Method and apparatus of postfiltering using a first spectrum parameter of an encoded sound signal and a second spectrum parameter of a lesser degree than the first spectrum parameter

• US 5,774,835 A
• Filed: 08/21/1995
• Issued: 06/30/1998
• Est. Priority Date: 08/22/1994
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Ozawa, Kazunori
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): ABEBE, DANIEL DEMELASH
• Application Number:
  US08/517,357
• Time in Patent Office: 1,044 Days
• Field of Search: 395/2.12, 395/2.25, 395/2.26, 395/2.28, 395/2.35, 395/2.37, 395/2.38, 395/2.71, 395/2.78, 704/205, 704/219, 704/220
• US Class Current: 704/205
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 25/06 the extracted parameters being correlation coefficients
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band

Abstract

A second spectrum parameter of which degree is lower than that of a first spectrum parameter is calculated based on the first spectrum parameter that is output from an encoder. A spectrum postfilter generates a transfer function having a denominator and a numerator wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, and filters the reduced signal with this transfer function. In addition, it adaptively generates a compensation coefficient based on the first and second parameters. A compensation filter generates a transfer function based the compensation coefficient and filters an output of the spectrum postfilter with this transfer function.

Claims

1. A postfilter for reproducing a sound signal that has been encoded with an encoder, by using a decoder and compensating a reproduced signal that was output from said decoder, said postfilter comprising:

first calculating means for calculating a second spectrum parameter based on a first spectrum parameter supplied from said encoder, said first spectrum parameter being related to said sound signal encoded by said encoder, wherein the degree of said second spectrum parameter is lower than that of said first spectrum parameter;

a spectrum postfilter for generating a first transfer function having a denominator and a numerator, wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, said spectrum postfilter receiving said reproduced signal output from said decoder and filtering said reproduced signal based on said first transfer function;

second calculating means for adaptively calculating a compensation coefficient based on said first spectrum parameter and said second spectrum parameter; and

a compensation filter for generating a second transfer function based on said compensation coefficient and filtering an output of said spectrum postfilter based on said second transfer function,

wherein an output of said compensation filter that corresponds to a filtered reproduced signal is a reproduction of said sound signal.

2. The postfilter of claim 1, further comprising:

said first calculating means for inputting a first linear predictive coefficient as said first spectrum parameter and calculating a second linear predictive coefficient of which degree is lower that that of said first linear predictive coefficient; and

said second calculating means for calculating said compensation coefficient based on said first linear predictive coefficient and said second linear predictive coefficient.

3. The postfilter of claim 1, comprising said spectrum postfilter for generating a transfer function of autoregressive moving average type.

4. The postfilter of claim 1, wherein said first calculating means further comprises:

means for converting said first spectrum parameter to preset k parameters;

means for extracting an arbitrary k parameter from among said k parameters; and

means for converting said extracted k parameter to a second spectrum parameter.

5. The postfilter of claim 1, wherein said second calculating means further comprises:

means for calculating an impulse response of said spectrum postfilter based on said first spectrum parameter and said second spectrum parameter;

means for calculating a preset autocorrelation function based on said calculated impulse response; and

means for calculating said compensation coefficient based on said calculated autocorrelation function.

6. The postfilter of claim 1, further comprising spectrum parameter calculating means for calculating a spectrum parameter in accordance with said reproduced signal, wherein said first calculating means comprising means for inputting said calculated spectrum parameter, instead of said first spectrum parameter, and calculating a spectrum parameter of which degree is lower than that of said calculated spectrum parameter.

17. The postfilter of claim 1, wherein the reproduced signal output by said decoder is based on reception of a signal that corresponds to said sound signal encoded by said encoder.

7. A postfilter for reproducing a sound signal that has been encoded with an encoder, by using a decoder and compensating a reproduced signal that was output from said decoder, said postfilter comprising:

means for converting a first linear predictive coefficient supplied from said encoder to preset k parameters, said first linear predictive coefficient being related to said sound signal encoded by said encoder;

means for extracting an arbitrary k parameter from among said k parameters;

means for converting said extracted k parameter to a second linear predictive coefficient, wherein the degree of said second linear predictive coefficient is lower than that of said first linear predictive coefficient;

a spectrum postfilter for generating a first transfer function of autoregressive moving average type having a denominator and a numerator, wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, said spectrum postfilter receiving said reproduced signal output from said decoder and filtering said reproduced signal based on said first transfer function;

means for calculating an impulse response of said spectrum postfilter based on said first linear predictive coefficient and said second linear predictive coefficient;

means for calculating a preset autocorrelation function based on said calculated impulse response;

means for calculating said compensation coefficient based on said calculated autocorrelation function; and

a compensation filter for generating a second transfer function based on said compensation coefficient and filtering an output of said spectrum postfilter based on said second transfer function,

wherein an output of said compensation filter that corresponds to a filtered reproduced signal is a reproduction of said sound signal.

18. The postfilter of claim 7, wherein the reproduced signal output by said decoder is based on reception of a signal that corresponds to said sound signal encoded by said encoder.

8. A postfilter for reproducing a sound signal that has been encoded with an encoder, by using a decoder and compensating a reproduced signal that was output from said decoder, said postfilter comprising:

means for calculating a first linear predictive coefficient in accordance with said reproduced signal received from said decoder;

means for converting a first linear predictive coefficient to preset k parameters;

means for extracting an arbitrary k parameter from among said k parameters;

means for converting said extracted k parameter to a second linear predictive coefficient, wherein the degree of said second linear predictive coefficient is lower than that of said first linear predictive coefficient;

a spectrum postfilter for generating a first transfer function of autoregressive moving average type having a denominator and a numerator, wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, said spectrum postfilter receiving said reproduced signal output from said decoder and filtering said reproduced signal based on said first transfer function;

means for calculating an impulse response of said spectrum postfilter based on said first linear predictive coefficient and said second linear predictive coefficient;

means for calculating a preset autocorrelation function based on said calculated impulse response;

means for calculating said compensation coefficient based on said calculated autocorrelation function; and

a compensation filter for generating a second transfer function based on said compensation coefficient and filtering an output of said spectrum postfilter based on said second transfer function,

wherein an output of said compensation filter that corresponds to a filtered reproduced signal is a reproduction of said sound signal.

19. The postfilter of claim 8, wherein the reproduced signal output by said decoder is based on reception of a signal that corresponds to said sound signal encoded by said encoder.

9. A method of postfiltering for reproducing a sound signal that has been encoded with an encoder, by using a decoder and postfiltering a reproduced signal that was output from said decoder, said method of postfiltering comprising the steps of:

sampling a preset sampling number of first spectrum parameter output from said encoder, said first spectrum parameter being related to said sound signal;

sampling a preset sampling number of said reproduced signal;

calculating a second spectrum parameter of which degree is lower than that of said sampled first spectrum parameter;

first filtering for generating a first transfer function having a denominator and a numerator, wherein said first spectrum parameter is included in said denominator and said second spectrum parameter is included in said numerator, and filtering said sampled reproduced signal output from said decoder based on said first transfer function;

adaptively calculating a compensation coefficient based on said sampled first spectrum parameter and said second spectrum parameter; and

second filtering for generating a second transfer function based on said compensation coefficient and filtering a signal filtered in said first filtering step based on said second transfer function to obtain a re-filtered signal,

wherein said re-filtered signal corresponds to a reproduction of said sound signal.

10. The method of postfiltering of claim 9, wherein said first spectrum parameter and said second spectrum parameter are linear predictive coefficients.

11. The method of postfiltering of claim 9, wherein said first transfer function is of an autoregressive moving average type.

12. The method of postfiltering of claim 9, wherein said second transfer function is of an autoregressive moving average type.

13. The method of postfiltering of claim 9, wherein said step of calculating said second spectrum parameter further comprises the steps of:

converting said first spectrum parameter to preset k parameters;

extracting an arbitrary k parameter from among said k parameters; and

converting said extracted k parameter to a second spectrum parameter.

14. The method of postfiltering of claim 9, wherein said step of calculating said compensation coefficient comprises the steps of:

calculating an impulse response of said spectrum postfilter based on said first spectrum parameter and said second spectrum parameter;

calculating a preset autocorrelation function based on said calculated impulse response; and

calculating said compensation coefficient based on said calculated autocorrelation function.

15. The method of postfiltering of claim 14, wherein said step of calculating said compensation coefficient is a step of calculating a compensation coefficient from zero degree autocorrelation and one degree autocorrelation.

16. The method of postfiltering of claim 9, comprising a step of calculating said first spectrum parameter from said reproduced signal instead of said step of sampling said first spectrum parameter from said encoder.

20. The method of postfiltering of claim 9, wherein the reproduced signal output by said decoder is based on reception of a signal that corresponds to said sound signal encoded by said encoder.