Variable-rate speech coding: Coding unvoiced frames with 400 BPS

The following article describes a new variable-rate speech coder which combines the fortes of the principles of Harmonic Coding (HC) and Linear Prediction (LP). It presents an algorithm for the classification of voiced and unvoiced frames as well as a new method for coding unvoiced plosive and fricative phonemes with only 400 bps and 450 bps, respectively. Using the Improved Multiband Excitation (IMBE) version of 4.15 kbps for voiced frames results in an average rate of approximately 3.3 kbps for English speech.