the audio signal. 
     According to an aspect of another exemplary embodiment, there is provided a non-transitory information storage medium storing a bitstream having an audio signal, wherein the bitstream includes: bitstream information including an additional bitstream information area; at least one audio block including a skip field area; and an auxiliary data field including an auxiliary data bit area wherein at least one of the additional bitstream information area, the skip field area and the auxiliary data bit area includes additional information which is for performing at least one of a channel number expansion and a three-dimensional (3D) reproduction of the audio signal. 
     The additional information may include at least one of multi-channel restoration information, which is for expanding the number of channels to a number greater than a number of audio channels included in the bitstream, and 3D information of the audio signal. 
     The multi-channel restoration information may include at least one of information regarding the audio channels, information for down-mixing the audio signal according to a number of channels defined in the predetermined standard, and parameter information for up-mixing the down-mixed audio signal. 
     The bitstream information may include: additional bitstream existence information which indicates whether the additional bitstream information exists; and length information of the additional bitstream information, wherein the additional bitstream information includes the additional information. 
     The audio block may include: skip field existence information which indicates whether the skip field exists; and length information of the skip field, wherein the skip field includes the additional information. 
     The auxiliary data field may include: the auxiliary data bits which include the additional information; length information of the auxiliary data; and auxiliary data existence information which indicates whether the auxiliary data exists. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a block diagram of an audio system for transmitting and receiving an audio signal; 
         FIG. 2  is a block diagram of an encoding apparatus according to an exemplary embodiment and a block diagram of a decoding apparatus according to an exemplary embodiment; 
         FIG. 3  is a flowchart illustrating a signal processing method according to an exemplary embodiment; 
         FIG. 4  is a configuration diagram of a bitstream according to an exemplary embodiment; 
         FIG. 5  is a configuration diagram of a bitstream according to the AC-3 standard and a configuration diagram of a bitstream according to the Enhanced AC-3 standard; 
         FIG. 6  is a configuration diagram of a bitstream into which additional information is inserted, according to an exemplary embodiment; 
         FIG. 7  illustrates bitstream information including additional information; 
         FIG. 8  illustrates an audio block including additional information; 
         FIG. 9  illustrates an auxiliary data field including additional information; 
         FIG. 10  is a flowchart illustrating a signal processing method according to another exemplary embodiment; 
         FIG. 11  is a flowchart illustrating a signal processing method according to another exemplary embodiment; and 
         FIG. 12  is a flowchart illustrating a signal processing method according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram of an audio system  100  for transmitting and receiving an audio signal. 
     Referring to  FIG. 1 , the audio system  100  includes an encoding apparatus  110  that is a transmission end of an audio signal and a decoding apparatus  120  that is a reception end of the audio signal. 
     The encoding apparatus  110  receives an audio signal including a plurality of channels and compresses the audio signal according to a predetermined standard, e.g., the AC-3 or Enhanced AC-3 standard. Hereinafter, the audio system  100  operating according to the AC-3 standard is illustrated. That is, the encoding apparatus  110  performs AC-3 encoding and transmits an encoded bitstream to the decoding apparatus  120 . 
     The decoding apparatus  120  receives the encoded bitstream and decodes the encoded bitstream to output the original audio signal. That is, the decoding apparatus  120  generates a restored audio signal by performing AC-3 decoding. 
     In general, the encoding apparatus  110  outputs a bitstream having the number of channels limited to 5.1 channels according to the AC-3 standard. Also, the decoding apparatus  120  typically outputs an audio signal having 5.1 channels by restoring the bitstream. That is, the decoding apparatus  120  can only generate audio signals having 5.1 channels but cannot generate an audio signal having an expanded number of channels more than the 5.1 channels. 
     Hereinafter, a signal processing method capable of performing at least one of channel number expansion and 3D reproduction of an audio signal by inserting additional information into a bitstream according to an exemplary embodiment, an encoding apparatus therefor, a decoding apparatus therefor, and an information storage medium will be described in detail with reference to  FIGS. 2 to 12 . 
       FIG. 2  is a block diagram of an encoding apparatus  210  according to an exemplary embodiment and a block diagram of a decoding apparatus  250  according to an exemplary embodiment. The encoding apparatus  210  and the decoding apparatus  250  may perform encoding and decoding according to at least one of the AC-3 standard and the Enhanced AC-3 standard, respectively. 
     Hereinafter, it is illustrated that the encoding apparatus  210  and the decoding apparatus  250  perform encoding and decoding according to the AC-3 standard, respectively. 
       FIG. 2A  is a block diagram of the encoding apparatus  210  according to an exemplary embodiment. 
     Referring to  FIG. 2A , the encoding apparatus  210  includes an encoder  220 , a formatter  225 , and a controller  230 . 
     Hereinafter, the controller  230  included in the encoding apparatus  210  is called a first controller  230 , and a controller  270  included in the decoding apparatus  250  is called a second controller  270 . 
     The encoder  220  receives an audio signal and encodes the received audio signal under a control of the first controller  230 . 
     In detail, the received audio signal may be an audio signal of 10.2 channels. The encoder  220  may compress the received audio signal to an audio signal of maximum 5.1 channels according to the AC-3 standard. Thus, the encoder  220  generates and outputs an audio signal of 5.1 channels by down-mixing the audio signal of 10.2 channels. 
     The formatter  225  formats the encoded audio signal to a bitstream including bitstream information (BSI), at least one audio block (AB), and an auxiliary data field (Aux) under a control of the first controller  230 . 
     The first controller  230  controls to insert additional information into at least one of additional BSI (addbsi) included in the BSI, a skip field (skipfld) included in the AB, and auxiliary data bits (auxbits) included in the auxiliary data field. 
     The additional information includes at least one of multi-channel restoration information for expanding the number of channels to a number greater than the number of audio channels included in the bitstream and 3D information of the audio signal. 
     For example, when the bitstream output from the encoding apparatus  210  includes 5.1 channels, i.e., 6 channels, the multi-channel restoration information may be a parameter value required for the decoding apparatus  250  to perform decoding in order to receive the bitstream including 5.1 channels and output an audio signal including 10.2 channels. 
     In detail, the multi-channel restoration information may include at least one of information regarding the audio channels, a method of down-mixing the audio signal to meet the number of channels defined in the predetermined standard, and parameter information used to up-mix the down-mixed audio signal. 
     In detail, the information regarding the audio channels includes the number of layers, the number of speakers per layer, and a speaker configuration per layer. For example, in a case of 5.1 channels, there are front and rear layers, wherein the front layer includes 3 speakers on the left, right and center, and the rear layer includes 2 speakers on the left and right. The left, right and center speakers of the front layer may be disposed in a predetermined configuration. 
     The down-mixing method includes a formatting method or formatting information for down-mixing an audio signal including the number of channels more than the number of channels allowed in the predetermined standard to meet the allowed number of channels. In detail, the down-mixing method includes a formatting method or formatting information for down-mixing channels more than the number of channels allowed in an AC-3 audio coding mode (acmod). 
     The parameter information may include spatial parameter information applied when the decoding apparatus  250  performs up-mixing. In detail, the spatial parameter information may include at least one of a parameter indicating a signal level relationship between an input signal and an output signal, a parameter indicating a phase relationship between the input signal and the output signal, and correlation information between the input signal and the output signal. For example, the input signal corresponds to signal before encoding and the output signal corresponds to signal after encoding. 
     The 3D information of the audio signal may include at least one of depth information and layer information of the audio signal. 
     The first controller  230  may transmit the bitstream into which the additional information is inserted to the decoding apparatus  250 . 
       FIG. 2B  is a block diagram of the decoding apparatus  250  according to an exemplary embodiment. 
     Referring to  FIG. 2B , the decoding apparatus  250  includes a decoder  260 , a deformatter  265 , and the second controller  270 . 
     The deformatter  265  receives the bitstream including the BSI, the AB, and the auxiliary data field and deformats the received bitstream. In detail, the deformatter  265  deformats the format of the received bitstream so that the received bitstream has the format before passing through the formatter  225 . 
     The second controller  270  extracts the additional information from at least one of the additional BSI included in the BSI, the skip field included in the AB, and auxiliary data bits included in the auxiliary data field. 
     The decoder  260  decodes the deformatted bitstream according to the predetermined standard. 
     In detail, the second controller  270  may determine whether an expanded channel exists, based on the extracted additional information. If an expanded channel exists as a result of the determination, the second controller  270  controls the decoder  260  to decode the bitstream deformatted by the deformatter  265  to meet the expanded number of channels. In this case, the second controller  270  controls the decoder  260  to decode the bitstream by using the extracted additional information. 
     Whether an expanded channel exists may be determined by checking whether the multi-channel restoration information is included in the additional information. 
     For example, if the bitstream received to the decoding apparatus  250  includes 5.1 channels according to the AC-3 standard, the additional information may include the multi-channel restoration information for expanding the bitstream of 5.1 channels to an audio signal of 10.2 channels. In this case, the second controller  270  controls the decoder  260  to extract the additional information including the multi-channel restoration information and output the audio signal of 10.2 channels from the bitstream of 5.1 channels by using the multi-channel restoration information. 
     If the 3D information is included in the extracted additional information, the second controller  270  may control the decoder  260  to reproduce the audio signal in a 3D way by using the 3D information. In detail, the decoder  260  decodes the bitstream to output an audio signal having a predetermined depth under a control of the second controller  270 . 
     If both the multi-channel restoration information and the 3D information are included in the extracted additional information, the second controller  270  may control the decoder  260  to decode the bitstream so as to have more than the number of channels according to the predetermined standard and output audio signals, each audio signal having a predetermined depth. 
     Operations of the encoding apparatus  210  and the decoding apparatus according to an exemplary embodiment are the same as operations of the signal processing methods according to exemplary embodiments to be described with reference to  FIGS. 3 to 12 . 
       FIG. 3  is a flowchart illustrating a signal processing method  300  according to an exemplary embodiment. 
     Referring to  FIG. 3 , according to the signal processing method  300 , in operation  310 , additional information that is information for performing at least one of channel number expansion and 3D reproduction of an audio signal is extracted or generated. Operation  310  may be performed by the first controller  230  of the encoding apparatus  210 . The additional information may be input to the encoding apparatus  210  from the outside, wherein the first controller  230  extracts the input additional information. Alternatively, the additional information may be generated by the first controller  230  according to a request of a user or a determination of the encoding apparatus  210 . 
     In operation  320 , an audio signal input to the encoding apparatus  210  is encoded according to a predetermined standard. Here, if the number of channels included in the input audio signal is greater than the number of channels allowed in the predetermined standard, the input audio signal is down-mixed. 
     For example, if the encoding apparatus  210  conforms to the AC-3 standard, the input audio signal is encoded to meet 5.1 channels. In detail, when the input audio signal exceeds 5.1 channels, e.g., if the input audio signal is a 10.2-channel audio signal, the input audio signal is down-mixed to 5.1 channels. In this case, the additional information may include restoration information for expanding the 5.1 channels to the 10.2-channels. Operation  320  may be performed by the encoder  220  under a control of the first controller  230 . 
     In operation  330 , the encoded audio signal output from the encoder  220  is formatted to a bitstream including BSI, at least one AB, and an auxiliary data field. Operation  330  may be performed by the formatter  255  under a control of the first controller  230 . The bitstream generated in operation  330  is described in detail with reference to  FIGS. 4 and 5  below. 
       FIG. 4  is a configuration diagram of a bitstream according to an exemplary embodiment. An information storage medium according to an exemplary embodiment records and stores the bitstreams illustrated in  FIGS. 4 and 5 . 
     Referring to  FIG. 4 , a bitstream  400  generated in operation  330  includes a plurality of consecutive frames  410 . A single frame  410  includes BSI  402 , an AB field  403 , and an auxiliary data field  404 . The AB field  403  includes at least one AB. The frame  410  further includes synchronization information (SI)  401 . The frame  410  may further include a cyclic redundancy check (CRC) code  405  or an error detection code (not shown). 
     The SI indicates the start of a frame and has a fixed number of bits. The BSI  402  includes information required to reproduce an actual audio signal or information required to decode an audio signal. The AB field  403  is a field on which an actual audio signal is carried. 
     The auxiliary data field  404  may include data remaining by excluding the actual audio signal in the single frame  410 . The auxiliary data field  404  may also exist to perform a buffer control. 
       FIG. 5  is a configuration diagram of a bitstream according to the AC-3 standard and a configuration diagram of a bitstream according to the Enhanced AC-3 standard. 
       FIG. 5A  is a configuration diagram of a bitstream according to the AC-3 standard. Since a frame  510 , SI  511 , BSI  512 , an AB field  513 , and auxiliary data field  514 , and a CRC code  515  in  FIG. 5A  respectively correspond to the frame  410 , the SI  401 , the BSI  402 , the AB field  403 , the auxiliary data field  404 , and the CRC code  405  in  FIG. 4 , the description made in  FIG. 4  is not repeated again. 
     In  FIG. 5A , according to the AC-3 standard, the AB field  513  includes 6 audio blocks AB 0 , AB 1 , AB 2 , AB 3 , AB 4 , and AB 5 , each AB having a variable length and including an actual audio signal. 
     In detail, an actual audio signal having maximum 5.1 channels according to the AC-3 standard is carried on the audio blocks AB 0 , AB 1 , AB 2 , AB 3 , AB 4 , and AB 5  and transmitted to the decoding apparatus  250 . 
       FIG. 5B  is a configuration diagram of a bitstream according to the Enhanced AC-3 standard. Since a frame  560 , SI  561 , BSI  562 , an AB field  563 , and auxiliary data field  564 , and a CRC code  565  in  FIG. 5B  respectively correspond to the frame  410 , the SI  401 , the BSI  402 , the AB field  403 , the auxiliary data field  404 , and the CRC code  405  in  FIG. 4 , the description made in  FIG. 4  is not repeated again. 
     In  FIG. 5B , according to the Enhanced AC-3 standard, the AB field  563  includes an audio frame (AudFrm) and n audio blocks. According to the Enhanced AC-3 standard, n may be 1, 2, 3, or 6.  FIG. 5B  illustrates a case where n=6. Each of 6 audio blocks AB 0 , AB 1 , AB 2 , AB 3 , AB 4 , and AB 5  has a variable length and includes an actual audio signal. 
     In detail, an actual audio signal having maximum 13.1 channels according to the Enhanced AC-3 standard is carried on the audio blocks AB 0 , AB 1 , AB 2 , AB 3 , AB 4 , and AB 5  and transmitted to the decoding apparatus  250 . 
       FIG. 6  is a configuration diagram of a bitstream  600  into which additional information is inserted, according to an exemplary embodiment. The bitstream  600  illustrated in  FIG. 6  is a bitstream according to the AC-3 standard. Thus, the bitstream  600  illustrated in  FIG. 6  corresponds to the bitstream  600  illustrated in  FIG. 5A . Operation  340  is described with reference to  FIG. 6 . 
     In operation  340 , the additional information extracted in operation  310  is inserted into at least one of additional BSI (addbsi)  610  included in BSI  612 , skip fields  620 ,  630 ,  640 ,  650 ,  660 , and/or  670  included in audio blocks AB 0 , AB 1 , AB 2 , AB 3 , AB 4 , and/or AB 5 , and auxiliary data bits (auxbits)  680  included in an auxiliary data field. When the additional information is inserted into the at least one audio blocks AB 0 , AB 1 , AB 2 , AB 3 , AB 4 , and/or AB 5 , the additional information may be inserted into at least one of the skip fields  620 ,  630 ,  640 ,  650 ,  660 , and  670  respectively corresponding to the audio blocks AB 0 , AB 1 , AB 2 , AB 3 , AB 4 , and AB 5 . 
     Structures of BSI including additional information, an audio block including additional information, and an auxiliary data field including additional information are described in detail with reference to  FIGS. 7 to 9 . 
       FIG. 7  illustrates BSI  700  including additional information. 
     Referring to  FIG. 7 , the BSI  700  (referred to as ‘bsi’ in  FIG. 7 ) includes additional bitstream information existence (addbsie) information  710  indicating the presence or absence of additional bitstream information (addbsi), additional bitstream information length (addbsil) information  720 , and additional bitstream information (addbsi)  730 . 
     In detail, the addbsie information  710  indicates whether additional bitstream information (addbsi) exists. The addbsil information  720  includes information regarding a data length of the additional bitstream information (addbsi). The additional bitstream information (addbsi)  730  includes the additional information. 
       FIG. 8  illustrates an audio block  800  including additional information. 
     Referring to  FIG. 8 , the audio block  800  (referred to as ‘audblk’ in  FIG. 8 ) includes skip length existence (skiple) information  810  indicating the presence or absence of a skip field (skipfld), skip length (skipl) information  820  indicating a length of the skip field (skipfld), and a skip field (skipfld)  830  including the additional information. 
       FIG. 9  illustrates an auxiliary data field  900  including additional information. 
     Referring to  FIG. 9 , the auxiliary data field  900  (referred to as ‘auxdata’ in  FIG. 9 ) includes auxiliary data bits (auxbits)  910  including the additional information, auxiliary data length (auxdatal) information  920 , and auxiliary data existence (auxdatae) information  930  indicating the presence/absence of auxiliary data. 
       FIG. 10  is a flowchart illustrating a signal processing method  1000  according to another exemplary embodiment. Since operations  1010 ,  1020 ,  1030 , and  1040  in  FIG. 10  are identical to operations  310 ,  320 ,  330 , and  340  in  FIG. 3 , the description made in  FIG. 3  is not repeated again. Comparing with the signal processing method  300 , the signal processing method  1000  may further include at least one of operations  1005 ,  1050 , and  1060 . 
     In detail, in operation  1005 , it is determined whether at least one of channel number expansion and 3D reproduction of an audio signal is performed. The determination in operation  1005  may be performed by the first controller  230  according to a request of a user or a determination of the encoding apparatus  210 . 
     The channel number expansion indicates that an audio signal having more than the number of channels allowed in a predetermined standard is generated when the decoding apparatus  250  decodes and outputs the audio signal. For example, the channel number expansion indicates allowing the decoding apparatus  250  conforming to the AC-3 standard to output an audio signal having 10.2 channels even though the AC-3 standard allows up to maximum 5.1 channels. The 3D reproduction of an audio signal indicates that audio signals have depth information, wherein each audio signal is reproduced with a different stereoscopic sense according its own depth information. 
     If it is determined in operation  1005  that at least one of the channel number expansion and the 3D reproduction of an audio signal is performed, the signal processing method  1000  proceeds to operation  1010 . 
     If it is determined in operation  1005  that any one of the channel number expansion and the 3D reproduction of an audio signal is not performed, the audio signal is encoded according to the predetermined standard in operation  1050  without performing operation  1010  to extract additional information for the channel number expansion and the 3D reproduction of the audio signal. 
     In operation  1060 , the encoded audio signal is formatted to a bitstream defined by the predetermined standard. 
       FIG. 11  is a flowchart illustrating a signal processing method  1100  according to another exemplary embodiment. Since operations  1110 ,  1120 ,  1130 , and  1140  of the signal processing method  1100  are identical to operations  310 ,  320 ,  330 , and  340  in  FIG. 3 , the description made in  FIG. 3  is not repeated again. Comparing with the signal processing method  300 , the signal processing method  1100  of  FIG. 11  may further include at least one of operations  1150 ,  1160 ,  1170 , and  1180 . 
     After operation  1140 , a bitstream into which additional information is inserted is transmitted from the encoding apparatus  210  to the decoding apparatus  250  in operation  1150 . 
     In the signal processing method  1100 , an operation block  1105  is performed by the encoding apparatus  210 , and a subsequent operation block  1155  is performed by the decoding apparatus  250 . 
     In operation  1160 , the decoding apparatus  250  receives the bitstream transmitted in operation  1150  and deformats the received bitstream. Operation  1160  may be performed by the deformatter  265 . In detail, operation  1160  restores the audio signal formatted according to the predetermined standard to the format before performing operation  1130 . 
     In operation  1170 , the decoding apparatus  250  extracts the additional information from at least one of additional BSI (addbsi), a skip field (skipfld, and auxiliary data bits (auxbits) included in the deformatted bitstream. In detail, operation  1170  may be performed by the decoding apparatus  250  under a control of the second controller  270 . In more detail, operation  1170  may be performed by a parser (not shown) included in the decoding apparatus  250  under a control of the second controller  270 . 
     In operation  1180 , the decoding apparatus  250  decodes the bitstream deformatted in operation  1160  according to the predetermined standard. In detail, if the extracted additional information includes multi-channel restoration information, the decoding apparatus  250  decodes the bitstream so that the number of channels included in the bitstream, i.e., the number of channels equal to or less than that allowed in the predetermined standard, is expanded using the multi-channel restoration information. For example, if the extracted additional information includes restoration information for expanding 5.1 channels to 10.2 channels, the decoder  260  receives the bitstream having 5.1 channels and outputs an audio signal of 10.2 channels. 
     If the extracted additional information includes 3D information, the bitstream may be decoded by adding depths according to the 3D information thereto. The decoded audio signals may have predetermined depths and accordingly may be reproduced with different stereoscopic senses. 
       FIG. 12  is a flowchart illustrating a signal processing method according to another exemplary embodiment. Since operations  1220  and  1215  of  FIG. 12  respectively correspond to operations  1170  and  1180  of  FIG. 11 , the description made in  FIG. 11  is not repeated again. 
     Referring to  FIG. 12 , after operation  1160 , it is determined in operation  1210  whether the decoding apparatus  250 , which has received the bitstream, can perform the channel number expansion. 
     If the decoding apparatus  250 , which has received the bitstream, cannot perform the channel number expansion as a result of the determination of operation  1210 , the decoding apparatus  250  decodes the deformatted bitstream without extracting the additional information in operation  1215 . 
     If the decoding apparatus  250 , which has received the bitstream, can perform the channel number expansion as a result of the determination of operation  1210 , the decoding apparatus  250  extracts the additional information from the received bitstream in operation  1220 . 
     In operation  1230 , the decoding apparatus  250  determines whether an expanded channel exists. Operation  1230  may be performed by decoding the additional information extracted in operation  1220  and determining whether multi-channel restoration information is included the decoded additional information. 
     If an expanded channel exists as a result of the determination of operation  1230 , the decoding apparatus  250  decodes the deformatted bitstream to meet the expanded number of channels by using the additional information in operation  1235 . If an expanded channel exists and the additional information includes 3D information, a depth is added to the audio signal decoded to meet the expanded number of channels. If no expanded channel exists as a result of the determination of operation  1230 , the decoding apparatus  250  determines in operation  1240  whether the additional information includes 3D information. 
     If the additional information does not include 3D information as a result of the determination of operation  1240 , the decoding apparatus  250  decodes the deformatted bitstream without performing channel expansion or adding a depth in operation  1250 . 
     If the additional information includes 3D information as a result of the determination of operation  1240 , the decoding apparatus  250  decodes the deformatted bitstream so that 3D reproduction of the audio signal can be performed and adds a depth to the decoded audio signal in operation  1245 . 
     The method invention can also be embodied as computer-readable codes or programs on a computer-readable recording medium. The computer-readable recording medium is any data storage device that can store programs or data which can be thereafter read by a computer system. Examples of the computer-readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, hard disks, floppy disks, flash memory, optical data storage devices, and so on. The computer-readable recording medium can also be distributed over network coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.