Speech codec employing noise classification for noise compensation

• US 6,240,386 B1
• Filed: 11/24/1998
• Issued: 05/29/2001
• 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: Benyassine, Adil, Gao, Yang, Su, Huan-Yu, Thyssen, Jes
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Nolan, Daniel A
• Application Number:
  US09/198,414
• Time in Patent Office: 917 Days
• Field of Search: 704/215, 704/201, 704/219-226
• 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 19/20 using sound class specific coding, hybrid encoders or object based coding
• 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. The multi-rate speech codec may employ distributed detection and compensation processing the speech signal. For high quality perceptual speech reproduction, the speech codec may perform noise detection in both an encoder and a decoder. The noise detection may be coordinated between the encoder and decoder. Similarly, noise compensation may be performed in a distributed manner among both the decoder and the encoder.

Claims

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

an encoder that generates speech parameters from the speech signal;

a decoder, communicatively coupled to the encoder, that reproduces the speech signal from the speech parameters;

at least one of the encoder and the decoder performs noise classification; and

at least one of the encoder and the decoder utilizing the noise classification in performing noise compensation.

2. The speech codec of claim 1, wherein both the encoder and the decoder perform the noise classification.

3. The speech codec of claim 1, wherein both the encoder and the decoder perform the noise compensation.

4. The speech codec of claim 1, wherein a codevector excitation is used in the reproduction of the speech signal.

5. The speech codec of claim 1, wherein a pulse-like excitation is used for the reproduction of the speech signal.

6. The speech codec of claim 1, wherein at least one of the encoder and the decoder smoothes a gain when reproducing the speech signal.

7. The speech codec of claim 1, wherein the at least one of the varying characteristics of the speech signal comprises a pitch parameter.

8. The speech codec of claim 1, wherein the encoder performs at least a portion of the noise classification and at least a portion of the noise compensation through selection of one of a plurality of source encoding approaches.

9. The speech codec of claim 1, wherein the decoder performs at least a portion of the noise classification and at least a portion of the noise compensation through insertion of noise during the reproduction of the speech signal.

10. A speech codec using an analysis by synthesis approach on a speech signal having varying characteristics, the speech codec comprising:

a processing circuit that selectively applies noise compensation upon identification of at least one of the varying characteristics of the speech signal to improve reproduction quality of the speech signal, the varying characteristics comprise characteristics indicative of at least one of noise, pulse-like speech, and noise-like speech; and

a speech reproduction circuit, communicatively coupled to the processing circuit, that reproduces the speech signal.

11. The speech codec of claim 10, wherein a pulse-like excitation is used for speech reproduction.

12. The speech codec of claim 10, wherein the processing circuit applies noise classification of the speech signal.

13. The speech codec of claim 10, wherein the speech codec further comprises a decoder, and at least a portion of the processing circuit is in the decoder.

14. The speech codec of claim 10, wherein an encoding scheme is applied that involves the use of a pulse-like excitation.

15. The speech codec of claim 10, wherein the processing circuit smoothes a gain that is used to perform reproduction of the speech signal.

16. The speech codec of claim 10, wherein the at least one of the varying characteristics of the speech signal comprises a pitch parameter.

17. The speech codec of claim 10, wherein the speech signal is partitioned into a plurality of frames;

and

the encoder processing circuit selectively applies an encoding scheme on a frame basis.

18. A method used by a speech codec that applies an analysis by synthesis coding approach to a speech signal having varying characteristics, the method comprising:

applying noise classification upon identification of at least one of the varying characteristics of the speech signal;

applying noise compensation in response to the noise classification; and

reproducing the speech signal after the compensation has been applied.

19. The method of claim 18, further comprising smoothing a gain when reproducing the speech signal.

20. The method of claim 18, wherein the noise compensation comprises performing noise insertion.