Sound signal encoding method, sound signal decoding method, sound signal encoding device, sound signal decoding device, program product, and recording medium

Abstract

The downmix unit 110 obtains a downmix signal obtained by mixing an input sound signal of a left channel and an input sound signal of a right channel. When the left channel is in the leading position, the downmix signal is used as it is in the left channel subtraction gain estimation unit 120 and the left channel signal subtraction unit 130, and the delayed downmix signal is used in the right channel subtraction gain estimation unit 140 and the right channel signal subtraction unit 150. When the right channel is in the leading position, the downmix signal is used as it is in the right channel subtraction gain estimation unit 140 and the right channel signal subtraction unit 150, and the delayed downmix signal is used in the left channel subtraction gain estimation unit 120 and the left channel signal subtraction unit 130.

Description

Technical Field

[0001] The present invention relates to a technology for embedded coding / decoding of dual-channel sound signals. Background Art

[0002] As a technology for embedded encoding / decoding of a two-channel sound signal and a monaural sound signal, there is the technology of Patent Document 1. Patent Document 1 discloses a technology for obtaining a monaural signal obtained by adding an input left-channel sound signal and an input right-channel sound signal, encoding the monaural signal (mono encoding) to obtain a monaural code, decoding the monaural code (mono decoding) to obtain a monaural local decoded signal, and encoding the difference (prediction residual signal) between the input sound signal and a prediction signal obtained from the monaural local decoded signal for each of the left and right channels. In the technology of Patent Document 1, for each channel, a signal obtained by delaying and applying an amplitude ratio to a monaural local decoded signal is used as a prediction signal, and a prediction signal having a delay and an amplitude ratio with which the error between an input sound signal and the prediction signal is minimized is selected, or a prediction signal having a delay difference and an amplitude ratio with which the mutual correlation between the input sound signal and the monaural local decoded signal is maximized is used, and the prediction signal is subtracted from the input sound signal to obtain a prediction residual signal, and the prediction residual signal is set as an object of encoding / decoding, thereby suppressing the sound quality degradation of the decoded sound signal of each channel.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: WO2006 / 070751 Summary of the invention

[0006] Problems to be solved by the invention

[0007] The technology of Patent Document 1 can efficiently encode even when the correlation between channel signals of an input audio signal is small. However, the technology of Patent Document 1 has a problem that the amount of computational processing and the amount of code become redundant in a utilization method such as a telephone conference, in which a two-channel audio signal obtained by picking up a sound from a sound source in a certain space using two microphones arranged in the space is the object of encoding.

[0008] The present invention aims to provide embedded coding / decoding for a two-channel sound signal, with less computational processing and code amount than before, thereby suppressing the deterioration of the sound quality of decoded sound signals of each channel, such as when the two-channel sound signal is a sound signal obtained by picking up sound emitted by a sound source in a certain space using two microphones arranged in the space.

[0009] One embodiment of the present invention is a sound signal encoding method for encoding an input sound signal for each frame, characterized in that it includes: a downmixing step of obtaining a downmixed signal, wherein the downmixed signal is a signal obtained by mixing an input left channel input sound signal and an input right channel input sound signal; a mono encoding step of encoding the downmixed signal to obtain a mono code CM; a left-right relationship estimation step of obtaining a left-right time difference τ and a left-right time difference code Cτ from the left channel input sound signal and the right channel input sound signal, wherein the left-right time difference code is a code indicating the left-right time difference τ; a time shifting step of determining a time difference between the left channel subtraction gain estimation step and the left channel signal subtraction gain estimation step when the left-right time difference τ indicates that the left channel is in a leading position. The method step uses the downmix signal as it is, and determines to use a signal obtained by delaying the downmix signal by an amount represented by the left-right time difference τ in the right channel subtraction gain estimation step and the right channel signal subtraction step, that is, a delayed downmix signal. When the left-right time difference τ indicates that the right channel is in a leading position, it is determined to use the downmix signal as it is in the right channel subtraction gain estimation step and the right channel signal subtraction step, and determines to use a signal obtained by delaying the downmix signal by an amount represented by the left-right time difference τ in the left channel subtraction gain estimation step and the left channel signal subtraction step, that is, a delayed downmix signal. When the left-right time difference τ indicates that any channel is not in a leading position, it is determined to use the downmix signal as it is in the right channel subtraction gain estimation step and the right channel signal subtraction step. The left channel subtraction gain estimation step, the left channel signal subtraction step, the right channel subtraction gain estimation step and the right channel signal subtraction step use the downmix signal as is; the left channel subtraction gain estimation step obtains a left channel subtraction gain α and a left channel subtraction gain code Cα from the left channel input sound signal and the downmix signal or the delayed downmix signal determined in the time shift step, wherein the left channel subtraction gain code is a code representing the left channel subtraction gain α; the left channel signal subtraction step obtains, for each corresponding sample t, a value based on the subtraction of the sample value of the downmix signal or the delayed downmix signal determined in the time shift step from the sample value of the left channel input sound signal. The right channel subtraction gain estimation step obtains a right channel subtraction gain β and a right channel subtraction gain code Cβ from the right channel input sound signal and the downmix signal or the delayed downmix signal determined in the time shift step, wherein the right channel subtraction gain code is a code representing the right channel subtraction gain β; the right channel signal subtraction step obtains a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the downmix signal or the delayed downmix signal determined in the time shift step by the right channel subtraction gain β from the sample value of the right channel input sound signal for each corresponding sample t, as the right channel difference signal;and a stereo encoding step, encoding the left channel differential signal and the right channel differential signal to obtain a stereo code CS.;

[0010] One embodiment of the present invention is a sound signal encoding method for encoding an input sound signal for each frame, characterized in that it includes: a downmixing step to obtain a downmixed signal, wherein the downmixed signal is a signal obtained by mixing an input left channel input sound signal and an input right channel input sound signal; a mono encoding step to encode the downmixed signal to obtain a mono code CM and a quantized downmixed signal; a left-right relationship estimation step to obtain a left-right time difference τ and a left-right time difference code Cτ from the left-channel input sound signal and the right-channel input sound signal, wherein the left-right time difference code is a code indicating the left-right time difference τ; and a time shifting step to obtain a left-right time difference τ when the left-right time difference τ indicates that the left channel is in a leading state. , it is determined that the quantized downmix signal is used as is in the left channel subtraction gain estimation step and the left channel signal subtraction step, and it is determined that a signal obtained by delaying the quantized downmix signal by an amount represented by the left and right time difference τ is used in the right channel subtraction gain estimation step and the right channel signal subtraction step, that is, a delayed quantized downmix signal. When the left and right time difference τ indicates that the right channel is in a leading position, it is determined that the quantized downmix signal is used as is in the right channel subtraction gain estimation step and the right channel signal subtraction step, and it is determined that the quantized downmix signal is used by delaying the quantized downmix signal by the left and right time difference τ in the left channel subtraction gain estimation step and the left channel signal subtraction step. The signal obtained by the amount of the size represented by the time difference τ, that is, the delayed quantized downmix signal, when the above-mentioned left and right time difference τ indicates that any channel is not in the leading position, it is decided to use the above-mentioned quantized downmix signal as it is in the above-mentioned left channel subtraction gain estimation step, the above-mentioned left channel signal subtraction step, the above-mentioned right channel subtraction gain estimation step and the above-mentioned right channel signal subtraction step; the above-mentioned left channel subtraction gain estimation step, obtains the left channel subtraction gain α and the left channel subtraction gain code Cα from the above-mentioned left channel input sound signal and the above-mentioned quantized downmix signal determined in the above-mentioned time shift step or the above-mentioned delayed quantized downmix signal, and the above-mentioned left channel subtraction gain code is a signal indicating the above-mentioned left channel subtraction gain. The left channel signal subtraction step obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the quantized downmix signal or the delayed quantized downmix signal determined in the time shift step by the left channel subtraction gain α from the sample value of the left channel input sound signal as a left channel difference signal; the right channel subtraction gain estimation step obtains a right channel subtraction gain β and a right channel subtraction gain code Cβ from the right channel input sound signal and the quantized downmix signal or the delayed quantized downmix signal determined in the time shift step, wherein the right channel subtraction gain code is a code indicating the right channel subtraction gain β;The right channel signal subtraction step obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the quantized downmix signal or the delayed quantized downmix signal determined in the time shift step by the right channel subtraction gain β from the sample value of the right channel input sound signal as a right channel difference signal; and a stereo encoding step encodes the left channel difference signal and the right channel difference signal to obtain a stereo code CS.;

[0011] One embodiment of the present invention is a sound signal decoding method for decoding an input code for each frame to obtain a sound signal, characterized in that it includes: a mono decoding step of decoding an input mono code CM to obtain a mono decoded sound signal; a stereo decoding step of decoding an input stereo code CS to obtain a left channel decoded differential signal and a right channel decoded differential signal; a left-right time difference decoding step of obtaining a left-right time difference τ from an input left-right time difference code Cτ; a time shifting step of determining to keep the original left-right time difference τ in a left channel signal adding step when the left-right time difference τ indicates that the left channel is in the leading position The mono decoded sound signal is used in the same manner, and it is determined that in the right channel signal adding step, a delayed mono decoded sound signal is used, which is a signal obtained by delaying the mono decoded sound signal by an amount indicated by the left and right time difference τ. When the left and right time difference τ indicates that the right channel is in the leading position, it is determined that in the right channel signal adding step, the mono decoded sound signal is used as it is, and it is determined that in the left channel signal adding step, a delayed mono decoded sound signal is used, which is a signal obtained by delaying the mono decoded sound signal by an amount indicated by the left and right time difference τ. In the case where the left-right time difference τ indicates that none of the channels is in the leading position, it is decided to keep using the above-mentioned mono decoded sound signal as is in the above-mentioned left channel signal addition step and the above-mentioned right channel signal addition step; in the left channel subtraction gain decoding step, the input left channel subtraction gain code Cα is decoded to obtain the left channel subtraction gain α; in the above-mentioned left channel signal addition step, a sample value of the above-mentioned left channel decoded differential signal and the sample value of the above-mentioned mono decoded sound signal or the above-mentioned delayed mono decoded sound signal determined in the above-mentioned time shift step are obtained according to each corresponding sample t. A sequence of values ​​obtained by adding the multiplied values ​​of the left channel subtraction gain α is used as the left channel decoded sound signal; a right channel subtraction gain decoding step, decoding the input right channel subtraction gain code Cβ to obtain the right channel subtraction gain β; and the right channel signal addition step, for each corresponding sample t, obtaining a sequence of values ​​based on adding the sample value of the right channel decoded differential signal and the sample value of the monaural decoded sound signal or the delayed monaural decoded sound signal determined in the time shift step and the value multiplied by the right channel subtraction gain β as the right channel decoded sound signal.

[0012] According to the present invention, it is possible to provide embedded encoding / decoding for a two-channel sound signal, which can suppress the degradation of the sound quality of the decoded sound signal of each channel, such as when the two-channel sound signal is a sound signal obtained by picking up a sound emitted by a sound source in a certain space using two microphones arranged in the space, with less computing processing and code amount than before. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a block diagram showing an example of a coding device using a reference method.

[0014] Figure 2 This is a flowchart showing an example of processing by a coding apparatus using a reference method.

[0015] Figure 3 This is a block diagram showing an example of a decoding device using a reference method.

[0016] Figure 4 This is a flowchart showing an example of processing by a decoding device using a reference method.

[0017] Figure 5 1 is a flowchart showing an example of processing by a left channel subtraction gain estimation unit and a right channel subtraction gain estimation unit in a reference method.

[0018] Figure 6 1 is a flowchart showing an example of processing by a left channel subtraction gain estimation unit and a right channel subtraction gain estimation unit in a reference method.

[0019] Figure 7 1 is a flowchart showing an example of processing by the left channel subtraction gain decoding unit and the right channel subtraction gain decoding unit in the reference method.

[0020] Figure 8 1 is a flowchart showing an example of processing by a left channel subtraction gain estimation unit and a right channel subtraction gain estimation unit in a reference method.

[0021] Fig. 9 1 is a flowchart showing an example of processing by a left channel subtraction gain estimation unit and a right channel subtraction gain estimation unit in a reference method.

[0022] Fig.10 This is a block diagram showing an example of the encoding device according to the first embodiment and the second embodiment.

[0023] Fig.11 This is a flowchart showing an example of processing by the encoding device according to the first embodiment.

[0024] Fig.12 This is a block diagram showing an example of a decoding device according to the first embodiment.

[0025] Fig.13 This is a flowchart showing an example of processing by the decoding device according to the first embodiment.

[0026] Fig.14 This is a flowchart showing an example of processing by the encoding device according to the second embodiment.

[0027] Fig.15This is a diagram showing an example of the functional configuration of a computer that realizes each device in the embodiment of the present invention. DETAILED DESCRIPTION

[0028] <Reference method>

[0029] Before describing the embodiments of the invention, a coding device and a decoding device that are the basic methods for implementing the invention will be described as reference methods. In addition, in the specification and claims, a coding device may be referred to as a sound signal coding device, a coding method may be referred to as a sound signal coding method, a decoding device may be referred to as a sound signal decoding device, and a decoding method may be referred to as a sound signal decoding method.

[0030] 《Encoding device 100》

[0031] like Figure 1 As shown in FIG. 1 , the coding device 100 of the reference method includes a downmixing unit 110, a left channel subtraction gain estimation unit 120, a left channel signal subtraction unit 130, a right channel subtraction gain estimation unit 140, a right channel signal subtraction unit 150, a monaural coding unit 160, and a stereo coding unit 170. The coding device 100 codes the audio signal of the time region of the two-channel stereo input, for example, in a frame unit of a predetermined time length of 20 ms, obtains and outputs the monaural code CM, the left channel subtraction gain code Cα, the right channel subtraction gain code Cβ, and the stereo code CS described later. The audio signal of the time region of the two-channel stereo input to the coding device is, for example, a digital voice signal or acoustic signal obtained by picking up sounds such as voices and music using two microphones and performing AD conversion, and is composed of an input audio signal of a left channel and an input audio signal of a right channel. The codes output by the encoding device, namely, the mono code CM, the left channel subtraction gain code Cα, the right channel subtraction gain code Cβ, and the stereo code CS are input to the decoding device. The encoding device 100 performs Figure 2 The processing of steps S110 to S170 is illustrated.

[0032] [Downmixing unit 110]

[0033] The input audio signal of the left channel input to the encoding device 100 and the input audio signal of the right channel input to the encoding device 100 are input to the downmixing unit 110. The downmixing unit 110 obtains a downmix signal obtained by mixing the input audio signal of the left channel and the input audio signal of the right channel from the input audio signal of the left channel and the input audio signal of the right channel, and outputs the downmix signal (step S110).

[0034] For example, assuming that the number of samples per frame is T, the input audio signal x of the left channel input to the encoding device 100 in units of frames is input to the downmixing unit 110.L (1), x L (2), ..., x L (T) and the input sound signal x of the right channel R (1), x R (2), ..., x R (T). Here, if T is a positive integer, for example, if the frame length is 20 ms and the sampling frequency is 32 kHz, then T is 640. The downmixing unit 110 obtains a sequence of average values ​​of sample values ​​of each sample corresponding to the input audio signal of the left channel and the input audio signal of the right channel as the downmixed signal x M (1), x M (2), ..., x M (T) and output. That is, if each sample number is set to t, then x M (t) = (x L (t)+x R (t)) / 2.

[0035] [Left Channel Subtraction Gain Estimation Unit 120]

[0036] The left channel subtraction gain estimation unit 120 receives as input the left channel input audio signal x L (1), x L (2), ..., x L (T) and the downmix signal x output by the downmixing unit 110 M (1), x M (2), ..., x M (T). The left channel subtraction gain estimation unit 120 obtains and outputs the left channel subtraction gain α and the left channel subtraction gain code Cα from the input sound signal of the input left channel and the downmix signal. The left channel subtraction gain code is a code representing the left channel subtraction gain α (step S120). The left channel subtraction gain estimation unit 120 obtains the left channel subtraction gain α and the left channel subtraction gain code Cα by the method for obtaining the amplitude ratio g in Patent Document 1, the known method exemplified in the method for encoding the amplitude ratio g, or the newly proposed method based on the principle of minimizing the quantization error. The principle of minimizing the quantization error and the method based on the principle will be described later.

[0037] [Left channel signal subtraction unit 130]

[0038] The left channel signal subtraction unit 130 receives the input audio signal x of the left channel input to the encoding device 100. L (1), x L (2), ..., x L (T), the downmix signal x output by the downmixing unit 110 M(1), x M (2), ..., x M (T), and the left channel subtraction gain α output by the left channel subtraction gain estimation unit 120. The left channel signal subtraction unit 130 obtains the sample value x of the downmix signal according to each corresponding sample t. M The value α×x obtained by multiplying (t) by the left channel subtraction gain α M (t), the sample value x of the input sound signal from the left channel L The value x is obtained by subtracting L (t)-α×x M (t) sequence, as the left channel differential signal y L (1) y L (2), ..., y L (T), and output (step S130). L (t) = x L (t)-α×x M In order to avoid delay and computational processing required to obtain a local decoded signal in the encoding device 100, the left channel signal subtraction unit 130 may use the unquantized downmix signal x obtained by the downmix unit 110. M (t) is used instead of the monaural encoded local decoded signal, that is, the quantized downmix signal. However, in the case where the left channel subtraction gain estimation unit 120 obtains the left channel subtraction gain α not by a method based on the principle of minimizing the quantization error but by a known method as exemplified in Patent Document 1, a unit for obtaining a local decoded signal corresponding to the monaural code CM may be provided in the subsequent stage of the monaural encoding unit 160 of the encoding device 100 or in the monaural encoding unit 160, and in the left channel signal subtraction unit 130, the downmix signal x is replaced. M (1), x M (2), ..., x M (T) Using the quantized downmix signal ^x, which is a local decoded signal of monaural encoding, as in the conventional encoding apparatus such as Patent Document 1 M (1), ^x M (2), ..., ^x M (T) to obtain the left channel differential signal.

[0039] [Right Channel Subtraction Gain Estimation Unit 140]

[0040] The right channel subtraction gain estimation unit 140 receives as input the right channel input audio signal x R (1), x R (2), ..., x R (T) and the downmix signal x output by the downmixing unit 110M (1), x M (2), ..., x M (T). The right channel subtraction gain estimation unit 140 obtains and outputs the right channel subtraction gain β and the right channel subtraction gain code Cβ from the input sound signal of the input right channel and the downmix signal, and the right channel subtraction gain code is a code representing the right channel subtraction gain β (step S140). The right channel subtraction gain estimation unit 140 obtains the right channel subtraction gain β and the right channel subtraction gain code Cβ by using the method for obtaining the amplitude ratio g in Patent Document 1, the known method exemplified in the method for encoding the amplitude ratio g, or the newly proposed method based on the principle of minimizing the quantization error. The principle of minimizing the quantization error and the method based on the principle will be described later.

[0041] [Right channel signal subtraction unit 150]

[0042] The right channel signal subtraction unit 150 receives the right channel input audio signal x input to the encoding device 100. R (1), x R (2), ..., x R (T), the downmix signal x output by the downmixing unit 110 M (1), x M (2), ..., x M (T) and the right channel subtraction gain β output by the right channel subtraction gain estimation unit 140. The right channel signal subtraction unit 150 obtains the sample value x of the downmix signal according to each corresponding sample t. M (t) is multiplied by the right channel subtraction gain β M (t) Sample value x of the input sound signal from the right channel R (t) minus the value x R (t)-β×x M (t) sequence, as the right channel differential signal y R (1) y R (2), ..., y R (T), and output (step S150). R (t) = x R (t)-β×x M In the right channel signal subtraction unit 150, similarly to the left channel signal subtraction unit 130, in order to avoid the delay and computational processing required to obtain the local decoded signal in the encoding device 100, the unquantized downmix signal x obtained by the downmix unit 110 may be used. M(t) is used instead of the monaural encoded local decoded signal, that is, the quantized downmix signal. However, in the case where the right channel subtraction gain estimation unit 140 obtains the right channel subtraction gain β by a known method illustrated in Patent Document 1 instead of a method based on the principle of minimizing the quantization error, it is also possible that a unit for obtaining a local decoded signal corresponding to the monaural code CM is provided in the subsequent stage of the monaural encoding unit 160 of the encoding device 100 or in the monaural encoding unit 160, and similarly to the left channel signal subtraction unit 130, in the right channel signal subtraction unit 150, the downmix signal x is replaced. M (1), x M (2), ..., x M (T) As in the conventional encoding apparatus of Patent Document 1, the quantized downmix signal ^x which is a local decoded signal of monaural encoding is used. M (1), ^x M (2), ..., ^x M (T) to obtain the right channel differential signal.

[0043] [Monaural encoding unit 160]

[0044] The monaural encoding unit 160 receives the downmix signal x output by the downmix unit 110. M (1), x M (2), ..., x M (T). The mono encoding unit 160 uses a predetermined encoding method to encode the M The input downmix signal is encoded by 10 bits to obtain a mono code CM, and then output (step S160). M (1), x M (2), ..., x M (T) Get b M As the encoding method, any method may be used, for example, an encoding method such as the 3GPP EVS standard may be used.

[0045] [Stereo encoding unit 170]

[0046] The left channel difference signal y output from the left channel signal subtraction unit 130 is input to the stereo encoding unit 170. L (1) y L (2), ..., y L (T) and the right channel difference signal y output by the right channel signal subtraction unit 150 R (1) y R (2), ..., y R (T). The stereo encoding unit 170 uses a predetermined encoding method to generate a total of bs The input left channel differential signal and right channel differential signal are encoded by 10 bits, and a stereo code CS is obtained and output (step S170). L (1) y L (2), ..., y L (T) and the right channel difference signal y of the input T samples R (1) y R (2), ..., y R (T) Get the total b S As the encoding method, any method may be used, for example, a stereo encoding method corresponding to the stereo decoding method of the MPEG-4AAC standard may be used, or a method of encoding the input left channel differential signal and the right channel differential signal independently may be used, as long as all the codes obtained by encoding are combined together to form the stereo code CS.

[0047] When the input left channel difference signal and right channel difference signal are encoded independently, the stereo encoding unit 170 uses b L The left channel differential signal is encoded with b R That is, the stereo encoding unit 170 encodes the right channel difference signal y from the input T samples of the left channel difference signal y L (1) y L (2), ..., y L (T) Get b L The left channel differential code CL of bits is obtained from the right channel differential signal y of T samples of the input R (1) y R (2), ..., y R (T) Get b R The right channel differential code CR of the left channel is output as the stereo code CS by combining the left channel differential code CL and the right channel differential code CR. L Bit and b R The total number of bits is b S Bit.

[0048] When the input left channel difference signal and right channel difference signal are encoded together in one encoding method, the stereo encoding unit 170 uses the total b S That is, the stereo encoding unit 170 encodes the left channel difference signal y of the input T samples. L (1) y L (2), ..., y L(T) and the right channel difference signal y of the input T samples R (1) y R (2), ..., y R (T) Get b S bits of stereo code CS and output.

[0049] 《Decoding Device 200》

[0050] like Figure 3 As shown, the reference decoding device 200 includes: a mono decoding unit 210, a stereo decoding unit 220, a left channel subtraction gain decoding unit 230, a left channel signal adding unit 240, a right channel subtraction gain decoding unit 250 and a right channel signal adding unit 260. The decoding device 200 decodes the input mono code CM, the left channel subtraction gain code Cα, the right channel subtraction gain code Cβ and the stereo code CS in frame units of the same time length as the corresponding encoding device 100, obtains the decoded sound signal of the time area of ​​2-channel stereo in frame units (the left channel decoded sound signal and the right channel decoded sound signal described later) and outputs it. Figure 3 As shown by the dotted line in the middle, the decoding device 200 may also output a decoded audio signal in a monaural time domain (a monaural decoded audio signal described later). The decoded audio signal output by the decoding device 200 is audible by, for example, being DA-converted and reproduced by a speaker. The decoding device 200 performs a DA conversion on each frame. Figure 4 The processing of steps S210 to S260 is illustrated.

[0051] [Monaural decoding unit 210]

[0052] The monaural code CM input to the decoding device 200 is input to the monaural decoding unit 210. The monaural decoding unit 210 decodes the input monaural code CM using a predetermined decoding method to obtain a monaural decoded audio signal ^x M (1), ^x M (2), ..., ^x M (T) and output (step S210). As the predetermined decoding method, a decoding method corresponding to the encoding method used in the monaural encoding unit 160 of the corresponding encoding device 100 is used. The number of bits of the monaural code CM is b M .

[0053] [Stereo decoding unit 220]

[0054] The stereo code CS input to the decoding device 200 is input to the stereo decoding unit 220. The stereo decoding unit 220 decodes the input stereo code CS using a predetermined decoding method to obtain a left channel decoded differential signal y L (1) ^yL (2), ..., ^y L (T) and right channel decoded differential signal ^y R (1) ^y R (2), ..., ^y R (T) and outputs it (step S220). As the predetermined decoding method, a decoding method corresponding to the encoding method used in the stereo encoding unit 170 of the corresponding encoding device 100 is used. The total number of bits of the stereo code CS is b S .

[0055] [Left channel subtraction gain decoding unit 230]

[0056] The left channel subtraction gain code Cα input to the decoding device 200 is input to the left channel subtraction gain decoding unit 230. The left channel subtraction gain decoding unit 230 decodes the left channel subtraction gain code Cα, obtains the left channel subtraction gain α, and outputs it (step S230). The left channel subtraction gain decoding unit 230 decodes the left channel subtraction gain code Cα by a decoding method corresponding to the method used in the left channel subtraction gain estimation unit 120 of the corresponding encoding device 100, and obtains the left channel subtraction gain α. When the left channel subtraction gain estimation unit 120 of the corresponding encoding device 100 obtains the left channel subtraction gain α and the left channel subtraction gain code Cα by a method based on the principle of minimizing the quantization error, the method by which the left channel subtraction gain decoding unit 230 decodes the left channel subtraction gain code Cα to obtain the left channel subtraction gain α will be described later.

[0057] [Left channel signal adding section 240]

[0058] The left channel signal adding section 240 receives the monaural decoded audio signal ^x outputted from the monaural decoding section 210. M (1), ^x M (2), ..., ^x M (T), the left channel decoded differential signal output by the stereo decoding unit 220 L (1) ^y L (2), ..., ^y L (T) and the left channel subtraction gain α output by the left channel subtraction gain decoding unit 230. The left channel signal adding unit 240 obtains the sample value ^x of the mono decoded audio signal according to each corresponding sample t. M (t) The value after multiplying the left channel subtraction gain α by α×^x M (t), and the sample value of the left channel decoded differential signal ^y L (t) The value obtained by adding ^y L (t)+α×^x M(t) sequence, as the left channel decoded sound signal ^x L (1), ^x L (2), ..., ^x L (T), and output (step S240). That is, ^x L (t) = ^y L (t)+α×^x M (t).

[0059] [Right Channel Subtraction Gain Decoding Unit 250]

[0060] The right channel subtraction gain decoding unit 250 is input with the right channel subtraction gain code Cβ input to the decoding device 200. The right channel subtraction gain decoding unit 250 decodes the right channel subtraction gain code Cβ, obtains the right channel subtraction gain β and outputs it (step S250). The right channel subtraction gain decoding unit 250 decodes the right channel subtraction gain code Cβ to obtain the right channel subtraction gain β by a decoding method corresponding to the method used in the right channel subtraction gain estimation unit 140 of the corresponding encoding device 100. The method by which the right channel subtraction gain decoding unit 250 decodes the right channel subtraction gain code Cβ to obtain the right channel subtraction gain β when the right channel subtraction gain estimation unit 140 of the corresponding encoding device 100 obtains the right channel subtraction gain β and the right channel subtraction gain code Cβ by a method based on the principle of minimizing the quantization error will be described later.

[0061] [Right channel signal adding unit 260]

[0062] The right channel signal adding section 260 receives the monaural decoded audio signal ^x outputted from the monaural decoding section 210. M (1), ^x M (2), ..., ^x M (T), the right channel decoded differential signal output by the stereo decoding unit 220 R (1) ^y R (2), ..., ^y R (T) and the right channel subtraction gain β output by the right channel subtraction gain decoding unit 250. The right channel signal adding unit 260 obtains the sample value ^x of the mono decoded audio signal according to each corresponding sample t. M (t) The value after multiplying the right channel subtraction gain β β×^x M (t), and the sample value of the right channel decoded differential signal ^y R (t) The value obtained by adding ^y R (t)+β×^x M (t) sequence, as the right channel decoded sound signal ^x R (1), ^x R(2), ..., ^x R (T), and output (step S260). That is, ^x R (t) = ^y R (t)+β×^x M (t).

[0063] [Principle of minimizing quantization error]

[0064] The principle of minimizing the quantization error is described below. When the input left channel difference signal and right channel difference signal are encoded together in one encoding method in the stereo encoding unit 170, the number of bits b used in encoding the left channel difference signal is L The number of bits used in encoding the right channel difference signal is b R Although it may not be determined clearly, in the following, it is assumed that the number of bits used in encoding the left channel difference signal is b. L , the number of bits used in encoding the right channel differential signal is b R In addition, the following mainly describes the left channel, but the right channel is also the same.

[0065] The encoding device 100 is based on b L bits, for the downmixed signal x M (1), x M (2), ..., x M The value obtained by multiplying each sample value of (T) by the left channel subtraction gain α is obtained from the input audio signal x of the left channel. L (1), x L (2), ..., x L The left channel difference signal y is composed of the value obtained by subtracting the sample values ​​of (T) L (1) y L (2), ..., y L (T) is encoded with b M Bit-pair downmix signal x M (1), x M (2), ..., x M (T) is encoded. In addition, the above decoding device 200 is L The decoded left channel differential signal is decoded by using the bit code ^y L (1) ^y L (2), ..., ^y L (T) (hereinafter also referred to as "quantized left channel differential signal"), from b M bit code to decode the mono decoded sound signal^x M (1), ^x M (2), ..., ^xM After (T) (hereinafter also referred to as "quantized downmix signal"), the quantized downmix signal obtained by decoding is converted into M (1), ^x M (2), ..., ^x M The value obtained by multiplying each sample value of (T) by the left channel subtraction gain α and the quantized left channel difference signal ^y obtained by decoding L (1) ^y L (2), ..., ^y L The sample values ​​of (T) are added to obtain the decoded sound signal of the left channel, that is, the decoded sound signal of the left channel ^x L (1), ^x L (2), ..., ^x L (T) The encoding device 100 and the decoding device 200 should be designed so that the energy of the quantization error of the decoded audio signal of the left channel obtained by the above-mentioned processing becomes small.

[0066] In most cases, the energy of the quantization error (hereinafter referred to as "quantization error due to encoding") of the decoded signal obtained by encoding / decoding the input signal is roughly proportional to the energy of the input signal, and tends to decrease exponentially with respect to the value of the number of bits per sample used in the encoding. Therefore, the average energy per sample of the quantization error due to encoding of the left channel difference signal can be expressed as a positive number σ L 2 The average energy per sample of the quantization error generated by coding of the downmix signal can be estimated using a positive number σ M 2 The estimation is performed as shown in the following formula (1-0-2).

[0067] [Mathematical formula 1]

[0068]

[0069] [Mathematical formula 2]

[0070]

[0071] Here, it is assumed that the sample values ​​are close to each other so that the input audio signal x of the left channel L (1), x L (2), ..., x L (T) and the downmixed signal x M (1), x M (2), ..., x M (T) are considered as the same sequence. For example, the input sound signal x of the left channelL (1), x L (2), ..., x L (T) and the right channel input signal x R (1), x R (2), ..., x R (T) is the signal obtained by picking up the sound from the sound source at the same distance from the two microphones in an environment with little background noise and echo. L (1) y L (2), ..., y L Each sample value of (T) is equivalent to the downmix signal x M (1), x M (2), ..., x M The value obtained by multiplying each sample value of (T) by (1-α). Therefore, since (1-α) of the energy of the downmix signal is used 2 times the energy of the left channel differential signal, so the above σ L 2 It is possible to use the above σ M 2 And the replacement is (1-α) 2 ×σ M 2 Therefore, the average energy per sample of the quantization error generated by encoding of the left channel difference signal can be estimated as shown in the following equation (1-1).

[0072] [Mathematical formula 3]

[0073]

[0074] In addition, the average energy per sample of the quantization error of the signal added to the quantized left channel difference signal in the decoding device, that is, the average energy per sample of the quantization error of the sequence of values ​​obtained by multiplying each sample value of the quantized downmix signal obtained by decoding by the left channel subtraction gain α, can be estimated as shown in the following formula (1-2).

[0075] [Formula 4]

[0076]

[0077] If it is assumed that the quantization error of the left channel difference signal caused by encoding and the quantization error of the sequence of values ​​obtained by multiplying each sample value of the quantized downmix signal obtained by decoding by the left channel subtraction gain α are not correlated with each other, the average energy per sample of the quantization error of the decoded audio signal of the left channel can be estimated by the sum of equations (1-1) and (1-2). As shown in the following equation (1-3), the left channel subtraction gain α that minimizes the energy of the quantization error of the decoded audio signal of the left channel is calculated.

[0078] [Formula 5]

[0079]

[0080] In other words, the sample values ​​are close to each other so that the input audio signal x L (1), x L (2), ..., x L (T) and the downmixed signal x M (1), x M (2), ..., x M (T) is considered as the same sequence, in order to minimize the quantization error of the decoded sound signal of the left channel, the left channel subtraction gain estimation unit 120 can calculate the left channel subtraction gain α through equation (1-3). The left channel subtraction gain α obtained by equation (1-3) is a value greater than 0 and less than 1. L With b M When they are equal, it is 0.5, which is the number of bits b used to encode the left channel differential signal. L The larger the number of bits b used to encode the downmix signal, the M , the closer the value is to 0 compared to 0.5, the number of bits b used to encode the downmix signal M The larger the bit number b used to encode the left channel differential signal, the L , is a value closer to 1 than 0.5.

[0081] The same is true for the right channel. When the sample values ​​are close to each other, the input audio signal x of the right channel is R (1), x R (2), ..., x R (T) and the downmixed signal x M (1), x M (2), ..., x M In order to minimize the quantization error of the decoded audio signal of the right channel under the condition that (T) is regarded as the same sequence, the right channel subtraction gain estimation unit 140 may calculate the right channel subtraction gain β by the following equation (1-3-2).

[0082] [Mathematical formula 6]

[0083]

[0084] The right channel subtraction gain β obtained by formula (1-3-2) is a value greater than 0 and less than 1. The number of bits used in the encoding of the two, i.e., b R With b M When they are equal, it is 0.5, which is the number of bits b used to encode the right channel differential signal. R The larger the number of bits b used to encode the downmix signal, the M , the closer the value is to 0 compared to 0.5, the number of bits b used to encode the downmix signal M The larger the bit number b used to encode the right channel differential signal, the R , is a value closer to 1 than 0.5.

[0085] Next, the input audio signal x including the left channel L (1), x L (2), ..., x L (T) and the downmixed signal x M (1), x M (2), ..., x M (T) The principle of minimizing the energy of the quantization error in the decoded audio signal of the left channel without considering the case of the same sequence will be described.

[0086] The input sound signal of the left channel is x L (1), x L (2), ..., x L (T) and the downmixed signal x M (1), x M (2), ..., x M The normalized inner product value r of (T) L It is represented by the following formula (1-4).

[0087] [Formula 7]

[0088]

[0089] The normalized inner product value r obtained by formula (1-4) L is a real value, in the downmixed signal x M (1), x M (2), ..., x M Each sample value of (T) is multiplied by the real value r L 'To get the sequence r of sample values L '×x M(1) r L '×x M (2), ..., r L '×x M (T) is the sequence x obtained by the difference between the obtained sequence of sample values ​​and each sample value of the input audio signal of the left channel. L (1)-r L '×x M (1), x L (2)-r L '×x M (2), ..., x L (T)-r L '×x M The energy of (T) becomes the smallest real value r L 'Same value.

[0090] The input sound signal of the left channel is x L (1), x L (2), ..., x L (T) can be decomposed into x for each sample number t L (t) = r L × M (t)+(x L (t)-r L × M (t)). Here, if x L (t)-r L × M The sequence of values ​​of (t) is set as the orthogonal signal x L '(1), x L '(2),...,x L '(T), then according to the decomposition, the sample values ​​y of the left channel differential signal L (t) = x L (t)-αx M (t), which is equivalent to downmixing the signal x M (1), x M (2), ..., x M (T) each sample value x M (t) is multiplied by the normalized inner product value r L and the left channel subtraction gain α (r L -α) to obtain the value (r L -α)×x M (t) and then the sample values ​​x of the orthogonal signal L '(t) and (r L -α)×x M (t)+x L '(t). Orthogonal signal xL '(1), x L '(2),...,x L '(T) for the downmix signal x M (1), x M (2), ..., x M (T) shows orthogonality, in other words, it shows the property of inner product being 0, so the energy of the left channel difference signal is obtained by performing (r L -α) 2 It is expressed as the sum of the energy obtained by the multiplication of the energy and the energy of the orthogonal signal. L The average energy per sample of the quantization error caused by encoding the left channel difference signal with a bit can be expressed using a positive number σ 2 The estimation is performed as shown in the following formula (1-5).

[0091] [Mathematical formula 8]

[0092]

[0093] If it is assumed that the quantization error of the left channel difference signal caused by encoding and the quantization error of the sequence of values ​​obtained by multiplying each sample value of the quantized downmix signal obtained by decoding by the left channel subtraction gain α are not correlated with each other, the average energy per sample of the quantization error of the decoded sound signal of the left channel is estimated by the sum of equations (1-5) and (1-2). The left channel subtraction gain α that minimizes the energy of the quantization error of the decoded sound signal of the left channel is calculated as shown in the following equation (1-6).

[0094] [Mathematical formula 9]

[0095]

[0096] In other words, in order to minimize the quantization error of the decoded audio signal of the left channel, the left channel subtraction gain estimation unit 120 can calculate the left channel subtraction gain α by using equation (1-6). That is, if the principle of minimizing the energy of the quantization error is considered, the normalized inner product value r should be used for the left channel subtraction gain α. L and the number of bits used by the encoding, i.e., b L and b M The determined value is the value obtained by multiplying the correction coefficient. The correction coefficient is a value greater than 0 and less than 1. The number of bits b used to encode the left channel difference signal L and the number of bits b used to encode the downmix signal M When the two channels are the same, it is 0.5, which is the number of bits b used to encode the left channel differential signal. LThe larger the number of bits b used to encode the downmix signal, the M , the closer it is to 0 compared to 0.5, the number of bits b used to encode the left channel differential signal L The smaller the bit number b used to encode the downmix signal, the M , is a value closer to 1 than 0.5.

[0097] The same is true for the right channel. In order to minimize the quantization error of the decoded audio signal of the right channel, the right channel subtraction gain estimation unit 140 may calculate the right channel subtraction gain β using the following equation (1-6-2).

[0098] [Formula 10]

[0099]

[0100] Here, r R is the input sound signal x of the right channel R (1), x R (2), ..., x R (T) and the downmixed signal x M (1), x M (2), ..., x M The normalized inner product value of (T) is expressed by the following formula (1-4-2).

[0101] [Mathematical formula 11]

[0102]

[0103] That is, if the principle of minimizing the energy of the quantization error is taken into consideration, the normalized inner product value r should be used for the right channel subtraction gain β. R and the number of bits used in the encoding, i.e., b R and b M The determined value is the value obtained by multiplying the correction coefficient. The correction coefficient is a value greater than 0 and less than 1, and is used to encode the number of bits b of the right channel difference signal. R The larger the number of bits b used to encode the downmix signal, the M , the closer it is to 0 compared to 0.5, the less the number of bits used to encode the right channel differential signal is than the number of bits used to encode the downmix signal, and the closer it is to 1 compared to 0.5.

[0104] [Estimation and decoding of subtraction gain based on the principle of minimizing quantization error]

[0105] Specific examples of estimation and decoding of subtraction gain based on the above-mentioned principle of minimizing quantization error are described. In each example, the left channel subtraction gain estimation unit 120 and the right channel subtraction gain estimation unit 140 that estimate the subtraction gain in the encoding device 100, and the left channel subtraction gain decoding unit 230 and the right channel subtraction gain decoding unit 250 that decode the subtraction gain in the decoding device 200 are described.

[0106] 〔〔Example 1〕〕

[0107] Example 1 is based on an input sound signal x that also includes the left channel L (1), x L (2), ..., x L (T) and the downmixed signal x M (1), x M (2), ..., x M (T) The principle of minimizing the energy of the quantization error of the decoded audio signal of the left channel when the decoded audio signal of the left channel is not regarded as the same sequence, and the input audio signal x of the right channel is also included R (1), x R (2), ..., x R (T) and the downmixed signal x M (1), x M (2), ..., x M (T) The case where the principle of minimizing the energy of the quantization error of the decoded audio signal of the right channel is not considered to be the same sequence.

[0108] [[[Left channel subtraction gain estimation unit 120]]]

[0109] The left channel subtraction gain estimation unit 120 stores in advance a plurality of sets (A sets, a=1, . . . , A) of candidate left channel subtraction gain values ​​α. cand (a) The code Cα corresponding to the candidate cand (a) group. The left channel subtraction gain estimation unit 120 performs Figure 5 The following steps S120 - 11 to S120 - 14 are shown.

[0110] The left channel subtraction gain estimation unit 120 first obtains the input audio signal x of the left channel from the input audio signal x L (1), x L (2), ..., x L (T) and the downmixed signal x M (1), x M (2), ..., x M (T), and the normalized inner product value r of the input audio signal of the left channel of the downmix signal is obtained by equation (1-4): L(Step S120 - 11 ) In addition, the left channel subtraction gain estimation unit 120 uses the left channel difference signal y in the stereo encoding unit 170 L (1) y L (2), ..., y L The number of bits b used in the encoding of (T) L , the downmix signal x in the mono encoding unit 160 M (1), x M (2), ..., x M The number of bits b used in the encoding of (T) M , and the number of samples per frame T, the left channel correction coefficient c is obtained by the following formula (1-7): L (Step S120-12).

[0111] [Mathematical formula 12]

[0112]

[0113] The left channel subtraction gain estimation unit 120 then obtains the normalized inner product value r obtained in step S120-11. L and the left channel correction coefficient c obtained in step S120-12 L The left channel subtraction gain estimation unit 120 then obtains the stored candidate α of the left channel subtraction gain. cand (1), ..., α cand (A) is closest to the multiplication value c obtained in step S120-13 L × L Candidate (multiplication value c L × L quantized value), as the left channel subtraction gain α, and obtain the stored code Cα cand (1), ..., Cα cand The code corresponding to the left channel subtraction gain α in (A) is made into the left channel subtraction gain code Cα (step S120 - 14 ).

[0114] In addition, the left channel difference signal y in the stereo encoding unit 170 L (1) y L (2), ..., y L The number of bits b used in the encoding of (T) L If it cannot be determined clearly, the number of bits b of the stereo code CS output by the stereo coding unit 170 is s One-half of (i.e., b s / 2) is used as the bit number b L In addition, the left channel correction coefficient c LIt may not be the value obtained by equation (1-7) itself, but a value greater than 0 and less than 1. L (1) y L (2), ..., y L The number of bits b used to encode (T) L With the downmix signal x M (1), x M (2), ..., x M The number of bits b used to encode (T) M If the same, it is 0.5, the number of bits is b L The larger the bit number b is, the M , then the closer to 0 than 0.5, the number of bits b L The smaller the bit number b is, the M , it is a value closer to 1 than 0.5. This is also the same in each example described below.

[0115] [Right channel subtraction gain estimation unit 140]

[0116] The right channel subtraction gain estimation unit 140 stores in advance a plurality of sets (B sets, b=1, . . . , B) of candidate β values ​​for the right channel subtraction gain. cand (b) The code Cβ corresponding to the candidate cand (b) group. The right channel subtraction gain estimation unit 140 performs Figure 5 The following steps S140 - 11 to S140 - 14 are shown.

[0117] The right channel subtraction gain estimation unit 140 first calculates the right channel input audio signal x R (1), x R (2), ..., x R (T) and the downmixed signal x M (1), x M (2), ..., x M (T), and the normalized inner product value r of the input audio signal of the right channel of the downmix signal is obtained by equation (1-4-2): R (Step S140 - 11 ) In addition, the right channel subtraction gain estimation unit 140 uses the right channel difference signal y in the stereo encoding unit 170 R (1) y R (2), ..., y R The number of bits b used in the encoding of (T) R , the downmix signal x in the mono encoding unit 160 M (1), x M (2), ..., x M The number of bits b used in the encoding of (T)M And the number of samples per frame T, the right channel correction coefficient c is obtained by the following formula (1-7-2): R (Step S140-12).

[0118] [Mathematical formula 13]

[0119]

[0120] The right channel subtraction gain estimation unit 140 then obtains the normalized inner product value r obtained in step S140-11. R and the right channel correction coefficient c obtained in step S140-12 R The right channel subtraction gain estimation unit 140 then obtains the stored candidate β of the right channel subtraction gain. cand (1), ..., β cand (B) is closest to the multiplication value c obtained in step S140-13 R × R Candidate (multiplication value c R × R quantized value), as the right channel subtraction gain β, to obtain the stored code Cβ cand (1), ..., Cβ cand The code corresponding to the right channel subtraction gain β in (B) is made into the right channel subtraction gain code Cβ (step S140 - 14 ).

[0121] In addition, the right channel difference signal y in the stereo encoding unit 170 R (1) y R (2), ..., y R The number of bits b used in the encoding of (T) R If it cannot be determined clearly, the number of bits b of the stereo code CS output by the stereo coding unit 170 is s One-half of (i.e., b s / 2) is used as the bit number b R In addition, the right channel correction coefficient c R It may not be the value obtained by equation (1-7-2) itself, but a value greater than 0 and less than 1. R (1) y R (2), ..., y R The number of bits b used to encode (T) R With the downmix signal x M (1), x M (2), ..., x M The number of bits b used to encode (T) MIf the same, it is 0.5, the number of bits is b R The larger the bit number b is, the M , then the closer to 0 than 0.5, the number of bits b R The smaller the bit number b is, the M , it is a value closer to 1 than 0.5. This is also the same in each example described below.

[0122] [[[Left channel subtraction gain decoding unit 230]]]

[0123] In the left channel subtraction gain decoding unit 230, a plurality of sets (A sets, a=1, . . . , A) of candidate α values ​​of the left channel subtraction gain are stored in advance, similarly to those stored in the corresponding left channel subtraction gain estimation unit 120 of the encoding device 100. cand (a) The code Cα corresponding to the candidate cand The left channel subtraction gain decoding unit 230 obtains the stored code Cα cand (1), ..., Cα cand The candidate of the left channel subtraction gain corresponding to the input left channel subtraction gain code Cα in (A) is set as the left channel subtraction gain α (step S230 - 11 ).

[0124] [[[Right channel subtraction gain decoding unit 250]]]

[0125] In the right channel subtraction gain decoding unit 250, a plurality of sets (B sets, b=1, . . . , B) of candidate β values ​​of the right channel subtraction gain are stored in advance, similarly to those stored in the corresponding right channel subtraction gain estimation unit 140 of the encoding device 100. cand (b) The code Cβ corresponding to the candidate cand (b) The right channel subtraction gain decoding unit 250 obtains the stored code Cβ cand (1), ..., Cβ cand The candidate of the right channel subtraction gain corresponding to the input right channel subtraction gain code Cβ in (B) is set as the right channel subtraction gain β (step S250 - 11 ).

[0126] In addition, the same candidate code of the subtraction gain may be used for the left channel and the right channel, and the above-mentioned A and B may be set to the same value, and the candidate code of the left channel subtraction gain stored in the left channel subtraction gain estimation unit 120 and the left channel subtraction gain decoding unit 230 may be set to the same value. cand (a) The code Cα corresponding to the candidate cand (a), and the candidate β of the right channel subtraction gain stored in the right channel subtraction gain estimation unit 140 and the right channel subtraction gain decoding unit 250. cand (b) The code Cβ corresponding to the candidate candThe groups of (b) are the same.

[0127] [[Variation of Example 1]]

[0128] Since the number of bits b used for encoding the left channel differential signal in the encoding device 100 is L is the number of bits used for decoding the left channel difference signal in the decoding device 200, and is the number of bits used for encoding the downmix signal in the encoding device 100. M The value of is the number of bits used for decoding the downmix signal in the decoding device 200, so for the correction coefficient c L , whether the encoding device 100 or the decoding device 200 can calculate the same value. Therefore, the normalized inner product value r L The quantized value of the inner product value normalized in the encoding device 100 and the decoding device 200 is set as the object of encoding and decoding. L Multiply by the correction factor c L The left channel subtraction gain α is obtained. The same is true for the right channel. This method is described as a modification of Example 1.

[0129] [[[Left channel subtraction gain estimation unit 120]]]

[0130] The left channel subtraction gain estimation unit 120 stores in advance a plurality of sets (A sets, a=1, . . . , A) of candidates for normalized inner product values ​​of the left channel. Lcand (a) The code Cα corresponding to the candidate cand (a) group. Figure 6 As shown, the left channel subtraction gain estimation unit 120 performs step S120 - 11 and step S120 - 12 described in Example 1, and step S120 - 15 and step S120 - 16 described below.

[0131] The left channel subtraction gain estimation unit 120 first calculates the input audio signal x of the left channel from the input audio signal x of the left channel in the same manner as step S120-11 of the left channel subtraction gain estimation unit 120 in Example 1. L (1), x L (2), ..., x L (T) and the downmixed signal x M (1), x M (2), ..., x M (T), the normalized inner product value r of the input audio signal of the left channel of the downmix signal is obtained by equation (1-4) L (Step S120 - 11 ) The left channel subtraction gain estimation unit 120 then obtains the stored normalized inner product value candidate r of the left channel. Lcand (1), ..., r Lcand(A) is closest to the normalized inner product value r obtained in step S120-11 L Candidate (normalized inner product value r L Quantitative value of L , and obtain the stored code Cα cand (1), ..., Cα cand The closest candidate in (A) L The corresponding code is used as the left channel subtraction gain code Cα (step S120-15). In addition, the left channel subtraction gain estimation unit 120 uses the left channel difference signal y in the stereo encoding unit 170 in the same manner as step S120-12 of the left channel subtraction gain estimation unit 120 in Example 1. L (1) y L (2), ..., y L The number of bits b used to encode (T) L , the downmix signal x is generated in the mono encoding unit 160 M (1), x M (2), ..., x M The number of bits b used to encode (T) M And the number of samples per frame T, the left channel correction coefficient c is obtained by formula (1-7) L (Step S120-12) The left channel subtraction gain estimation unit 120 then obtains a quantized value of the normalized inner product value obtained in step S120-15. L and the left channel correction coefficient c obtained in step S120-12 L The multiplied value is used as the left channel subtraction gain α (step S120 - 16 ).

[0132] [Right channel subtraction gain estimation unit 140]

[0133] The right channel subtraction gain estimation unit 140 stores in advance a plurality of sets (B sets, b=1, . . . , B) of candidates for normalized inner product values ​​of the right channel. Rcand (b) The code Cβ corresponding to the candidate cand (b) group. Figure 6 As shown, the right channel subtraction gain estimation unit 140 performs steps S140 - 11 and S140 - 12 also described in Example 1, and steps S140 - 15 and S140 - 16 described below.

[0134] The right channel subtraction gain estimation unit 140 first calculates the input audio signal x of the right channel from the input audio signal x of the right channel in the same manner as step S140 - 11 of the right channel subtraction gain estimation unit 140 in Example 1. R (1), x R (2), ..., xR (T) and the downmixed signal x M (1), x M (2), ..., x M (T), the normalized inner product value r of the input audio signal of the right channel of the downmix signal is obtained by equation (1-4-2): R (Step S140 - 11 ) Next, the right channel subtraction gain estimation unit 140 obtains the stored normalized inner product value candidate r of the right channel. Rcand (1), ..., r Rcand (B) is closest to the normalized inner product value r obtained in step S140-11 R Candidate (normalized inner product value r R Quantitative value of R , and obtain the stored code Cβ cand (1), ..., Cβ cand (B) The closest candidate R The corresponding code is used as the right channel subtraction gain code Cβ (step S140-15). In addition, the right channel subtraction gain estimation unit 140 uses the right channel difference signal y in the stereo encoding unit 170 in the same manner as step S140-12 of the right channel subtraction gain estimation unit 140 in Example 1. R (1) y R (2), ..., y R The number of bits b used to encode (T) R , the downmix signal x in the mono encoding unit 160 M (1), x M (2), ..., x M The number of bits b used to encode (T) M And the number of samples per frame T, the right channel correction coefficient c is obtained by formula (1-7-2) R (Step S140-12) The right channel subtraction gain estimation unit 140 then obtains a quantized value of the normalized inner product value obtained in step S140-15. R and the right channel correction coefficient c obtained in step S140-12 R The multiplied value is used as the right channel subtraction gain β (step S140-16).

[0135] [[[Left channel subtraction gain decoding unit 230]]]

[0136] In the left channel subtraction gain decoding unit 230, similarly to the left channel subtraction gain estimation unit 120 of the corresponding encoding device 100, a plurality of sets (A sets, a=1, . . . , A) of left channel normalized inner product value candidates r are stored in advance. Lcand(a) The code Cα corresponding to the candidate cand (a) group. The left channel subtraction gain decoding unit 230 performs Figure 7 The following steps S230 - 12 to S230 - 14 are shown.

[0137] The left channel subtraction gain decoding unit 230 obtains the stored code Cα cand (1), ..., Cα cand The candidate of the normalized inner product value of the left channel corresponding to the input left channel subtraction gain code Cα in (A) is the decoded value of the normalized inner product value of the left channel ^r L (Step S230-12). In addition, the left channel subtraction gain decoding unit 230 uses the left channel decoded differential signal y in the stereo decoding unit 220. L (1) ^y L (2), ..., ^y L The number of bits b used for decoding (T) L , the mono decoded audio signal ^x in the mono decoding unit 210 M (1), ^x M (2), ..., ^x M The number of bits b used for decoding (T) M And the number of samples per frame T, the left channel correction coefficient c is obtained by formula (1-7) L (Step S230-13) The left channel subtraction gain decoding unit 230 then obtains a decoded value of the normalized inner product value obtained in step S230-12. L and the left channel correction coefficient c obtained in step S230-13 L The multiplied value is used as the left channel subtraction gain α (step S230 - 14 ).

[0138] In addition, when the stereo code CS is a code obtained by combining the left channel differential code CL and the right channel differential code CR, the left channel decoded differential signal ^y in the stereo decoding unit 220 is L (1) ^y L (2), ..., ^y L The number of bits b used for decoding (T) L The left channel differential code CL is the number of bits. L (1) ^y L (2), ..., ^y L The number of bits b used for decoding (T) L If it cannot be determined clearly, the number of bits b of the stereo code CS input to the stereo decoding unit 220 is sOne-half of (i.e., b s / 2) is used as the bit number b L The mono decoded audio signal ^x in the mono decoding unit 210 M (1),^x M (2), ..., ^x M The number of bits b used for decoding (T) M Refers to the number of bits of the mono code CM. Left channel correction coefficient c L The value obtained by the equation (1-7) itself may be a value greater than 0 and less than 1. The left channel decoded differential signal ^y L (1) ^y L (2), ..., ^y L The number of bits b used for decoding (T) L Decoding mono audio signal^x M (1), ^x M (2), ..., ^x M The number of bits b used for decoding (T) M If the same, it is 0.5, the number of bits is b L The larger the bit number b is, the M , then it is closer to 0 than 0.5, and the number of bits is b L The smaller the bit number b is, the M , it is a value closer to 1 than 0.5.

[0139] [[[Right channel subtraction gain decoding unit 250]]]

[0140] In the right channel subtraction gain decoding unit 250, similarly to those stored in the corresponding right channel subtraction gain estimation unit 140 of the encoding device 100, a plurality of sets (B sets, b=1, . . . , B) of candidates for normalized inner product values ​​of the right channel are stored in advance. Rcand (b) The code Cβ corresponding to the candidate cand (b) The right channel subtraction gain decoding unit 250 performs Figure 7 The following steps S250 - 12 to S250 - 14 are shown.

[0141] The right channel subtraction gain decoding unit 250 obtains the stored code Cβ cand (1), ..., Cβ cand The candidate of the normalized inner product value of the right channel corresponding to the input right channel subtraction gain code Cβ in (B) is the decoded value of the normalized inner product value of the right channel ^r R (Step S250-12). In addition, the right channel subtraction gain decoding unit 250 uses the right channel decoded differential signal y in the stereo decoding unit 220. R (1) ^yR (2), ..., ^y R The number of bits b used for decoding (T) R , the mono decoded audio signal ^x in the mono decoding unit 210 M (1), ^x M (2), ..., ^x M The number of bits b used for decoding (T) M And the number of samples per frame T, the right channel correction coefficient c is obtained by formula (1-7-2) R (Step S250-13) The right channel subtraction gain decoding unit 250 then obtains a decoded value of the normalized inner product value obtained in step S250-12. R and the right channel correction coefficient c obtained in step S250-13 R The multiplied value is used as the right channel subtraction gain β (step S250-14).

[0142] In addition, when the stereo code CS is a code obtained by combining the left channel differential code CL and the right channel differential code CR, the right channel decoded differential signal ^y in the stereo decoding unit 220 is R (1) ^y R (2), ..., ^y R The number of bits b used for decoding (T) R The right channel differential code CR is the number of bits. R (1) ^y R (2), ..., ^y R The number of bits b used for decoding (T) R If it cannot be determined clearly, the number of bits b of the stereo code CS input to the stereo decoding unit 220 is s One-half of (i.e., b s / 2) is used as the bit number b R The mono decoded audio signal ^x in the mono decoding unit 210 M (1), ^x M (2), ..., ^x M The number of bits b used for decoding (T) M Refers to the number of bits of the mono code CM. Right channel correction coefficient c R The value obtained by the formula (1-7-2) itself may be a value greater than 0 and less than 1. The differential signal ^y decoded in the right channel R (1) ^y R (2), ..., ^y R The number of bits b used for decoding (T) RDecoding mono audio signal^x M (1), ^x M (2), ..., ^x M The number of bits b used for decoding (T) M If the same, it is 0.5, the number of bits is b R The larger the bit number b is, the M , then it is closer to 0 than 0.5, and the number of bits is b R The smaller the bit number b is, the M , it is a value closer to 1 than 0.5.

[0143] In addition, the same normalized inner product value candidate code may be used for the left channel and the right channel. The above-mentioned A and B may be set to the same value, so that the normalized inner product value candidate code of the left channel stored in the left channel subtraction gain estimation unit 120 and the left channel subtraction gain decoding unit 230 is equal to Lcand (a) The code Cα corresponding to the candidate cand (a), and the candidates r of the normalized inner product value of the right channel stored in the right channel subtraction gain estimation unit 140 and the right channel subtraction gain decoding unit 250. Rcand (b) The code Cβ corresponding to the candidate cand The groups of (b) are the same.

[0144] In addition, the code Cα is actually a code corresponding to the left channel subtraction gain α and is called a left channel subtraction gain code for the purpose of matching the terms in the description of the encoding device 100 and the decoding device 200. However, from the point of view that it is a code representing a normalized inner product value, it may also be called a left channel inner product code, etc. The same is true for the code Cβ, and it may also be called a right channel inner product code, etc.

[0145] 〔〔Example 2〕〕

[0146] As Example 2, an example of using a value in consideration of input values ​​of past frames as a normalized inner product value is described. Strictly speaking, in Example 2, although the optimality within a frame, that is, the minimization of the energy of the quantization error of the decoded sound signal of the left channel and the minimization of the energy of the quantization error of the decoded sound signal of the right channel cannot be strictly guaranteed, the sharp change between frames of the left channel subtraction gain α and the sharp change between frames of the right channel subtraction gain β are reduced, thereby reducing the noise generated in the decoded sound signal due to the change. That is, in addition to reducing the energy of the quantization error of the decoded sound signal, Example 2 also takes the auditory quality of the decoded sound signal into consideration.

[0147] The encoding side of Example 2, that is, the left channel subtraction gain estimation unit 120 and the right channel subtraction gain estimation unit 140 are different from those of Example 1, but the decoding side, that is, the left channel subtraction gain decoding unit 230 and the right channel subtraction gain decoding unit 250 are the same as those of Example 1. The following description will focus on the differences between Example 2 and Example 1.

[0148] [[[Left channel subtraction gain estimation unit 120]]]

[0149] like Figure 8 As shown, the left channel subtraction gain estimation unit 120 performs the following steps S120 - 111 to S120 - 113 and steps S120 - 12 to S120 - 14 described in Example 1.

[0150] The left channel subtraction gain estimation unit 120 first uses the input left channel input audio signal x L (1), x L (2), ..., x L (T), input downmix signal x M (1), x M (2), ..., x M (T) and the inner product value E used in the previous frame L (-1), the inner product value E used in the current frame is obtained by the following formula (1-8): L (0)(Step S120-111).

[0151] [Formula 14]

[0152]

[0153] Here, ε L is a predetermined value greater than 0 and less than 1, and is stored in advance in the left channel subtraction gain estimation unit 120. In addition, the left channel subtraction gain estimation unit 120 obtains the inner product value E L (0) is stored in the left channel subtraction gain estimation unit 120 as the "inner product value E used in the previous frame" L (-1)" and use it in the next frame.

[0154] The left channel subtraction gain estimation unit 120 also uses the input downmix signal x M (1), x M (2), ..., x M (T) and the energy E of the downmix signal used in the previous frame M (-1), the energy E of the downmix signal used in the current frame is obtained by the following formula (1-9): M (0)(Step S120-112).

[0155] [Mathematical formula 15]

[0156]

[0157] Here, ε M is a predetermined value greater than 0 and less than 1, and is stored in advance in the left channel subtraction gain estimation unit 120. In addition, the left channel subtraction gain estimation unit 120 obtains the energy E of the downmix signal. M (0) is stored in the left channel subtraction gain estimation unit 120 so as to be used as the “energy E of the downmix signal used in the previous frame”. M (-1)" and use it in the next frame.

[0158] The left channel subtraction gain estimation unit 120 then uses the inner product value E used in the current frame obtained in step S120-111. L (0) and the energy E of the downmix signal used in the current frame obtained in step S120-112 M (0), the normalized inner product value r is obtained by the following formula (1-10): L (Step S120-113).

[0159] [Formula 16]

[0160] r L =E L (0) / E M (0)…(1-10)

[0161] The left channel subtraction gain estimation unit 120 further performs step S120-12, and then replaces the normalized inner product value r obtained in step S120-11 with L The normalized inner product value r obtained in the above steps S120-113 is used L Perform step S120 - 13 , and perform step S120 - 14 .

[0162] In addition, the above ε L and ε M The closer it is to 1, the smaller the normalized inner product value r L The more likely it is to include the influence of the left channel input sound signal and the downmix signal of the past frame, and the normalized inner product value r L , through the normalized inner product value r L The obtained left channel subtraction gain α has a smaller variation between frames.

[0163] [Right channel subtraction gain estimation unit 140]

[0164] like Figure 8As shown, the right channel subtraction gain estimation unit 140 performs the following steps S140 - 111 to S140 - 113 and steps S140 - 12 to S140 - 14 described in Example 1.

[0165] The right channel subtraction gain estimation unit 140 first uses the input audio signal x of the right channel R (1), x R (2), ..., x R (T), input downmix signal x M (1), x M (2), ..., x M (T) and the inner product value E used in the previous frame R (-1), the inner product value E used in the current frame is obtained by the following formula (1-8-2): R (0)(Step S140-111).

[0166] [Mathematical formula 17]

[0167]

[0168] Here, ε R is a predetermined value greater than 0 and less than 1, and is stored in advance in the right channel subtraction gain estimation unit 140. In addition, the right channel subtraction gain estimation unit 140 obtains the inner product value E R (0) is stored in the right channel subtraction gain estimation unit 140 as the "inner product value E used in the previous frame" R (-1)" and use it in the next frame.

[0169] The right channel subtraction gain estimation unit 140 also uses the input downmix signal x M (1), x M (2), ..., x M (T) and the energy E of the downmix signal used in the previous frame M (-1), the energy E of the downmix signal used in the current frame is obtained by equation (1-9) M (0) (Step S140-112). The right channel subtraction gain estimation unit 140 obtains the energy E of the downmix signal. M (0) is stored in the right channel subtraction gain estimation unit 140 as the “energy E of the downmix signal used in the previous frame”. M (-1)” and used in the next frame. In addition, the energy E of the downmix signal used in the current frame is also obtained by the left channel subtraction gain estimation unit 120 through equation (1-9). M(0), therefore, only one of step S120 - 112 performed by the left channel subtraction gain estimation unit 120 and step S140 - 112 performed by the right channel subtraction gain estimation unit 140 may be performed.

[0170] The right channel subtraction gain estimation unit 140 then uses the inner product value E used in the current frame obtained in step S140-111. R (0) and the energy E of the downmix signal used in the current frame obtained in step S140-112 M (0), the normalized inner product value r is obtained by the following formula (1-10-2): R (Step S140-113).

[0171] [Mathematical formula 18]

[0172] r R =E R (0) / E M (0)…(1-10-2)

[0173] The right channel subtraction gain estimation unit 140 further performs step S140 - 12 , and then replaces the normalized inner product value r obtained in step S140 - 11 with R The normalized inner product value r obtained in the above step S140-113 is used R Perform step S140 - 13 , and perform step S140 - 14 .

[0174] In addition, the above ε R and ε M The closer it is to 1, the smaller the normalized inner product value r R The more likely it is to include the influence of the input sound signal of the right channel and the downmix signal of the past frame, and the normalized inner product value r R , through the normalized inner product value r R The variation between frames of the obtained right channel subtraction gain β becomes smaller.

[0175] [[Variation of Example 2]]

[0176] Regarding Example 2, the same modification as that of the modification of Example 1 for Example 1 can be performed. This method will be described as a modification of Example 2. The encoding side of the modification of Example 2, that is, the left channel subtraction gain estimation unit 120 and the right channel subtraction gain estimation unit 140 are different from those of the modification of Example 1, but the decoding side, that is, the left channel subtraction gain decoding unit 230 and the right channel subtraction gain decoding unit 250 are the same as those of the modification of Example 1. The difference between the modification of Example 2 and the modification of Example 1 is the same as that of Example 2, so the modification of Example 2 will be described below with reference to the modification of Example 1 and Example 2 as appropriate.

[0177] [[[Left channel subtraction gain estimation unit 120]]]

[0178] In the left channel subtraction gain estimation unit 120, similarly to the left channel subtraction gain estimation unit 120 of the modification of Example 1, a plurality of sets (A sets, a=1, . . . , A) of left channel normalized inner product value candidates r are stored in advance. Lcand (a) The code Cα corresponding to the candidate cand (a) group. Fig. 9 As shown, the left channel subtraction gain estimation unit 120 performs steps S120 - 111 to S120 - 113 similar to Example 2, and steps S120 - 12 , S120 - 15 , and S120 - 16 similar to the modified example of Example 1. Specifically, it is as follows.

[0179] The left channel subtraction gain estimation unit 120 first uses the input left channel input audio signal x L (1), x L (2), ..., x L (T), input downmix signal x M (1), x M (2), ..., x M (T) and the inner product value E used in the previous frame L (-1), and the inner product value E used in the current frame is obtained through formula (1-8) L (0) (step S120-111). The left channel subtraction gain estimation unit 120 further uses the input downmix signal x M (1), x M (2), ..., x M (T) and the energy E of the downmix signal used in the previous frame M (-1), and through formula (1-9), the energy E of the downmix signal used in the current frame is obtained M(0) (Step S120-112) The left channel subtraction gain estimation unit 120 then uses the inner product value E used in the current frame obtained in step S120-111. L (0) and the energy E of the downmix signal used in the current frame obtained in step S120-112 M (0), and the normalized inner product value r is obtained by formula (1-10) L (Step S120-113) The left channel subtraction gain estimation unit 120 then obtains the stored normalized inner product value candidate r of the left channel. Lcand (1), ..., r Lcand (A) is closest to the normalized inner product value r obtained in step S120-113 L Candidate (normalized inner product value r L Quantitative value of L , and obtain the stored code Cα cand (1), ..., Cα cand The closest candidate in (A) L The corresponding code is used as the left channel subtraction gain code Cα (step S120-15). In addition, the left channel subtraction gain estimation unit 120 uses the left channel difference signal y in the stereo encoding unit 170 L (1) y L (2), ..., y L The number of bits b used to encode (T) L , the downmix signal x in the mono encoding unit 160 M (1), x M (2), ..., x M The number of bits b used to encode (T) M And the number of samples per frame T, the left channel correction coefficient c is obtained by formula (1-7) L (Step S120-12) The left channel subtraction gain estimation unit 120 then obtains a quantized value of the normalized inner product value obtained in step S120-15. L and the left channel correction coefficient c obtained in step S120-12 L The multiplied value is used as the left channel subtraction gain α (step S120 - 16 ).

[0180] [Right channel subtraction gain estimation unit 140]

[0181] In the right channel subtraction gain estimation unit 140, similarly to the right channel subtraction gain estimation unit 140 of the modification of Example 1, a plurality of sets (B sets, b=1, . . . , B) of candidates for normalized inner product values ​​of the right channel are stored in advance. Rcand(b) The code Cβ corresponding to the candidate cand (b) group. Fig. 9 As shown, the right channel subtraction gain estimation unit 140 performs steps S140 - 111 to S140 - 113 similar to Example 2, and steps S140 - 12 , S140 - 15 , and S140 - 16 similar to the modified example of Example 1. Specifically, it is as follows.

[0182] The right channel subtraction gain estimation unit 140 first uses the input audio signal x of the right channel R (1), x R (2), ..., x R (T), input downmix signal x M (1), x M (2), ..., x M (T) and the inner product value E used in the previous frame R (-1), and the inner product value E used in the current frame is obtained through formula (1-8-2) R (0) (step S140-111). The right channel subtraction gain estimation unit 140 also uses the input downmix signal x M (1), x M (2), ..., x M (T) and the energy E of the downmix signal used in the previous frame M (-1), the energy E of the downmix signal used in the current frame is obtained by equation (1-9) M (0) (Step S140 - 112 ) The right channel subtraction gain estimation unit 140 then uses the inner product value E used in the current frame obtained in step S140 - 111 . R (0) and the energy E of the downmix signal used in the current frame obtained in step S140-112 M (0), and the normalized inner product value r is obtained by formula (1-10-2) R (Step S140-113) The right channel subtraction gain estimation unit 140 then obtains the stored normalized inner product value candidate r of the right channel. Rcand (1), ..., r Rcand (B) is closest to the normalized inner product value r obtained in step S140-113 R Candidate (normalized inner product value r R Quantitative value of R , and obtain the stored code Cβ cand (1), ..., Cβ cand (B) The closest candidate RThe corresponding code is used as the right channel subtraction gain code Cβ (step S140-15). In addition, the right channel subtraction gain estimation unit 140 uses the right channel difference signal y in the stereo encoding unit 170 R (1) y R (2), ..., y R The number of bits b used to encode (T) R , the downmix signal x in the mono encoding unit 160 M (1), x M (2), ..., x M The number of bits b used to encode (T) M And the number of samples per frame T, the right channel correction coefficient c is obtained by formula (1-7-2) R (Step S140-12) The right channel subtraction gain estimation unit 140 then obtains a quantized value of the normalized inner product value obtained in step S140-15. R and the right channel correction coefficient c obtained in step S140-12 R The multiplied value is used as the right channel subtraction gain β (step S140-16).

[0183] 〔〔Example 3〕〕

[0184] For example, there is a problem that when the voice, music, or other sound included in the input sound signal of the left channel is different from the voice, music, or other sound included in the input sound signal of the right channel, the downmix signal may include both the components of the input sound signal of the left channel and the components of the input sound signal of the right channel. Therefore, the larger the value used as the left channel subtraction gain α, the more it sounds like the left channel decoded sound signal contains the sound originating from the input sound signal of the right channel that should not be heard originally; and the larger the value used as the right channel subtraction gain β, the more it sounds like the right channel decoded sound signal contains the sound originating from the input sound signal of the left channel that should not be heard originally. Therefore, although the energy of the quantization error of the decoded sound signal is not strictly guaranteed to be minimized, the left channel subtraction gain α and the right channel subtraction gain β can be set to smaller values ​​than the values ​​obtained by Example 1 in consideration of auditory quality. In addition, similarly, the left channel subtraction gain α and the right channel subtraction gain β can be set to smaller values ​​than the values ​​obtained by Example 2.

[0185] Specifically, for the left channel, in Example 1 and Example 2, the normalized inner product value r L and the left channel correction coefficient c L The multiplication value c L × L The quantized value is set as the left channel subtraction gain α, but in Example 3, the normalized inner product value r L, left channel correction coefficient c L and a predetermined value greater than 0 and less than 1, namely λ L The multiplication value λ L ×c L × L The quantized value of is set as the left channel subtraction gain α. Therefore, similarly to Example 1 and Example 2, it can also be set as L × L The multiplication value c is represented by the left channel subtraction gain code Cα as the object of encoding in the left channel subtraction gain estimation unit 120 and decoding in the left channel subtraction gain decoding unit 230. L × L The left channel subtraction gain estimation unit 120 and the left channel subtraction gain decoding unit 230 convert the multiplication value c L × L The quantized value and λ L Multiply to obtain the left channel subtraction gain α. Alternatively, the normalized inner product value r L , left channel correction coefficient c L and the predetermined value λ L The multiplication value λ L ×c L × L The left channel subtraction gain code Cα, which is the object of encoding in the left channel subtraction gain estimation unit 120 and decoding in the left channel subtraction gain decoding unit 230, represents the multiplication value λ. L ×c L × L Quantified value of .

[0186] Similarly, for the right channel, in Example 1 and Example 2, the normalized inner product value r R and the right channel correction coefficient c R The multiplication value c R × R The quantized value is used as the right channel subtraction gain β. In Example 3, the normalized inner product value r R , right channel correction coefficient c R and a predetermined value greater than 0 and less than 1, namely λ R The multiplication value λ R ×c R × R The quantized value of is used as the right channel subtraction gain β. Therefore, similarly to Example 1 and Example 2, it can be assumed that the multiplication value c R × R The right channel subtraction gain code Cβ, which is the object of encoding in the right channel subtraction gain estimation unit 140 and decoding in the right channel subtraction gain decoding unit 250, represents the multiplication value c R ×R The right channel subtraction gain estimation unit 140 and the right channel subtraction gain decoding unit 250 convert the multiplication value c R × R The quantized value of R Multiply to obtain the right channel subtraction gain β. Alternatively, the normalized inner product value r R , left channel correction coefficient c R and the predetermined value λ R The multiplication value λ R ×c R × R , which is the object of encoding in the right channel subtraction gain estimation unit 140 and decoding in the right channel subtraction gain decoding unit 250, the right channel subtraction gain code Cβ represents the multiplication value λ R ×c R × R In addition, λ R Can be set to be equal to λ L Same value.

[0187] [[Variation of Example 3]]

[0188] As mentioned above, for the correction coefficient c L , the same value can be calculated in both the encoding device 100 and the decoding device 200. Therefore, similarly to the modification of Example 1 and the modification of Example 2, the normalized inner product value r can be set to L The left channel subtraction gain code Cα, which is the object of encoding in the left channel subtraction gain estimation unit 120 and decoding in the left channel subtraction gain decoding unit 230, represents the normalized inner product value r L The left channel subtraction gain estimation unit 120 and the left channel subtraction gain decoding unit 230 convert the normalized inner product value r L Quantized value, left channel correction coefficient c L and a predetermined value greater than 0 and less than 1, namely λ L Multiply to obtain the left channel subtraction gain α. Alternatively, it can also be set to normalize the inner product value r L and a predetermined value greater than 0 and less than 1, namely λ L The multiplication value λ L × L The left channel subtraction gain code Cα, which is the object of encoding in the left channel subtraction gain estimation unit 120 and decoding in the left channel subtraction gain decoding unit 230, represents the multiplication value λ. L × L The left channel subtraction gain estimation unit 120 and the left channel subtraction gain decoding unit 230 convert the multiplication value λ L × LThe quantized value and the left channel correction coefficient c L Multiply to obtain the left channel subtraction gain α.

[0189] The same is true for the right channel. For the correction factor c R , the same value can be calculated in both the encoding device 100 and the decoding device 200. Therefore, similarly to the modification of Example 1 and the modification of Example 2, the normalized inner product value r can be set to R The right channel subtraction gain code Cβ, which is the object of encoding in the right channel subtraction gain estimation unit 140 and decoding in the right channel subtraction gain decoding unit 250, represents the normalized inner product value r R The right channel subtraction gain estimation unit 140 and the right channel subtraction gain decoding unit 250 convert the normalized inner product value r R Quantized value, right channel correction coefficient c R and a predetermined value greater than 0 and less than 1, namely λ R Multiply to obtain the right channel subtraction gain β. Alternatively, it can be set to the normalized inner product value r R and a predetermined value greater than 0 and less than 1, namely λ R The multiplication value λ R × R The right channel subtraction gain code Cβ, which is the object of encoding in the right channel subtraction gain estimation unit 140 and decoding in the right channel subtraction gain decoding unit 250, represents the multiplication value λ. R × R The right channel subtraction gain estimation unit 140 and the right channel subtraction gain decoding unit 250 convert the multiplication value λ R × R The quantized value and the right channel correction coefficient c R Multiply to obtain the right channel subtraction gain β.

[0190] 〔〔Example 4〕〕

[0191] The problem of auditory quality described at the beginning of Example 3 occurs when the correlation between the input sound signal of the left channel and the input sound signal of the right channel is small, but this problem is less likely to occur when the correlation between the input sound signal of the left channel and the input sound signal of the right channel is large. Therefore, in Example 4, the correlation coefficient between the input sound signal of the left channel and the input sound signal of the right channel, that is, the left-right correlation coefficient γ, is used instead of the predetermined value of Example 3, so that the greater the correlation between the input sound signal of the left channel and the input sound signal of the right channel, the more priority is given to reducing the energy of the quantization error of the decoded sound signal, and the smaller the correlation between the input sound signal of the left channel and the input sound signal of the right channel, the more priority is given to suppressing the deterioration of auditory quality.

[0192] The encoding side of Example 4 is different from that of Examples 1 and 2, but the decoding side, that is, the left channel subtraction gain decoding unit 230 and the right channel subtraction gain decoding unit 250 are the same as those of Examples 1 and 2. The differences between Example 4 and Examples 1 and 2 are described below.

[0193] [[Left-right relationship information estimation unit 180]]]

[0194] like Figure 1 As shown by the middle dotted line, the encoding device 100 of Example 4 also includes a left-right relationship information estimation unit 180. The left-right relationship information estimation unit 180 receives an input audio signal of a left channel input to the encoding device 100 and an input audio signal of a right channel input to the encoding device 100. The left-right relationship information estimation unit 180 obtains a left-right correlation coefficient γ from the input audio signal of the left channel and the input audio signal of the right channel, and outputs the obtained result (step S180).

[0195] The left-right correlation coefficient γ is the correlation coefficient between the input audio signal of the left channel and the input audio signal of the right channel, and may also be the sample sequence x of the input audio signal of the left channel. L (1), x L (2), ..., x L (T) and the sample sequence x of the input audio signal of the right channel R (1), x R (2), ..., x R (T) Correlation coefficient γ 0 , or a correlation coefficient that takes into account the time difference, for example, the correlation coefficient γ between the sample sequence of the input sound signal of the left channel and the sample sequence of the input sound signal of the right channel that is shifted backward by τ samples compared to the sample sequence τ .

[0196] This τ is information corresponding to the difference between the arrival time from the sound source that mainly emits sound in the space to the microphone for the left channel and the arrival time from the sound source to the microphone for the right channel (the so-called arrival time difference), assuming that the sound signal obtained by AD conversion of the sound picked up by the microphone for the left channel arranged in a certain space is the input sound signal for the left channel, and the sound signal obtained by AD conversion of the sound picked up by the microphone for the right channel arranged in the space is the input sound signal for the right channel. Hereinafter, it is referred to as the left-right time difference. The left-right time difference τ can be obtained by any known method, and can be obtained by the left-right relationship information estimation unit 181 of the first embodiment by the method described in the description, etc. That is, the above-mentioned correlation coefficient γ τ This is information corresponding to the correlation coefficient between a sound signal that reaches the left channel microphone from a sound source and is picked up, and a sound signal that reaches the right channel microphone from the sound source and is picked up.

[0197] [[[Left channel subtraction gain estimation unit 120]]]

[0198] The left channel subtraction gain estimation unit 120 obtains the normalized inner product value r obtained in step S120-11 or step S120-113 instead of step S120-13. L , the left channel correction coefficient c obtained in step S120-12 L and the value obtained by multiplying the left-right correlation coefficient γ obtained in step S180 (step S120-13"). Next, the left channel subtraction gain estimation unit 120 replaces step S120-14 and obtains the stored candidate α of the left channel subtraction gain. cand (1), ..., α cand (A) is closest to the multiplication value γ×c obtained in step S120-13". L × L Candidates (multiplication value γ×c L × L quantized value), as the left channel subtraction gain α, and obtain the stored code Cα cand (1), ..., Cα cand The code corresponding to the left channel subtraction gain α in (A) is used as the left channel subtraction gain code Cα (step S120-14").

[0199] [Right channel subtraction gain estimation unit 140]

[0200] The right channel subtraction gain estimation unit 140 obtains the normalized inner product value r obtained in step S140-11 or step S140-113 instead of step S140-13. R , the right channel correction coefficient c obtained in step S140-12 R and the value obtained by multiplying the left-right correlation coefficient γ obtained in step S180 (step S140-13"). The right channel subtraction gain estimation unit 140 then obtains the stored candidate β of the right channel subtraction gain instead of step S140-14. cand (1), ..., β cand (B) is closest to the multiplication value γ×c obtained in step S140-13". R × R Candidates (multiplication value γ×c R × R quantized value), as the right channel subtraction gain β, and obtain the stored code Cβ cand (1), ..., Cβ candThe code corresponding to the right channel subtraction gain β in (B) is used as the right channel subtraction gain code Cβ (step S140-14").

[0201] [[Variation of Example 4]]

[0202] As mentioned above, for the correction coefficient c L , the same value can be calculated in both the encoding device 100 and the decoding device 200. Therefore, it can be assumed that the normalized inner product value r L The multiplication value of the left and right correlation coefficient γ is γ×r L The left channel subtraction gain code Cα, which is the object of encoding in the left channel subtraction gain estimation unit 120 and decoding in the left channel subtraction gain decoding unit 230, represents the multiplication value γ×r L The left channel subtraction gain estimation unit 120 and the left channel subtraction gain decoding unit 230 convert the multiplication value γ×r L The quantized value and the left channel correction coefficient c L Multiply to obtain the left channel subtraction gain α.

[0203] The same is true for the right channel. For the correction factor c R , the same value can be calculated in both the encoding device 100 and the decoding device 200. Therefore, it can be assumed that the normalized inner product value r R The multiplication value of the left and right correlation coefficient γ is γ×r R The right channel subtraction gain code Cβ, which is the object of encoding in the right channel subtraction gain estimation unit 140 and decoding in the right channel subtraction gain decoding unit 250, represents the multiplication value γ×r R The right channel subtraction gain estimation unit 140 and the right channel subtraction gain decoding unit 250 convert the multiplication value γ×r R The quantized value and the right channel correction coefficient c R Multiply to obtain the right channel subtraction gain β.

[0204] <First embodiment>

[0205] The encoding device and decoding device according to the first embodiment will be described.

[0206] 《Encoding device 101》

[0207] like Fig.10As shown in FIG. 1 , the encoding device 101 of the first embodiment includes a downmixing unit 110, a left channel subtraction gain estimation unit 120, a left channel signal subtraction unit 130, a right channel subtraction gain estimation unit 140, a right channel signal subtraction unit 150, a monaural encoding unit 160, a stereo encoding unit 170, a left-right relationship information estimation unit 181, and a time shifting unit 191. The encoding device 101 of the first embodiment is different from the encoding device 100 of the reference mode in that the left-right relationship information estimation unit 181 and the time shifting unit 191 are included, and the left channel subtraction gain estimation unit 120, the left channel signal subtraction unit 130, the right channel signal subtraction unit 140, and the right channel signal subtraction unit 150 use the signal output by the time shifting unit 191 instead of the signal output by the downmixing unit 110, and output the left-right time difference code Cτ described later in addition to the above-mentioned codes. The other structures and operations of the encoding device 101 of the first embodiment are the same as those of the encoding device 100 of the reference embodiment. The encoding device 101 of the first embodiment performs Fig.11 The processing of step S110 to step S191 is illustrated. Hereinafter, the differences between the encoding device 101 of the first embodiment and the encoding device 100 of the reference embodiment will be described.

[0208] [Left-right relationship information estimation unit 181]

[0209] The left-right relationship information estimation unit 181 receives an input audio signal of the left channel input to the encoding device 101 and an input audio signal of the right channel input to the encoding device 101. The left-right relationship information estimation unit 181 obtains a left-right time difference τ and a left-right time difference code Cτ from the input audio signal of the left channel and the input audio signal of the right channel, and outputs the obtained left-right time difference τ (step S181).

[0210] The left-right time difference τ is information corresponding to the difference between the arrival time from the sound source that mainly emits sound in the space to the microphone for the left channel and the arrival time from the sound source to the microphone for the right channel (so-called arrival time difference), assuming that the sound signal obtained by AD conversion of the sound picked up by the microphone for the left channel arranged in a certain space is the input sound signal for the left channel, and the sound signal obtained by AD conversion of the sound picked up by the microphone for the right channel arranged in the space is the input sound signal for the right channel. In addition, not only the arrival time difference but also information on which microphone arrives earlier is included in the left-right time difference τ, so the left-right time difference τ is set to take a positive value or a negative value based on either input sound signal. That is, the left-right time difference τ is information indicating to what extent the same sound signal is included earlier in which signal of the input sound signal of the left channel and the input sound signal of the right channel. In the following, when the same sound signal is included in the input sound signal of the left channel earlier than the input sound signal of the right channel, it is also referred to as the left channel being in the leading position, and when the same sound signal is included in the input sound signal of the right channel earlier than the input sound signal of the left channel, it is also referred to as the right channel being in the leading position.

[0211] The left-right time difference τ can be obtained by any known method. For example, the left-right relationship information estimation unit 181 calculates the left-right time difference τ from the predetermined max to τ min (For example, τ max is a positive number, τ min is a negative number) cand , calculate the sample sequence representing the input sound signal of the left channel and the candidate sample number τ compared to the sample sequence cand The value of the correlation of the sample sequence of the input audio signal of the right channel at the position shifted backward by the amount (hereinafter referred to as the correlation value) γ cand , and obtain the correlation value γ cand Become the maximum number of candidate samples τ cand As the left-right time difference τ. That is, in this example, when the left channel is in the leading position, the left-right time difference τ is a positive value, and when the right channel is in the leading position, the left-right time difference τ is a negative value. The absolute value of the left-right time difference τ is a value indicating how much the leading channel is in the leading position relative to the other channel (the number of samples in the leading position). For example, when calculating the correlation value γ using only samples in the frame cand In the case of τ cand When the value is positive, the partial sample sequence x of the input audio signal of the right channel is calculated. R (1+τ cand ), x R (2+τ cand),...,x R (T) is compared with the number of candidate samples τ in the sample column cand The amount of the partial sample column x of the input sound signal of the left channel shifted forward L (1), x L (2), ..., x L (T-τ cand ) is taken as the absolute value of the correlation coefficient of cand , in τ cand When the value is negative, the partial sample sequence x of the input audio signal of the left channel L (1-τ cand ), x L (2-τ cand ),...,x L (T) is compared with the number of candidate samples-τ in the sample column cand The amount of the partial sample column x of the input sound signal of the right channel shifted forward R (1), x R (2), ..., x R (T+τ cand ) is taken as the absolute value of the correlation coefficient of cand Of course, in order to calculate the correlation value γ cand Alternatively, one or more samples of past input sound signals that are continuous with the sample sequence of the input sound signal of the current frame may be used. In this case, the sample sequence of the input sound signal of the past frame may be stored in a storage unit (not shown) within the left-right relationship information estimation unit 181 in a predetermined number of frames.

[0212] In addition, for example, instead of the absolute value of the correlation coefficient, the correlation value γ may be calculated using information on the phase of the signal as follows: cand In this example, the left-right relationship information estimation unit 181 first calculates the left channel input audio signal x as shown in the following equations (3-1) and (3-2). L (1), x L (2), ..., x L (T) and the input sound signal x of the right channel R (1), x R (2), ..., x R (T) Perform Fourier transform to obtain the spectrum X at each frequency k from 0 to T-1 L (k) and X R (k).

[0213] [Mathematical formula 19]

[0214]

[0215] [Mathematical formula 20]

[0216]

[0217] The left-right relationship information estimation unit 181 uses the obtained spectrum X L (k) and X R (k), the spectrum of the phase difference at each frequency k is obtained by the following formula (3-3):

[0218] [Mathematical formula 21]

[0219]

[0220] By performing inverse Fourier transform on the obtained spectrum of the phase difference, as shown in the following equation (3-4), max ~τ min The number of candidate samples τ cand , and obtain the phase difference signal ψ(τ cand ).

[0221] [Mathematical formula 22]

[0222]

[0223] The obtained phase difference signal ψ(τ cand ) represents the absolute value of the input sound signal x of the left channel L (1), x L (2), ..., x L (T) and the input sound signal x of the right channel R (1), x R (2), ..., x R The likelihood of the time difference of (T) corresponds to a certain correlation, which will be relative to the number of candidate samples τ cand The phase difference signal ψ(τ cand ) is used as the correlation value γ cand The left-right relationship information estimation unit 181 obtains the phase difference signal ψ(τ cand ) is the absolute value of the correlation value γ cand Become the maximum number of candidate samples τ cand Alternatively, the phase difference signal ψ(τ cand ) is taken as the correlation value γ cand This point, for example, for each τ cand , using the phase difference signal ψ(τ cand ) is the absolute value of candFor each of the multiple candidate samples before and after, the relative difference between the absolute value of the phase difference signal and the average is normalized. In other words, for each τ cand , or you can use a predetermined positive number τ range , the average value is obtained by the following formula (3-5), and the average value ψ is used c (τ cand ) and the phase difference signal ψ(τ cand ) The normalized correlation value obtained by the following formula (3-6) is used as γ cand .

[0224] [Mathematical formula 23]

[0225]

[0226] [Mathematical formula 24]

[0227]

[0228] In addition, the normalized correlation value obtained by equation (3-6) is a value greater than or equal to 0 and less than or equal to 1, which indicates that τ cand As the time difference between the left and right sides, the higher the likelihood, the closer it is to 1, τ cand The less likely the left and right time differences are, the closer they are to 0.

[0229] In addition, the left-right relationship information estimation unit 181 encodes the left-right time difference τ by a predetermined encoding method to obtain a left-right time difference code Cτ, which is a code that can uniquely identify the left-right time difference τ. As the predetermined encoding method, a known encoding method such as scalar quantization can be used. In addition, the predetermined number of candidate samples can be selected from τ max to τ min The integer values ​​of may also include the integer values ​​of max to τ min The fractional value or decimal value between τ max to τ min Any integer value between . In addition, it can be τ max =-τ min , which may not be the case. In addition, when a special input audio signal such as an arbitrary channel must be in the leading position is taken as the object, it can be set to τ max and τ min are all positive numbers, or τ max and τ min Are all negative numbers.

[0230] Furthermore, when the encoding device 101 estimates the subtraction gain based on the principle of minimizing the quantization error in Example 4 or a variation of Example 4 described in the reference mode, the left-right relationship information estimation unit 181 further calculates the correlation value between the sample sequence of the input sound signal of the left channel and the sample sequence of the input sound signal of the right channel which is shifted backward by the left-right time difference τ compared with the sample sequence, that is, for the sample sequence from τ max to τ min The number of candidate samples τ cand The calculated correlation value γ cand The maximum value among them is output as the left-right correlation coefficient γ (step S180).

[0231] [Time shift unit 191]

[0232] The time shift unit 191 receives the downmix signal x output from the downmix unit 110. M (1), x M (2), ..., x M (T) and the left-right time difference τ output by the left-right relationship information estimation unit 181. When the left-right time difference τ is a positive value (that is, when the left-right time difference τ indicates that the left channel is in the leading position), the time shift unit 191 shifts the downmix signal x M (1), x M (2), ..., x M (T) is outputted to the left channel subtraction gain estimation unit 120 and the left channel signal subtraction unit 130 as it is (i.e., is determined to be used in the left channel subtraction gain estimation unit 120 and the left channel signal subtraction unit 130), and the signal x obtained by delaying the downmix signal by |τ| samples (the number of samples corresponding to the absolute value of the left and right time difference τ, the number of samples corresponding to the magnitude represented by the left and right time difference τ) is obtained. M (1-|τ|), x M (2-|τ|),...,x M (T-|τ|) is the delayed downmix signal x M '(1), x M '(2),...,x M '(T), output to the right channel subtraction gain estimation unit 140 and the right channel signal subtraction unit 150 (i.e., determined to be used in the right channel subtraction gain estimation unit 140 and the right channel signal subtraction unit 150), when the left and right time difference τ is a negative value (i.e., the left and right time difference τ indicates that the right channel is in the leading state), the downmix signal is delayed by |τ| samples to obtain a signal x M (1-|τ|), x M (2-|τ|),...,x M (T-|τ|) is the delayed downmix signal x M '(1), xM '(2),...,x M '(T) is output to the left channel subtraction gain estimation unit 120 and the left channel signal subtraction unit 130 (ie, is determined to be used in the left channel subtraction gain estimation unit 120 and the left channel signal subtraction unit 130), and the downmix signal x M (1), x M (2), ..., x M (T) is outputted to the right channel subtraction gain estimation unit 140 and the right channel signal subtraction unit 150 as it is (i.e., it is determined to be used in the right channel subtraction gain estimation unit 140 and the right channel signal subtraction unit 150), and when the left-right time difference τ is 0 (i.e., the left-right time difference τ indicates that none of the channels is in the leading position), the downmix signal x is M (1), x M (2), ..., x M (T) is outputted as it is to the left channel subtraction gain estimation unit 120, the left channel signal subtraction unit 130, the right channel subtraction gain estimation unit 140, and the right channel signal subtraction unit 150 (i.e., it is determined to be used in the left channel subtraction gain estimation unit 120, the left channel signal subtraction unit 130, the right channel subtraction gain estimation unit 140, and the right channel signal subtraction unit 150) (step S191). That is, for the channel with the shorter arrival time among the left and right channels, the input downmix signal is outputted as it is to the subtraction gain estimation unit and the signal subtraction unit of the channel, and for the channel with the longer arrival time among the left and right channels, the input downmix signal is delayed by the absolute value |τ| of the left-right time difference τ, and is outputted to the subtraction gain estimation unit and the signal subtraction unit of the channel. In addition, in the time shift unit 191, the downmix signal of the past frame is used to obtain the delayed downmix signal, so the downmix signal input in the past frame of the predetermined number of frames is stored in the storage unit (not shown) in the time shift unit 191. In addition, when the left channel subtraction gain estimation unit 120 and the right channel subtraction gain estimation unit 140 obtain the left channel subtraction gain α and the right channel subtraction gain β not by the method based on the principle of minimizing the quantization error but by the well-known method exemplified in Patent Document 1, a unit for obtaining a local decoded signal corresponding to the monaural code CM is provided in the subsequent stage of the monaural encoding unit 160 of the encoding device 101 or in the monaural encoding unit 160, and in the time shift unit 191, the downmix signal x may be replaced. M (1), x M (2), ..., x M (T), and the local decoded signal encoded using mono is the quantized downmix signal^x M (1), ^x M (2), ..., ^xM (T) to perform the above processing. At this time, the time shift unit 191 replaces the downmix signal x M (1), x M (2), ..., x M (T) and output the quantized downmixed signal ^x M (1), ^x M (2), ..., ^x M (T), instead of the delayed downmix signal x M '(1), x M '(2),...,x M '(T) and the output delayed quantization completed downmix signal ^x M '(1), ^x M '(2),...,^x M '(T).

[0233] [Left channel subtraction gain estimation unit 120, left channel signal subtraction unit 130, right channel subtraction gain estimation unit 140, right channel signal subtraction unit 150]

[0234] The left channel subtraction gain estimation unit 120, the left channel signal subtraction unit 130, the right channel subtraction gain estimation unit 140, and the right channel signal subtraction unit 150 replace the downmix signal x output by the downmix unit 110. M (1), x M (2), ..., x M (T), and using the downmix signal x input from the time shift unit 191 M (1), x M (2), ..., x M (T) or delayed downmix signal x M '(1),x M '(2),...,x M '(T), the same operations as those described in the reference method are performed (steps S120, S130, S140, S150). That is, the left channel subtraction gain estimation unit 120, the left channel signal subtraction unit 130, the right channel subtraction gain estimation unit 140, and the right channel signal subtraction unit 150 use the downmix signal x determined by the time shift unit 191. M (1), x M (2), ..., x M (T) or delayed downmix signal x M '(1), x M '(2),...,x M '(T) performs the same operation as described in the reference mode. In addition, the time shift unit 191 replaces the downmix signal x M (1), x M(2), ..., x M (T) and output the quantized downmixed signal ^x M (1), ^x M (2), ..., ^x M (T), instead of the delayed downmix signal x M '(1), x M '(2),...,x M '(T) and the output delayed quantization completed downmix signal ^x M '(1), ^x M '(2),...,^x M In the case of '(T), the left channel subtraction gain estimation unit 120, the left channel signal subtraction unit 130, the right channel subtraction gain estimation unit 140 and the right channel signal subtraction unit 150 use the quantized downmix signal ^x input from the time shift unit 191. M (1), ^x M (2), ..., ^x M (T) or delayed quantization completed downmix signal ^x M '(1), ^x M '(2),...,^x M '(T) to carry out the above processing.

[0235] 《Decoding Device 201》

[0236] like Fig.12 As shown in FIG. 1 , the decoding device 201 of the first embodiment includes a mono decoding unit 210, a stereo decoding unit 220, a left channel subtraction gain decoding unit 230, a left channel signal adding unit 240, a right channel signal adding unit 250, a right channel signal adding unit 260, a left-right time difference decoding unit 271, and a time shifting unit 281. The decoding device 201 of the first embodiment is different from the decoding device 200 of the reference method in that, in addition to the above-mentioned codes, a left-right time difference code Cτ described later is input, the left-right time difference decoding unit 271 and the time shifting unit 281 are included, and the left channel signal adding unit 240 and the right channel signal adding unit 260 use the signal output by the time shifting unit 281 instead of the signal output by the mono decoding unit 210. The other structures and operations of the decoding device 201 of the first embodiment are the same as those of the decoding device 200 of the reference method. The decoding device 201 of the first embodiment performs a decoding operation on each frame. Fig.13 The processing of step S210 to step S281 is illustrated. The following describes the differences between the decoding apparatus 201 of the first embodiment and the decoding apparatus 200 of the reference embodiment.

[0237] [Left-right time difference decoding unit 271]

[0238] Input to the left-right time difference decoding unit 271: the left-right time difference code Cτ input to the decoding device 201. The left-right time difference decoding unit 271 decodes the left-right time difference code Cτ by a prescribed decoding method, obtains the left-right time difference τ and outputs it (step S271). As the prescribed decoding method, a decoding method corresponding to the encoding method used in the left-right relationship information estimation unit 181 of the corresponding encoding device 101 is used. The left-right time difference τ obtained by the left-right time difference decoding unit 271 is the same value as the left-right time difference τ obtained by the left-right relationship information estimation unit 181 of the corresponding encoding device 101, and is obtained from τ max to τ min Any value within the range of .

[0239] [Time shift unit 281]

[0240] The time shift unit 281 receives the monaural decoded audio signal ^x output from the monaural decoding unit 210. M (1), ^x M (2), ..., ^x M (T) and the left-right time difference τ output by the left-right time difference decoding unit 271. When the left-right time difference τ is a positive value (that is, the left-right time difference τ indicates that the left channel is in the leading position), the time shift unit 281 converts the monaural decoded audio signal ^x M (1), ^x M (2), ..., ^x M (T) is outputted to the left channel signal adding section 240 as it is (that is, it is determined to be used in the left channel signal adding section 240), and a signal obtained by delaying the monaural decoded audio signal by |τ| samples is outputted to the left channel signal adding section 240 as it is (that is, it is determined to be used in the left channel signal adding section 240). M (1-|τ|), ^x M (2-|τ|),...,^x M (T-|τ|) is the delayed mono decoded audio signal^x M '(1), ^x M '(2),...,^x M '(T), output to the right channel signal adding unit 260 (i.e., determined to be used in the right channel signal adding unit 260), when the left and right time difference τ is a negative value (i.e., the left and right time difference τ indicates that the right channel is in the leading position), the signal ^x obtained by delaying the mono decoded sound signal by |τ| samples M (1-|τ|), ^x M (2-|τ|),...,^x M (T-|τ|) is the delayed mono decoded audio signal^x M '(1), ^x M '(2),...,^x M'(T) is output to the left channel signal adding section 240 (ie, it is determined to be used in the left channel signal adding section 240), and the mono decoded audio signal is converted into M (1), ^x M (2), ..., ^x M (T) is output to the right channel signal adding unit 260 as it is (i.e., is determined to be used in the right channel signal adding unit 260), and when the left-right time difference τ is 0 (i.e., the left-right time difference τ indicates that any channel is not in the leading position), the mono decoded sound signal ^x M (1), ^x M (2), ..., ^x M (T) is outputted to the left channel signal adding unit 240 and the right channel signal adding unit 260 as it is (i.e., it is determined to be used in the left channel signal adding unit 240 and the right channel signal adding unit 260) (step S281). In addition, in order to obtain the delayed monaural decoded sound signal in the time shifting unit 281, the monaural decoded sound signal of the past frame is used, so the monaural decoded sound signal inputted in the past frame for a predetermined number of frames is stored in a storage unit (not shown) in the time shifting unit 281.

[0241] [Left channel signal adding unit 240, right channel signal adding unit 260]

[0242] In the left channel signal adding section 240 and the right channel signal adding section 260, the monaural decoded audio signal ^x outputted from the monaural decoding section 210 is replaced. M (1), ^x M (2), ..., ^x M (T), and using the monaural decoded audio signal ^x input from the time shift unit 281 M (1), ^x M (2), ..., ^x M (T) or delayed mono decoded sound signal^x M '(1), ^x M '(2),...,^x M '(T), and perform the same operation as described in the reference method (steps S240, S260). That is, the left channel signal adding unit 240 and the right channel signal adding unit 260 use the monaural decoded audio signal ^x determined by the time shifting unit 281. M (1), ^x M (2), ..., ^x M (T) or delayed mono decoded sound signal^x M '(1), ^x M '(2),...,^x M'(T), to perform the same actions as described in the reference method.

[0243] <Second embodiment>

[0244] The encoding device 101 of the first embodiment can be modified as follows, that is, a downmix signal is generated by considering the relationship between the input audio signal of the left channel and the input audio signal of the right channel, and this method is described as the second embodiment. In addition, the code obtained by the encoding device of the second embodiment can be decoded by the decoding device 201 of the first embodiment, so the description of the decoding device is omitted.

[0245] 《Encoding device 102》

[0246] like Fig.10 As shown in FIG. 1 , the encoding device 102 of the second embodiment includes a downmixing unit 112, a left channel subtraction gain estimating unit 120, a left channel signal subtracting unit 130, a right channel subtraction gain estimating unit 140, a right channel signal subtracting unit 150, a mono encoding unit 160, a stereo encoding unit 170, a left-right relationship information estimating unit 182, and a time shifting unit 191. The encoding device 102 of the second embodiment is different from the encoding device 101 of the first embodiment in that the left-right relationship information estimating unit 181 is replaced with a left-right relationship information estimating unit 182, and the downmixing unit 112 is replaced with the downmixing unit 110. Fig.10 As shown by the dotted line in the middle, the left-right relationship information estimation unit 182 obtains the left-right correlation coefficient γ and the leading channel information and outputs them. The output left-right correlation coefficient γ and the leading channel information are input to the downmixing unit 112 for use. The other structures and operations of the encoding device 102 of the second embodiment are the same as those of the encoding device 101 of the first embodiment. The encoding device 102 of the third embodiment performs the following steps for each frame: Fig.14 The processing of step S112 to step S191 is illustrated. The following describes the differences between the encoding device 102 of the second embodiment and the encoding device 101 of the first embodiment.

[0247] [Left-right relationship information estimation unit 182]

[0248] The left-right relationship information estimation unit 182 receives the input audio signal of the left channel and the input audio signal of the right channel of the encoding device 102. The left-right relationship information estimation unit 182 obtains the left-right time difference τ, the left-right time difference code Cτ representing the left-right time difference τ, the left-right correlation coefficient γ, and the leading channel information from the input audio signal of the left channel and the input audio signal of the right channel, and outputs them (step S182). The processing of obtaining the left-right time difference τ and the left-right time difference code Cτ by the left-right relationship information estimation unit 182 is the same as that of the left-right relationship information estimation unit 181 of the first embodiment.

[0249] The left-right correlation coefficient γ is information corresponding to the correlation coefficient between the sound signal that reaches the microphone for the left channel and is picked up from the sound source and the sound signal that reaches the microphone for the right channel and is picked up from the sound source in the above-mentioned assumption in the description of the left-right relationship information estimation unit 181 of the first embodiment. The leading channel information is information corresponding to which microphone the sound emitted by the sound source reaches first, and is information indicating whether the same sound signal is included first in the input sound signal of the left channel and the input sound signal of the right channel, and is information indicating which channel of the left channel and the right channel is leading.

[0250] In the above example in the description of the left-right relationship information estimation unit 181 of the first embodiment, the left-right relationship information estimation unit 182 obtains the correlation value between the sample sequence of the input sound signal of the left channel and the sample sequence of the input sound signal of the right channel which is located later than the sample sequence by the left-right time difference τ, that is, the correlation value for τ max ~τ min The number of candidate samples τ cand The calculated correlation value γ cand The maximum value of is taken as the left-right correlation coefficient γ and outputted. In addition, when the left-right time difference τ is a positive value, the left-right relationship information estimation unit 182 obtains information indicating that the left channel is in the leading position as the leading channel information and outputs it, and when the left-right time difference τ is a negative value, the left-right relationship information estimation unit 182 obtains information indicating that the right channel is in the leading position as the leading channel information and outputs it. When the left-right time difference τ is 0, the left-right relationship information estimation unit 182 may obtain information indicating that the left channel is in the leading position as the leading channel information and output it, or may obtain information indicating that the right channel is in the leading position as the leading channel information and output it, or may obtain information indicating that no channel is in the leading position as the leading channel information and output it.

[0251] [Downmixing unit 112]

[0252] The downmixing unit 112 is input with: an input audio signal of the left channel input to the encoding device 102, an input audio signal of the right channel input to the encoding device 102, a left-right correlation coefficient γ output from the left-right relationship information estimating unit 182, and leading channel information output from the left-right relationship information estimating unit 182. The downmixing unit 112 performs weighted averaging on the input audio signal of the left channel and the input audio signal of the right channel, obtains a downmixed signal, and outputs the downmixed signal such that the larger the left-right correlation coefficient γ, the larger the input audio signal of the leading channel in the downmixed signal including the input audio signal of the left channel and the input audio signal of the right channel (step S112).

[0253] For example, if the absolute value of the correlation coefficient or the normalized value is used as the correlation value in the description of the left-right relationship information estimation unit 181 of the first embodiment as in the above example, the obtained left-right correlation coefficient γ is a value greater than or equal to 0 and less than or equal to 1, and therefore the downmix unit 112 uses the weight specified by the left-right correlation coefficient γ to adjust the input audio signal x of the left channel for each corresponding sample number t. L (t) and the input sound signal x of the right channel R The signal obtained by weighted summation is set as the downmix signal x M Specifically, when the leading channel information is information indicating that the left channel is in the leading position, that is, when the left channel is in the leading position, the downmixing unit 112 obtains x M (t) = ((1 + γ) / 2) × x L (t)+((1-γ) / 2)×x R (t); The leading channel information is the information indicating that the right channel is in the leading position, that is, when the right channel is in the leading position, obtain x M (t) = ((1-γ) / 2) × x L (t)+((1+γ) / 2)×x R (t), as the downmix signal x M (t). By obtaining the downmix signal in this way by the downmixing unit 112, the smaller the left-right correlation coefficient γ is, in other words, the smaller the correlation between the input sound signal of the left channel and the input sound signal of the right channel is, the closer the downmix signal is to the signal obtained by averaging the input sound signal of the left channel and the input sound signal of the right channel; the larger the left-right correlation coefficient γ is, in other words, the greater the correlation between the input sound signal of the left channel and the input sound signal of the right channel is, the closer the downmix signal is to the input sound signal of the leading channel of the input sound signal of the left channel and the input sound signal of the right channel.

[0254] In addition, when no channel is in the leading position, the downmixing unit 112 may average the input sound signal of the left channel and the input sound signal of the right channel to obtain a downmix signal and output it, so that the input sound signal of the left channel and the input sound signal of the right channel are included in the downmix signal with the same weight. Therefore, when the leading channel information indicates that no channel is in the leading position, the downmixing unit 112 averages the input sound signal of the left channel x for each sample number t. L (t) and the input sound signal x of the right channel R (t) The averaged x M (t) = (x L (t)+x R (t)) / 2, set as the downmix signal x M (t).

[0255] <Program and recording medium>

[0256] In addition, the processing of each part of each encoding device and each decoding device can be realized by a computer. In this case, the processing content of the function that each device should have is described by a program. And, by reading the program into Fig.15 The storage unit 1020 of the computer shown in the figure causes the arithmetic processing unit 1010, the input unit 1030, the output unit 1040, etc. to operate, so that various processing functions in the above-mentioned devices are realized on the computer.

[0257] The program describing the processing content can be recorded in a computer-readable recording medium. The computer-readable recording medium may be, for example, a non-transitory recording medium, specifically, a magnetic recording device, an optical disk, or the like.

[0258] In addition, the program can be circulated by selling, transferring, lending, etc. a removable recording medium such as a DVD or CD-ROM on which the program is recorded. Furthermore, the program can also be circulated by storing the program in a storage device of a server computer and forwarding the program from the server computer to other computers via a network.

[0259] The computer executing such a program, for example, first temporarily stores the program recorded in the removable recording medium or the program forwarded from the server computer in its own non-temporary storage device, namely the auxiliary recording unit 1050. Moreover, when executing the process, the computer reads the program stored in its own non-temporary storage device, namely the auxiliary recording unit 1050, into the storage unit 1020, and executes the process according to the read program. In addition, as another execution method of the program, the computer can also read the program directly from the removable recording medium to the storage unit 1020 and execute the process according to the program. Furthermore, it can also be set to execute the process according to the acquired program one by one each time the program is forwarded from the server computer to the computer. In addition, it can also be set to not forward the program from the server computer to the computer, but to execute the above-mentioned process through the so-called ASP (Application Service Provider: Application Service Provider) type service that realizes the processing function only by the execution instruction and result acquisition. In addition, the program in this method includes information for processing by the electronic computer, namely information according to the program (data that is not a direct instruction to the computer but has the nature of specifying the processing of the computer, etc.).

[0260] In this embodiment, the present device may be configured by executing a predetermined program on a computer, or at least a part of the processing may be realized by hardware.

[0261] Furthermore, it is of course possible to make appropriate changes within the scope not departing from the spirit of the present invention.

Claims

1. A sound signal encoding method, which is a sound signal encoding method for encoding an input sound signal for each frame, characterized in that: include: A downmixing step to obtain a downmixed signal, wherein the downmixed signal is a signal obtained by mixing the input left channel input sound signal and the input right channel input sound signal; A mono encoding step of encoding the downmix signal to obtain a mono code CM; A left-right relationship estimation step, obtaining a left-right time difference τ and a left-right time difference code Cτ from the left channel input sound signal and the right channel input sound signal, wherein the left-right time difference code is a code representing the left-right time difference τ; a time shifting step, in which, when the left-right time difference τ indicates that the left channel is in a leading position, the downmix signal is used as it is in the left channel subtraction gain estimation step and the left channel signal subtraction step, and a delayed downmix signal is used in the right channel subtraction gain estimation step and the right channel signal subtraction step, the delayed downmix signal being a signal obtained by delaying the downmix signal by an amount indicated by the left-right time difference τ, In a case where the left-right time difference τ indicates that the right channel is in a leading position, it is determined to use the downmix signal as it is in the right channel subtraction gain estimation step and the right channel signal subtraction step, and it is determined to use a delayed downmix signal in the left channel subtraction gain estimation step and the left channel signal subtraction step, the delayed downmix signal being a signal obtained by delaying the downmix signal by an amount indicated by the left-right time difference τ, When the left-right time difference τ indicates that any channel is not in the leading position, it is determined to use the downmix signal as it is in the left channel subtraction gain estimation step, the left channel signal subtraction step, the right channel subtraction gain estimation step, and the right channel signal subtraction step; The left channel subtraction gain estimation step obtains a left channel subtraction gain α and a left channel subtraction gain code Cα from the left channel input sound signal and the downmix signal or the delayed downmix signal determined in the time shift step, wherein the left channel subtraction gain code is a code representing the left channel subtraction gain α; The left channel signal subtraction step obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the downmix signal or the delayed downmix signal determined in the time shift step by the left channel subtraction gain α from the sample value of the left channel input sound signal, as a left channel difference signal; The right channel subtraction gain estimation step obtains a right channel subtraction gain β and a right channel subtraction gain code Cβ from the right channel input sound signal and the downmix signal or the delayed downmix signal determined in the time shift step, wherein the right channel subtraction gain code is a code representing the right channel subtraction gain β; The right channel signal subtraction step obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the downmix signal or the delayed downmix signal determined in the time shift step by the right channel subtraction gain β from the sample value of the right channel input sound signal, as a right channel difference signal; as well as In the stereo encoding step, the left channel differential signal and the right channel differential signal are encoded to obtain a stereo code CS.

2. A sound signal encoding method, which is a sound signal encoding method for encoding an input sound signal for each frame, characterized in that: include: A downmixing step to obtain a downmixed signal, wherein the downmixed signal is a signal obtained by mixing the input left channel input sound signal and the input right channel input sound signal; A mono encoding step, encoding the downmix signal to obtain a mono code CM and a quantized downmix signal; A left-right relationship estimation step, obtaining a left-right time difference τ and a left-right time difference code Cτ from the left channel input sound signal and the right channel input sound signal, wherein the left-right time difference code is a code representing the left-right time difference τ; a time shifting step, in which, when the left-right time difference τ indicates that the left channel is in a leading position, the quantized downmix signal is used as is in the left channel subtraction gain estimation step and the left channel signal subtraction step, and a delayed quantized downmix signal is used in the right channel subtraction gain estimation step and the right channel signal subtraction step, wherein the delayed quantized downmix signal is a signal obtained by delaying the quantized downmix signal by an amount indicated by the left-right time difference τ, In a case where the left-right time difference τ indicates that the right channel is in a leading position, it is determined to use the quantized downmix signal as is in the right channel subtraction gain estimation step and the right channel signal subtraction step, and it is determined to use a delayed quantized downmix signal in the left channel subtraction gain estimation step and the left channel signal subtraction step, wherein the delayed quantized downmix signal is a signal obtained by delaying the quantized downmix signal by an amount indicated by the left-right time difference τ. When the left-right time difference τ indicates that any channel is not in the leading position, it is determined to use the quantized downmix signal as is in the left channel subtraction gain estimation step, the left channel signal subtraction step, the right channel subtraction gain estimation step, and the right channel signal subtraction step; The left channel subtraction gain estimation step obtains a left channel subtraction gain α and a left channel subtraction gain code Cα from the left channel input sound signal and the quantized downmix signal or the delayed quantized downmix signal determined in the time shift step, wherein the left channel subtraction gain code is a code representing the left channel subtraction gain α; The left channel signal subtraction step obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the quantized downmix signal or the delayed quantized downmix signal determined in the time shift step by the left channel subtraction gain α from the sample value of the left channel input sound signal, as a left channel difference signal; The right channel subtraction gain estimation step obtains a right channel subtraction gain β and a right channel subtraction gain code Cβ from the right channel input sound signal and the quantized downmix signal or the delayed quantized downmix signal determined in the time shift step, wherein the right channel subtraction gain code is a code representing the right channel subtraction gain β; The right channel signal subtraction step obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the quantized downmix signal or the delayed quantized downmix signal determined in the time shift step by the right channel subtraction gain β from the sample value of the right channel input sound signal, as a right channel difference signal; as well as In the stereo encoding step, the left channel differential signal and the right channel differential signal are encoded to obtain a stereo code CS.

3. The sound signal encoding method according to claim 1 or 2, characterized in that: Also includes: a step of obtaining leading channel information and a left-right correlation coefficient, wherein the leading channel information is information indicating which of the left channel input sound signal and the right channel input sound signal is the leading one, and the left-right correlation coefficient is a correlation coefficient between the left channel input sound signal and the right channel input sound signal, In the downmixing step, based on the leading channel information and the left-right correlation coefficient, the left-channel input sound signal and the right-channel input sound signal are weighted averaged to obtain the downmixed signal, so that the larger the left-right correlation coefficient is, the larger the input sound signal of the leading channel contained in the left-channel input sound signal and the right-channel input sound signal is.

4. A sound signal decoding method, which is a sound signal decoding method for obtaining a sound signal by decoding an input code for each frame, characterized in that: include: A mono decoding step, decoding the input mono code CM to obtain a mono decoded sound signal; A stereo decoding step, decoding the input stereo code CS to obtain a left channel decoded differential signal and a right channel decoded differential signal; The left-right time difference decoding step obtains the left-right time difference τ from the input left-right time difference code Cτ; a time shifting step, in which, when the left-right time difference τ indicates that the left channel is in the leading position, the monaural decoded sound signal is used as it is in the left channel signal adding step, and a delayed monaural decoded sound signal is used in the right channel signal adding step, wherein the delayed monaural decoded sound signal is a signal obtained by delaying the monaural decoded sound signal by an amount indicated by the left-right time difference τ, When the left-right time difference τ indicates that the right channel is in the leading position, it is determined to use the mono decoded sound signal as it is in the right channel signal adding step, and it is determined to use a delayed mono decoded sound signal in the left channel signal adding step, wherein the delayed mono decoded sound signal is a signal obtained by delaying the mono decoded sound signal by an amount indicated by the left-right time difference τ. When the left-right time difference τ indicates that any channel is not in the leading position, it is determined to use the mono decoded audio signal as it is in the left channel signal adding step and the right channel signal adding step; A left channel subtraction gain decoding step, decoding the input left channel subtraction gain code Cα to obtain a left channel subtraction gain α; The left channel signal adding step obtains, for each corresponding sample t, a sequence of values ​​obtained by adding a value obtained by multiplying the sample value of the mono decoded sound signal or the delayed mono decoded sound signal determined in the time shifting step by the left channel subtraction gain α to the sample value of the left channel decoded difference signal, as the left channel decoded sound signal; a right channel subtraction gain decoding step, decoding the input right channel subtraction gain code Cβ to obtain the right channel subtraction gain β; and The right channel signal addition step obtains, for each corresponding sample t, a sequence of values ​​obtained by adding a value obtained by multiplying the sample value of the mono decoded sound signal or the delayed mono decoded sound signal determined in the time shift step by the right channel subtraction gain β and adding the value to the sample value of the right channel decoded differential signal, as the right channel decoded sound signal.

5. A sound signal encoding device, which encodes an input sound signal for each frame, characterized in that: include: A downmixing unit, which obtains a downmixed signal, wherein the downmixed signal is a signal obtained by mixing an input left channel input sound signal and an input right channel input sound signal; a mono encoding unit, encoding the downmix signal to obtain a mono code CM; A left-right relationship estimation unit obtains a left-right time difference τ and a left-right time difference code Cτ from the left channel input sound signal and the right channel input sound signal, wherein the left-right time difference code is a code indicating the left-right time difference τ; a time shifting unit that, when the left-right time difference τ indicates that the left channel is in a leading position, determines to use the downmix signal as it is in the left-channel subtraction gain estimation unit and the left-channel signal subtraction unit, and determines to use a delayed downmix signal in the right-channel subtraction gain estimation unit and the right-channel signal subtraction unit, the delayed downmix signal being a signal obtained by delaying the downmix signal by an amount indicated by the left-right time difference τ, When the left-right time difference τ indicates that the right channel is in the leading position, it is determined that the right channel subtraction gain estimation unit and the right channel signal subtraction unit use the downmix signal as it is, and it is determined that the left channel subtraction gain estimation unit and the left channel signal subtraction unit use a delayed downmix signal, the delayed downmix signal being a signal obtained by delaying the downmix signal by an amount indicated by the left-right time difference τ. When the left-right time difference τ indicates that any channel is not in the leading position, it is determined that the left channel subtraction gain estimation unit, the left channel signal subtraction unit, the right channel subtraction gain estimation unit, and the right channel signal subtraction unit use the downmix signal as it is, The left channel subtraction gain estimation unit obtains a left channel subtraction gain α and a left channel subtraction gain code Cα from the left channel input sound signal and the downmix signal or the delayed downmix signal determined by the time shift unit, wherein the left channel subtraction gain code is a code indicating the left channel subtraction gain α; The left channel signal subtraction unit obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the downmix signal or the delayed downmix signal determined by the time shift unit by the left channel subtraction gain α from the sample value of the left channel input sound signal as a left channel difference signal; The right channel subtraction gain estimation unit obtains a right channel subtraction gain β and a right channel subtraction gain code Cβ from the right channel input sound signal and the downmix signal or the delayed downmix signal determined by the time shift unit, wherein the right channel subtraction gain code is a code representing the right channel subtraction gain β; The right channel signal subtraction unit obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying the sample value of the downmix signal or the delayed downmix signal determined by the time shift unit by the right channel subtraction gain β from a sample value of the right channel input sound signal as a right channel difference signal; and The stereo encoding unit encodes the left channel difference signal and the right channel difference signal to obtain a stereo code CS.

6. A sound signal encoding device, which encodes an input sound signal for each frame, characterized in that: include: A downmixing unit, which obtains a downmixed signal, wherein the downmixed signal is a signal obtained by mixing an input left channel input sound signal and an input right channel input sound signal; A mono encoding unit, encoding the downmix signal to obtain a mono code CM and a quantized downmix signal; A left-right relationship estimation unit obtains a left-right time difference τ and a left-right time difference code Cτ from the left channel input sound signal and the right channel input sound signal, wherein the left-right time difference code is a code indicating the left-right time difference τ; The time shifting unit determines to use the quantized downmix signal as is in the left channel subtraction gain estimation unit and the left channel signal subtraction unit, and determines to use the delayed quantized downmix signal in the right channel subtraction gain estimation unit and the right channel signal subtraction unit, when the left-right time difference τ indicates that the left channel is in the leading position, wherein the delayed quantized downmix signal is a signal obtained by delaying the quantized downmix signal by an amount indicated by the left-right time difference τ. In a case where the left-right time difference τ indicates that the right channel is in the leading position, it is determined that the quantized downmix signal is used as it is in the right channel subtraction gain estimation unit and the right channel signal subtraction unit, and it is determined that a delayed quantized downmix signal is used in the left channel subtraction gain estimation unit and the left channel signal subtraction unit, wherein the delayed quantized downmix signal is a signal obtained by delaying the quantized downmix signal by an amount indicated by the left-right time difference τ. When the left-right time difference τ indicates that any channel is not in the leading position, the left channel subtraction gain estimation unit, the left channel signal subtraction unit, the right channel subtraction gain estimation unit, and the right channel signal subtraction unit are used as is. The left channel subtraction gain estimation unit obtains a left channel subtraction gain α and a left channel subtraction gain code Cα from the left channel input sound signal and the quantized downmix signal or the delayed quantized downmix signal determined by the time shift unit, wherein the left channel subtraction gain code is a code indicating the left channel subtraction gain α; The left channel signal subtraction unit obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying a sample value of the quantized downmix signal or the delayed quantized downmix signal determined by the time shift unit by the left channel subtraction gain α from a sample value of the left channel input sound signal as a left channel difference signal; The right channel subtraction gain estimation unit obtains a right channel subtraction gain β and a right channel subtraction gain code Cβ from the right channel input sound signal and the quantized downmix signal or the delayed quantized downmix signal determined by the time shift unit, wherein the right channel subtraction gain code is a code indicating the right channel subtraction gain β; The right channel signal subtraction unit obtains, for each corresponding sample t, a sequence of values ​​obtained by subtracting a value obtained by multiplying a sample value of the quantized downmix signal or the delayed quantized downmix signal determined by the time shift unit by the right channel subtraction gain β from a sample value of the right channel input sound signal as a right channel difference signal; and The stereo encoding unit encodes the left channel difference signal and the right channel difference signal to obtain a stereo code CS.

7. The sound signal encoding device according to claim 5 or 6, wherein: Also includes: a unit for obtaining leading channel information and a left-right correlation coefficient, wherein the leading channel information is information indicating which of the left channel input sound signal and the right channel input sound signal is the leading one, and the left-right correlation coefficient is a correlation coefficient between the left channel input sound signal and the right channel input sound signal, The downmix unit obtains the downmix signal by performing weighted averaging on the left channel input sound signal and the right channel input sound signal based on the leading channel information and the left-right correlation coefficient, so that the larger the left-right correlation coefficient is, the larger the input sound signal of the leading channel of the left channel input sound signal and the right channel input sound signal is.

8. A sound signal decoding device, which is a sound signal decoding device that decodes an input code for each frame to obtain a sound signal, characterized in that: include: A mono decoding unit, which decodes the input mono code CM to obtain a mono decoded sound signal; A stereo decoding unit, which decodes the input stereo code CS to obtain a left channel decoded differential signal and a right channel decoded differential signal; The left-right time difference decoding unit obtains the left-right time difference τ from the input left-right time difference code Cτ; a time shifting unit that, when the left-right time difference τ indicates that the left channel is in the leading position, determines to use the monaural decoded sound signal as it is in the left-channel signal adding unit, and determines to use the delayed monaural decoded sound signal in the right-channel signal adding unit, the delayed monaural decoded sound signal being a signal obtained by delaying the monaural decoded sound signal by an amount indicated by the left-right time difference τ, When the left-right time difference τ indicates that the right channel is in the leading position, the right channel signal adding unit is used to keep the monaural decoded sound signal as it is, and the left channel signal adding unit is used to use a delayed monaural decoded sound signal, the delayed monaural decoded sound signal being a signal obtained by delaying the monaural decoded sound signal by an amount indicated by the left-right time difference τ. When the left-right time difference τ indicates that any channel is not in the leading position, it is determined that the monaural decoded audio signal is used as it is in the left-channel signal adding section and the right-channel signal adding section; A left channel subtraction gain decoding unit, which decodes the input left channel subtraction gain code Cα to obtain a left channel subtraction gain α; The left channel signal adding unit obtains, for each corresponding sample t, a sequence of values ​​obtained by adding a value obtained by multiplying a sample value of the monaural decoded sound signal or the delayed monaural decoded sound signal determined by the time shift unit by the left channel subtraction gain α to a sample value of the left channel decoded difference signal, as a left channel decoded sound signal; a right channel subtraction gain decoding unit, which decodes the input right channel subtraction gain code Cβ to obtain the right channel subtraction gain β; and The right channel signal adding unit obtains, for each corresponding sample t, a sequence of values ​​obtained by adding a value obtained by multiplying the sample value of the monaural decoded sound signal or the delayed monaural decoded sound signal determined by the time shift unit by the right channel subtraction gain β and the sample value of the right channel decoded differential signal, as the right channel decoded sound signal.

9. A computer program product comprising a program for causing a computer to execute the steps of the encoding method according to claim 1 or 2.

10. A computer program product comprising a program for causing a computer to execute the steps of the decoding method according to claim 4.

11. A computer-readable recording medium having a program recorded thereon, wherein the program is used to cause a computer to execute each step of the encoding method according to claim 1 or 2.

12. A computer-readable recording medium having a program recorded thereon, the program being for causing a computer to execute each step of the decoding method according to claim 4.

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