WO2024142360A1 - 音信号処理装置、音信号処理方法、プログラム - Google Patents

音信号処理装置、音信号処理方法、プログラム Download PDF

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WO2024142360A1
WO2024142360A1 PCT/JP2022/048531 JP2022048531W WO2024142360A1 WO 2024142360 A1 WO2024142360 A1 WO 2024142360A1 JP 2022048531 W JP2022048531 W JP 2022048531W WO 2024142360 A1 WO2024142360 A1 WO 2024142360A1
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channel
signal
input sound
sound signal
value
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French (fr)
Japanese (ja)
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健弘 守谷
登 原田
優 鎌本
亮介 杉浦
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NTT Inc
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Nippon Telegraph and Telephone Corp
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/008—Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing

Definitions

  • One aspect of the present invention is a sound signal processing device that obtains a two-channel stereo encoding target signal consisting of encoding target signals of two channels that are subject to stereo encoding by a stereo encoding device, from a two-channel stereo input sound signal consisting of input sound signals of two channels, wherein a first condition is that when conditions other than the bit rate of the stereo encoding are the same, the signal has a broadly monotonically increasing relationship with respect to the bit rate of the stereo encoding.
  • a second condition is that when conditions other than the absolute value of the inter-channel time difference of the two-channel stereo input sound signal are the same, the signal has a broadly monotonically decreasing relationship with respect to the absolute value of the inter-channel time difference of the two-channel stereo input sound signal.
  • One aspect of the present invention is a sound signal processing device that obtains a two-channel stereo encoding target signal consisting of encoding target signals of two channels that are subject to stereo encoding by a stereo encoding device, from a two-channel stereo input sound signal consisting of input sound signals of two channels, wherein a fourth condition is that when conditions other than the bit rate of the stereo encoding are the same, the signal has a broadly monotonically decreasing relationship with respect to the bit rate of the stereo encoding.
  • a fifth condition is that when conditions other than the absolute value of the inter-channel time difference of the two-channel stereo input sound signal are the same, the signal has a broadly monotonically increasing relationship with respect to the absolute value of the inter-channel time difference of the two-channel stereo input sound signal.
  • the sound signal encoding system 300 obtains a stereo code, which is a code corresponding to the two-channel stereo input sound signal, from the two-channel stereo input sound signal.
  • the stereo code obtained by the sound signal encoding system 300 is output from the sound signal encoding system 300.
  • the sound signal encoding system 300 performs the processes of steps S100 and S200 shown in FIG. 2.
  • An example of a signal in which the input sound signal of each channel is mixed with the input sound signal of the other channel is a signal in which the input sound signal of the channel is weighted and added with the input sound signal of the other channel, or more specifically, a signal in which, for each time, the input sound signal of the channel at that time and the input sound signal of the other channel at that time are weighted and added.
  • the first channel signal mixer 120-1 may calculate and obtain the first-channel encoding target signal x' 1 (t) using the above formula (2-1), or may use another calculation method or the like to obtain the first-channel encoding target signal x' 1 (t) represented by the above formula (2-1).
  • the second channel signal mixer 120-2 may calculate and obtain the second-channel encoding target signal x' 2 (t) using the above formula (2-2), or may use another calculation method or the like to obtain the second-channel encoding target signal x' 2 (t) represented by the above formula (2-2).
  • weight value w1 has a broadly monotonically increasing relationship with the stereo encoding bitrate, which means that (1- w1 ) in the above formula (2-1) has a broadly monotonically decreasing relationship with the stereo encoding bitrate.
  • weight value w2 has a broadly monotonically increasing relationship with the stereo encoding bitrate, which means that (1- w2 ) in the above formula (2-2) has a broadly monotonically decreasing relationship with the stereo encoding bitrate.
  • the fact that the second type of value is in a broadly monotonically increasing relationship with the first type of value means that in the entire range in which the first type of value can be, the second type of value is in a monotonically increasing relationship with the first type of value, or that in a portion of the range in which the first type of value can be (the first type of range), the second type of value is constant regardless of the first type of value, and in a range other than the portion of the range in which the first type of value can be (the range other than the first type of range, the second type of range), the second type of value is in a monotonically increasing relationship with the first type of value.
  • There are one or more ranges for each of the first type of range and the second type of range That is, there may be a plurality of first type ranges, and there may be a plurality of second type ranges. Naturally, “broadly monotonically increasing” may be read as "monotonically non-decreasing".
  • the second type of value being in a broadly monotonically decreasing relationship with the first type of value means that the second type of value when the first type of value is the minimum value in the range that the first type of value can take is greater than the second type of value when the first type of value is the maximum value in the range that the first type of value can take, and that, within the entire range that the first type of value can take, the second type of value when the first type of value is a certain value is greater than or equal to the second type of value when the first type of value is greater than the aforementioned certain value.
  • the fact that the second type of value has a monotonically decreasing relationship with the first type of value means that the second type of value has a negative correlation with the first type of value, and that the smaller the first type of value is, the larger the second type of value is, and vice versa. Note that “monotonically decreasing” may be read as “strictly defined monotonically decreasing.”
  • a set of each bit rate and each weight value corresponding to each bit rate that is predetermined so that the weight value has a broad monotonically increasing relationship with the bit rate is stored in the signal mixing unit 120 in advance, and the signal mixing unit 120 obtains a weight value corresponding to the stereo encoding bit rate of the frame from the stored weight values for each channel of each frame, and sets the obtained weight value as the weight of the input sound signal of that channel.
  • the signal mixing unit 120 obtains, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel, and in other cases, i.e., when the stereo encoding bit rate is equal to or less than the predetermined value mentioned above, obtains, for each channel, a signal in which the input sound signal of that channel is mixed with the input sound signal of the other channel in all ranges in which the stereo encoding bit rate can be, and the higher the stereo encoding bit rate, the closer the signal is to the input sound signal of that channel, or obtains, for a part of the range in which the stereo encoding bit rate can be, a signal in which the input sound signal of that channel is mixed with the input sound signal of the other channel, In the range (first type of range), a signal obtained for each channel is a mixture of the input sound signal of the channel and the input sound signal of the other channel, and the signal is the same in closeness to the input sound signal of the
  • the signal mixing unit 120 obtains, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel, and in a second range in which the stereo encoding bit rate is a range other than the first range of possible bit rates (i.e., the second case in which the first case is a case other than the first case, specifically, when the stereo encoding bit rate is equal to or less than the predetermined value described above), for each channel, a signal in which the input sound signal of that channel and the input sound signal of the other channel are weighted together, wherein the weight of the input sound signal of that channel in the weighted addition is a value that has a broad-sense monotonically increasing relationship with the stereo encoding bit rate in the second range, and the weight of the input sound signal of the other channel
  • the signal to be encoded for each channel may be obtained using a weighting value between the bit rate of the immediately preceding frame and the bit rate of the current frame.
  • the first channel signal mixer 120-1 stores the weight value w c1 of the current frame and uses it as the weight value w p1 in processing the next frame.
  • the second channel signal mixer 120-2 stores the weight value w c2 of the current frame and uses it as the weight value w p2 in processing the next frame.
  • the signal mixer 120 obtaining the encoding target signal for each channel using the above formulas (2-4) and (2-6), it is possible to maintain the continuity of the waveform of the encoding target signal at the frame boundary even if the bit rate of the current frame is different from the bit rate of the immediately preceding frame.
  • the second embodiment may be implemented by including a process of calculating an index value according to a bit rate of stereo encoding by the stereo encoding device 200.
  • An embodiment including a process of calculating an index value according to a bit rate of stereo encoding will be described as a first modification of the second embodiment.
  • the sound signal processing device 100 of the first modification of the second embodiment is as shown by the dashed and solid lines in Fig. 3, and includes an index value calculation unit 110 and a signal mixing unit 120.
  • the sound signal processing device 100 performs processes of steps S110 and S120 shown by the dashed and solid lines in Fig. 4. The following description will focus on the differences between the first modification of the second embodiment and the second embodiment.
  • the index value calculation unit 110 calculates an index value ⁇ that has a broad-sense monotonically increasing relationship with the stereo encoding bit rate of the stereo encoding device 200, or an index value ⁇ ' that has a broad-sense monotonically decreasing relationship with the stereo encoding bit rate of the stereo encoding device 200 (step S110).
  • the index value ⁇ or the index value ⁇ ' obtained by the index value calculation unit 110 is output to the signal mixer 120.
  • the value that has a broadly monotonically increasing relationship with the stereo encoding bit rate of stereo encoding device 200 is, for example, the function value of a broadly monotonically increasing function with the stereo encoding bit rate of stereo encoding device 200 as an argument. Therefore, for example, the broadly monotonically increasing function can be stored in advance in index value calculation unit 110, and index value calculation unit 110 can obtain a function value for each frame by providing the broadly monotonically increasing function with the stereo encoding bit rate of the frame as an argument, and obtain the obtained function value as index value ⁇ .
  • the index value calculation unit 110 may store in advance a set of information specifying the stereo encoding bit rate belonging to each of a plurality of partial ranges that divide the possible range of the stereo encoding bit rate, and each function value corresponding to each partial range that is predetermined so that the function value has a broad monotonic function relationship with the stereo encoding bit rate, and the index value calculation unit 110 may obtain, for each frame, a function value corresponding to the stereo encoding bit rate of the frame from among the stored function values, and obtain the obtained function value as the index value ⁇ .
  • the index value calculation unit 110 may use the stereo encoding bit rate itself as the index value ⁇ .
  • the value that has a broadly monotonically decreasing relationship with the stereo encoding bit rate of stereo encoding device 200 is, for example, the function value of a broadly monotonically decreasing function that has the stereo encoding bit rate of stereo encoding device 200 as an argument. Therefore, for example, the broadly monotonically decreasing function can be stored in advance in index value calculation unit 110, and index value calculation unit 110 can obtain a function value for each frame by providing the broadly monotonically decreasing function with the stereo encoding bit rate of the frame as an argument, and obtain the obtained function value as index value ⁇ '.
  • a set of information specifying the stereo encoding bit rate belonging to each partial range and each function value corresponding to each partial range that is predefined so that the function value has a broad-sense monotonically decreasing relationship with the stereo encoding bit rate is stored in the index value calculation unit 110 in advance, and the index value calculation unit 110 acquires, for each frame, a function value that corresponds to the stereo encoding bit rate of that frame from among the stored function values, and obtains the acquired function value as the index value ⁇ '.
  • the signal mixing unit 120 receives as input a first channel input sound signal and a second channel input sound signal which are input sound signals of two channels constituting the two-channel stereo input sound signal input to the sound signal processing device 100, and the index value ⁇ or the index value ⁇ ' output from the index value calculation unit 110.
  • the signal mixing unit 120 to which the index value ⁇ is input obtains, for each of the first and second channels, a signal obtained by mixing the input sound signal of the channel with the input sound signal of the other channel, where the larger the index value ⁇ , the closer the signal is to the input sound signal of the channel, as a signal to be coded for the channel
  • the signal mixing unit 120 to which the index value ⁇ ' is input obtains, for each of the first and second channels, a signal obtained by mixing the input sound signal of the channel with the input sound signal of the other channel, where the smaller the index value ⁇ ', the closer the signal is to the input sound signal of the channel (step S120).
  • the two-channel encoding target signals i.e., two-channel stereo encoding target signals
  • the two-channel encoding target signals obtained by the signal mixer 120 are output to the stereo encoding device 200 as output signals of the sound signal processing device 100 .
  • the signal mixing unit 120 may include a first channel signal mixing unit 120-1 and a second channel signal mixing unit 120-2, as shown in Figure 3.
  • the first channel signal mixing unit 120-1 to which the index value ⁇ is input may obtain, as the first channel encoding target signal, a signal obtained by mixing the first channel input sound signal and the second channel input sound signal, where the larger the index value ⁇ , the closer the signal is to the first channel input sound signal
  • the first channel signal mixing unit 120-1 to which the index value ⁇ ' is input may obtain, as the first channel encoding target signal, a signal obtained by mixing the first channel input sound signal and the second channel input sound signal, where the smaller the index value ⁇ ', the closer the signal is to the first channel input sound signal.
  • the second channel signal mixing unit 120-2 to which the index value ⁇ is input may obtain, as the second channel encoding target signal, a signal obtained by mixing the second channel input sound signal and the first channel input sound signal, where the larger the index value ⁇ , the closer the signal is to the second channel input sound signal; and the second channel signal mixing unit 120-2 to which the index value ⁇ ' is input may obtain, as the second channel encoding target signal, a signal obtained by mixing the second channel input sound signal and the first channel input sound signal, where the smaller the index value ⁇ ', the closer the signal is to the second channel input sound signal.
  • the signal mixing unit 120 to which the index value ⁇ ' is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be coded for that channel, and in any other case, that is, when the index value ⁇ ' is equal to or greater than the predetermined value described above, may obtain, for each channel, a signal in which the input sound signal of that channel is mixed with the input sound signal of the other channel, and the smaller the index value ⁇ ', the closer the signal is to the input sound signal of that channel (step S120).
  • the signal mixer 120 may, for each frame, set the index value ⁇ calculated by the index value calculation unit 110 for the immediately preceding frame as ⁇ p and the index value ⁇ calculated by the index value calculation unit 110 for the current frame as ⁇ c , set the value obtained by the following equation (2-9) as the index value ⁇ (t) for each time from the first time (i.e., the 1st time) to the T 0 -1th time of the current frame, and set ⁇ c as the index value ⁇ (t) for each time from the T 0th time to the last time (i.e., the Tth time) of the current frame, and may obtain a first-channel encoding target signal x' 1 (t) represented by the following equation (2-10) instead of the above equation (2-7), or may obtain a second-channel encoding target signal x' 2 (t) represented by the following equation (2-11) instead of the above equation (2-8), for each time t of
  • Index value calculation unit 110 obtains index value ⁇ ' which is greater than or equal to 0 and less than or equal to 0.5 and which has a monotonically decreasing relationship in a broad sense with the stereo encoding bitrate of stereo encoding device 200. For example, index value calculation unit 110 obtains index value ⁇ ' which is 0 when the stereo encoding bitrate of stereo encoding device 200 is the maximum value that the bitrate can take, is 0.5 when the stereo encoding bitrate of stereo encoding device 200 is the minimum value that the bitrate can take, and is a larger value as the stereo encoding bitrate of stereo encoding device 200 is lower.
  • the signal mixer 120 obtains, for each time t, a first-channel encoding target signal x'1 (t) represented by the following equation (2-12) and a second-channel encoding target signal x'2 (t) represented by the following equation (2-13).
  • the second embodiment may be implemented by including a process of mixing two-channel stereo input sound signals to generate a downmix signal.
  • An embodiment including a process of generating a downmix signal will be described as Modification 2 of the second embodiment.
  • the sound signal processing device 100 of Modification 2 of the second embodiment is as shown by a solid line in Fig. 5 and includes a signal mixing unit 120, which includes a downmix signal generating unit 1201 and a mixing unit 1211.
  • the sound signal processing device 100 performs the process of step S120 in steps S1201 and S1211.
  • the modification 2 of the second embodiment will be described mainly with respect to the differences from the second embodiment.
  • the first channel mixing unit 1211-1 may obtain a first-channel encoding target signal x' 1 ( t ) represented by the following equation (2-17) for each time t
  • the second channel mixing unit 1211-2 may obtain a second-channel encoding target signal x' 2 (t) represented by the following equation (2-18) for each time t, with w 1 and w 2 being weight values between 0 and 1 inclusive and positively correlated with the stereo encoding bit rate, i.e., weight values which are larger as the stereo encoding bit rate of stereo encoding device 200 is higher.
  • Weight value w 1 and weight value w 2 may be the same value or different values.
  • the mixing unit 1211 obtains, for each channel, a signal obtained by mixing the input sound signal of that channel with the downmix signal in the entire range of possible stereo encoding bit rates, and the higher the stereo encoding bit rate, the closer the signal is to the input sound signal of that channel (i.e., the lower the stereo encoding bit rate, the closer the signal is to the downmix signal), as the signal to be encoded for that channel; or, in a portion of the range of possible stereo encoding bit rates (a first type of range), obtains, for each channel, a signal obtained by mixing the input sound signal of that channel with the downmix signal, and the closer the signal is to the downmix signal, regardless of the stereo encoding bit rate.
  • a signal in which the input sound signal of the channel is mixed with the downmix signal, and the higher the stereo encoding bit rate is, the closer the signal is to the input sound signal of the channel (i.e., the lower the stereo encoding bit rate is, the closer the signal is to the downmix signal) is obtained as the encoding target signal of the channel (step S1211).
  • Each of the first type of range and the second type of range is one or more ranges. That is, there may be a plurality of first type ranges, and there may be a plurality of second type ranges.
  • the value having a broad monotonically increasing relationship with the stereo encoding bit rate is, for example, a function value of a broad monotonically increasing function with the stereo encoding bit rate as an argument. Therefore, for example, a broad monotonically increasing function for each channel may be stored in the mixer 1211 in advance, and the mixer 1211 may obtain a function value for each channel of each frame by providing the stereo encoding bit rate of the frame as an argument to the broad monotonically increasing function for that channel, and use the obtained function value as the weight of the input sound signal of that channel.
  • a pair of each bit rate and each weight value corresponding to each bit rate that is predetermined so that the weight value has a broad monotonically increasing relationship with the bit rate may be stored in the mixer 1211 in advance, and the mixer 1211 may obtain a weight value corresponding to the stereo encoding bit rate of the frame from among the stored weight values for each channel of each frame, and use the obtained weight value as the weight of the input sound signal of that channel.
  • the value having a broad monotonically decreasing relationship with the stereo encoding bit rate is, for example, a function value of a broad monotonically decreasing function with the stereo encoding bit rate as an argument. Therefore, for example, a broad monotonically decreasing function for each channel may be stored in the mixer 1211 in advance, and the mixer 1211 may obtain a function value for each channel of each frame by providing the stereo encoding bit rate of the frame as an argument to the broad monotonically decreasing function for that channel, and use the obtained function value as the weight of the downmix signal.
  • the weighting value w1 is 1, the first-channel encoding target signal x'1 (t) expressed by the above equation (2-17) is the same as the first-channel input sound signal x1 (t), and when the weighting value w2 is 1, the second-channel encoding target signal x'2 (t) expressed by the above equation (2-18) is the same as the second-channel input sound signal x2 (t).
  • the mixer 1211 may, for each channel, use the input sound signal of that channel as it is as the encoding target signal for that channel when the stereo encoding bit rate is the maximum value that the bit rate can take or is within a predetermined range including the maximum value.
  • the first-channel encoding target signal x'1 (t) expressed by the above equation (2-17) is the same as the downmix signal xM (t)
  • the weighting value w2 is 0, the second-channel encoding target signal x'2 (t) expressed by the above equation (2-18) is the same as the downmix signal xM (t).
  • the mixer 1211 may perform an operation in which the above-mentioned "greater than a predetermined value” and “equal to or less than a predetermined value” are respectively read as “equal to or more than a predetermined value” and "smaller than a predetermined value”.
  • Each of the first type of range and the second type of range is one or more ranges. That is, there may be multiple first-type ranges, and there may be multiple second-type ranges.
  • the mixer 1211 may perform an operation in which the above-mentioned "smaller than a predetermined value” and “equal to or greater than a predetermined value” are respectively read as “equal to or less than a predetermined value” and "equal to or greater than a predetermined value”.
  • Each of the first type of range and the second type of range is one or more ranges. That is, there may be multiple first-type ranges, and there may be multiple second-type ranges.
  • the mixing unit 1211 obtains, for each channel, the downmix signal as is as the signal to be encoded for that channel, and in a second range in which the stereo encoding bitrate is a range other than the first range in which the stereo encoding bitrate is possible (i.e., the second case in which the first case is other than the first case, specifically, when the stereo encoding bitrate is equal to or greater than the predetermined value described above), obtains, for each channel, a signal in which the input sound signal and downmix signal of that channel are weighted together, where the weight of the input sound signal of that channel in the weighted addition is a value that has a broad-sense monotonically increasing relationship with the stereo encoding bitrate in the second range, and the weight of the downmix signal in the weighted addition is a value that has a broad-sense monotonically increasing relationship with the stereo encoding bitrate in the second range, and the weight of the downmix signal in the weighted addition is a value that has a broad-sense monotonically
  • the mixing unit 1211 obtains, for each channel, the input sound signal of that channel as is as the encoding target signal for that channel, and when the stereo encoding bit rate is equal to or less than a predetermined second value that is smaller than the above-mentioned predetermined first value, the mixing unit 1211 obtains, for each channel, the downmix signal as is as the encoding target signal for that channel, and when neither of the above two cases applies, i.e., when the stereo encoding bit rate is equal to or less than the above-mentioned predetermined first value and greater than the above-mentioned predetermined second value, the mixing unit 1211 obtains, for each channel, a signal obtained by mixing the input sound signal and the downmix signal for that channel, in the entire range of the possible stereo encoding bit rate, and in which the higher the stereo encoding bit rate, the closer the signal is to the input sound signal for that channel (i.e., the lower the
  • the mixer 1211 to which the index value ⁇ ' is input may obtain, for each channel, the input sound signal of that channel as is as the encoding target signal for that channel when the index value ⁇ ' is smaller than a predetermined value, and may obtain, for each channel, a signal obtained by mixing the input sound signal of that channel with the downmix signal, in which the smaller the index value ⁇ ' is, the closer the signal is to the input sound signal of that channel (i.e., the larger the index value ⁇ ' is, the closer the signal is to the downmix signal), as the encoding target signal for that channel (step S1211).
  • the mixing unit 1211 to which the index value ⁇ ' is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel if the index value ⁇ ' is smaller than a predetermined first value, and may obtain, for each channel, the downmix signal as is as the signal to be encoded for that channel if the index value ⁇ ' is equal to or greater than a predetermined second value greater than the above-mentioned predetermined first value, and may obtain, for each channel, a signal obtained by mixing the input sound signal and the downmix signal for that channel, where the smaller the index value ⁇ ' is, the closer the signal is to the input sound signal of that channel (i.e., the larger the index value ⁇ ' is, the closer the signal is to the downmix signal) as the signal to be encoded for that channel (step S1211).
  • the index value calculation unit 110 obtains an index value ⁇ of 1 when the stereo encoding device 200 has a stereo encoding bitrate of 32 kbps, obtains an index value ⁇ of 0.8 when the stereo encoding device 200 has a stereo encoding bitrate of 24.4 kbps, obtains an index value ⁇ of 0.6 when the stereo encoding device 200 has a stereo encoding bitrate of 16.4 kbps, and obtains an index value ⁇ of 0.4 when the stereo encoding device 200 has a stereo encoding bitrate of 13.2 kbps.
  • the mixer 1211 may obtain a first-channel encoding target signal x' 1 (t) represented by the following equation (2-31) instead of the above equation (2-28), or may obtain a second-channel encoding target signal x' 2 (t) represented by the following equation (2-32) instead of the above equation (2-29).
  • the inter-channel time difference ITD is a value that corresponds to the time required for a sound emitted by a main sound source in a space to reach one of the first channel microphone and the second channel microphone arranged in the space and then reach the other microphone.
  • the index value calculation unit 110 does not need to distinguish which microphone the sound emitted by the main sound source reaches first, or which microphone the sound emitted by the main sound source reaches last, and it is sufficient for the index value calculation unit 110 to calculate the absolute value of the inter-channel time difference
  • the index value calculation unit 110 may calculate the inter-channel time difference ITD first and then obtain the absolute value of the inter-channel time difference
  • the inter-channel time difference ITD is a positive value
  • the inter-channel time difference ITD is a negative value
  • the index value calculation unit 110 obtains a phase difference signal ⁇ ( ⁇ cand ) by performing an inverse Fourier transform of the following equation (3-4) using the phase difference spectrum ⁇ (k) for each number of candidate samples ⁇ cand from ⁇ max to ⁇ min (step S110-B4).
  • ⁇ max and ⁇ min are the same as those in the first example.
  • of the inter-channel time difference is, for example, the function value of a broadly monotonically increasing function with the absolute value
  • the weighting value w1 is 1, the first-channel encoding target signal x'1 (t) expressed by the above formula (2-1) is the same as the first-channel input sound signal x1 (t), and when the weighting value w2 is 1, the second-channel encoding target signal x'2 (t) expressed by the above formula (2-2) is the same as the second-channel input sound signal x2 (t).
  • the signal mixing unit 120 obtains, for each channel, the input sound signal of that channel as is as the signal to be coded for that channel, and in cases other than the above, i.e., when the absolute value of the inter-channel time difference
  • the signal mixing unit 120 obtains, for each channel, the input sound signal of that channel as is as the encoding target signal for that channel, and in a second range in which the absolute value
  • the signal mixer 120 may operate by replacing the above-mentioned "smaller than a predetermined value” and “equal to or greater than a predetermined value” with “equal to or less than a predetermined value” and “greater than a predetermined value”, respectively.
  • of the previous frame is set to w p1
  • of the current frame is set to w c1
  • the first channel signal mixing unit 120-1 may set the value obtained by the above equation (2-3) as the weighting value w 1 (t) for each time from the first time (i.e., the 1st time) to the T 0 -1th time of the current frame, and set w c1 as the weighting value w 1 (t) for each time from the T 0th time to the last time (i.e., the Tth time) of the current frame, thereby obtaining the first channel encoding target signal x' 1 (t) represented by the above equation (2-4) instead of the above equation (2-1) for each time
  • of the inter-channel time difference of the previous frame is defined as w p2
  • of the inter-channel time difference of the current frame is defined as w c2 .
  • the second channel signal mixing unit 120-2 may use the value obtained by the above equation (2-5) as the weighting value w 2 (t) for each time from the first time (i.e., the 1st time) to the T 0 -1th time of the current frame, and use w c2 as the weighting value w 2 (t) for each time from the T 0th time to the last time (i.e., the Tth time) of the current frame, thereby obtaining the second channel encoding target signal x' 2 (t) represented by the above equation (2-6) instead of the above equation (2-2) for each time t of the current frame.
  • the third embodiment may be implemented by including a process of calculating an index value according to the absolute value
  • of the inter-channel time difference will be described as Modification 1 of the third embodiment.
  • the sound signal processing device 100 of Modification 1 of the third embodiment is as shown by the dashed line, dashed line, and solid line in Fig. 3, and includes an index value calculation unit 110 and a signal mixing unit 120.
  • the sound signal processing device 100 performs the processes of steps S110 and S120 shown by the dashed line and solid line in Fig. 4. The following description will focus on the differences between Modification 1 of the third embodiment and the third embodiment.
  • the index value calculation unit 110 receives a first channel input sound signal and a second channel input sound signal, which are input sound signals of two channels constituting the two-channel stereo input sound signal input to the sound signal processing device 100.
  • the index value calculation unit 110 calculates an index value ⁇ that is in a monotonically decreasing relationship in a broad sense with respect to the absolute value
  • the index value ⁇ or the index value ⁇ ' obtained by the index value calculation unit 110 is output to the signal mixing unit 120.
  • the index value calculation unit 110 may calculate the absolute value
  • of the inter-channel time difference of a two-channel stereo input sound signal is, for example, a function value of a broad-sense monotonically decreasing function with the absolute value
  • of the inter-channel time difference can be performed, for example, by storing the broad-sense monotonically decreasing function in advance in the index value calculation unit 110, and by the index value calculation unit 110 providing the absolute value
  • can be performed by, for example, storing in advance in the index value calculation unit 110 a set of information specifying the absolute value of the inter-channel time difference
  • of the inter-channel time difference of a two-channel stereo input sound signal is, for example, a function value of a broad monotonically increasing function with the absolute value
  • of the inter-channel time difference can be performed, for example, by storing the broad monotonically increasing function in advance in the index value calculation unit 110, and by the index value calculation unit 110 providing the absolute value
  • of the inter-channel time difference can be performed by, for example, storing in advance in the index value calculation unit 110 a set of information specifying the absolute value
  • the index value calculation unit 110 may set the absolute value
  • the signal mixer 120 to which the index value ⁇ is input obtains, for each of the first and second channels, a signal obtained by mixing an input sound signal of the first channel with an input sound signal of the other channel, where the larger the index value ⁇ , the closer the signal is to the input sound signal of the first channel
  • the signal mixer 120 to which the index value ⁇ ' is input obtains, for each of the first and second channels, a signal obtained by mixing an input sound signal of the first channel with an input sound signal of the other channel, where the smaller the index value ⁇ ', the closer the signal is to the input sound signal of the first channel (step S120).
  • the encoding target signals of the two channels obtained by the signal mixer 120 i.e., two-channel stereo encoding target signals
  • the signal mixing unit 120 to which the index value ⁇ is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be coded for that channel, and in other cases, that is, when the index value ⁇ is equal to or less than the predetermined value described above, may obtain, for each channel, a signal in which the input sound signal of that channel is mixed with the input sound signal of the other channel, and the larger the index value ⁇ , the closer the signal is to the input sound signal of that channel (step S120).
  • the signal mixing unit 120 may operate by replacing the previously described "greater than the predetermined value” and “equal to or less than the predetermined value” with “equal to or greater than the predetermined value” and “equal to or less than the predetermined value", respectively.
  • the signal mixing unit 120 to which the index value ⁇ ' is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be coded for that channel, and in any other case, that is, when the index value ⁇ ' is equal to or greater than the predetermined value described above, may obtain, for each channel, a signal in which the input sound signal of that channel is mixed with the input sound signal of the other channel, and the smaller the index value ⁇ ', the closer the signal is to the input sound signal of that channel (step S120).
  • the signal mixing unit 120 may operate by replacing the previously described "smaller than a predetermined value” and “equal to or greater than a predetermined value” with “equal to or less than a predetermined value” and “equal to or greater than a predetermined value”, respectively.
  • the index value calculation unit 110 obtains an index value ⁇ that is 0.5 when the absolute value
  • the signal mixer 120 obtains, for each time t, the first-channel encoding target signal x'1 (t) represented by the above equation (2-7) and the second-channel encoding target signal x'2 (t) represented by the above equation (2-8).
  • the signal mixer 120 may, for each frame, take the index value ⁇ calculated by the index value calculation unit 110 for the immediately preceding frame as ⁇ p and the index value ⁇ calculated by the index value calculation unit 110 for the current frame as ⁇ c , set the value obtained by the above equation (2-9) as the index value ⁇ (t) for each time from the first time (i.e., the 1st time) to the T 0 -1th time of the current frame, and set ⁇ c as the index value ⁇ (t) for each time from the T 0th time to the last time (i.e., the Tth time) of the current frame, and may obtain the first-channel encoding target signal x' 1 (t) represented by the above equation (2-10) instead of the above equation (2-7) for each time t of the current frame, or may obtain the second-channel encoding target signal x' 2 (t) represented by the above equation (2-11) instead of the above equation (2
  • the index value calculation unit 110 obtains an index value ⁇ ' that is 0 when the absolute value
  • the signal mixer 120 obtains, for each time t, the first-channel encoding target signal x'1 (t) expressed by the above equation (2-12) and the second-channel encoding target signal x'2 (t) expressed by the above equation (2-13).
  • the signal mixer 120 may obtain the first-channel encoding target signal x' 1 (t) represented by the above equation (2-15) instead of the above equation (2-12), or may obtain the second-channel encoding target signal x' 2 (t) represented by the above equation (2-16) instead of the above equation (2-13).
  • the third embodiment may be implemented by including a process of mixing two-channel stereo input sound signals to generate a downmix signal.
  • An embodiment including a process of generating a downmix signal will be described as Modification 2 of the third embodiment.
  • the sound signal processing device 100 of Modification 2 of the third embodiment is as shown by the dashed line, dashed line, and solid line in Fig. 5, and includes an index value calculation unit 110 and a signal mixing unit 120, and the signal mixing unit 120 includes a downmix signal generation unit 1201 and a mixing unit 1211.
  • the sound signal processing device 100 performs a process of step S110 and a process of step S120 by steps S1201 and S1211.
  • the modification 2 of the third embodiment will be described mainly with respect to the differences from the third embodiment.
  • index value calculation unit 110 receives a first channel input sound signal and a second channel input sound signal, which are input sound signals of two channels constituting the two-channel stereo input sound signal input to the sound signal processing device 100.
  • the index value calculation unit 110 calculates an absolute value
  • of the inter-channel time difference obtained by the index value calculation unit 110 is output to the signal mixing unit 120.
  • the input/output and operation of the downmix signal generation unit 1201 are the same as those of the second and third modifications of the second embodiment, and are as described in the second modification of the second embodiment.
  • the downmix signal generation unit 1201 receives a first channel input sound signal and a second channel input sound signal, which are input sound signals of two channels constituting a two-channel stereo input sound signal input to the sound signal processing device 100.
  • the downmix signal generation unit 1201 mixes the first channel input sound signal and the second channel input sound signal to generate a downmix signal (step S1201).
  • the downmix signal obtained by the downmix signal generation unit 1201 is output to a mixer 1211.
  • the mixer 1211 receives as input a first channel input sound signal and a second channel input sound signal which are input sound signals of two channels constituting the two-channel stereo input sound signal input to the sound signal processing device 100, a downmix signal output from the downmix signal generation unit 1201, and an absolute value
  • the mixer 1211 obtains, as a coding target signal for that channel (step S1211), a signal obtained by mixing the downmix signal with the input sound signal of that channel, where the smaller the absolute value
  • the first channel mixer 1211-1 may obtain the first-channel encoding target signal x' 1 (t) represented by the above formula (2-17) for each time t
  • the second channel mixer 1211-2 may obtain the second-channel encoding target signal x' 2 (t) represented by the above formula (2-18) for each time t, using weight values w 1 and w 2 that are between 0 and 1 and have a negative correlation with the absolute value
  • the weight values w 1 and w 2 may be the same value or different values.
  • the weight values w1 and w2 may be constant regardless of the absolute value
  • of the inter-channel time difference is, for example, the function value of a broadly-sense monotonically decreasing function with the absolute value
  • the mixer 1211 may store in advance a set of information for identifying the absolute value
  • of the inter-channel time difference is, for example, a function value of a broad monotonically increasing function with the absolute value
  • the mixer 1211 may store in advance a set of information for identifying the absolute value
  • the weighting value w1 is 1, the first-channel encoding target signal x'1 (t) expressed by the above equation (2-17) is the same as the first-channel input sound signal x1 (t), and when the weighting value w2 is 1, the second-channel encoding target signal x'2 (t) expressed by the above equation (2-18) is the same as the second-channel input sound signal x2 (t).
  • the first-channel encoding target signal x'1 (t) expressed by the above formula (2-17) is the same as the downmix signal xM (t)
  • the weighting value w2 is 0, the second-channel encoding target signal x'2 (t) expressed by the above formula (2-18) is the same as the downmix signal xM (t).
  • the mixer 1211 may treat the downmix signal as it is for each channel as the encoding target signal for that channel when the absolute value
  • the mixer 1211 obtains, for each channel, the input sound signal of that channel as is as the signal to be coded for that channel, and in cases other than the above, i.e., when the absolute value
  • the mixing unit 1211 may perform an operation in which the above-mentioned "smaller than a predetermined value” and “equal to or greater than a predetermined value” are respectively interpreted as “equal to or less than a predetermined value” and "equal to or greater than a predetermined value”.
  • the mixer 1211 obtains, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel, and in a second range in which the absolute value
  • the mixer 1211 may perform an operation in which the above-mentioned "smaller than a predetermined value” and “equal to or greater than a predetermined value” are respectively interpreted as “equal to or less than a predetermined value” and "equal to or greater than a predetermined value”.
  • the mixer 1211 obtains, for each channel, the downmix signal as it is as the signal to be coded for that channel, and in any other case, i.e., when the absolute value
  • the mixer 1211 may perform an operation in which the above-mentioned "greater than a predetermined value” and “equal to or less than a predetermined value” are respectively read as “equal to or more than a predetermined value” and "equal to or less than a predetermined value”.
  • the mixer 1211 obtains the downmix signal for each channel as it is as the signal to be coded for that channel, and in a second range in which the absolute value
  • the mixing unit 1211 may operate by replacing the previously mentioned “greater than a predetermined first value” and “less than or equal to a predetermined first value” with “greater than or equal to a predetermined first value” and “less than a predetermined first value”, respectively, and may operate by replacing the previously mentioned "greater than a predetermined second value” and “less than or equal to a predetermined second value” with “greater than or equal to a predetermined second value” and “less than a predetermined second value", respectively.
  • Two-channel stereo input sound signals usually contain sounds emitted by one or more sound sources.
  • a two-channel stereo input sound signal obtained by AD-converting sounds picked up by two microphones placed in a certain space
  • the two-channel stereo input sound signal mainly contains only sounds emitted by that one sound source
  • the two-channel stereo input sound signal mainly contains sounds emitted by the multiple sound sources.
  • the single-source-likeliness of a two-channel stereo input sound signal refers to the likelihood that the two-channel stereo input sound signal mainly contains only sounds emitted by one sound source.
  • the process of obtaining the index value ⁇ using the index value of the single sound source-likeness of the two-channel stereo input sound signal can be performed, for example, by storing the broad monotonically increasing function in advance in the index value calculation unit 110, and by the index value calculation unit 110 providing the index value of the single sound source-likeness of the two-channel stereo input sound signal of the frame as an argument to the broad monotonically increasing function to obtain a function value, and setting the obtained function value as the index value ⁇ .
  • the value that has a broad-sense monotonically decreasing relationship with the index value of the single-sound-source-likeness of the two-channel stereo input sound signal is, for example, the function value of a broad-sense monotonically decreasing function with the index value of the single-sound-source-likeness of the two-channel stereo input sound signal as an argument.
  • the index value calculation unit 110 may first perform step S110-C1-A1, and obtain the maximum value of the absolute values ⁇ cand of the correlation coefficients obtained in step S110-C1-A1 as an index value for the single sound source-likeliness of the two-channel stereo input sound signals (step S110-C1-A2').
  • the second example is an example using a correlation value using information on the phase of the signal.
  • the index value calculation unit 110 first performs a Fourier transform of the first channel input sound signals x 1 (1), x 1 (2), ..., x 1 (T) according to the above formula (3-1) to obtain a first channel frequency spectrum X 1 (k) at each frequency k from 0 to T-1 (step S110-C1-B1).
  • the index value calculation unit 110 obtains a phase difference signal ⁇ ( ⁇ cand ) by performing an inverse Fourier transform of the above equation (3-4) using the phase difference spectrum ⁇ (k) for each number of candidate samples ⁇ cand from ⁇ max to ⁇ min (step S110-C1-B4).
  • ⁇ max and ⁇ min are the same as those in the first example.
  • the index value calculation unit 110 then obtains the difference
  • the index value calculation unit 110 may perform an operation in which the above-mentioned “greater than the threshold TH ⁇ " and “equal to or smaller than the threshold TH ⁇ " are respectively read as “equal to or greater than the threshold TH ⁇ " and “smaller than the threshold TH ⁇ ".
  • the index value calculation unit 110 may use a predetermined positive number ⁇ range to obtain an average value for each ⁇ cand using the above formula (3-5), and obtain a normalized correlation value obtained by the above formula (3-6) using the obtained average value ⁇ c ( ⁇ cand ) and the phase difference signal ⁇ ( ⁇ cand ) as ⁇ cand (step S110-C1-B5').
  • the third example is an example using the ratio of energies of phase difference correlation signals.
  • the index value calculation unit 110 first performs steps S110-C1-B1 to S110-C1-B6 described in the second example. In this case, the index value calculation unit 110 may perform step S110-C1-B5' described in the second example instead of step S110-C1-B5.
  • the index value calculation unit 110 then obtains the ratio of the sum of the energy of the phase difference signal ⁇ ( ⁇ cand ) within a predetermined range around ⁇ 1 to the sum of the energy of the phase difference signal ⁇ ( ⁇ cand ) excluding that range as an index value of the single sound source-likeness of the two-channel stereo input sound signal (steps S110-C1-C7).
  • the index value calculation unit 110 may obtain a value obtained by the following formula (4-1) as an index value of the single sound source-likeness of the two-channel stereo input sound signal.
  • the signal mixing unit 120 receives a first channel input sound signal and a second channel input sound signal, which are input sound signals of two channels constituting the two-channel stereo input sound signal input to the sound signal processing device 100, and the index value ⁇ or the index value ⁇ ' output from the index value calculation unit 110.
  • the signal mixing unit 120 to which the index value ⁇ is input obtains, for each channel, a signal obtained by weighting and adding the input sound signal of that channel and the input sound signal of the other channel, where the weight of the input sound signal of that channel in the weighting and adding is a value or index value ⁇ that has a monotonically increasing relationship with the index value ⁇ , and the weight of the input sound signal of the other channel in the weighting and adding is a value that has a monotonically decreasing relationship with the index value ⁇ , as the signal to be coded for that channel.
  • the value that is in a monotonically increasing relationship with the index value ⁇ is, for example, the function value of a monotonically increasing function with the index value ⁇ as an argument. Therefore, for example, a monotonically increasing function for each channel is stored in the signal mixing unit 120 in advance, and the signal mixing unit 120 obtains a function value for each channel of each frame by giving the index value ⁇ as an argument to the monotonically increasing function for that channel, and sets the obtained function value as the weight of the input sound signal of that channel.
  • the monotonically increasing function for the first channel and the monotonically increasing function for the second channel may be the same or different.
  • a set of information specifying the index value ⁇ that belongs to each partial range and each weight value corresponding to each partial range that is predetermined so that the weight value has a monotonically decreasing relationship with the index value ⁇ may be stored in advance in the signal mixing unit 120 for each channel, and the signal mixing unit 120 may acquire, for each channel of each frame, a weight value that corresponds to the index value ⁇ of that frame from the stored weight values, and set the acquired weight value as the weight of the input sound signal of the other channel.
  • the sets stored in advance may be the same or different for the first and second channels.
  • a value that has a monotonically decreasing relationship with the index value ⁇ ' is, for example, a function value of a monotonically decreasing function with the index value ⁇ ' as an argument. Therefore, for example, a monotonically decreasing function for each channel is stored in advance in the signal mixing unit 120, and for each channel of each frame, the signal mixing unit 120 provides the index value ⁇ ' as an argument to the monotonically decreasing function for that channel to obtain a function value, and sets the obtained function value as the weight of the input sound signal for that channel.
  • the monotonically decreasing function for the first channel and the monotonically decreasing function for the second channel may be the same or different.
  • a set of information specifying the index value ⁇ ' that belongs to each partial range and each weight value corresponding to each partial range that is predetermined so that the weight value has a monotonically decreasing relationship with the index value ⁇ ' may be stored in advance in the signal mixing unit 120 for each channel, and the signal mixing unit 120 may acquire, for each channel of each frame, the weight value that corresponds to the index value ⁇ ' of that frame from the stored weight values, and set the acquired weight value as the weight of the input sound signal of that channel.
  • the sets stored in advance may be the same or different for the first and second channels.
  • a value that has a monotonically increasing relationship with the index value ⁇ ' is, for example, the function value of a monotonically increasing function with the index value ⁇ ' as an argument. Therefore, for example, a monotonically increasing function for each channel is stored in advance in the signal mixing unit 120, and for each channel of each frame, the signal mixing unit 120 provides the index value ⁇ ' as an argument to the monotonically increasing function for that channel to obtain a function value, and sets the obtained function value as the weight of the input sound signal of the other channel.
  • the monotonically increasing function for the first channel and the monotonically increasing function for the second channel may be the same or different.
  • a set of information specifying the index value ⁇ ' that belongs to each partial range and each weight value corresponding to each partial range that is predetermined so that the weight value has a monotonically increasing relationship with the index value ⁇ ' may be stored in advance in the signal mixing unit 120 for each channel, and the signal mixing unit 120 may acquire, for each channel of each frame, the weight value that corresponds to the index value ⁇ ' of that frame from the stored weight values, and set the acquired weight value as the weight of the input sound signal of the other channel.
  • the sets stored in advance may be the same or different for the first and second channels.
  • stereo coding methods are designed with consideration given to the reproducibility of the sound itself emitted by the sound source and the reproducibility of the localization of the sound source.
  • a signal to be coded on two channels contains mainly sounds emitted by a single sound source
  • the amount of information required to represent the localization of the sound source is small, so not only is the reproducibility of the localization of the sound source high, but the reproducibility of the sound itself emitted by the sound source is also high.
  • a signal to be coded on two channels contains mainly sounds emitted by multiple sound sources, a large amount of information is required to represent the localization of the multiple sound sources, which may result in poor reproducibility of the sound itself emitted by the sound source.
  • the more the two-channel stereo input sound signal resembles a single sound source i.e., the more the two-channel stereo input sound signal resembles a multiple sound source
  • the more the two-channel stereo input sound signal resembles a single sound source i.e., the more the two-channel stereo input sound signal resembles a multiple sound source
  • the closer the encoding target signal of each channel is to the same single signal, thereby suppressing deterioration in the auditory quality of the decoded sound signal when the inter-channel time difference of the two-channel stereo input sound signal is large.
  • the signal mixing unit 120 to which the index value ⁇ is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be coded for that channel, and in other cases, that is, when the index value ⁇ is equal to or less than the predetermined value described above, may obtain, for each channel, a signal in which the input sound signal of that channel is mixed with the input sound signal of the other channel, and the larger the index value ⁇ , the closer the signal is to the input sound signal of that channel (step S120).
  • the signal mixing unit 120 may operate by replacing the previously described "greater than the predetermined value” and “equal to or less than the predetermined value” with “equal to or greater than the predetermined value” and “equal to or less than the predetermined value", respectively.
  • the signal mixing unit 120 may operate by replacing the previously described "smaller than a predetermined value” and “equal to or greater than a predetermined value” with “equal to or less than a predetermined value” and “equal to or greater than a predetermined value”, respectively.
  • the fourth embodiment may be implemented by including a process of mixing two-channel stereo input sound signals to generate a downmix signal.
  • An embodiment including a process of generating a downmix signal will be described as Modification 1 of the fourth embodiment.
  • the sound signal processing device 100 of Modification 1 of the fourth embodiment is as shown by the dashed line, dashed line, and solid line in Fig. 5, and includes an index value calculation unit 110 and a signal mixing unit 120, and the signal mixing unit 120 includes a downmix signal generation unit 1201 and a mixing unit 1211.
  • the sound signal processing device 100 performs a process of step S110 and a process of step S120 by steps S1201 and S1211.
  • the modification 1 of the fourth embodiment will be described mainly with respect to the differences from the fourth embodiment.
  • index value calculation unit 110 receives a first channel input sound signal and a second channel input sound signal, which are two channel input sound signals constituting the two-channel stereo input sound signal input to the sound signal processing device 100.
  • the index value calculation unit 110 calculates an index value ⁇ that is in a broadly monotonically increasing relationship with respect to the single sound source-likeness of the two-channel stereo input sound signal, or an index value ⁇ ' that is in a broadly monotonically decreasing relationship with respect to the single sound source-likeness of the two-channel stereo input sound signal (step S110).
  • the index value ⁇ or the index value ⁇ ' obtained by the index value calculation unit 110 is output to the signal mixing unit 120.
  • the mixer 1211 to which the index value ⁇ ' is input obtains, for each channel, a signal obtained by weighting and adding the input sound signal and downmix signal of that channel, where the weight of the input sound signal of that channel in the weighting and addition is a value that has a monotonically decreasing relationship with the index value ⁇ ', and the weight of the downmix signal in the weighting and addition is a value that has a monotonically increasing relationship with the index value ⁇ ' or a signal that is the index value ⁇ ', as the signal to be coded for that channel.
  • the value that has a monotonically increasing relationship with the index value ⁇ ' is, for example, the function value of a monotonically increasing function with the index value ⁇ ' as an argument. Therefore, for example, a monotonically increasing function for each channel is stored in advance in the mixer 1211, and for each channel of each frame, the mixer 1211 obtains a function value by providing the index value ⁇ ' as an argument to the monotonically increasing function for that channel, and sets the obtained function value as the weight of the downmix signal.
  • the monotonically increasing function for the first channel and the monotonically increasing function for the second channel may be the same or different.
  • a set of information specifying the index value ⁇ ' belonging to each partial range and each weight value corresponding to each partial range that is predetermined so that the weight value has a monotonically increasing relationship with the index value ⁇ ' may be stored in advance in the mixer 1211 for each channel, and the mixer 1211 may acquire, for each channel of each frame, a weight value corresponding to the index value ⁇ ' of the frame from among the stored weight values, and set the acquired weight value as the weight of the downmix signal.
  • the sets stored in advance may be the same or different for the first and second channels.
  • the mixing unit 1211 to which the index value ⁇ is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel in a first range in which the index value ⁇ can take is greater than a predetermined value (i.e., the first case in which the index value ⁇ is greater than the predetermined value), and may obtain, for each channel, a signal in which the input sound signal of that channel and the downmix signal are weighted together, in which the weight of the input sound signal of that channel in the weighted addition is a value or index value ⁇ that is monotonically increasing with respect to the index value ⁇ in the second range, and the weight of the downmix signal in the weighted addition is a value that is monotonically decreasing with respect to the index value ⁇ in the second range.
  • the mixing unit 1211 may operate by replacing the previously mentioned "greater than a specified value" and “less than or equal to a specified value” with "greater than or equal to a specified value” and "less than a specified value
  • the mixer 1211 to which the index value ⁇ is input may obtain, for each channel, the downmix signal as is as the encoding target signal for that channel when the index value ⁇ is smaller than a predetermined value, and may obtain, for each channel, a signal obtained by mixing the input sound signal and the downmix signal for that channel, and the larger the index value ⁇ , the closer the signal is to the input sound signal for that channel (i.e., the smaller the index value ⁇ , the closer the signal is to the downmix signal), as the encoding target signal for that channel (step S1211).
  • the mixing unit 1211 may operate by replacing the previously mentioned “greater than a predetermined first value” and “less than or equal to a predetermined first value” with “greater than or equal to a predetermined first value” and “less than a predetermined first value”, respectively, and may operate by replacing the previously mentioned "greater than a predetermined second value” and “less than or equal to a predetermined second value” with “greater than or equal to a predetermined second value” and “less than a predetermined second value", respectively.
  • the mixing unit 1211 to which the index value ⁇ ' is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel in a first range in which the index value ⁇ ' can be in a range in which the index value ⁇ ' is smaller than a predetermined value (i.e., in the first case in which the index value ⁇ ' is smaller than the predetermined value), and may obtain, for each channel, a signal in which the input sound signal of that channel and the downmix signal are weighted together, where the weight of the input sound signal of that channel in the weighted addition is a value that is in a monotonically decreasing relationship with the index value ⁇ ' in the second range, and the weight of the downmix signal in the weighted addition is a value or index value ⁇ ' that is in a monotonically increasing relationship with the index value ⁇ ' in the second range.
  • the mixing unit 1211 may operate by replacing the previously mentioned "smaller than a predetermined value" and "greater than or equal to a
  • the mixer 1211 to which the index value ⁇ ' is input may obtain, for each channel, the downmix signal as is as the encoding target signal for that channel when the index value ⁇ ' is greater than a predetermined value, and may obtain, for each channel, a signal obtained by mixing the input sound signal and the downmix signal for that channel, and in which the smaller the index value ⁇ ' is, the closer the signal is to the input sound signal for that channel (i.e., the larger the index value ⁇ ' is, the closer the signal is to the downmix signal) as the encoding target signal for that channel (step S1211).
  • the mixer 1211 may perform an operation in which the above-mentioned "greater than the predetermined value” and “equal to or less than the predetermined value” are respectively interpreted as “equal to or greater than the predetermined value” and “equal to or less than the predetermined value”.
  • a third range which is a range that is neither the first range nor the second range (that is, in the third case which is neither the first case nor the second case, specifically, when the index value ⁇ ' is equal to or greater than the above-mentioned predetermined first value and smaller than the above-mentioned predetermined second value)
  • a signal obtained by weighting together an input sound signal and a downmix signal of the channel in which the weight of the input sound signal of the channel in the weighting addition is a value that has a monotonically decreasing relationship with the index value ⁇ ' in the third range, and the weight of the downmix signal in the weighting addition is a value that has a monotonically increasing relationship with the index value ⁇ ' in the third range or the index value ⁇ ', may be obtained as the encoding target signal of the channel.
  • the mixer 1211 obtains, for each time t, the first-channel encoding target signal x' 1 (t) expressed by the above equation (2-23), and obtains the second-channel encoding target signal x' 2 (t) expressed by the above equation (2-24).
  • the mixer 1211 may take the index value ⁇ calculated by the index value calculation unit 110 for the immediately preceding frame as ⁇ p and the index value ⁇ calculated by the index value calculation unit 110 for the current frame as ⁇ c , set the value obtained by the above equation (2-25) as the index value ⁇ (t) for each time from the first time (i.e., the 1st time) to the T 0 -1th time of the current frame, and set ⁇ c as the index value ⁇ (t) for each time from the T 0th time to the last time (i.e., the Tth time) of the current frame.
  • the mixer 1211 obtains, for each time t, the first-channel encoding target signal x' 1 (t) expressed by the above equation (2-28) and the second-channel encoding target signal x' 2 (t) expressed by the above equation (2-29).
  • the signal mixing unit 120 receives a first channel input sound signal and a second channel input sound signal, which are input sound signals of two channels constituting the two-channel stereo input sound signal input to the sound signal processing device 100, and the index value ⁇ or the index value ⁇ ' output from the index value calculation unit 110.
  • the signal mixer 120 to which the index value ⁇ is input obtains, for each of the first and second channels, a signal obtained by mixing an input sound signal of the first channel and an input sound signal of the other channel, where the larger the index value ⁇ , the closer the signal is to the input sound signal of the first channel, and the signal mixer 120 to which the index value ⁇ ' is input obtains, for each of the first and second channels, a signal obtained by weighting and adding an input sound signal of the first channel and an input sound signal of the other channel, where the smaller the index value ⁇ ', the closer the signal is to the input sound signal of the first channel (step S120).
  • the encoding target signals of the two channels obtained by the signal mixer 120 i.e., two-channel stereo encoding target signals
  • the signal mixing unit 120 to which the index value ⁇ ' is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be coded for that channel, and in any other case, that is, when the index value ⁇ ' is equal to or greater than the predetermined value described above, may obtain, for each channel, a signal in which the input sound signal of that channel is mixed with the input sound signal of the other channel, and the smaller the index value ⁇ ', the closer the signal is to the input sound signal of that channel (step S120).
  • the value that is in a monotonically decreasing relationship with the index value ⁇ is, for example, a function value of a monotonically decreasing function with the index value ⁇ as an argument. Therefore, for example, a monotonically decreasing function for each channel may be stored in the mixer 1211 in advance, and the mixer 1211 may obtain a function value for each channel of each frame by providing the index value ⁇ as an argument to the monotonically decreasing function for that channel, and use the obtained function value as the weight of the downmix signal.
  • the monotonically decreasing function for the first channel and the monotonically decreasing function for the second channel may be the same or different.
  • a set of information specifying the index value ⁇ ' belonging to each partial range and each weight value corresponding to each partial range that is predetermined so that the weight value has a monotonically increasing relationship with the index value ⁇ ' may be stored in the mixer 1211 for each channel in advance, and the mixer 1211 may acquire, for each channel of each frame, a weight value corresponding to the index value ⁇ ' of the frame from among the stored weight values, and set the acquired weight value as the weight of the downmix signal.
  • the sets stored in advance may be the same or different for the first and second channels.
  • the mixer 1211 may perform an operation in which the above-mentioned "greater than the predetermined value” and “equal to or less than the predetermined value” are respectively interpreted as “equal to or greater than the predetermined value” and “equal to or less than the predetermined value”.
  • the mixing unit 1211 to which the index value ⁇ is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel in a first range in which the index value ⁇ can take is greater than a predetermined value (i.e., the first case in which the index value ⁇ is greater than the predetermined value), and may obtain, for each channel, a signal in which the input sound signal of that channel and the downmix signal are weighted together, in which the weight of the input sound signal of that channel in the weighted addition is a value or index value ⁇ that is monotonically increasing with respect to the index value ⁇ in the second range, and the weight of the downmix signal in the weighted addition is a value that is monotonically decreasing with respect to the index value ⁇ in the second range.
  • the mixing unit 1211 may operate by replacing the previously mentioned "greater than a specified value” and “less than a specified value” with "greater than a specified value” and "less than a specified value", respectively.
  • the mixing unit 1211 may operate by replacing the previously mentioned “greater than a predetermined first value” and “less than or equal to a predetermined first value” with “greater than or equal to a predetermined first value” and “less than a predetermined first value”, respectively, and may operate by replacing the previously mentioned "greater than a predetermined second value” and “less than or equal to a predetermined second value” with “greater than or equal to a predetermined second value” and “less than a predetermined second value", respectively.
  • the mixing unit 1211 to which the index value ⁇ ' is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel in a first range in which the index value ⁇ ' can be in a range in which the index value ⁇ ' is smaller than a predetermined value (i.e., in the first case in which the index value ⁇ ' is smaller than the predetermined value), and may obtain, for each channel, a signal in which the input sound signal of that channel and the downmix signal are weighted together, where the weight of the input sound signal of that channel in the weighted addition is a value that is in a monotonically decreasing relationship with the index value ⁇ ' in the second range, and the weight of the downmix signal in the weighted addition is a value or index value ⁇ ' that is in a monotonically increasing relationship with the index value ⁇ ' in the second range.
  • the mixing unit 1211 may operate by replacing the previously mentioned "smaller than a predetermined value" and "greater than or equal to a
  • the mixer 1211 to which the index value ⁇ ' is input may obtain, for each channel, the downmix signal as is as the encoding target signal for that channel when the index value ⁇ ' is greater than a predetermined value, and may obtain, for each channel, a signal obtained by mixing the input sound signal and the downmix signal for that channel, and in which the smaller the index value ⁇ ' is, the closer the signal is to the input sound signal for that channel (i.e., the larger the index value ⁇ ' is, the closer the signal is to the downmix signal) as the encoding target signal for that channel (step S1211).
  • the mixer 1211 may perform an operation in which the above-mentioned "greater than the predetermined value” and “equal to or less than the predetermined value” are respectively interpreted as “equal to or greater than the predetermined value” and “equal to or less than the predetermined value”.
  • the mixing unit 1211 to which the index value ⁇ ' is input may obtain, for each channel, the downmix signal as is as the signal to be encoded for that channel in a first range in which the index value ⁇ ' can be in a range in which the index value ⁇ is greater than a predetermined value (i.e., in the first case in which the index value ⁇ ' is greater than the predetermined value), and may obtain, for each channel, a signal in which the input sound signal and the downmix signal for that channel are weighted together, where the weight of the input sound signal for that channel in the weighted addition is a value that is in a monotonically decreasing relationship with the index value ⁇ ' in the second range, and the weight of the downmix signal in the weighted addition is a value or index value ⁇ ' that is in a monotonically increasing relationship with the index value ⁇ ' in the second range.
  • the mixing unit 1211 may operate by replacing the previously mentioned "greater than a specified value” and "less than a specified value” with "greater than
  • the mixing unit 1211 to which the index value ⁇ ' is input may obtain, for each channel, the input sound signal of that channel as is as the signal to be encoded for that channel if the index value ⁇ ' is smaller than a predetermined first value, and may obtain, for each channel, the downmix signal as is as the signal to be encoded for that channel if the index value ⁇ ' is equal to or greater than a predetermined second value greater than the above-mentioned predetermined first value, and may obtain, for each channel, a signal obtained by mixing the input sound signal and the downmix signal of that channel, where the smaller the index value ⁇ ' is, the closer the signal is to the input sound signal of that channel (i.e., the larger the index value ⁇ ' is, the closer the signal is to the downmix signal) as the signal to be encoded for that channel (step S1211).
  • the mixer 1211 to which the index value ⁇ ' is input obtains, for each channel, the input sound signal of the channel as is as the signal to be coded for the channel in a first range in which the index value ⁇ ' can be taken, where the index value ⁇ ' is a range smaller than a predetermined first value (i.e., in the first case where the index value ⁇ ' is smaller than the predetermined first value), and obtains, for each channel, the downmix signal as is as the signal to be coded for the channel in a second range in which the index value ⁇ ' can be taken, where the index value ⁇ ' is equal to or greater than a predetermined second value larger than the first value described above (i.e., in the second case where the index value ⁇ ' is equal to or greater than a predetermined second value larger than the first value described above).
  • a third range which is a range that is neither the first range nor the second range (that is, in the third case which is neither the first case nor the second case, specifically, when the index value ⁇ ' is equal to or greater than the above-mentioned predetermined first value and smaller than the above-mentioned predetermined second value)
  • a signal obtained by weighting together an input sound signal and a downmix signal of the channel in which the weight of the input sound signal of the channel in the weighting addition is a value that has a monotonically decreasing relationship with the index value ⁇ ' in the third range, and the weight of the downmix signal in the weighting addition is a value that has a monotonically increasing relationship with the index value ⁇ ' in the third range or the index value ⁇ ', may be obtained as the encoding target signal of the channel.
  • the mixing unit 1211 may operate by replacing the previously mentioned “smaller than a predetermined first value” and “greater than or equal to a predetermined first value” with “smaller than a predetermined first value” and “greater than a predetermined first value”, respectively, and may operate by replacing the previously mentioned "smaller than a predetermined second value” and “greater than or equal to a predetermined second value” with “smaller than a predetermined second value” and “greater than a predetermined second value", respectively.
  • the index value calculation unit 110 obtains an index value ⁇ that is 0 or more and 1 or less and satisfies two or more of the first condition, the second condition, and the third condition. Specifically, the index value calculation unit 110 obtains any one of the index value ⁇ that is 0 or more and 1 or less and satisfies the first condition and the second condition, the index value ⁇ that is 0 or more and 1 or less and satisfies the first condition and the third condition, the index value ⁇ that is 0 or more and 1 or less and satisfies the second condition and the third condition, and the index value ⁇ that is 0 or more and 1 or less and satisfies the first condition, the second condition, and the third condition.
  • the index value calculation unit 110 may obtain ⁇ cand when ⁇ cand is at its maximum value as the absolute value of the inter-channel time difference
  • the index value calculation unit 110 may obtain w expressed by the following equation (5-6) when the inter-channel time difference ITD is greater than 0 or equal to or greater than 0, and obtain w expressed by the following equation (5-7) in cases other than the above, i.e., when the inter-channel time difference ITD is less than or equal to 0, and may define the value expressed by the following equation (5-8) as u, define the value expressed by the above equation (5-2) using bias, range, and u as v, and obtain the value expressed by the above equation (5-3) using the absolute value of the inter-channel time difference
  • the index value calculation unit 110 may obtain the value v expressed by the above formula (5-2) as the index value ⁇ that satisfies the first and third conditions.
  • the mixer 1211 obtains, for each time t, the first-channel encoding target signal x' 1 (t) expressed by the above equation (2-23), and obtains the second-channel encoding target signal x' 2 (t) expressed by the above equation (2-24).
  • the mixer 1211 may take the index value ⁇ calculated by the index value calculation unit 110 for the immediately preceding frame as ⁇ p and the index value ⁇ calculated by the index value calculation unit 110 for the current frame as ⁇ c , set the value obtained by the above equation (2-25) as the index value ⁇ (t) for each time from the first time (i.e., the 1st time) to the T 0 -1th time of the current frame, and set ⁇ c as the index value ⁇ (t) for each time from the T 0th time to the last time (i.e., the Tth time) of the current frame.
  • the mixer 1211 may obtain the first-channel encoding target signal x' 1 (t) represented by the above equation (2-26) instead of the above equation (2-23), or may obtain the second-channel encoding target signal x' 2 (t) represented by the above equation (2-27) instead of the above equation (2-24).
  • the index value calculation unit 110 obtains an index value ⁇ ' that is 0 or more and 1 or less and satisfies two or more of the fourth, fifth, and sixth conditions. Specifically, the index value calculation unit 110 obtains any one of the index value ⁇ ' that is 0 or more and 1 or less and satisfies the fourth and fifth conditions, the index value ⁇ ' that is 0 or more and 1 or less and satisfies the fourth and sixth conditions, the index value ⁇ ' that is 0 or more and 1 or less and satisfies the fifth and sixth conditions, and the index value ⁇ ' that is 0 or more and 1 or less and satisfies the fourth, fifth, and sixth conditions.
  • the mixer 1211 obtains, for each time t, the first-channel encoding target signal x' 1 (t) expressed by the above equation (2-28) and the second-channel encoding target signal x' 2 (t) expressed by the above equation (2-29).
  • the mixer 1211 may obtain, for each frame, the first-channel encoding target signal x' 1 ( t) represented by the above equation (2-31) instead of the above equation (2-28) or the second-channel encoding target signal x' 2 ( t ) represented by the above equation (2-32) instead of the above equation (2-29), using, for each frame, the index value ⁇ ' calculated by the index value calculation unit 110 for the immediately preceding frame as ⁇ ' p and the index value ⁇ ' calculated by the index value calculation unit 110 for the current frame as ⁇ ' c , and using the value obtained by the above equation (2-30) as the index value ⁇ '(t) for each time from the first time (i.e., the 1st time ) to the T 0 -1th time of the current frame, and using ⁇ ' c as the index value ⁇ ' (t) for each time from the T 0th time to the last time (i.e.
  • the downmix signal generating unit 1201 receives a first channel input sound signal and a second channel input sound signal, which are input sound signals of two channels constituting the two-channel stereo input sound signal input to the sound signal processing device 100.
  • the downmix signal generating unit 1201 generates a signal obtained by weighting and adding the first channel input sound signal and the second channel input sound signal so that the input sound signal of the preceding channel out of the first channel input sound signal and the second channel input sound signal is included to a greater extent the greater the correlation between the first channel input sound signal and the second channel input sound signal (step S1201).
  • the downmix signal generating unit 1201 obtains the downmix signal by performing each of the following processes.
  • the downmix signal generating unit 1201 then obtains the maximum value ⁇ of ⁇ cand .
  • ⁇ cand is a positive value when ⁇ cand is the maximum value ⁇
  • the downmix signal generating unit 1201 obtains information indicating that the first channel is leading as the leading channel information
  • ⁇ cand is a negative value when ⁇ cand is the maximum value ⁇
  • the downmix signal generating unit 1201 obtains information indicating that the second channel is leading as the leading channel information.
  • the downmix signal generating unit 1201 may obtain information indicating that none of the channels is leading as the leading channel information, but may also obtain information indicating that the first channel is leading as the leading channel information, or may obtain information indicating that the second channel is leading as the leading channel information.
  • the leading channel information is information that corresponds to whether the sound emitted by the main sound source in a space reaches the first channel microphone placed in that space first, or the second channel microphone placed in that space first.
  • the leading channel information is information that indicates whether the same sound signal is contained first in the first channel input sound signal or the second channel input sound signal. If the same sound signal is contained first in the first channel input sound signal, it is said that the first channel is leading, and if the same sound signal is contained first in the second channel input sound signal, it is said that the second channel is leading.
  • the leading channel information is information that indicates whether the first channel or the second channel is leading.
  • the downmix signal generating unit 1201 then generates a downmix signal that is a weighted addition of the first channel input sound signal and the second channel input sound signal, such that the input sound signal of the preceding channel out of the first channel input sound signal and the second channel input sound signal is included to a greater extent the greater the correlation between the first channel input sound signal and the second channel input sound signal.
  • each part of the above-mentioned system and each device may be realized by a computer, in which case the processing contents of the functions that each device should have are described by a program. Then, by loading this program into the storage unit 2020 of the computer 2000 shown in Fig. 9 and operating the arithmetic processing unit 2010, the input unit 2030, the output unit 2040, etc., various processing functions of the above-mentioned system and each of the above-mentioned devices are realized on the computer.
  • the system and device of the present invention as a single hardware entity, for example, has an input unit capable of inputting signals from outside the hardware entity, an output unit capable of outputting signals to outside the hardware entity, a communication unit to which a communication device (e.g. a communication cable) capable of communicating with outside the hardware entity can be connected, a CPU (which may also have a central processing unit, cache memory, registers, etc.), memories such as RAM and ROM, an external storage device such as a hard disk, and buses connecting the input unit, output unit, communication unit, CPU, RAM, ROM, and external storage device so that data can be exchanged between them.
  • the hardware entity may also be provided with a device (drive) capable of reading and writing recording media such as a CD-ROM.
  • a device drive
  • An example of a physical entity equipped with such hardware resources is a general-purpose computer.
  • the external storage device of the hardware entity stores the programs required to realize the above-mentioned functions and the data required in the processing of these programs (not limited to an external storage device, the programs may be stored in a ROM, which is a read-only storage device, for example). Data obtained by the processing of these programs is stored appropriately in the RAM, the external storage device, etc.
  • the program describing this processing can be recorded on a computer-readable recording medium.
  • a computer-readable recording medium is, for example, a non-transitory recording medium, specifically, a magnetic recording device, an optical disk, etc.
  • the server computer may not transfer the program to this computer, but may instead execute the above-mentioned processing using a so-called ASP (Application Service Provider) type service that realizes processing functions only by issuing execution instructions and obtaining results.
  • ASP Application Service Provider
  • the program includes information used for processing by an electronic computer that is equivalent to a program (such as data that is not a direct command to a computer but has properties that dictate computer processing).
  • system and device are configured by executing a specific program on a computer, but at least a portion of the processing content may be realized by hardware.

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JPH1132399A (ja) * 1997-05-13 1999-02-02 Sony Corp 符号化方法及び装置、並びに記録媒体
WO2006080358A1 (ja) * 2005-01-26 2006-08-03 Matsushita Electric Industrial Co., Ltd. 音声符号化装置および音声符号化方法
JP2013033189A (ja) * 2011-07-01 2013-02-14 Sony Corp オーディオ符号化装置、オーディオ符号化方法、およびプログラム
JP2018533056A (ja) * 2015-09-25 2018-11-08 ヴォイスエイジ・コーポレーション ステレオ音声信号をプライマリチャンネルおよびセカンダリチャンネルに時間領域ダウンミックスするために左チャンネルと右チャンネルとの間の長期相関差を使用する方法およびシステム
WO2021181746A1 (ja) * 2020-03-09 2021-09-16 日本電信電話株式会社 音信号ダウンミックス方法、音信号符号化方法、音信号ダウンミックス装置、音信号符号化装置、プログラム及び記録媒体

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH1132399A (ja) * 1997-05-13 1999-02-02 Sony Corp 符号化方法及び装置、並びに記録媒体
WO2006080358A1 (ja) * 2005-01-26 2006-08-03 Matsushita Electric Industrial Co., Ltd. 音声符号化装置および音声符号化方法
JP2013033189A (ja) * 2011-07-01 2013-02-14 Sony Corp オーディオ符号化装置、オーディオ符号化方法、およびプログラム
JP2018533056A (ja) * 2015-09-25 2018-11-08 ヴォイスエイジ・コーポレーション ステレオ音声信号をプライマリチャンネルおよびセカンダリチャンネルに時間領域ダウンミックスするために左チャンネルと右チャンネルとの間の長期相関差を使用する方法およびシステム
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