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Audio signal compression and decoding using band division and polynomial approximation

外国特許コード F110003342
整理番号 A221-19WO
掲載日 2011年6月23日
出願国 アメリカ合衆国
出願番号 99725209
公報番号 20110106547
公報番号 8666733
出願日 平成21年6月3日(2009.6.3)
公報発行日 平成23年5月5日(2011.5.5)
公報発行日 平成26年3月4日(2014.3.4)
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
  • 特願2008-167143 (2008.6.26) JP
  • 特願2008-167144 (2008.6.26) JP
  • 特願2008-167145 (2008.6.26) JP
  • 2009JP060110 (2009.6.3) WO
発明の名称 (英語) Audio signal compression and decoding using band division and polynomial approximation
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 adapted to divide a digital audio signal into a plurality of frequency bands;
a function approximation means 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, wherein n is an integral number equal to or more than 2; and
an encoding means adapted to encode parameters which are coefficient values of the n-degree polynomial having been function-approximated by the function approximation means,
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.
[claim2]
2. The audio signal compression device according to claim 1, wherein the sampling function used in the function approximation means 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.
[claim3]
3. The audio signal compression device according to claim 1, wherein the band dividing means includes:
a first band separation filter adapted to separate a low register signal, which is a first frequency band, from the inputted digital audio signal;
a third band separation filter adapted to separate a high register signal, which is a third frequency band, from the inputted digital audio signal;
an addition means 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 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.
[claim4]
4. The audio signal compression device according claim 1, wherein the band dividing means includes:
a first band separation filter adapted to separate the signal of a first frequency band of the inputted digital audio signal;
a first subtraction means 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 adapted to separate the signal of a second frequency band from the output of the first subtraction means; and
a second subtraction means 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.
[claim5]
5. The audio signal compression device according to claim 1, wherein the band dividing means includes:
a first band separation filter adapted to separate the signal of a first frequency band from the inputted digital audio signal;
a second band separation filter adapted to separate the signal of a second frequency band from the inputted digital audio signal;
an addition means 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 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.
[claim6]
6. The audio signal compression device according to claim 1, 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 a unit of the scale frequency.
[claim7]
7. The audio signal compression device according to claim 6, 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.
[claim8]
8. The audio signal compression device according to claim 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.about.11, times of the lowest band frequency of a predetermined one octave scale.
[claim9]
9. The audio signal compression device according to claim 6, 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, wherein n is 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.
[claim10]
10. An audio signal compression device comprising: a band dividing means adapted to divide a digital audio signal into a plurality of frequency bands;
a function approximation means 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, wherein n is an integral number equal to or more than 2;
an encoding means adapted to encode parameters which are coefficient values of the n-degree polynomial having been function-approximated by the function approximation means; and
a down-sampling means adapted to thin out a sampling period of the digital audio signal divided into each band by the band dividing means,
wherein the function approximation means function-approximates the digital audio signal whose sampling period has been thinned out by the down-sampling means.
[claim11]
11. An audio signal compression device comprising: a band dividing means adapted to divide a digital audio signal into a plurality of frequency bands;
a function approximation means 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, wherein n is an integral number equal to or more than 2; and
an encoding means adapted to encode parameters which are coefficient values of the n-degree polynomial having been function-approximated by the function approximation means,
wherein, the band dividing means has an i-th, wherein i=1.about.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 is separated and outputted from the subtracted output of an n-th subtraction means.
[claim12]
12. An audio signal compression method comprising the step 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, wherein n is an integral number equal to or more than 2;
encoding parameters of the function having been function-approximated for each band; and
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.
[claim13]
13. An audio signal compression method according to claim 12, 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 of separating the signal of a first frequency band of the inputted digital audio signal;
a first subtraction process step 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 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 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.
[claim14]
14. An audio signal compression method according to claim 12, 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 of separating the signal of a first frequency band of the inputted digital audio signal;
a second band-separating process step of separating the signal of a second frequency band of the inputted digital audio signal;
an addition process step 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 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.
[claim15]
15. 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, wherein n is an integral number equal to or more than 2; and
encoding parameters of the function having been function-approximated for each band,
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 of separating the signal of a first frequency band from the inputted digital audio signal;
a first subtraction process step 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 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 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.
[claim16]
16. 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, wherein n is an integral number equal to or more than 2; and
encoding parameters of the function having been function-approximated for each band,
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 of separating a low register signal, which is a first frequency band, from the inputted digital audio signal;
a second band-separating process step of separating a high register signal, which is a third frequency band, from the inputted digital audio signal;
a addition process step 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 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.
  • 発明者/出願人(英語)
  • TORAICHI KAZUO
  • NAKAMURA MITSUTERU
  • MOROOKA YASUO
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
国際特許分類(IPC)
米国特許分類/主・副
  • 704/206
  • 704/201
  • 704/205
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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