Audio encoding with different coding models

• US 20050261892A1
• Filed: 05/06/2005
• Published: 11/24/2005
• Est. Priority Date: 05/17/2004
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Ojala, Pasi, Lakaniemi, Ari, Makinen, Jari
• Granted Patent: US 8,069,034 B2
• Time in Patent Office: Days
• US Class Current: 704/200.100
• CPC Class Codes: G10L 19/20 using sound class specific coding, hybrid encoders or object based coding

Abstract

A method for supporting an encoding of an audio signal is shown, wherein at least a first and a second coder mode are available for encoding a section of the audio signal. The first coder mode enables a coding based on two different coding models. A selection of a coding model is enabled by a selection rule which is based on signal characteristics which have been determined for a certain analysis window. In order to avoid a misclassification of a section after a switch to the first coder mode, it is proposed that the selection rule is activated only when sufficient sections for the analysis window have been received. The invention relates equally to a module 2,3 in which this method is implemented, to a device 1 and a system comprising such a module 2,3, 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 a first coder mode and a second coder mode are available for encoding a specific section of said audio signal, wherein at least said first coder mode enables a coding of a specific section of said audio signal based on at least two different coding models, and wherein in said first coder mode a selection of a respective coding model for encoding said specific section of an audio signal is enabled by at least one selection rule which is based on signal characteristics, which signal characteristics have at least partly been determined from an analysis window, which analysis window covers at least one section of said audio signal preceding said specific section, said method comprising after a switch from said second coder mode to said first coder mode activating said at least one selection rule in response to having received at least as many sections of said audio signal as are covered by said analysis window.

2. A method according to claim 1, wherein in said first coder mode a selection of a respective coding model for encoding a specific section of an audio signal is further enabled by at least one further selection rule using no information on sections of said audio signal preceding said specific section, said at least one further selection rule being applied at least as long as the number of received sections is less than the number of sections covered by an analysis window, in which signal characteristics are determined for said at least one selection rule.

3. A method according to claim 1, wherein said at least one selection rule, which is based on signal characteristics that have been determined from an analysis window, comprises a first selection rule, which is based on signal characteristics that have been determined in a shorter analysis window, and a second selection rule, which is based on signal characteristics that have been determined in a longer analysis window, wherein said first selection rule is activated as soon as sufficient sections of said audio signal for said shorter analysis window have been received, and wherein said second selection rule is activated as soon as sufficient sections of said audio signal for said longer analysis window have been received.

4. A method according to claim 3, wherein a respective section of said audio signal corresponds to a respective audio signal frame having a length of 20 ms, wherein said shorter window covers an audio signal frame for which a coding model is to be selected and in addition four preceding audio signal frames, and wherein said longer window covers an audio signal frame for which a coding model is to be selected and in addition sixteen preceding audio signal frames.

5. A method according to claim 1, wherein said signal characteristics comprise a standard deviation of energy related values in a respective analysis window.

6. A method according to claim 1, wherein said first coder mode is an extension mode of an extended adaptive multi-rate wideband codec and enables a coding based on an algebraic code-excited linear prediction coding model and in addition a coding based on a transform coding model, and wherein said second coder mode is an adaptive multi-rate wideband mode of said extended adaptive multi-rate wideband codec and enables a coding based on an algebraic code-excited linear prediction coding model.

7. A method according to claim 1, wherein said section is a frame or a sub-frame of said audio signal.

8. A module (2,3) for supporting an encoding of an audio signal, said module (2,3) comprising:

a first coder mode portion (5) adapted to encode a respective section of an audio signal in a first coder mode;

a second coder mode portion (4) adapted to encode a respective section of an audio signal in a second coder mode;

switching means (6) for switching between said first coder mode portion (5) and said second coder mode portion (4);

comprised by said first coder mode portion (5) an encoding portion (19) which is adapted to encode a respective section of said audio signal based on at least two different coding models; and

further comprised by said first coder mode portion (5) a selection portion (13,14,15) adapted to apply at least one selection rule for selecting a specific coding model, which coding model is to be used by said encoding portion (19) for encoding said specific section of an audio signal, wherein said at least one selection rule is based on signal characteristics, which have at least partly been determined from an analysis window covering at least one section of an audio signal preceding said specific section, and wherein said selection portion (13,14,15) is adapted to activate said at least one selection rule after a switch by said switching means (6) from said second coder mode portion (4) to said first coder mode portion (5) in response to having received at least as many sections of said audio signal as are covered by said analysis window.

9. A module (2,3) according to claim 8, further comprising a counter (12) adapted to count the number of sections of said audio signal, which are provided to said first coder mode portion (5) after a switch from said second coder mode portion (4) to said first coder mode portion (5).

10. A module (2,3) according to claim 8, wherein said first coder mode portion (5) further comprises at least one further selection portion (16,17,18), which is adapted to apply at least one further selection rule for selecting a respective coding model, which coding model is to be used by said encoding portion (19) for encoding a specific section of an audio signal, wherein said at least one further selection rule uses no information on sections of said audio signal preceding said specific section, and wherein said at least one further selection rule is applied after a switch from said second coder mode portion (4) to said first coder mode portion (5) at least as long as the number of sections received by said first coder portion (5) is less than the number of sections covered by an analysis window employed for said at least one selection rule which is based on an analysis of signal characteristics in an analysis window

11. A module (2,3) according to claim 8, wherein said at least one selection portion (13,14,15) comprises a first selection portion (14) adapted to apply a first selection rule which is based on signal characteristics which have been determined in a shorter analysis window and a second selection portion (13) adapted to apply a second selection rule, which is based on signal characteristics that have been determined in a longer analysis window, wherein said first selection rule is activated as soon as sufficient sections of said audio signal for said shorter analysis window have been received by said first coder model portion (5) after a switch from said second coder mode portion (4) to said first coder mode portion (5), and wherein said second selection rule is activated as soon as sufficient sections of said audio signal for said longer analysis window have been received by said first coder model portion (5) after a switch from said second coder mode portion (4) to said first coder mode portion (5).

20. An audio coding system (1,2) comprising a module (2,3) according to claim 8 and a decoder (20) for decoding audio signals, which have been encoded by said module (2,3).

21. An audio coding system (1,2) according to claim 20, further comprising a first coder mode portion (5) adapted to encode a respective section of an audio signal in a first coder mode.

22. An audio coding system (1,2) according to claim 21, further comprising a second coder mode portion (4) adapted to encode a respective section of an audio signal in a second coder mode.

23. An audio coding system (1,2) according to claim 22, further comprising switching means (6) for switching between said first coder mode portion (5) and said second coder mode portion (4).

12. An electronic device (1) supporting an encoding of an audio signal, said electronic device (2,3) comprising:

a first coder mode portion (5) adapted to encode a respective section of an audio signal in a first coder mode;

a second coder mode portion (4) adapted to encode a respective section of an audio signal in a second coder mode;

switching means (6) for switching between said first coder mode portion (5) and said second coder mode portion (4);

comprised by said first coder mode portion (5) an encoding portion (19) which is adapted to encode a respective section of said audio signal based on at least two different coding models; and

further comprised by said first coder mode portion (5) a selection portion (13,14,15) adapted to apply at least one selection rule for selecting a specific coding model, which coding model is to be used by said encoding portion (19) for encoding said specific section of an audio signal, wherein said at least one selection rule is based on signal characteristics, which have at least partly been determined from an analysis window covering at least one section of an audio signal preceding said specific section, and wherein said selection portion (13,14,15) is adapted to activate said at least one selection rule after a switch by said switching means (6) from said second coder mode portion (4) to said first coder mode portion (5) in response to having received at least as many sections of said audio signal as are covered by said analysis window.

13. An electronic device (1) according to claim 12, further comprising a counter (12) adapted to count the number of sections of said audio signal, which are provided to said first coder mode portion (5) after a switch from said second coder mode portion (4) to said first coder mode portion (5).

14. An electronic device (1) according to claim 12, wherein said first coder mode portion (5) further comprises at least one further selection portion (16,17,18), which is adapted to apply at least one further selection rule for selecting a respective coding model, which coding model is to be used by said encoding portion (19) for encoding a specific section of an audio signal, wherein said at least one further selection rule uses no information on sections of said audio signal preceding said specific section, and wherein said at least one further selection rule is applied after a switch from said second coder mode portion (4) to said first coder mode portion (5) at least as long as the number of sections received by said first coder portion (5) is less than the number of sections covered by an analysis window employed for said at least one selection rule which is based on an analysis of signal characteristics in an analysis window

15. An electronic device (1) according to claim 12, wherein said at least one selection portion (13,14,15) comprises a first selection portion (14) adapted to apply a first selection rule which is based on signal characteristics which have been determined in a shorter analysis window and a second selection portion (13) adapted to apply a second selection rule, which is based on signal characteristics that have been determined in a longer analysis window, wherein said first selection rule is activated as soon as sufficient sections of said audio signal for said shorter analysis window have been received by said first coder model portion (5) after a switch from said second coder mode portion (4) to said first coder mode portion (5), and wherein said second selection rule is activated as soon as sufficient sections of said audio signal for said longer analysis window have been received by said first coder model portion (5) after a switch from said second coder mode portion (4) to said first coder mode portion (5).

16. An electronic device (1) according to claim 15, wherein a respective section of said audio signal corresponds to a respective audio signal frame having a length of 20 ms, wherein said shorter window covers an audio signal frame for which a coding model is to be selected and in addition four preceding audio signal frames, and wherein said longer window covers an audio signal frame for which a coding model is to be selected and in addition sixteen preceding audio signal frames.

17. An electronic device (1) according to claim 12, wherein said first coder mode portion (5) further comprises a signal characteristics determination portion (11), which determines signal characteristics of said audio signal in a respective analysis window and which provides said signal characteristics to said selection portion (13,14,15), said signal characteristics including a standard deviation of energy related values in a respective analysis window.

18. An electronic device (1) according to claim 12, wherein said first coder mode is an extension mode of an extended adaptive multi-rate wideband codec, said encoding portion (9) of said first coder mode portion (5) being adapted to encode sections of an audio signal based on an algebraic code-excited linear prediction coding model and in addition based on a transform coding model, and wherein said second coder mode is an adaptive multi-rate wideband mode of said extended adaptive multi-rate wideband codec, said second coder mode portion (4) being adapted to encode sections of an audio signal based on an algebraic code-excited linear prediction coding model.

19. An electronic device supporting an encoding of an audio signal, said electronic device comprising:

means for encoding a respective section of an audio signal in a first coder mode based on at least two different coding models;

means for encoding a respective section of an audio signal in a second coder mode;

means for switching between said means for encoding a respective section of an audio signal in said first coder mode and said means for encoding a respective section of an audio signal in said second coder mode;

means for applying at least one selection rule for selecting a specific coding model, which coding model is to be used for encoding a specific section of an audio signal in said first coder mode, wherein said at least one selection rule is based on signal characteristics, which have at least partly been determined from an analysis window covering at least one section of an audio signal preceding said specific section; and

means for activating said at least one selection rule after a switch from said means for encoding a respective section of an audio signal in said second coder mode to said means for encoding a respective section of an audio signal in said first coder mode in response to having received at least as many sections of said audio signal as are covered by said analysis window.

24. A software program product, in which a software code for supporting an encoding of an audio signal is stored, wherein at least a first coder mode and a second coder mode are available for encoding a respective section of said audio signal, wherein at least said first coder mode enables a coding of a respective section of said audio signal based on at least two different coding models, and wherein in said first coder mode a selection of a respective coding model for encoding a specific section of an audio signal is enabled by at least one selection rule, which is based on signal characteristics that have been determined from an analysis window, which covers at least one section of said audio signal preceding said specific section, said software code realizing the following step when running in a processing component (3) of an encoder (2):

activating said at least one selection rule after a switch from said second coder mode to said first coder mode in response to having received at least as many sections of said audio signal as are covered by said analysis window.