METHOD AND APPARATUS FOR SELECTING AN ENCODING RATE IN A VARIABLE RATE VOCODER

摘要

The present invention provides a method by which to reduce the probability of coding low energy unvoiced speech as background noise. An encoding rate is determined by dividing the input signal into subbands using digital subband filters (4) and (6) and comparing the energy in those bands to a set of thresholds in subband rate decision elements (12) and (14) and then examining those comparisons in an encoding rate selector (16). By this method, unvoiced speech can be distinguished from background noise. The present invention, also, provides a means for setting the threshold levels using the signal to noise ratio of the input signal, and the present invention provides a method for coding music through a variable rate vocoder by examining the periodicity of the input signal to distinguish the music from background noise.