GAIN ESTMATION SCHEME FOR LPC VOCODERS WITH A SHAPE INDEX BASED ON SIGNAL ENVELOPES

A gain estimation method for an LPC vocoder which utilizes shape indexes. The gain is estimated based on the envelope of the speech waveform. The gain is estimated such that the maximum amplitude of the synthetic speech just reaches the speech waveform envelope. The gain during voiced subframes is estimated as the minimum of the absolute value of ratio of the envelope and the impulse response of the LPC filter. The gain during unvoiced subframes is estimated as the minimum of the absolute value of the ratio of the envelope and the noise response of the LPC filter. The method results in a fast technique for estimating the gain.