Audio encoding with different coding frame lengths

• US 20050267742A1
• Filed: 05/13/2005
• Published: 12/01/2005
• Est. Priority Date: 05/17/2004
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Makinen, Jari
• Granted Patent: US 7,860,709 B2
• Time in Patent Office: Days
• US Class Current: 704/219
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding

Abstract

The invention relates to a method for supporting an encoding of an audio signal, wherein at least one section of the audio signal is to be encoded with a coding model that allows the use of different coding frame lengths. In order to enable a simple selection of the respectively best suited coding frame length, it is proposed that at least one control parameter is determined based on signal characteristics of the audio signal. The control parameter is then used for limiting the options of possible coding frame lengths for the at least one section. The invention relates equally to a module 10,11 in which this method is implemented, to a device 1 and a system comprising such a module 10,11, and to a software program product including a software code for realizing the proposed method.

Claims

1. A method for supporting an encoding of an audio signal, wherein at least one section of said audio signal is to be encoded with a coding model that allows the use of different coding frame lengths, said method comprising:

determining at least one control parameter based at least partly on signal characteristics of said audio signal; and

limiting options of possible coding frame lengths for said at least one section by means of said at least one control parameter.

2. The method according to claim 1, further comprising determining the said at least one control parameter on the basis of at least one of the following parameters:

an indicator of a spectral distance between the current frame and an earlier frame;

the number of frames in the superframe selected to be coded with an other coding model.

3. The method according to claim 1, further comprising:

in case more than one option of possible coding frame lengths remains after said limitation, encoding said at least one section with each of said remaining transform coding frame lengths;

decoding said encoded sections with the respectively used transform coding frame length; and

selecting for said at least one section a coding frame length which results in the best-decoded audio signal in said at least one section.

4. The method according to claim 3, wherein a coding frame length which results in the best decoded section is determined by comparing a signal-to-noise ratio resulting for each of said coding frame lengths.

5. The method according to claim 4, wherein for said signal-to-noise ratio of an audio signal obtained with a particular coding frame length, first a segmental signal-to-noise ratio is determined separately for a plurality of subframes in a respective coding frame, and wherein said segmental signal-to-noise ratios of said subframes of a coding frame are then averaged for the entire coding frame to obtain said signal-to-noise ratio for said at least one section.

6. The method according to claim 1, further comprising a step of determining for each section of said audio signal, based on audio signal characteristics for a respective section, whether said coding model or another coding model is to be employed, wherein said at least one control parameter comprises an indication of the sections for which said other coding model has been selected.

7. The method according to claim 6, wherein said coding model is a transform coding model and wherein said other coding model is an Algebraic Code-Excited Linear Prediction coding model.

8. The method according to claim 6, wherein each section of said audio signal has a predetermined length and wherein said indication of the sections for which said other coding model has been selected is provided for a respective supersection comprising a predetermined number of said sections.

9. The method according to claim 1, wherein each section of said audio signal has a predetermined length, wherein a predetermined number of consecutive sections, respectively, form a respective supersection, and wherein said coding frame length options for a particular section are limited by the boundaries of the supersection to which said section belongs.

10. The method according to claim 7, wherein each section of said audio signal has a length of 20 ms, wherein four consecutive sections, respectively, form a supersection, wherein said transform coding model allows the use of coding frame lengths of 20 ms, 40 ms and 80 ms, and wherein said coding frame length options for a section are limited by the boundaries of the supersection to which said section belongs.

11. The method according to claim 1, wherein said at least one control parameter comprises an indicator indicating whether a shorter or a longer coding frame length is to be employed, an indication that a shorter coding frame length is to be employed excluding at least a longest coding frame length option and an indication that a longer coding frame length is to be employed excluding at least a shortest coding frame length option.

12. A module (10,11) for supporting an encoding of an audio signal, wherein at least one section of said audio signal is to be encoded with a coding model that allows the use of different coding frame lengths, said module comprising:

a parameter selection portion (12,13) adapted to determine at least one control parameter based at least partly on signal characteristics of said audio signal; and

a frame length selection portion (14) adapted to limit options of possible coding frame lengths for at least one section by means of at least one control parameter provided by said first evaluation portion (13).

13. The module (10,11) according to claim 12, further comprising determining the said at least one control parameter on the basis of at least one of the following parameters:

a short frame indicator, which is determined at least on basis of spectral distance; and

the number of selected Algebraic Code-Excited linear predictor-frames in the superframe.

14. The module (10,11) according to claim 12, wherein said frame length selection portion (14) is further adapted to encode said at least one section with each of said remaining transform coding frame lengths, in case more than one option of possible coding frame lengths remains after said limitation, to decode said encoded sections again with the respectively used transform coding frame, and to select for said at least one section a coding frame length which results in the best decoded audio signal in said at least one section.

15. The module (10,11) according to claim 14, wherein said frame length selection portion (14) is adapted to determine a coding frame length which results in the best decoded section is determined by comparing a signal-to-noise ratio resulting for each of said coding frame lengths.

16. The module (10,11) according to claim 15, wherein for determining said signal-to-noise ratio of an audio signal obtained with a particular coding frame length, said frame length selection portion (14) is adapted to determine first a segmental signal-to-noise ratio separately for a plurality of subframes in a respective coding frame, and to average said segmental signal-to-noise ratios of said subframes of a coding frame for the entire coding frame to obtain said signal-to-noise ratio for said at least one section.

17. The module (10,11) according to claim 12, wherein said parameter selection portion (12,13) is further adapted to determine at least for some sections of an audio signal, based on audio signal characteristics for a respective section of said audio signal, whether said coding model or another coding model is to be employed, and to provide as one of said at least one control parameter an indication of the sections for which said other coding model has been selected.

18. The module (10,11) according to claim 17, wherein said coding model is a transform coding model and wherein said other coding model is an Algebraic Code-Excited Linear Prediction coding model.

31. An audio coding system (1,2) comprising a module (10,11) according to claim 12 and a decoder (20) for decoding audio signals which have been encoded with variable coding frame lengths.

32. The audio coding system (1,2) according to claim 31 further comprising determination of at least one control parameter based at least partly on signal characteristics of said audio signal

33. The audio coding system (1,2) according to claim 31 further comprising limiting said options of possible coding frame lengths by means of said at least one control parameter.

34. The audio coding system (1,2) according to claim 32, further comprising

in case more than one option of possible coding frame lengths remains after said limitation, encoding said at least one section with each of said remaining transform coding frame lengths;

decoding said encoded sections with the respectively used transform coding frame length; and

selecting for said at least one section a coding frame length which results in the best-decoded audio signal in said at least one section.

19. An electronic device (1) comprising a module (10,11) for supporting an encoding of an audio signal, wherein at least one section of said audio signal is to be encoded with a coding model that allows the use of different coding frame lengths, said module comprising:

a parameter selection portion (12,13) adapted to determine at least one control parameter based at least partly on signal characteristics of said audio signal; and

a frame length selection portion (14) adapted to limit options of possible coding frame lengths for at least one section by means of at least one control parameter provided by said first evaluation portion (13).

20. The electronic device (1) according to claim 19, further comprising determining the said at least one control parameter on the basis of at least one of the following parameters:

a short frame indicator, which is determined at least on basis of spectral distance; and

the number of selected Algebraic Code-Excited linear predictor-frames in the superframe.

21. The electronic device (11) according to claim 19, wherein said frame length selection portion (14) is further adapted to encode said at least one section with each of said remaining transform coding frame lengths, in case more than one option of possible coding frame lengths remains after said limitation, to decode said encoded sections again with the respectively used transform coding frame, and to select for said at least one section a coding frame length which results in the best decoded audio signal in said at least one section.

22. The electronic device (1) according to claim 21, wherein said frame length selection portion (14) is adapted to determine a coding frame length which results in the best decoded section is determined by comparing a signal-to-noise ratio resulting for each of said coding frame lengths.

23. The electronic device (1) according to claim 22, wherein for determining said signal-to-noise ratio of an audio signal obtained with a particular coding frame length, said frame length selection portion (14) is adapted to determine first a segmental signal-to-noise ratio separately for a plurality of subframes in a respective coding frame, and to average said segmental signal-to-noise ratios of said subframes of a coding frame for the entire coding frame to obtain said signal-to-noise ratio for said at least one section.

24. The electronic device (1) according to claim 21, wherein said parameter selection portion (12,13) is further adapted to determine at least for some sections of an audio signal, based on audio signal characteristics for a respective section of said audio signal, whether said coding model or another coding model is to be employed, and to provide as one of said at least one control parameter an indication of the sections for which said other coding model has been selected.

25. The electronic device (1) according to claim 24, wherein said coding model is a transform coding model and wherein said other coding model is an Algebraic Code-Excited Linear Prediction coding model.

26. The electronic device (1) according to claim 24, wherein each section of said audio signal has a predetermined length and wherein said parameter selection portion (12,13) is adapted to provide an indication of the sections for which said other coding model has been selected for a respective supersection comprising a predetermined number of said sections.

27. The electronic device (1) according to claim 19, wherein each section of said audio signal has a predetermined length, wherein a predetermined number of consecutive sections, respectively, form a respective supersection, and wherein said frame length selection portion (14) is adapted to limit the coding frame length options for a particular section based on the boundaries of the supersection to which said section belongs.

28. The electronic device (1) according to claim 25, wherein each section of said audio signal has a length of 20 ms, wherein four consecutive sections, respectively, form a supersection, wherein said transform coding model allows the use of coding frame lengths of 20 ms, 40 ms and 80 ms, and wherein said frame length selection portion (14) is adapted to limit the coding frame length options for a section based on the boundaries of the supersection to which said section belongs.

29. The electronic device (1) according to claim 19, wherein said parameter selection portion (12,13) is adapted to provide as one of said at least one control parameter an indicator indicating whether a shorter or a longer coding frame length is to be employed, an indication that a shorter coding frame length is to be employed excluding at least a longest coding frame length option and an indication that a longer coding frame length is to be employed excluding at least a shortest coding frame length option.

30. An electronic device for supporting an encoding of an audio signal, wherein at least one section of said audio signal is to be encoded with a coding model that allows the use of different coding frame lengths, said electronic device comprising:

means for determining at least one control parameter based at least partly on signal characteristics of said audio signal; and

means for limiting options of possible coding frame lengths for at least one section by means of at least one control parameter provided by said first evaluation portion.

35. A software program product in which a software code for supporting an encoding of an audio signal is stored, wherein at least one section of said audio signal is to be encoded with a coding model which allows the use of different coding frame lengths, said software code realizing the following steps when running in a processing component (11) of an encoder (10);

determining at least one control parameter based at least partly on signal characteristics of said audio signal; and

limiting options of possible coding frame lengths for said at least one section by means of said at least one control parameter.