Speech encoder using voice activity detection in coding noise

• US 6,823,303 B1
• Filed: 09/18/1998
• Issued: 11/23/2004
• Est. Priority Date: 08/24/1998
• Status: Expired due to Term

• Current Assignee: MACOM Technology Solutions Holdings, Inc.
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Su, Huan-Yu, Thyssen, Jes, Benyassine, Adil
• Primary Examiner(s): Tsang, Fan
• Assistant Examiner(s): Opsasnick, Michael N.
• Application Number:
  US09/156,832
• Time in Patent Office: 2,258 Days
• Field of Search: 704/220, 704/213, 704/214, 704/201
• US Class Current: 704/220
• CPC Class Codes: G10L 19/002 Dynamic bit allocation for perceptual audio coders G10L19/032
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• 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 19/083 the excitation function being an excitation gain G10L25/90 takes precedence
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor
• CPC Class Codes: G10L 19/10 the excitation function being a multipulse excitation
• 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 19/125 Pitch excitation, e.g. pitch synchronous innovation CELP [PSI-CELP]
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• CPC Class Codes: G10L 2019/0005 Multi-stage vector quantisation
• CPC Class Codes: G10L 2019/0007 Codebook element generation
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation
• CPC Class Codes: G10L 21/0364 for improving intelligibility

Abstract

A multi-rate speech codec supports a plurality of encoding bit rate modes by adaptively selecting encoding bit rate modes to match communication channel restrictions. In higher bit rate encoding modes, an accurate representation of speech through CELP (code excited linear prediction) and other associated modeling parameters are generated for higher quality decoding and reproduction. For each bit rate mode selected, pluralities of fixed or innovation subcodebooks are selected for use in generating innovation vectors. The speech coder distinguishes various voice signals as a function of their voice content. For example, a Voice Activity Detection (VAD) algorithm selects an appropriate coding scheme depending on whether the speech signal comprises active or inactive speech. The encoder may consider varying characteristics of the speech signal including sharpness, a delay correlation, a zero-crossing rate, and a residual energy. In another embodiment of the present invention, code excited linear prediction is used for voice active signals whereas random excitation is used for voice inactive signals; the energy level and spectral content of the voice inactive signal may also be used for noise coding.

Claims

1. A speech encoding system using an analysis by synthesis approach on a speech signal having varying characteristics, the speech encoding system comprising:

an encoder processing circuit that selectively applies a first or a second encoding scheme upon identification of varying characteristics of the speech signal;

where the varying characteristics are utilized to classify the speech signal as having one of active voice content and inactive voice content;

the first encoding scheme utilizes a first analysis-by-synthesis speech coding approach on a speech signal classified as active voice content; and

the second encoding scheme utilizes a second analysis-by-synthesis speech coding approach on a speech signal classified as inactive voice content, the inactive voice content comprising background noise.

2. The speech encoding system of claim 1, wherein the varying characteristics of the speech signal comprises pitch characteristics.

3. The speech encoding system of claim 1, wherein the varying characteristics of the speech signal comprises periodicity characteristics.

4. The speech encoding system of claim 1, wherein the varying characteristics of the speech signal comprises intensity characteristics.

5. The speech encoding system of claim 1, wherein the encoder processing circuit selectively applies one of the first and the second encoding scheme at one of a plurality of bit rates.

11. The speech encoding system of claim 1, wherein the first encoding scheme selects operation in one of a long term predictor (LTP) mode and a pitch preprocessing (PP) mode.

12. The speech encoding system of claim 1, wherein the second encoding scheme selects a random excitation sequence after considering an energy level and spectral information of the speech signal.

13. The speech encoding system of claim 1, wherein a speech signal classified as inactive voice comprises silence.

14. The speech encoding system of claim 1, wherein a speech signal classified as inactive voice comprises background noise.

6. A speech encoding system for processing a speech signal having varying characteristics, the speech encoding system comprising:

an encoder processing circuit that selectively applies a first or a second analysis-by-synthesis encoding scheme based upon at least one of the varying characteristics of the speech signal;

the encoder processing circuit applies the first analysis-by-synthesis encoding scheme following identification of an active voice frame of the speech signal; and

the encoder processing circuit applies the second analysis-by-synthesis encoding scheme following identification of an inactive voice frame of the speech signal, the inactive voice frame comprising background noise.

7. The speech encoding system of claim 6, wherein the second encoding scheme selects a random excitation sequence to encode the speech signal.

8. The speech encoding system of claim 6, wherein the encoder processing circuit selectively applies one of the first and the second encoding scheme at one of a plurality of bit rates.

9. The speech encoding system of claim 6, wherein the second encoding scheme identifies an energy level.

10. The speech encoding system of claim 6, wherein the second encoding scheme identifies a spectral information.

15. The speech encoding system of claim 6, wherein the first encoding scheme selects operation in one of a long term predictor (LTP) mode and a pitch preprocessing (PP) mode.

16. A method of encoding a speech signal comprising:

classifying the speech signal as having one of active voice content and inactive voice content, the inactive voice content comprising background noise;

applying a first encoding scheme comprising analysis-by-synthesis when the speech signal is classified as having active voice content; and

applying a second encoding scheme comprising analysis-by-synthesis when the speech signal is classified as having inactive voice content.

17. The method of claim 16, further comprising identifying an energy level and spectral information of the speech signal when the second encoding scheme is applied.

18. The method of claim 17, further comprising performing encoding with a selected random excitation sequence after identifying the energy level and the spectral information.

19. The method of claim 16, further comprising applying one of the first encoding scheme and the second encoding scheme at one of a plurality of bit rates.

20. The method of claim 16, further comprising encoding a first frame of the speech signal with the first encoding scheme at a bit rate and encoding a second frame of the speech signal with the second encoding scheme at the same bit rate.