Systems, methods, and apparatus for gain coding

• US 20080126086A1
• Filed: 04/03/2006
• Published: 05/29/2008
• Est. Priority Date: 04/01/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Vos, Koen Bernard, Kandhadai, Ananthapadmanabhan Aasanipalai
• Granted Patent: US 8,140,324 B2
• Time in Patent Office: Days
• US Class Current: 704/225
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/038 Vector quantisation, e.g. TwinVQ audio
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

A wideband speech encoder according to one embodiment includes a lowband encoder and a highband encoder. The lowband encoder is configured to encode a lowband portion of a wideband speech signal as a set of filter parameters and an encoded excitation signal. The highband encoder is configured to calculate values for coding parameters that specify a spectral envelope and a temporal envelope of a highband portion of the wideband speech signal. The temporal envelope is based on a highband excitation signal that is derived from the encoded excitation signal. In one such example, the temporal envelope is based on a difference in levels between the highband portion and a synthesized highband signal, wherein the synthesized highband signal is generated according to the highband excitation signal and a set of highband filter parameters.

Claims

1. A method of encoding a highband portion of a speech signal having a lowband portion and the highband portion, said method comprising:

calculating a plurality of filter parameters that characterize a spectral envelope of the highband portion;

calculating a spectrally extended signal by extending the spectrum of a signal derived from the lowband portion;

generating a synthesized highband signal according to (A) a highband excitation signal based on the spectrally extended signal and (B) the plurality of filter parameters; and

calculating a gain envelope based on a relation between the highband portion and a signal based on the lowband portion.

2. The method according to claim 1, wherein said calculating a spectrally extended signal comprises extending the spectrum of a signal derived from the lowband portion by applying a nonlinear function to the signal.

3. The method according to claim 1, wherein said calculating a gain envelope is based on a relation between energy of the highband portion and energy of a signal based on the lowband portion.

4. The method according to claim 3, wherein said calculating a gain envelope is based on a relation between energy of the highband portion and energy of the synthesized highband signal.

5. A method of speech processing, said method comprising:

generating a highband excitation signal based on a lowband excitation signal;

generating a synthesized highband signal based on a highband speech signal and the highband excitation signal; and

calculating a plurality of gain factors based on a relation between the highband speech signal and a signal based on the lowband excitation signal.

6. The method according to claim 5, wherein each of the plurality of gain factors is based on a relation between energy of a portion in time of the highband speech signal and energy of a corresponding portion in time of a signal based on the lowband excitation signal.

7. The method according to claim 5, wherein said calculating a plurality of gain factors comprises calculating a plurality of gain factors based on a relation between the highband speech signal and the synthesized highband signal.

8. The method according to claim 7, wherein each of the plurality of gain factors is based on a relation between energy of a portion in time of the highband speech signal and energy of a corresponding portion in time of the synthesized highband signal.

9. The method according to claim 5, wherein generating a synthesized highband signal includes generating the synthesized highband signal based on the highband excitation signal and a plurality of filter parameters derived from the highband speech signal.

10. A method of decoding a highband portion of a speech signal having a lowband portion and the highband portion, said method comprising:

receiving a plurality of filter parameters that characterize a spectral envelope of the highband portion and a plurality of gain factors that characterize a temporal envelope of the highband portion;

calculating a spectrally extended signal by extending the spectrum of a signal that is based on a lowband excitation signal;

generating a synthesized highband signal according to (A) the plurality of filter parameters and (B) a highband excitation signal based on the spectrally extended signal; and

modulating a gain envelope of the synthesized highband signal according to the plurality of gain factors.

11. The method according to claim 10, wherein said calculating a spectrally extended signal comprises extending the spectrum of a signal that is based on a lowband excitation signal by applying a nonlinear function to the signal.

12. The method according to claim 10, wherein said modulating a gain envelope includes modifying, according to the plurality of gain factors, an amplitude over time of at least one among a signal that is based on the lowband excitation signal, the spectrally extended signal, the highband excitation signal, and the synthesized highband signal.

13. An apparatus configured to encode a highband portion of a speech signal having a lowband portion and the highband portion, said apparatus comprising:

an analysis module configured to calculate a set of filter parameters that characterize a spectral envelope of the highband portion;

a spectrum extender configured to calculate a spectrally extended signal by extending the spectrum of a signal derived from the lowband portion;

a synthesis filter configured to generate a synthesized highband signal according to (A) a highband excitation signal based on the spectrally extended signal and (B) the set of filter parameters; and

a gain factor calculator configured to calculate a gain envelope based on a time-varying relation between the highband portion and a signal based on the lowband portion.

14. The apparatus according to claim 13, wherein said spectrum extender is configured to extend the spectrum of a signal derived from the lowband portion by applying a nonlinear function to the signal.

15. The apparatus according to claim 13, wherein said gain factor calculator is configured to calculate the gain envelope based on a time-varying relation between energy of the highband portion and energy of a signal based on the lowband portion.

16. The apparatus according to claim 15, wherein said gain factor calculator is configured to calculate the gain envelope based on a time-varying relation between energy of the highband portion and energy of the synthesized highband signal.

17. The apparatus according to claim 13, wherein said gain factor calculator is configured to calculate the gain envelope as a plurality of gain factors,

wherein each of the plurality of gain factors is based on a relation between energy of a portion in time of the highband speech signal and energy of a corresponding portion in time of the synthesized highband signal.

18. The apparatus according to claim 13, said apparatus comprising a cellular telephone.

19. A highband speech decoder configured to receive (A) a plurality of filter parameters that characterize a spectral envelope of a highband portion of a speech signal and (B) an encoded lowband excitation signal based on a lowband portion of the speech signal, said decoder comprising:

a spectrum extender configured to calculate a spectrally extended signal by extending the spectrum of a signal that is based on the encoded lowband excitation signal;

a synthesis filter configured to generate a synthesized highband signal according to the plurality of filter parameters and a highband excitation signal based on the spectrally extended signal; and

a gain control element configured to modulate a gain envelope of the synthesized highband signal according to a plurality of gain factors that characterize a temporal envelope of the highband portion.

20. The decoder according to claim 19, wherein said spectrum extender is configured to extend the spectrum of the signal based on the encoded lowband excitation signal by applying a nonlinear function to the signal.

21. The decoder according to claim 19, wherein said gain control element is configured to modify, according to the plurality of gain factors, an amplitude over time of at least one among the encoded lowband excitation signal, the spectrally extended signal, the highband excitation signal, and the synthesized highband signal.

22. The decoder according to claim 19, wherein said gain control element comprises at least one among a multiplier and an amplifier.