Chapter 10 A Speech Coder

10.1. Introduction

The program presented in this chapter does not, strictly speaking, simulate a speech coder. From the file of a telephone-band speech signal (F_e = 8 kHz) in wave format (quantized on 16 bits), it does not construct a file containing code words to transmit (the bitstream). It does the modeling stage which consists of determining the synthesis filter parameters and the characterizing parameters for the input signal to this filter for each analysis frame. To simulate a real coder, the parameter quantization stage must be realized and the parts realized by the encoder and decoder must be realized separately. Since a speech coder obeys a synthesis analysis scheme, the program simulating the decoder is reduced to a small sub-set of the whole program (mostly decoding the code words).

With the values suggested for the analysis frame length, the synthesis filter order, and the code book size, this program simulates a coder with a bit rate of the order of 10 kb/s.