Adaptive filter and filtering method for low bit rate coding

Details Adaptive filter and filtering method for low bit rate coding Adaptive filter and filtering method for low bit rate coding

1997-06-18

1999-10-12

Hudspeth, David R.

Data processing: speech signal processing, linguistics, language

Speech signal processing

For storage or transmission

704219, 704227, G10L 302, H04B 166

Patent

active

059666897

ABSTRACT:
An improved filtering method for use in an enhancement filter in a mixed excitation linear prediction (MELP) speech coder or a postfilter in a codebook excitation linear prediction (CELP) speech coder is disclosed which includes two filters. The first filter (62) has a transfer function of ##EQU1## where P is the set of prediction coefficients, .alpha. and .beta. are scaling factors, z is the inverse of the unit delay operation used in the transform representation of the transfer functions and sig-prob is signal probability estimator value and the second filter (65) has a transfer function of 1-.mu.z.sup.-1 * sig-prob, where .mu.= a scaling factor. The sig-prob is the signal probability value based on a comparison of power of the signals in a current frames to a long term estimate of noise power in signal probability estimator (63). The sig-prob value is 1 if the power of the signals is greater than the noise power plus 30 dB and the sig-prob is zero if the power is less than noise power plus 12 dB. Between these two conditions, sig-prob is (log gain-12 dB-noise gain)/18.

REFERENCES:
patent: 4969192 (1990-11-01), Chen et al.

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