Instability eradication for analysis-by-synthesis speech codecs

Details Instability eradication for analysis-by-synthesis speech codecs Instability eradication for analysis-by-synthesis speech codecs

1999-01-15

1999-11-16

Knepper, David D.

Data processing: speech signal processing, linguistics, language

Speech signal processing

For storage or transmission

704223, 704227, G10L 702, G10L 914

Patent

active

059874066

ABSTRACT:
Instability inherent in analysis-by-synthesis speech/audio codecs and caused in particular by channel errors during transmission of highly periodic signals such as high-frequency sine waves is removed. Analysis-by-synthesis techniques involve production, in response to the speech/audio signal and at regular time intervals called frames, of (a) a set of spectral parameters for use in driving a synthesis filter in view of synthesizing the speech/audio signal, and (b) a pitch gain for constructing a past-excitation-signal component supplied to the synthesis filter. In accordance with the instability eradication method, the first step consists of detecting a set of conditions including (i) a resonance condition assessed from the spectral parameters, (ii) a duration condition detected when the resonance condition has prevailed for at least the M most recent frames, M being an integer greater than 1, and (iii) a gain condition which evidences consistently-high values of the pitch gain in the N most recent frames, N being an integer greater than 1. To eradicate the occasional instability, the pitch gain is reduced to a value lower than a given threshold whenever these three conditions are detected.

REFERENCES:
patent: 5687284 (1997-11-01), Serizawa et al.
patent: 5708757 (1998-01-01), Massaloux
patent: 5943060 (1999-04-01), Honkanen et al.
ITU-T Recommendation G.729-Annex A: Reduced Complexity 8 KBIT/S CS-ACELP Speech Codec, 13 pages (Nov. 1996).

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