Variable Rate Speech Coding Using Discrete Time Waveletextrema

We describe a novel procedure for variable rate encoding of a speech signal starting from the discrete time wavelet extrema representation. We describe the bit reduction achievable by thresholding the extrema signal. We also demonstrate that the thresholding procedure provides a \denoising" eeect. We then reduce the bit rate further by using a bit allocation scheme that adopts a model for the extrema representation, based on the evolution of the maxima across scales of the decomposition. The algorithm automatically adjusts itself to speech activity thus lending itself to variable rate environments. Perceptual results are reported in comparison to the GSM 6.1 standard for speech corrupted with road noise. It has been observed that as the SNR falls below 15 db, the wavelet coder performs better.