Abstract: 2400 bit/s digital vocoder plays a very important role in narrow band speech communication. In this paper, a channel vocoder is presented, it is designed by using multiple 8085 microprocessors and some of special hardware.
The different designs can easily be modified in this efficient equipment to improve the quality of synthesis speech of the vocoder. In this study, special attentions were paid to the improvement of excitation signals by using all-pass filter, the combined response and group delay of the synthesis filter set that is adjusted by change bandwidth of filters and with antipolarity for adjacent filters, and the efficient method of encoding and decoding of Chinese speech parameters. The effect of all methods is obviously shown in the results of intelligibility tests.