Implementation of a multirate speech digitizer

The multirate algorithm used in the present implementation of a compact and efficient multirate speech digitizer is based on a residual excited linear prediction (RELP) vocoder having a transmission rate of 9.6 kbits/sec. If the residual in the RELP system is down-sampled before encoding, a 4.8 kbit/sec recorder can be realized. In the 4.8 and 9.6 kbit/sec coders, the pitch-implanted residual excitation method has been used to generate the excitation signal to the synthesis filter. With efficient hardware and software design, the multirate speech digitizer requires virtually the same hardware complexity as the conventional, 2.4 kbit/sec linear predictive coder vocoder.