Audio encoder/decoder with switching between first and second encoders/decoders using first and second framing rules

• US 8,892,449 B2
• Filed: 01/11/2011
• Issued: 11/18/2014
• Est. Priority Date: 07/11/2008
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., VoiceAge Corporation
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., VoiceAge Corporation
• Inventors: Lecomte, Jeremie, Gournay, Philippe, Bayer, Stefan, Multrus, Markus, Bessette, Bruno, Grill, Bernhard
• Primary Examiner(s): Lerner, Martin
• Application Number:
  US13/004,400
• Publication Number:
  US 20110173010A1
• Time in Patent Office: 1,407 Days
• Field of Search: 704/203, 704/205, 704/500, 704/501
• US Class Current: 704/500
• 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

An audio encoder for encoding audio samples has a first time domain aliasing introducing encoder configured to decode audio samples in a first encoding domain and having a first framing rule, a start window and a stop window. The audio encoder further has a second encoder configured to encode samples in a second encoding domain and having a predetermined frame size number of audio samples, and a coding warm-up period number of audio samples, the second encoder having a different second framing rule, a frame of the second encoder being an encoded representation of a number of successive audio samples that is equal to the predetermined frame size number of audio samples. The audio encoder further has a controller switching from the first to the second encoder and for modifying the second framing rule or for modifying the start or the stop window of the first encoder.

Claims

1. An audio encoding apparatus for encoding audio samples, comprising:

a first time domain aliasing introducing encoder for encoding audio samples in a first encoding domain, the first time domain aliasing introducing encoder comprising a first framing rule, a start window and a stop window and comprising a frequency domain transformer for transforming a first frame of subsequent audio samples to the frequency domain based on a modified discrete cosine transformation (MDCT);

a second encoder for encoding samples in a second encoding domain, the second encoder comprising a predetermined frame size number of audio samples, and a coding warm-up period number of audio samples, the second encoder comprising a different second framing rule, a frame of the second encoder being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

a controller for, using a processor, switching from the first encoder to the second encoder or vice versa in response to a characteristic of the audio samples, and for modifying the start window or the stop window of the first encoder to the extent that a zero part thereof extends across a first quarter of an MDCT size and cross fade starts in a second quarter of the MDCT size so that the cross fade begins after a MDCT folding axis relative to the zero part, wherein the second framing rule remains unmodified.

2. An audio encoding apparatus for encoding audio samples, comprising:

a first time domain aliasing introducing encoder for encoding audio samples in a first encoding domain, the first time domain aliasing introducing encoder comprising a first framing rule, a start window and a stop window;

a second encoder for encoding samples in a second encoding domain, the second encoder comprising a different second framing rule and comprising an AMR or AMR-WB+ encoder with the second framing rule being an AMR framing rule according to which a superframe comprises four AMR frames, the second encoder comprising a predetermined frame size number of audio samples for the superframe, and a coding warm-up period number of audio samples, a superframe of the second encoder being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

a controller for switching from the first encoder to the second encoder or vice versa in response to a characteristic of the audio samples, and for modifying the second framing rule in response to switching from the first encoder to the second encoder or from the second encoder to the first encoder to the extent that a first superframe at the switching comprises an increased frame size number of audio samples with comprising a fifth AMR frame in addition to the four AMR frames, with the fifth AMR frame respectively overlapping a fading part of a start window or a stop window of the first time domain aliasing introducing encoder.

3. The audio encoding apparatus of claim 2, wherein the first time-domain aliasing introducing encoder comprises a frequency domain transformer for transforming a first frame of subsequent audio samples to the frequency domain.

4. The audio encoding apparatus of claim 3, wherein the first time-domain aliasing introducing encoder is adapted for weighting the last frame with the start window when a subsequent frame is encoded by the second encoder and/or for weighting the first frame with the stop window when a preceding frame is to be encoded by the second encoder.

5. The audio encoding apparatus of claim 3, wherein the frequency domain transformer is adapted for transforming the first frame to the frequency domain based on a modified discrete cosine transformation (MDCT) and wherein the first time domain aliasing introducing encoder is adapted for adapting a MDCT size to the start and/or stop and/or modified start and/or stop windows.

6. The audio encoding apparatus of claim 2, wherein the first time-domain aliasing introducing encoder is adapted for utilizing a start window and/or a stop window comprising an aliasing part and/or an aliasing-free part.

7. The audio encoding apparatus of claim 6, wherein the controller is adapted to start the second encoder, such that the first frame of a sequence of frames of the second encoder comprises an encoded representation of a sample processed in the preceding aliasing-free part of the first encoder.

8. The audio encoding apparatus of claim 6, wherein the controller is adapted to start the second encoder, such that the coding warm-up period number of audio samples overlaps with the aliasing-free part of the start window of the first time-domain aliasing introducing encoder and the subsequent frame of the second encoder overlaps with the aliasing part of the stop window.

9. The audio encoding apparatus of claim 6, wherein the controller is adapted to start the second encoder, such that the coding warm-up period overlaps with the aliasing part of the start window.

10. The audio encoding apparatus of claim 2, wherein the first time-domain aliasing introducing encoder is adapted for utilizing a start window and/or a stop window comprising an aliasing-free part as a rising edge part of the window when the preceding frame is encoded by the second encoder and at a falling edge part when the subsequent frame is encoded by the second encoder.

11. A method for encoding audio frames, comprising:

encoding audio samples in a first encoding domain using a first framing rule, a start window and a stop window and by transforming a first frame of subsequent audio samples to the frequency domain based on a modified discrete cosine transformation (MDCT);

encoding audio samples in a second encoding domain using a predetermined frame size number of audio samples and a coding warm-up period number of audio samples and using a different second framing rule, the frame of the second encoding domain being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

using a processor, switching from the first encoding domain to the second encoding domain or vice versa, and modifying the start window or the stop window of the first encoding domain to the extent that a zero part thereof extends across a first quarter of an MDCT size and cross fade starts in a second quarter of the MDCT size so that the cross fade begins after a MDCT folding axis relative to the zero part, wherein the second framing rule remains unmodified.

12. A method for encoding audio frames, comprising:

encoding audio samples in a first encoding domain using a first framing rule, a start window and a stop window;

encoding audio samples in a second encoding domain using a different second framing rule by way of AMR or AMR-WB+ encoding with the second framing rule being an AMR framing rule according to which a superframe comprises four AMR frames, and using a predetermined frame size number of audio samples for the superframe, the superframe of the second encoding domain being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

using a processor, switching from the first encoding domain to the second encoding domain or vice versa, and modifying the second framing rule in response to switching from the first to the second encoding domain or from the second to the first encoding domain to the extent that a first superframe at the switching comprises an increased frame size number of audio samples with comprising a fifth AMR frame in addition to the four AMR frames, with the fifth AMR frame respectively overlapping a fading part of the start window or the stop window.

13. A non-transitory computer-readable medium having stored thereon a computer program comprising a program code for performing the method for encoding audio frames, the method comprising:

encoding audio samples in a first encoding domain using a first framing rule, a start window and a stop window and by transforming a first frame of subsequent audio samples to the frequency domain based on a modified discrete cosine transformation (MDCT);

encoding audio samples in a second encoding domain using a predetermined frame size number of audio samples and a coding warm-up period number of audio samples and using a different second framing rule, the frame of the second encoding domain being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples;

switching from the first encoding domain to the second encoding domain or vice versa; and

modifying the start window or the stop window of the first encoding domain to the extent that a zero part thereof extends across a first quarter of an MDCT size and cross fade starts in a second quarter of the MDCT size so that the cross fade begins after a MDCT folding axis relative to the zero part, wherein the second framing rule remains unmodified,

when the program code runs on a computer or processor.

14. A non-transitory computer-readable medium having stored thereon a computer program comprising a program code for performing the method for encoding audio frames, the method comprising:

encoding audio samples in a first encoding domain using a first framing rule, a start window and a stop window;

encoding audio samples in a second encoding domain using a different second framing rule by way of AMR or AMR-WB+ encoding with the second framing rule being an AMR framing rule according to which a superframe comprises four AMR frames, and using a predetermined frame size number of audio samples for the superframe, the superframe of the second encoding domain being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples;

switching from the first encoding domain to the second encoding domain or vice versa; and

modifying the second framing rule in response to switching from the first to the second encoding domain or from the second to the first encoding domain to the extent that a first superframe at the switching comprises an increased frame size number of audio samples with comprising a fifth AMR frame in addition to the four AMR frames, with the fifth AMR frame respectively overlapping a fading part of a start window or a stop window of the first time domain aliasing introducing encoder,

when the program code runs on a computer or processor.

15. An audio decoding apparatus for decoding encoded frames of audio samples, comprising:

a first time domain aliasing introducing decoder for decoding audio samples in a first decoding domain, the first time domain aliasing introducing decoder comprising a first framing rule, a start window and a stop window, the first decoder comprising a time domain transformer for transforming a first frame of decoded audio samples to the time domain based on an inverse modified discrete cosine transformation (IMDCT);

a second decoder for decoding audio samples in a second decoding domain and the second decoder comprising a predetermined frame size number of audio samples and a coding warm-up period number of audio samples, the second decoder comprising a different second framing rule, a frame of the second encoder being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

a controller for, using a processor, switching from the first decoder to the second decoder or vice versa based on an indication in the encoded frame of audio samples, wherein the controller is adapted for modifying the start window or the stop window of the first decoder to the extent that a zero part thereof extends across a first quarter of an MDCT size and cross fade starts in a second quarter of the MDCT size so that the cross fade begins after a MDCT folding axis relative to the zero part, wherein the second framing rule remains unmodified.

16. The audio decoding apparatus of claim 15, wherein the first time domain aliasing introducing decoder is adapted for utilizing a start window and/or a stop window comprising an aliasing-free part at a rising edge part of the window when the preceding frame is decoded by the second decoder and at a falling edge part when the subsequent frame is encoded by the second decoder.

17. The audio decoding apparatus of claim 15, wherein the controller is adapted for applying a cross-over fade between consecutive frames of decoded audio samples of different decoders.

18. The audio decoding apparatus of claim 15, wherein the controller is adapted for determining an aliasing in an aliasing part of the start or stop window from a decoded frame of the second decoder and for reducing the aliasing in the aliasing part based on the aliasing determined.

19. The audio decoding apparatus of claim 15, wherein the controller is adapted for discarding the coding warm-up period of audio samples from the second decoder.

20. An audio decoding apparatus for decoding encoded frames of audio samples, comprising:

a first time domain aliasing introducing decoder for decoding audio samples in a first decoding domain, the first time domain aliasing introducing decoder comprising a first framing rule, a start window and a stop window, the first decoder comprising a time domain transformer for transforming a first frame of decoded audio samples to the time domain based on an inverse modified discrete cosine transformation (IMDCT);

a second decoder for decoding audio samples in a second decoding domain, the second encoder comprising a different second framing rule and comprising an AMR or AMR-WB+ encoder with the second framing rule being an AMR framing rule according to which a superframe comprises four AMR frames, and the second decoder comprising a predetermined frame size number of audio samples for the superframe and a coding warm-up period number of audio samples, a superframe of the second encoder being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

a controller for, using a processor, switching from the first decoder to the second decoder or vice versa based on an indication in the encoded frame of audio samples, wherein the controller is adapted for modifying the second framing rule in response to switching from the first decoder to the second decoder or from the second decoder to the first decoder to the extent that a first superframe at the switching comprises an increased frame size number of audio samples with comprising a fifth AMR frame in addition to the four AMR frames, with the fifth AMR frame respectively overlapping a fading part of a start window or a stop window of the first time domain aliasing introducing decoder.

21. The audio decoding apparatus of claim 20, wherein the first decoder comprises a time domain transformer for transforming a first frame of decoded audio samples to the time domain.

22. The audio decoding apparatus of claim 21, wherein the time domain transformer is adapted for transforming the first frame to the time domain based on an inverse MDCT (IMDCT) and wherein the first time domain aliasing introducing decoder is adapted for adapting an IMDCT-size to the start and/or stop or modified start and/or stop windows.

23. The audio decoding apparatus of claim 20, wherein the first decoder is adapted for weighting the last decoded frame with the start window when the subsequent frame is decoded by the second decoder and/or for weighting the first decoded frame with the stop window when a preceding frame is to be decoded by the second decoder.

24. The audio decoding apparatus of claim 20, wherein the first time-domain aliasing introducing decoder is adapted for utilizing a start window and/or a stop window comprising an aliasing part and a aliasing-free part.

25. The audio decoding apparatus according to claim 24, wherein the controller is adapted to start the second decoder, such that the first frame of the sequence of frames of the second decoder comprises an encoded representation of a sample processed in the preceding aliasing-free part of the first encoder.

26. The audio decoding apparatus of claim 24, wherein the controller is adapted to start the second decoder, such that the coding warm-up period number of audio samples overlaps with the aliasing-free part of the start window of the first time domain aliasing introducing decoder and the subsequent frame of the second decoder overlaps with the aliasing part of the stop window.

27. A method for decoding encoded frames of audio samples, comprising

decoding audio samples in a first decoding domain, the first decoding domain introducing time aliasing, comprising a first framing rule, a start window and a stop window, and using transforming a first frame of decoded audio samples to the time domain based on an inverse modified discrete cosine transformation (IMDCT);

decoding audio samples in a second decoding domain, the second decoding domain comprising a predetermined frame size number of audio samples and a coding warm-up period number of audio samples, the second decoding domain comprising a different second framing rule, a frame of the second decoding domain being a decoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

using a processor, switching from the first decoding domain to the second decoding domain or vice versa based on an indication from the encoded frame of audio samples, and modifying the start window and/or the stop window of the first decoding domain to the extent that a zero part thereof extends across a first quarter of an MDCT size and cross fade starts in a second quarter of the MDCT size so that the cross fade begins after a MDCT folding axis relative to the zero part, wherein the second framing rule remains unmodified.

28. A method for decoding encoded frames of audio samples, comprising

decoding audio samples in a first decoding domain, the first decoding domain introducing time aliasing, comprising a first framing rule, a start window and a stop window, and using transforming a first frame of decoded audio samples to the time domain based on an inverse modified discrete cosine transformation (IMDCT);

decoding audio samples in a second decoding domain using a different second framing rule by AMR or AMR-WB+ encoding with the second framing rule being an AMR framing rule according to which a superframe comprises four AMR frames, the second decoding domain comprising a predetermined frame size number of audio samples and a coding warm-up period number of audio samples, a superframe of the second decoding domain being a decoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

using a processor, switching from the first decoding domain to the second decoding domain or vice versa based on an indication from the encoded frame of audio samples, and modifying the second framing rule in response to switching from the first decoding domain to the second decoding domain or from the second to the first coding domain to the extent that a first superframe at the switching comprises an increased frame size number of audio samples with comprising a fifth AMR frame in addition to the four AMR frames, with the fifth AMR frame respectively overlapping a fading part of the start window or the stop window.

29. An audio encoding apparatus for encoding audio samples, comprising:

a first time domain aliasing introducing encoder for encoding audio samples in a first encoding domain, the first time domain aliasing introducing encoder comprising a first framing rule, a start window and a stop window;

a second encoder for encoding samples in a second encoding domain, the second encoder being a CELP encoder and comprising a predetermined frame size number of audio samples, and a warm-up period of a coding warm-up period number of audio samples during which period the second encoder experiences increased quantization noise, the second encoder comprising a different second framing rule, a frame of the second encoder being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

a controller for, using a processor, switching from the first encoder to the second encoder and vice versa in response to a characteristic of the audio samples, and for modifying the second framing rule in response to the switching,

wherein the first time-domain aliasing introducing encoder is adapted for utilizing a start window and/or a stop window comprising an aliasing part and an aliasing-free part,

wherein the controller is adapted to, in response the switching, modify the second framing rule such that the first frame of a sequence of frames of the second encoder comprises an encoded representation of a sample processed in the aliasing-free part of the first encoder.

30. An audio decoding apparatus for decoding encoded frames of audio samples, comprising:

a first time domain aliasing introducing decoder for decoding audio samples in a first decoding domain, the first time domain aliasing introducing decoder comprising a first framing rule, a start window and a stop window;

a second decoder for decoding audio samples in a second decoding domain and the second decoder being a CELP decoder comprising a predetermined frame size number of audio samples and a warm-up period of a coding warm-up period number of audio samples during which period the second encoder experiences increased quantization noise, the second decoder comprising a different second framing rule, a frame of the second encoder being an encoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

a controller for, using a processor, switching from the first decoder to the second decoder and vice versa based on an indication in the encoded frame of audio samples, wherein the controller is adapted for modifying the second framing rule in response to the switching,

wherein the first time-domain aliasing introducing decoder is adapted for utilizing a start window and/or a stop window comprising an aliasing part and an aliasing-free part,

wherein the controller is adapted to, in response the switching, modify the second framing rule such that the first frame of a sequence of frames of the second decoder comprises an encoded representation of a sample processed in the aliasing-free part of the first decoder, with the second decoder being adapted to decode and discard the encoded representation of the sample.

31. A non-transitory computer-readable medium having stored thereon a computer program comprising a program code for performing the method for decoding encoded frames of audio samples, said method comprising

decoding audio samples in a first decoding domain, the first decoding domain introducing time aliasing, comprising a first framing rule, a start window and a stop window, and using transforming a first frame of decoded audio samples to the time domain based on an inverse modified discrete cosine transformation (IMDCT);

decoding audio samples in a second decoding domain, the second decoding domain comprising a predetermined frame size number of audio samples and a coding warm-up period number of audio samples, the second decoding domain comprising a different second framing rule, a frame of the second decoding domain being a decoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

switching from the first decoding domain to the second decoding domain or vice versa based on an indication from the encoded frame of audio samples;

modifying the start window and/or the stop window of the first decoding domain to the extent that a zero part thereof extends across a first quarter of an MDCT size and cross fade starts in a second quarter of the MDCT size so that the cross fade begins after a MDCT folding axis relative to the zero part, wherein the second framing rule remains unmodified,

when the program code runs on a computer or processor.

32. A non-transitory computer-readable medium having stored thereon a computer program comprising a program code for performing the method for decoding encoded frames of audio samples, said method comprising

decoding audio samples in a first decoding domain, the first decoding domain introducing time aliasing, comprising a first framing rule, a start window and a stop window, and using transforming a first frame of decoded audio samples to the time domain based on an inverse modified discrete cosine transformation (IMDCT);

decoding audio samples in a second decoding domain using a different second framing rule by AMR or AMR-WB+ encoding with the second framing rule being an AMR framing rule according to which a superframe comprises four AMR frames, the second decoding domain comprising a predetermined frame size number of audio samples and a coding warm-up period number of audio samples, a superframe of the second decoding domain being a decoded representation of a number of timely subsequent audio samples, the number being equal to the predetermined frame size number of audio samples; and

switching from the first decoding domain to the second decoding domain or vice versa based on an indication from the encoded frame of audio samples;

modifying the second framing rule in response to switching from the first decoding domain to the second decoding domain or from the second encoder to the first encoder to the extent that a first superframe at the switching comprises an increased frame size number of audio samples with comprising a fifth AMR frame in addition to the four AMR frames, with the fifth AMR frame respectively overlapping a fading part of a start window or a stop window of the first time domain aliasing introducing encoder,

when the program code runs on a computer or processor.