Transform-domain codebook in a CELP coder and decoder

• US 8,825,475 B2
• Filed: 05/11/2012
• Issued: 09/02/2014
• Est. Priority Date: 05/11/2011
• Status: Active Grant

• Current Assignee: VoiceAge EVS LLC (Government of ABU Dhabi)
• Original Assignee: VoiceAge Corporation
• Inventors: Eksler, Vaclav
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Le, Thuykhanh
• Application Number:
  US13/469,744
• Publication Number:
  US 20120290295A1
• Time in Patent Office: 844 Days
• Field of Search: None
• US Class Current: 704/219
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio
• CPC Class Codes: G10L 19/107 Sparse pulse excitation, e.g. by using algebraic codebook
• 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 19/22 Mode decision, i.e. based on audio signal content versus external parameters
• CPC Class Codes: G10L 2019/0005 Multi-stage vector quantisation
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10

Abstract

Codebook Arrangement for use in coding an input sound signal includes First and Second Codebook Stages. First Codebook Stage includes one of a time-domain CELP codebook and a transform-domain codebook. Second Codebook Stage follows the first codebook stage and includes the other of the time-domain CELP codebook and the transform-domain codebook. Codebook Stage includes an adaptive codebook may be provided before First Codebook Stage. A selector may be provided to select an order of the time-domain CELP codebook and the transform-domain codebook in First and Second Codebook Stages, respectively, as a function of characteristics of the input sound signal. The selector may also be responsive to both the characteristics of the input sound signal and a bit rate of the codec using Codebook Arrangement to bypass Second Codebook Stage. Codebook Arrangement can be used in a coder of an input sound signal.

Claims

1. A Code-Excited Linear Prediction (CELP) codebook coding device for encoding sound into first, second, and third sets of encoding parameters, comprising:

a first calculator of a first target signal for an adaptive codebook search in response to an input sound signal;

a CELP adaptive codebook stage structured to search, in response to the first target signal, an adaptive codebook to find an adaptive codebook index and an adaptive codebook gain, the adaptive codebook index and gain forming the first set of encoding parameters;

a CELP innovative codebook stage structured to search, in response to a second target signal, a CELP innovative codebook to find an innovative codebook index and an innovative codebook gain, the innovative codebook index and gain forming the second set of encoding parameters;

a transform-domain codebook stage structured to calculate, in response to a third target signal, transform-domain coefficients and a transform-domain codebook gain, the transform-domain coefficients and the transform-domain codebook gain forming the third set of encoding parameters;

a second calculator of the second target signal and a third calculator of the third target signal;

a selector of an order of the CELP innovative codebook stage and the transform-domain codebook stage as a function of at least one of (a) characteristics of the input sound signal and (b) a bit rate of a codec using the CELP codebook coding device, wherein the selector comprises switches having a first position where the CELP innovative codebook stage is first and followed by the transform-domain codebook stage and a second position where the transform-domain codebook stage is first and followed by the CELP innovative codebook stage, and wherein;

in the first position of the switches, the second calculator determines the second target signal using the first target signal and information from the CELP adaptive codebook stage and the third calculator determines the third target signal using the second target signal and information from the CELP innovative codebook stage; and

in the second position of the switches, the third calculator determines the third target signal using the first target signal and information from the CELP adaptive codebook stage and the second calculator determines the second target signal using the first target signal and information from the CELP adaptive codebook stage and the transform-domain codebook stage,

wherein each of the first calculator, the CELP adaptive codebook stage, the CELP innovative codebook stage, the transform-domain codebook stage, the second calculator, the third calculator, and the selector is configured to be processed by one or more processors, wherein the one or more processors is coupled to a memory.

2. A CELP codebook coding device as defined in claim 1, wherein the selector is responsive to both the characteristics of the input sound signal and a bit rate of the codec using the CELP codebook coding device to bypass a last codebook stage amongst the CELP adaptive codebook stage and the transform-domain codebook stage.

3. A CELP codebook coding device as defined in claim 1, wherein the selector comprises a classifier of the input sound signal, and the switches are controlled by the classifier to change the order of the CELP innovative codebook stage and the transform-domain codebook stage.

4. A CELP codebook coding device as defined in claim 3, wherein the classifier classifies each of successive segments of the input sound signal as active speech segment or inactive speech segment.

5. A CELP codebook coding device as defined in claim 1, wherein the transform-domain codebook stage comprises a calculator of a transform of the third target signal and a quantizer of the transform-domain coefficients from the transform calculator.

6. A CELP codebook coding device as defined in claim 5, wherein the transform is a discrete cosine transform and the quantizer is an algebraic vector quantizer.

7. A CELP codebook coding device as defined in claim 5, wherein the transform-domain codebook stage comprises a pre-emphasis filter processing the third target signal before supplying said third target signal to the transform calculator.

8. A CELP codebook coding device as defined in claim 5, wherein the transform-domain codebook stage further comprises a calculator of an inverse transform of the quantized transform-domain coefficients from the quantizer, a de-emphasis filter for processing the inverse transformed, quantized transform-domain coefficients to produce a time-domain excitation signal, a weighted synthesis filter for processing the time-domain excitation signal to produce a filtered transform-domain codebook excitation signal, and an amplifier using the transform-domain codebook gain for scaling the filtered transform-domain codebook excitation signal to produce a transform-domain codebook excitation contribution.

9. A CELP codebook coding device as defined in claim 5, wherein the adaptive codebook of the CELP adaptive codebook stage is supplied with an adaptive codebook index to produce an adaptive codebook vector, and wherein the calculator of the third target signal use the adaptive codebook vector when the transform-domain codebook follows the CELP adaptive codebook stage and the switches are in the second position.

10. A CELP codebook coding device as defined in claim 5, wherein:

the CELP adaptive codebook stage computes an adaptive codebook excitation contribution by supplying an adaptive codebook index to the adaptive codebook to produce an adaptive codebook vector, processing the adaptive codebook vector through a weighted synthesis filter to produce a filtered adaptive codebook excitation signal, and amplifying the filtered adaptive codebook excitation signal with an amplifier using an adaptive codebook gain to produce the adaptive codebook excitation contribution; and

the CELP innovative codebook stage computes an innovative codebook excitation contribution by applying an innovative codebook index to the CELP innovative codebook to produce an innovative codebook vector, processing the innovative codebook vector through a weighted synthesis filter to produce a filtered innovative codebook excitation signal, and amplifying the filtered innovative codebook excitation signal with an amplifier using an innovative codebook gain to produce the innovative codebook excitation contribution.

11. A CELP codebook coding device as defined in claim 10, wherein the third calculator uses the adaptive codebook excitation contribution and the innovative codebook excitation contribution when the transform-domain codebook stage is the last codebook stage and the switches are in the first position.

12. A CELP codebook coding device as defined in claim 5, wherein the transform-domain codebook stage comprises a bit budget allocated to the quantization by the quantizer that is a sum of a fixed bit budget and a floating number of bits.

13. A CELP codebook coding device as defined in claim 12, wherein the floating number of bits in a current sub-frame comprises bits unused for the quantization in a previous sub-frame.

14. A CELP codebook coding device as defined in claim 5, wherein the transform-domain codebook stage comprises a calculator of the transform-domain codebook gain using transform-domain coefficients from the transform calculator and quantized transform-domain coefficients from the quantizer.

15. A CELP codebook coding device as defined in claim 1, wherein the transform-domain codebook stage produces a transform-domain codebook excitation contribution, and wherein the CELP innovative codebook stage uses the transform-domain codebook excitation contribution to refine the adaptive codebook gain.

16. A CELP codebook coding device as defined in claim 1, comprising a limiter of the adaptive codebook gain in the presence of inactive sound signal segments.

17. A Code-Excited Linear Prediction (CELP) codebook coding method for encoding sound into first, second and third sets of encoding parameters, comprising:

receiving a sound signal on an input from a microphone or a storage device;

calculating a first target signal for an adaptive codebook search in response to the input sound signal;

in a CELP adaptive codebook stage, searching in response to the first target signal an adaptive codebook to find an adaptive codebook index and an adaptive codebook gain, the adaptive codebook index and gain forming the first set of encoding parameters;

in a CELP innovative codebook stage, searching in response to a second target signal a CELP innovative codebook to find an innovative codebook index and an innovative codebook gain, the innovative codebook index and gain forming the second set of encoding parameters;

in a transform-domain codebook stage, calculating in response to a third target signal transform-domain coefficients and a transform-domain codebook gain, the transform-domain coefficients and the transform-domain codebook gain forming the third set of encoding parameters;

calculating the second target signal and the third target signal;

selecting an order of the CELP innovative codebook stage and the transform-domain codebook stage as a function of at least one of (a) characteristics of the input sound signal and (b) a bit rate of a codec using the CELP codebook coding method, wherein;

in a selected order where the CELP innovative codebook stage is first and followed by the transform-domain codebook stage, the second target signal is determined using the first target signal and information from the CELP adaptive codebook stage and the third target signal is determined using the second target signal and information from the CELP innovative codebook stage; and

in a selected order where the transform-domain codebook stage is first and followed by the CELP innovative codebook stage, the third target signal is determined using the first target signal and information from the CELP adaptive codebook stage and the second target signal is determined using the first target signal and information from the CELP adaptive codebook stage and the transform-domain codebook stage wherein each of the receiving, calculating, searching and selecting operation is configured to be processed by one or more processors, wherein the one or more processors is coupled to a memory.

18. A CELP codebook coding method as defined in claim 17, comprising bypassing, in response to both the characteristics of the input sound signal and the bit rate of the codec using the CELP codebook coding method, a last codebook stage amongst the CELP innovative codebook stage and the transform-domain codebook stage.

19. A CELP codebook coding method as defined in claim 17, wherein the selection of the order of the CELP innovative codebook stage and the transform-domain codebook stage comprises classifying the input sound signal and changing the order of the CELP innovative codebook stage and the transform-domain codebook stage in response to said classification.

20. A CELP codebook coding method as defined in claim 19, wherein each of successive segments of the input sound signal is classified as active speech segment or inactive speech segment.

21. A CELP codebook coding method as defined in claim 17, wherein, in the transform-domain codebook stage, calculating transform-domain coefficients comprises calculating a transform of the third target signal and quantizing the transform-domain coefficients from the transform calculation.

22. A CELP codebook coding method as defined in claim 21, wherein the transform is a discrete cosine transform and the quantization of the transform-domain coefficients is an algebraic vector quantization.

23. A CELP codebook coding method as defined in claim 21, comprising processing, in the transform-domain codebook stage, the third target signal through a pre-emphasis filter before calculating the transform of said third target signal.

24. A CELP codebook coding method as defined in claim 21, comprising, in the transform-domain codebook stage, calculating an inverse transform of the quantized transform-domain coefficients, processing the inverse transformed, quantized transform-domain coefficients through a de-emphasis filter to produce a time-domain excitation signal, processing the time-domain excitation signal through a weighted synthesis filter to produce a filtered transform-domain codebook excitation signal, and amplifying the filtered transform-domain codebook excitation signal using the transform-domain codebook gain to scale the filtered transform-domain codebook excitation signal to produce a transform-domain codebook excitation contribution.

25. A CELP codebook coding method as defined in claim 21, comprising supplying the adaptive codebook of the CELP adaptive codebook stage with an adaptive codebook index to produce an adaptive codebook vector, and calculating the third target signal using the adaptive codebook vector when the transform-domain codebook stage follows the CELP adaptive codebook stage.

26. A CELP codebook coding method as defined in claim 21, comprising:

computing, in the CELP adaptive codebook stage, an adaptive codebook excitation contribution by supplying an adaptive codebook index to the adaptive codebook to produce an adaptive codebook vector, processing the adaptive codebook vector through a weighted synthesis filter to produce a filtered adaptive codebook excitation signal, and amplifying the filtered adaptive codebook excitation signal with an amplifier using an adaptive codebook gain to produce the adaptive codebook excitation contribution; and

computing, in the CELP innovative codebook stage, an innovative codebook excitation contribution by applying an innovative codebook index to the CELP innovative codebook to produce an innovative codebook vector, processing the innovative codebook vector through a weighted synthesis filter to produce a filtered innovative codebook excitation signal, and amplifying the filtered innovative codebook excitation signal with an amplifier using an innovative codebook gain to produce the innovative codebook excitation contribution.

27. A CELP codebook coding method as defined in claim 26, wherein the third target signal is calculated using the adaptive codebook excitation contribution and the innovative codebook excitation contribution when the transform-domain codebook stage is the last codebook stage.

28. A CELP codebook coding method as defined in claim 21, comprising allocating, in the transform-domain codebook stage, a bit budget to the quantization of the transform-domain coefficients that is a sum of a fixed bit budget and a floating number of bits.

29. A CELP codebook coding method as defined in claim 28, wherein the floating number of bits in a current sub-frame comprises bits unused for the quantization in a previous sub-frame.

30. A CELP codebook coding method as defined in claim 21, comprising, in the transform-domain codebook stage, calculating the transform-domain codebook gain using the transform-domain coefficients and the quantized transform-domain coefficients.

31. A CELP codebook coding method as defined in claim 17, comprising producing, in the transform-domain codebook stage, a transform-domain codebook excitation contribution, and using, in the CELP innovative codebook stage, the transform-domain codebook excitation contribution to refine the adaptive codebook gain.

32. A CELP codebook coding method as defined in claim 17, comprising limiting the adaptive codebook gain in the presence of inactive sound signal segments.