Natural quality variable-rate spectral speech coding below 3.0 kbps

We propose new techniques for natural quality variable rate spectral speech coding at an average rate of 2.2 kbps for dialog speech and 2.8 kbps for monolog speech. The coder models the Fourier spectrum of each frame and it builds on recent enhancements to the classical multiband excitation (MBE) approach. New techniques for robust pitch estimation and tracking, for e cient quantization of voiced and unvoiced spectra and encoding of partial phase information are the key features that result in improved quality over earlier spectral vocoders. Subjective performance results are reported which show that the coder is very close in quality to the ITU-T G.723.1 algorithm at 5.3 kbps.