FILTERING METHOD AND LOW BIT RATE VOICE COMMUNICATION SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide a filtering method including two filters which can be used as a reinforced filter of a mix excitation linear prediction voice coder or a post filter of a code book excitation linear prediction voice coder. ;SOLUTION: A first filter 62 has a transfer function of {1-P[z/(β.sig- prob)]}/{1-P[z/(α.sig-prob)]} assuming that P is a prediction value, α and βare magnification, z is an inverse of unit delay operator for conversion- displaying of a transfer function, and sig-prob is a signal probability estimation value, a second filter 65 has a transfer function of 1-μz^-1.sig-prob assuming that μ is magnification. Then sig-prob a signal probability value obtained by comparing signal power of the present frame with a long term estimation value of noise power in a signal probability estimation device 63, when signal power is larger than a value in which 30dB is added to noise power, a value of sig- prob is 1, and when signal power is smaller than a value in which 12dB is added to noise power. a value of sig-prob is 0. Between two states, sig-prob is (logarithm gain - 12dB - noise gain)/18.;COPYRIGHT: (C)1999,JPO