Gain control method and gain control apparatus for digital audio signals

• US 5,901,234 A
• Filed: 02/07/1996
• Issued: 05/04/1999
• Est. Priority Date: 02/14/1995
• Status: Expired due to Term

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Sonohara, Mito, Tsutsui, Kyoya
• Primary Examiner(s): Kuntz, Curtis A.
• Assistant Examiner(s): NGUYEN, DUC MINH
• Application Number:
  US08/597,829
• Time in Patent Office: 1,182 Days
• Field of Search: 395/2.13, 395/2.34-2.36, 395/2.38, 395/2.39, 395/2.67, 381/104, 381/106, 381/107, 704/204, 704/225, 704/227-230, 704/258
• US Class Current: 381/104
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: H03G 7/007 of digital or coded signals
• CPC Class Codes: H03G 9/005 of digital or coded signals
• CPC Class Codes: H03G 9/025 frequency-dependent volume compression or expansion, e.g. multiple-band systems H03G9/10, H03G9/18 take precedence

Abstract

A signal encoding method and apparatus for encoding an acoustic signal, a recording medium having the encoded signals, a method for transmitting the encoded signals, and a signal decoding apparatus for decoding the encoded signals, are disclosed. With the encoding apparatus, an attack portion detection circuit detects an attack portion of the waveform acoustic signal where the waveform elements of the waveform acoustic signal rise sharply. A gain control circuit controls the gain for waveform elements at least upstream of the attack portion using a gain control amount adaptively selected from plural gain control amounts specified by a pre-set power of 2. A forward orthogonal transform circuit transforms the waveform acoustic signal into plural spectral components. A normalization and encoding circuit normalizes, quantizes and encodes the gain control information an plural spectral components. With the encoding apparatus, the encoding efficiency may be improved without complicating the construction, while the pre-echo may be suppressed effectively.

Claims

1. An encoding method for encoding an acoustic signal, comprising the steps of:

detecting an attack portion where waveform elements of acoustic signals are acutely increased in level;

gain controlling the waveform elements upstream of said attack portion using a gain control amount adaptively selected responsive to characteristics of the acoustic signals from among plural gain control amounts represented by pre-set non-negative powers of 2;

transforming said acoustic signals into plural frequency components; and

encoding the control information for gain control and plural frequency components.

2. The encoding method as claimed in claim 1, wherein said gain control is performed by bit-shifting digital data corresponding to waveform elements of the acoustic signals towards left in an amount corresponding to the number of the power of 2.

3. The encoding method as claimed in claim 1, wherein a gain control amount smoothly changed between the gain control amount prior to change of the gain control amount and the gain control amount following such change is set in the vicinity of the point of such change of the gain control amount.

4. The encoding method as claimed in claim 1, wherein the acoustic signal is subdivided into plural small-sized domains each consisting of plural waveform elements and wherein said attack position is detected if the level variation of the waveform elements exceeds a pre-set limit value between two small-sized domains.

5. The encoding method as claimed in claim 1, wherein the control information for gain control at least includes the information specifying whether or not the attack portion has been detected, the information specifying the gain control amount for waveform elements upstream of the attack portion on detection of the attack portion, and the information specifying the position of the attack portion.

6. The encoding method as claimed in claim 1, wherein the processing of transforming the acoustic signal into plural frequency components comprises the steps of:

blocking the acoustic signal every plural waveform elements; and

orthogonally transforming the block-based waveform elements.

7. The encoding method as claimed in claim 1, wherein the characteristics of the acoustic signals in selecting the gain control amount are the degree of change in the acoustic signal based upon the level of the waveform elements upstream of the attack portion and the level of the waveform elements of the attack portion.

8. An encoding apparatus for encoding an acoustic signal, comprising:

means for detecting an attack portion where waveform elements of acoustic signals are acutely increased in level;

means for gain controlling the waveform elements upstream of said attack portion using a gain control amount adaptively selected responsive to characteristics of the acoustic signals from among plural gain control amounts represented by pre-set non-negative powers of 2;

means for transforming said acoustic signals into plural frequency components; and

means for encoding control information for gain control and the plural frequency components.

9. The encoding apparatus as claimed in claim 8, wherein said gain control is performed by bit-shifting digital data corresponding to waveform elements of the acoustic signals towards left in an amount corresponding to the number of the power of 2.

10. The encoding apparatus as claimed in claim 8, wherein a gain control amount smoothly changed between the gain control amount prior to change of the gain control amount and the gain control amount following such change is set in the vicinity of the point of such change of the gain control amount.

11. The encoding apparatus as claimed in claim 8, wherein the acoustic signal is subdivided into plural small-sized domains each consisting of plural waveform elements and wherein said attack position is detected if the level variation of the waveform elements exceeds a pre-set limit value between two small-sized domains.

12. The encoding apparatus as claimed in claim 8, wherein the control information for gain control at least includes the information specifying whether or not the attack portion has been detected, the information specifying the gain control amount for waveform elements upstream of the attack portion on detection of the attack portion, and the information specifying the position of the attack portion.

13. The encoding apparatus as claimed in claim 8, wherein the means for transforming the acoustic signal into plural frequency components blocks the acoustic signal every plural waveform elements and orthogonally transforms the block-based waveform elements.

14. The encoding apparatus as claimed in claim 8, wherein the characteristics of the acoustic signals in selecting the gain control amount are the degree of change in the acoustic signal based upon the level of the waveform elements upstream of the attack portion and the level of the waveform elements of the attack portion.

15. A decoding apparatus for decoding an encoded signal, said encoded signal being at least an encoded version of plural frequency components transformed from the acoustic signal and an encoded version of the control correction information for gain control correction for waveform elements upstream of the attack portion where the waveform elements of the acoustic signal rise acutely in signal level, comprising:

decoding means for decoding said encoded signals for producing plural frequency components and the control correction information;

transforming means for transforming the frequency components into an acoustic signal consisting of plural waveform elements;

gain control correction means for correcting the gain control of the waveform elements upstream of the attack portion, using a gain control correction amount selected based upon said control correction information from plural gain control amounts specified by pre-set negative powers of 2; and

means for restoring the acoustic signal from said waveform elements.

16. The decoding apparatus as claimed in claim 15, wherein said gain control correction is performed by bit-shifting digital data corresponding to waveform elements of the acoustic signal towards right in an amount corresponding to the number of the power of 2.

17. The decoding apparatus as claimed in claim 15, wherein, in the vicinity of the change point of said gain control correction amount, a gain control correction amount smoothly changed between the gain control correction amount prior to change and the gain control correction amount subsequent to change are selected from among plural sorts of smoothly changing gain control amounts previously set and held in a table.

18. The decoding apparatus as claimed in claim 15, wherein the control correction information for gain control correction at least includes the information specifying whether or not there is the attack portion, the information specifying the gain control correction amount for waveform elements upstream of the attack portion, if such attack portion exists, and the information specifying the position of the attack portion.

19. The decoding apparatus as claimed in claim 15, wherein the operation of transforming the frequency components into the acoustic signal consisting of plural waveform elements is a processing of inversely orthogonally transforming the frequency components for each block consisting of plural frequency components.

20. An information recording medium having recorded thereon encoded information obtained by encoding plural frequency components, said frequency components being obtained by transforming an acoustic signal, wherein waveform elements upstream of an attack portion of the acoustic signal, where at least the waveform elements of the acoustic signal rise sharply in level, are gain controlled using an adaptively selected gain control amount selected from among plural gain control amounts represented by pre-set non-negative powers of 2, with the control information for the above gain control being recorded along with the frequency components.

21. The information recording medium as claimed in claim 20, wherein said gain control is performed by bit-shifting digital data corresponding to waveform elements of the acoustic signals towards left in an amount corresponding to the number of the power of 2.

22. The information recording medium as claimed in claim 20, wherein the gain control for said acoustic signals in the vicinity of the change point of said gain control amount is smoothly changed between the gain control amount before change and the gain control amount after change.

23. The information recording medium as claimed in claim 20, wherein the control information for gain control at least includes the information specifying whether or not the attack portion has been detected, the information specifying the gain control amount for waveform elements upstream of the attack portion on detection of the attack portion, and the information specifying the attack portion.

24. The information recording medium as claimed in claim 20, wherein the processing of transforming the acoustic signal into plural frequency components is the processing of blocking the acoustic signal every plural waveform elements and orthogonally transforming the block-based waveform elements.

25. The information recording medium as claimed in claim 20, wherein the characteristics of the acoustic signals in selecting the gain control amount are the degree of change in the acoustic signal based upon the level of the waveform elements upstream of the attack portion and the level of the waveform elements of the attack portion.

26. A method for transmitting information, comprising the steps of:

transforming an acoustic signal, in which waveform elements upstream of an attack portion thereof, where at least the elements of the acoustic signal rise sharply in level, are gain controlled using an adaptively selected gain control amount selected from among plural gain control amounts represented by pre-set non-negative powers of 2, into plural frequency components;

encoding and transmitting said frequency components; and

encoding and transmitting the control information for the above gain control.

27. The method as claimed in claim 26, wherein said gain control is performed by bit-shifting digital data corresponding to waveform elements of the acoustic signals towards left in an amount corresponding to the number of the power of 2.

28. The method as claimed in claim 26, wherein a gain control amount smoothly changed between the gain control amount prior to change of the gain control amount and the gain control amount following such change in the vicinity of the point of such change of the gain control amount.

29. The method as claimed in claim 26, wherein the control information for gain control at least includes the information specifying whether or not the attack portion has been detected, the information-specifying the gain control amount for waveform elements upstream of the attack portion on detection of the attack portion, and the information specifying the attack portion.

30. The method as claimed in claim 26, wherein the processing of transforming the acoustic signal into plural frequency components is the processing of blocking the acoustic signal every plural waveform elements and orthogonally transforming the block-based waveform elements.

31. The method as claimed in claim 26 wherein the characteristics of the acoustic signals in selecting the gain control amount are the degree of change in the acoustic signal based upon the level of the waveform elements upstream of the attack portion and the level of the waveform elements of the attack portion.

32. A decoding method for decoding an encoded signal, said encoded signal being at least an encoded version of plural frequency components transformed from the acoustic signal and an encoded version of the control correction information for gain control correction for waveform elements upstream of the attack portion where the waveform elements of the acoustic signal rise acutely in signal level, comprising the steps of:

decoding said encoded signals for producing plural frequency components and the control correction information;

transforming the frequency components into an acoustic signal consisting of plural waveform elements;

correcting the gain control of the waveform elements upstream of the attack portion, using a gain control correction amount selected based upon said control correction information from plural gain control amounts specified by preset negative powers of 2; and

restoring the acoustic signal from said waveform elements.

33. The decoding method as claimed in claim 32, wherein said gain control correction is performed by bit-shifting digital data corresponding to waveform elements of the acoustic signal towards right in an amount corresponding to the number of the power of 2.

34. The decoding method as claimed in claim 32, wherein, in the vicinity of the change point of said gain control correction amount, a gain control correction amount smoothly changed between the gain control correction amount prior to change and the gain control correction amount subsequent to change are selected from among plural sorts of smoothly changing gain control amounts previously set and held in a table.

35. The decoding method as claimed in claim 32, wherein the control correction information for gain control correction at least includes the information specifying whether or not there is the attack portion, the information specifying the gain control correction amount for waveform elements upstream of the attack portion, if such attack portion exists, and the information specifying the position of the attack portion.

36. The decoding method as claimed in claim 32, wherein the operation of transforming the frequency components into the acoustic signal consisting of plural waveform elements is a processing of inversely orthogonally transforming the frequency components for each block consisting of plural frequency components.