Standards for low bit rate speech coding applications

In order to illustrate the increasing emphasis on providing timely and meaningful standards under mounting commercial pressure from network providers and manufacturers, examples of two such standardisations (AEEC 9.6 kbit/s aeronautical codec and CCITT 16 kbit/s low delay codec) are presented. The speech coding algorithms proposed for both of these standards are based on linear predictive coding (LPC) analysis by synthesis techniques. Speech is modelled by passing an excitation signal through an LPC filter, which uses filter coefficients derived from the speech signal. Obtaining the excitation signal involves finding a waveform, which when passed through the LPC filter, matches the input speech as closely as possible, given the constraints of the excitation encoding technique