Linear prediction based audio coding using improved probability distribution estimation

• US 9,536,533 B2
• Filed: 12/18/2014
• Issued: 01/03/2017
• Est. Priority Date: 06/28/2012
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Baeckstroem, Tom, Helmrich, Christian, Fuchs, Guillaume, Multrus, Markus, Dietz, Martin
• Primary Examiner(s): ABEBE, DANIEL DEMELASH
• Application Number:
  US14/574,830
• Publication Number:
  US 20150106108A1
• Time in Patent Office: 747 Days
• Field of Search: 704/500
• US Class Current: 1/1
• CPC Class Codes: G10L 19/0017 Lossless audio signal coding; Perfect reconstruction of coded audio signal by transmission of coding error G10L19/24 takes precedence
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 19/08 Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
• CPC Class Codes: G10L 25/12 the extracted parameters being prediction coefficients

Abstract

Linear prediction based audio coding is improved by coding a spectrum composed of a plurality of spectral components using a probability distribution estimation determined for each of the plurality of spectral components from linear prediction coefficient information. The linear prediction coefficient information is available anyway. Accordingly, it may be used for determining the probability distribution estimation at both encoding and decoding side. The latter determination may be implemented in a computationally simple manner by using, for example, an appropriate parameterization for the probability distribution estimation at the plurality of spectral components. The coding efficiency as provided by the entropy coding is compatible with probability distribution estimations as achieved using context selection, but its derivation is less complex. The derivation may be purely analytically and/or does not require any information on attributes of neighboring spectral lines such as previously coded/decoded spectral values of neighboring spectral lines as is the case in spatial context selection.

Claims

1. A linear prediction based audio decoder comprising:

a probability distribution estimator configured to determine, for each of a plurality of spectral components, a probability distribution estimation from linear prediction coefficient information comprised in a data stream into which an audio signal is encoded;

an entropy decoding and dequantization stage configured to entropy decode and dequantize a spectrum composed of the plurality of spectral components from the data stream using the probability distribution estimation as determined for each of the plurality of spectral components; and

a filter configured to shape the spectrum according to a transfer function depending on a linear prediction synthesis filter defined by the linear prediction coefficient information,

wherein the probability distribution estimator is configured to determine a spectral fine structure from long-term prediction parameters comprised in the data stream and determine, for each of the plurality of spectral components, a probability distribution parameter such that the probability distribution parameters spectrally follow a function which multiplicatively depends on the spectral fine structure, wherein, for each of the plurality of spectral components, the probability distribution estimation is a parameterizable function parameterized with the probability distribution parameter of the respective spectral component.

2. The linear prediction based audio decoder according to claim 1, further comprising:

a scale-factor determiner configured to determine scale factors based on the linear prediction coefficient information; and

a spectral shaper configured to spectrally shape the spectrum by scaling the spectrum using the scale factors,

wherein the scale factor determiner is configured to determine the scale factors such that same represent a transfer function depending on a linear prediction synthesis filter defined by the linear prediction coefficient information.

3. The linear prediction based audio decoder according to claim 1, wherein

the transfer function'"'"'s dependency on the linear prediction synthesis filter defined by the linear prediction coefficient information is such that the transfer function is perceptually weighted.

4. The linear prediction based audio decoder according to claim 1, wherein

the transfer function'"'"'s dependency on the linear prediction synthesis filter 1/A(z) defined by the linear prediction is such that the transfer function is a transfer function of 1/A(k·

z), where k is a constant.

5. The linear prediction based audio decoder according to claim 1, wherein the probability distribution estimator is configured such that the spectral fine structure is a comb-like structure defined by the long-term prediction parameters.

6. The linear prediction based audio decoder according to claim 1, wherein the long-term prediction parameters comprise a long-term prediction gain and a long-term prediction pitch.

7. The linear prediction based audio decoder according to claim 1, wherein, for each of the plurality of spectral components, the parameterizable function is defined such that the probability distribution parameter is a measure for a dispersion of the probability distribution estimation.

8. The linear prediction based audio decoder according to claim 1, wherein, for each of the plurality of spectral components, the parameterizable function is a Laplace distribution, and the probability distribution parameter of the respective spectral component forms a scale parameter of the respective Laplace distribution.

9. The linear prediction based audio decoder according to claim 1, further comprising a de-emphasis filter.

10. The linear prediction based audio decoder according to claim 1, wherein the entropy decoding and dequantization stage is configured to, in dequantizing and entropy decoding the spectrum of the plurality of spectral components, treat sign and magnitude at the plurality of spectral components separately with using the probability distribution estimation as determined for each of the plurality of spectral components for the magnitude.

11. The linear prediction based audio decoder according to claim 1, wherein the entropy decoding and dequantizing stage is configured to use the probability distribution estimation in entropy decoding a magnitude level of the spectrum per spectral component and dequantize the magnitude levels equally for all spectral components so as to acquire the spectrum.

12. The linear prediction based audio decoder according to claim 11, wherein the entropy decoding and quantization stage is configured to use a constant quantization step size for dequantizing the magnitude levels.

13. The linear prediction based audio decoder according to claim 1, further comprising

an inverse transformer configured to subject the spectrum to a real-valued critically sampled inverse transform so as to acquire an aliasing-suffering time-domain signal portion;

and

an overlap-adder configured to subject the aliasing-suffering time-domain signal portion to an overlap-and-add process with a preceding and/or succeeding time-domain portion so as to reconstruct the audio signal.

14. A linear prediction based audio encoder comprising:

a linear prediction analyzer configured to determine linear prediction coefficient information;

a probability distribution estimator configured to determine, for each of a plurality of spectral components, a probability distribution estimation from the linear prediction coefficient information; and

a spectrum determiner configured to determine a spectrum composed of the plurality of spectral components from an audio signal;

a quantization and entropy encoding stage configured to quantize and entropy encode the spectrum using the probability distribution estimation as determined for each of the plurality of spectral components,

wherein the spectrum determiner is configured to shape an original spectrum of the audio signal according to a transfer function which depends on an inverse of a linear prediction synthesis filter defined by the linear prediction coefficient information, and

wherein the linear prediction based audio encoder further comprises a long-term predictor configured to determine long-term prediction parameters and the probability distribution estimator is configured to determine a spectral fine structure from the long-term prediction parameters and determine, for each of the plurality of spectral components, a probability distribution parameter such that the probability distribution parameters spectrally follow a function which depends on a product of a transfer function of the linear prediction synthesis filter, an inverse of a transfer function of a perceptually weighted modification of the linear prediction synthesis filter, and the spectral fine structure, wherein, for each of the plurality of spectral components, the probability distribution estimation is a parameterizable function parameterized with the probability distribution parameter of the respective spectral component.

15. The linear prediction based audio encoder according to claim 14, wherein the spectrum determiner comprises:

a scale-factor determiner configured to determine scale factors based on the linear prediction coefficient information;

a transformer configured to spectrally decompose the audio signal to acquire the original spectrum; and

a spectral shaper configured to spectrally shape the original spectrum by scaling the spectrum using the scale factors,

wherein the scale factor determiner is configured to determine the scale factors such that the spectral shaping by the spectral shaper using the scale factors corresponds to a transfer function which depends on an inverse of a linear prediction synthesis filter defined by the linear prediction coefficient information.

16. The linear prediction based audio encoder according to claim 14, wherein

the transfer function'"'"'s dependency on the inverse of the linear prediction synthesis filter defined by the linear prediction is such that the transfer function is perceptually weighted.

17. The linear prediction based audio encoder according to claim 14, wherein

the transfer function'"'"'s dependency on the inverse of the linear prediction synthesis filter 1/A(z) defined by the linear prediction coefficient information such that the transfer function is an inverse of a transfer function of 1/A(k·

z), where k is a constant.

18. The linear prediction based audio encoder according to claim 14, wherein the probability distribution estimator is configured such that the spectral fine structure is a comb-like structure defined by the long-term prediction parameters.

19. The linear prediction based audio encoder according to claim 14, wherein the long-term prediction parameters comprise a long-term prediction gain and a long-term prediction pitch.

20. The linear prediction based audio encoder according to claim 14, wherein, for each of the plurality of spectral components, the parameterizable function is defined such that the probability distribution parameter is a measure for a dispersion of the probability distribution estimation.

21. The linear prediction based audio encoder according to claim 14, wherein, for each of the plurality of spectral components, the parameterizable function is a Laplace distribution, and the probability distribution parameter of the respective spectral component forms a scale parameter of the respective Laplace distribution.

22. The linear prediction based audio encoder according to claim 14, further comprising a pre-emphasis filter configured to subject the audio signal to a pre-emphasis.

23. The linear prediction based audio encoder according to claim 14, wherein the quantization and entropy encoding stage is configured to, in quantizing and entropy encoding the spectrum of the plurality of spectral components, treat sign and magnitude at the plurality of spectral components separately with using the probability distribution estimation as determined for each of the plurality of spectral components for the magnitude.

24. The linear prediction based audio encoder according to claim 14, wherein the quantization and entropy encoding stage is configured to quantize the spectrum equally for all spectral components so as to acquire magnitude levels for the spectral components and use the probability distribution estimation in entropy encoding the magnitude levels of the spectrum per spectral component.

25. The linear prediction based audio encoder according to claim 24, wherein the quantize and entropy encoding stage is configured to use a constant quantization step size for the quantizing.

26. The linear prediction based audio encoder according to claim 14, wherein the transformer is configured to perform a real-valued critically sampled transform.

27. A method for linear prediction based audio decoding, comprising:

determining, for each of a plurality of spectral components, a probability distribution estimation from linear prediction coefficient information comprised in a data stream into which an audio signal is encoded; and

entropy decoding and dequantizing a spectrum composed of the plurality of spectral components from the data stream using the probability distribution estimation as determined for each of the plurality of spectral components,

the method also comprising shaping the spectrum according to a transfer function depending on a linear prediction synthesis filter defined by the linear prediction coefficient information,

wherein the determination of the probability distribution estimation comprises determining a spectral fine structure from long-term prediction parameters comprised in the data stream and determining, for each of the plurality of spectral components, a probability distribution parameter such that the probability distribution parameters spectrally follow a function which multiplicatively depends on the spectral fine structure, wherein, for each of the plurality of spectral components, the probability distribution estimation is a parameterizable function parameterized with the probability distribution parameter of the respective spectral component.

29. A non-transitory computer readable medium including a computer program comprising a program code for performing, when running on a computer, a method according to claim 27.

28. A method for linear prediction based audio encoding, comprising:

determining linear prediction coefficient information;

determining, for each of a plurality of spectral components, a probability distribution estimation from the linear prediction coefficient information; and

determining a spectrum composed of the plurality of spectral components from an audio signal;

quantizing and entropy encoding the spectrum using the probability distribution estimation as determined for each of the plurality of spectral components,

wherein the determination of the spectrum comprises shaping an original spectrum of the audio signal according to a transfer function which depends on an inverse of a linear prediction synthesis filter defined by the linear prediction coefficient information, and

wherein the method further comprises determining long-term prediction parameters and the determination of the probability distribution comprises determining a spectral fine structure from the long-term prediction parameters and determining, for each of the plurality of spectral components, a probability distribution parameter such that the probability distribution parameters spectrally follow a function which depends on a product of a transfer function of the linear prediction synthesis filter, an inverse of a transfer function of a perceptually weighted modification of the linear prediction synthesis filter, and the spectral fine structure, wherein, for each of the plurality of spectral components, the probability distribution estimation is a parameterizable function parameterized with the probability distribution parameter of the respective spectral component.

30. A non-transitory computer readable medium including a computer program comprising a program code for performing, when running on a computer, a method according to claim 28.