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Audio signal compression device, audio signal compression method, audio signal decoding device, and audio signal decoding method

外国特許コード F110003620
整理番号 A221-19WO
掲載日 2011年6月30日
出願国 欧州特許庁(EPO)
出願番号 09769990
公報番号 2306453
公報番号 2306453
出願日 平成21年6月3日(2009.6.3)
公報発行日 平成23年4月6日(2011.4.6)
公報発行日 平成27年10月7日(2015.10.7)
国際出願番号 JP2009060110
国際公開番号 WO2009157280
国際出願日 平成21年6月3日(2009.6.3)
国際公開日 平成21年12月30日(2009.12.30)
優先権データ
  • 2009JP060110 (2009.6.3) WO
  • 特願2008-167143 (2008.6.26) JP
  • 特願2008-167144 (2008.6.26) JP
  • 特願2008-167145 (2008.6.26) JP
発明の名称 (英語) Audio signal compression device, audio signal compression method, audio signal decoding device, and audio signal decoding method
発明の概要(英語) When encoding an audio signal, it is possible to efficiently encode the audio signal while maintaining high register signal components, and prevent deterioration of sound quality of decoded signal.
A digital audio signal is divided into a plurality of frequency bands.
The digital audio signal having been divided into each band is function-approximated for each divided band.
Further, parameters of function having been function-approximated are encoded.
When performing decoding process, parameters of the function of each band are used to perform function interpolation, synthesize the function-interpolated signal of each band interpolated, and decode the signal.
Thus, when function-approximating each band, by suitably setting the function equation, it is possible to perform an encoding process while maintaining the high register components and perform a compression-coding process which enables reproduction with very good sound quality.
特許請求の範囲(英語) [claim1]
1. An audio signal compression device comprising: a band dividing means (10) adapted to divide a digital audio signal into a plurality of frequency bands; a function approximation means (20) prepared for each divided band and adapted to function-approximate a predetermined interval of the digital audio signal, which has been divided into each band by the band dividing means, using an n-degree polynomial, n being an integral number equal to or more than 2; and an encoding means (3) adapted to encode parameters which are coefficient values of the n-degree polynomial having been function-approximated by the function approximation means.
[claim2]
2. The audio signal compression device according to claim 1, wherein the predetermined interval is either an interval between a maximum value and a minimum value of the smallest frequency band among the plurality of frequency bands, or an interval between the maximum value, or the minimum value, and an inflection point of the smallest frequency band; and/or
wherein the n-degree polynomial is expressed by a linear combination expression of sampling functions classified by number of times at which the function is differentiable.
[claim3]
3. The audio signal compression device according to claim 2, wherein the sampling function used in the function approximation means (20) is a function including a fundamental term and a control term expressed separately from each other, and the characteristic of the sampling function is changed by setting a coefficient value of the control term.
[claim4]
4. The audio signal compression device according to any one of claims 1 to 3, further comprising: a down-sampling means (12) adapted to thin out a sampling period of the digital audio signal divided into each band by the band dividing means (10), wherein the function approximation means function-approximates the digital audio signal whose sampling period has been thinned out by the down-sampling means(12).
[claim5]
5. The audio signal compression device according to any one of claims 1 to 4,
wherein, the band dividing means (10) has an i-th, i=1~n, subtraction means adapted to subtract the output signal of an i-th band separation filter from the inputted digital audio signal, the i-th separation filter being adapted to separate the signal of an i-th frequency band, and
wherein the subtracted output of the i-th subtraction means is used as input signal of an (i+1)-th band separation filter to separate and output the signal of an (i+1)-th frequency band, and the signal of an n-th frequency band, i.e., the final frequency band, is separated and outputted from the subtracted output of an n-th subtraction means; or
wherein the band dividing means (10) includes: a first band separation filter (11a) adapted to separate a low register signal, which is a first frequency band, from the inputted digital audio signal; a third band separation filter (11c) adapted to separate a high register signal, which is a third frequency band, from the inputted digital audio signal; an addition means (14a) adapted to sum the low register signal of the first frequency band separated by the first band separation filter and the high register signal of the third frequency band separated by the third band separation filter; and a subtraction means (14b) adapted to subtract the summed signal of the low register signal of the first frequency band and the high register signal of the third frequency band summed by the addition means from the inputted digital audio signal, and wherein a mid register signal, which is a second frequency band, is separated from the subtracted output of the subtraction means; or wherein the band dividing means includes: a first band separation filter (11a) adapted to separate the signal of a first frequency band of the inputted digital audio signal; a first subtraction means (15a) adapted to subtract a signal obtained by function-approximating, with the function approximation means, the signal of the first frequency band separated by the first band separation filter and then function-interpolating the function-approximated signal from the inputted digital audio signal; a second band separation filter (11b) adapted to separate the signal of a second frequency band from the output of the first subtraction means; and a second subtraction means (15b) adapted to subtract a signal obtained by function-approximating, with the function approximation means, the signal of the second frequency band separated by the second band separation filter and then function-interpolating the function-approximated signal from the output signal of the first subtraction means, and wherein the signal of a third frequency band is separated from the output of the second subtraction means; or wherein the band dividing means includes a first band separation filter (11a) adapted to separate the signal of a first frequency band from the inputted digital audio signal; a second band separation filter (11b) adapted to separate the signal of a second frequency band from the inputted digital audio signal; an addition means (16) adapted to sum a first signal and a second signal, wherein the first signal is obtained by function-approximating the signal of the first frequency band separated by the first band separation filter and then function-interpolating the function-approximated signal, and the second signal is obtained by function-approximating the signal of the second frequency band separated by the second band separation filter and then function-interpolating the function-approximated signal; and a subtraction means (18) adapted to subtract the output of the addition means from the inputted digital audio signal, and wherein the signal of a third frequency band is separated from the output of the subtraction means; and/or wherein the band dividing means includes: a plurality of octave separation filters adapted to separate the digital audio signal into each octave frequency band; and scale-component separation filters adapted to separate the digital audio signal of each one octave band separated by the plurality of octave separation filters into twelve scales compliant bands corresponding to twelve scales, wherein the digital audio signal is separated in unit of the scale frequency.
[claim6]
6. The audio signal compression device according to claim 5, wherein the octave separation filter is a bandpass filter whose center frequency is the center scale frequency of a predetermined one octave scale and whose bandwidth is between a lowest band frequency and a highest band frequency, wherein the lowest band frequency is 1/2Root 2 times of the center scale frequency and the highest band frequency is 2Root 2 times of the center scale frequency.
[claim7]
7. The audio signal compression device according to claim 5 or 6, wherein the scale-component separation filters each separate the digital audio signal outputted from one octave separation filter into (k/12)-th power of 2, wherein k=0~11, times of the lowest band frequency of a predetermined one octave scale.
[claim8]
8. The audio signal compression device according to any one of claims 5 to 7, further comprising: a plurality of function approximation means adapted to input the signals in unit of the scale frequency separated by the scale-component separation filters, collect the same scale of the twelve scales compliant bands from a plurality of octaves separated by the octave separation filters to obtain a collection of a band corresponding to the same scale, and function-approximate the collection of the band corresponding to the same scale by an n-degree polynomial, n being an integral number equal to or more than 2; and a compression-coding means adapted to compression-code the signals from the plurality of function approximation means.
[claim9]
9. An audio signal compression method comprising the steps of: dividing an inputted digital audio signal into a plurality of frequency bands with band separation filters; function-approximating an arbitrary interval of the digital audio signal, which has been divided into the plurality of frequency bands, for each divided band using an n-degree polynomial, n being an integral number equal to or more than 2;and encoding parameters of the function having been function-approximated for each band.
[claim10]
10. An audio signal compression method according to claim 9, further comprising the step of: performing a down-sampling process to thin out a sampling period of the digital audio signal divided into each band, wherein the function approximation is performed on the digital audio signal whose sampling period has been thinned out by the down-sampling process.
[claim11]
11. An audio signal compression method according to claim 9 or 10, wherein the step of dividing the inputted digital audio signal into the plurality of frequency bands with the band separation filters comprises: a first band-separating process step (11a) of separating the signal of a first frequency band from the inputted digital audio signal; a first subtraction process step (13a) of subtracting the digital audio signal of the first frequency band separated by the first band-separating process from the inputted digital audio signal; a second band-separating process step (11b) of separating the signal of a second frequency band from the signal obtained by performing the first subtraction process; and a second subtraction process step (13b) of subtracting the digital audio signal of the second frequency band separated by the second band-separating process from the inputted digital audio signal, wherein the digital audio signal of a third frequency band, which is different from the first and second frequency bands, is band-separated by performing the second subtraction process; or wherein the step of dividing the inputted digital audio signal into the plurality of frequency bands with the band separation filters comprises: a first band-separating process step (11a) of separating a low register signal, which is a first frequency band, from the inputted digital audio signal; a third band-separating process (11c) step of separating a high register signal, which is a third frequency band, from the inputted digital audio signal; an addition process step (14a) of summing the low register signal, which is the first frequency band, separated by the first band-separating process and the high register signal, which is the third frequency band, separated by the second band-separating process; and a subtraction process step (14b) of subtracting the summed signal of the low register signal of the first frequency band and the high register signal of the third frequency band from the inputted digital audio signal, wherein a mid register signal, which is a second frequency band of the inputted digital audio signal, is separated by the subtraction process; orwherein the step of dividing the inputted digital audio signal into the plurality of frequency bands with the band separation filters comprises: a first band-separating process step (11a) of separating the signal of a first frequency band of the inputted digital audio signal; a first subtraction process step (15a) of subtracting a signal, which is obtained by function-approximating, with the function approximation means, the signal of the first frequency band separated by the first band-separating process and then function-interpolating the function-approximated signal, from the inputted digital audio signal; a second band-separating process step (11b) of separating the signal of a second frequency band from the output obtained by performing the first subtraction process; and a second subtraction process step (15b) of subtracting a signal, which is obtained by function-approximating the signal of the second frequency band separated by the second band-separating process and then function-interpolating the function-approximated signal, from the signal obtained by performing the first subtraction process, wherein the signal of a third frequency band, which is different from the first and second frequency bands, is separated by performing the second subtraction process; orwherein the step of dividing the inputted digital audio signal into the plurality of frequency bands with the band separation filters comprises: a first band-separating process step (11a) of separating the signal of a first frequency band of the inputted digital audio signal; a second band-separating process step (11b) of separating the signal of a second frequency band of the inputted digital audio signal; an addition process step (16) of summing a first signal and a second signal, wherein the first signal is obtained by function-approximating the signal of the first frequency band separated by the first band-separating process and then function-interpolating the function-approximated signal, and the second signal is obtained by function-approximating the signal of the second frequency band separated by the second band-separating process and then function-interpolating the function-approximated signal; and a subtraction process step (18) of subtracting the output signal summed by the addition process from the inputted digital audio signal, wherein the signal of a third frequency band, which is different from the first and second frequency bands, is separated by performing the subtraction process.
[claim12]
12. An audio signal decoding device comprising: a decoding means (52) adapted to decode parameters of a function of each of a plurality of divided bands of a digital audio signal, wherein the parameters of the function correspond to a compressed digital audio signal which is obtained by: function-approximating a predetermined interval of the digital audio signal divided into the plurality of frequency bands by using an n-degree polynomial, n being an integral number equal to or more than 2, and then encoding and compressing parameters which represent the coefficient values of the n-degree polynomial; a function interpolation means (54) adapted to function-interpolate the compressed digital audio signal based on the parameters of the function of each of the divided bands decoded by the decoding means, and reconstruct sampling values of each of the divided bands; and a band-synthesizing means (60) adapted to band-synthesize the sampling values reconstructed by the function interpolation means.
[claim13]
13. The audio signal decoding device according to claim 12, wherein the decoding means is further adapted to decode an audio signal compression-coded for each collection of twelve scales compliant bands obtained by collecting, from a plurality of octaves, each twelve scales compliant band of one octave, wherein the function interpolation means (54) is further adapted to perform function interpolation for each collection of the twelve scales compliant bands decoded by the decoding means; and
wherein the band synthesizing means (60) is further adapted to synthesize the collections of twelve scales compliant bands from the function interpolation means and collect digital audio signal for each octave.
[claim14]
14. An audio signal decoding method comprising the steps of: decoding parameters of a function of each of a plurality of divided bands of a digital audio signal, wherein the parameters of the function correspond to a compressed digital audio signal which is obtained by: function-approximating a predetermined interval of the digital audio signal divided into the plurality of frequency bands by using an n-degree polynomial, n being an integral number equal to or more than 2, and then encoding and compressing parameters which represent the coefficient values of the n-degree polynomial; function-interpolating the compressed digital audio signal based on the decoded parameters of the function of each of the divided bands, and reconstructing sampling values of each of the divided bands; and band-synthesizing the sampling values reconstructed by the function interpolation.
[claim15]
15. The audio signal decoding method according to claim 14, wherein an audio signal compression-coded for each collection of twelve scales compliant bands obtained by collecting, from a plurality of octaves, each twelve scales compliant band of one octave is decoded in the decoding step,
wherein function interpolation for each collection of the twelve scales compliant bands decoded by the decoding step is performed in the function interpolation step;
wherein the collection of twelve scales compliant bands obtained by the function interpolation is synthesized and outputs divided into a plurality of pieces for each band of octave are synthesized and a digital audio signal for each octave is collected in the band synthesizing step.
  • 出願人(英語)
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • 発明者(英語)
  • TORAICHI KAZUO
  • NAKAMURA MITSUTERU
  • MOROOKA YASUO
国際特許分類(IPC)
欧州特許分類/主・副
  • G10L019/02S1
指定国 Contracting States: AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO SE SI SK TR
参考情報 (研究プロジェクト等) CREST New High-Performance Information Processing Technology Supporting Information-Oriented Society - Aiming at the Creation of New High-Speed, Large-Capacity Computing Technology Based on Quantum Effects, Molecular Functions, Parallel Processing, etc.- AREA
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