Method and Apparatus for Processing Audio Frames to Transition Between Different Codecs

• US 20130173259A1
• Filed: 01/03/2012
• Published: 07/04/2013
• Est. Priority Date: 01/03/2012
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola Mobility, Inc. (Lenovo Group Ltd.)
• Inventors: Mittal, Udar, Ashley, James P.
• Granted Patent: US 9,043,201 B2
• Time in Patent Office: Days
• US Class Current: 704/201
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes

Abstract

A method (700, 800) and apparatus (100, 200) processes audio frames to transition between different codecs. The method can include producing (720), using a first coding method, a first frame of coded output audio samples by coding a first audio frame in a sequence of frames. The method can include forming (730) an overlap-add portion of the first frame using the first coding method. The method can include generating (740) a combination first frame of coded audio samples based on combining the first frame of coded output audio samples with the overlap-add portion of the first frame. The method can include initializing (760) a state of a second coding method based on the combination first frame of coded audio samples. The method can include constructing (770) an output signal based on the initialized state of the second coding method.

Claims

1. A method for processing audio frames comprising:

producing, using a first coding method, a first frame of coded output audio samples by coding a first audio frame in a sequence of frames wherein the coded output audio samples are sampled at a first sampling rate;

forming an overlap-add portion of the first frame using the first coding method;

generating a combination first frame of coded audio samples based on combining the first frame of coded output audio samples with the overlap-add portion of the first frame;

initializing a state of a second coding method based on the combination first frame of coded audio samples; and

constructing an output signal based on the initialized state of the second coding method.

2. The method according to claim 1, wherein the generating a combination first frame comprises:

resampling the combination first frame of coded audio samples at a second sampling rate to generate a resampled combination first frame of coded audio samples,

wherein the initializing comprises initializing the state of the second coding method based on the resampled combination first frame of coded audio samples.

3. The method according to claim 2, wherein the initializing comprises:

initializing the state of at least a resampling filter of the second coding method based on the resampled combination first frame of coded audio samples.

4. The method according to claim 2, wherein the combination first frame of coded audio samples is generated based on combining the first frame of coded output audio samples with the overlap-add portion of the first frame to compensate for a delay from resampling the combination first frame of coded audio samples at the second sampling rate.

5. The method according to claim 1, wherein the overlap-add portion of the first frame comprises a modified discrete cosine transform synthesis memory portion of the first frame.

6. The method according to claim 1, wherein the first coding method is a generic audio coding method, and the second coding method is a speech coding method.

7. The method according to claim 6, wherein the generating a combination first frame comprises:

downsampling the combination first frame of coded audio samples at a second sampling rate to generate a downsampled combination first frame of coded audio samples,

wherein the initializing comprises initializing the state of the speech coding method based on the downsampled combination first frame of coded audio samples.

8. The method according to claim 1, wherein the generating a combination first frame comprises:

generating the combination first frame of coded audio samples based on appending the overlap-add portion of the first frame to the first frame of coded output audio samples.

9. The method according to claim 1, wherein the constructing an output signal comprises:

constructing the output signal for a second frame following the first frame based on the initialized state of the second coding method.

10. A method for processing audio frames comprising:

producing, using a first decoding method, a first frame of decoded output audio samples by decoding a bitstream frame in a sequence of frames wherein the decoded output audio samples are sampled at a first sampling rate;

forming an overlap-add portion of the first frame using the first decoding method;

generating a combination first frame of decoded audio samples based on combining the first frame of decoded output audio samples with the overlap-add portion of the first frame;

initializing a state of a second decoding method based on the combination first frame of decoded audio samples; and

constructing an output signal based on the initialized state of the second decoding method.

11. The method according to claim 10, wherein the generating a combination first frame comprises:

resampling the combination first frame of decoded audio samples at a second sampling rate to generate a resampled combination first frame of decoded audio samples,

wherein the initializing comprises initializing the state of the second decoding method based on the resampled combination first frame of decoded audio samples.

12. The method according to claim 11, wherein the initializing comprises:

initializing the state of at least a resampling filter of the second decoding method based on the resampled combination first frame of decoded audio samples.

13. The method according to claim 11, wherein the combination first frame of decoded audio samples is generated based on combining the first frame of decoded output audio samples with the overlap-add portion of the first frame to compensate for a delay from resampling the combination first frame of decoded audio samples at the second sampling rate.

14. The method according to claim 10, wherein the overlap-add portion of the first frame comprises a modified discrete cosine transform synthesis memory portion of the first frame.

15. The method according to claim 10, wherein the first decoding method is a generic audio decoding method, the second decoding method is a speech decoding method, and the output signal is an audible speech signal.

16. The method according to claim 15, wherein the generating a combination first frame comprises:

downsampling the combination first frame of decoded audio samples at a second sampling rate to generate a downsampled combination first frame of decoded audio samples,

wherein initializing comprises initializing the state of the speech decoding method based on the downsampled combination first frame of decoded audio samples.

17. The method according to claim 10, wherein the generating a combination first frame comprises:

generating the combination first frame of decoded audio samples based on appending the overlap-add portion of the first frame to the first frame of decoded output audio samples.

18. The method according to claim 10, wherein the constructing an output signal comprises:

constructing the output signal for a second frame following the first frame based on the initialized state of the second decoding method.

19. An apparatus for processing audio frames comprising:

a first coder configured to produce, using a first coding method, a first frame of coded output audio samples by coding a first audio frame in a sequence of frames wherein the coded output audio samples are sampled at a first sampling rate, the first coder also configured to form an overlap-add portion of the first frame using the first coding method;

a transition audio combiner configured to generate a combination first frame of coded audio samples based on combining the first frame of coded output audio samples with the overlap-add portion of the first frame;

a second coder state generator configured to initialize a state of a second coding method based on the combination first frame of coded audio samples; and

a second coder configured to construct an output signal based on the initialized state of the second coding method.

20. The apparatus according to claim 19,

wherein the transition audio combiner is configured to resample the combination first frame of coded audio samples at a second sampling rate to generate a resampled combination first frame of coded audio samples,

wherein the second coder state generator is configured to initialize the state of the second coding method based on the resampled combination first frame of coded audio samples.

21. The apparatus according to claim 20, wherein the first coding method is a generic audio coding method, and the second coding method is a speech coding method.

22. The apparatus according to claim 20, wherein the transition audio combiner is configured to generate the combination first frame of coded audio samples based on appending the overlap-add portion of the first frame to the first frame of coded output audio samples.

23. An apparatus for processing audio frames comprising:

a first decoder configured to produce, using a first decoding method, a first frame of decoded output audio samples by decoding a bitstream frame in a sequence of frames wherein the decoded output audio samples are sampled at a first sampling rate, the first decoder also configured to form an overlap-add portion of the first frame using the first decoding method;

a transition audio combiner configured to generate a combination first frame of decoded audio samples based on combining the first frame of decoded output audio samples with the overlap-add portion of the first frame;

a second decoder state generator configured to initialize a state of a second decoding method based on the combination first frame of decoded audio samples; and

a second decoder configured to construct an output signal based on the initialized state of the second decoding method.

24. The apparatus according to claim 23,

wherein the transition audio combiner is configured to resample the combination first frame of decoded audio samples at a second sampling rate to generate a resampled combination first frame of decoded audio samples,

wherein the second decoder state generator is configured to initialize the state of the second decoding method based on the resampled combination first frame of decoded audio samples.

25. The apparatus according to claim 23, wherein the first decoding method is a generic audio decoding method, the second decoding method is a speech decoding method, and the output signal is an audible speech signal.

26. The apparatus according to claim 23, wherein the transition audio combiner is configured to generate the combination first frame of decoded audio samples based on appending the overlap-add portion of the first frame to the first frame of decoded output audio samples.