A fixed-point DSP implementation for a low bit rate vocoder

Abstract

Fixed-point DSP implementation of the decoder and the synthesizer of a real time vocoder with 1.4 kbps bit rate has been accomplished instead of the usual realization of low bit rate vocoder in floating point DSP. Replacing floating point values with fixed-point ones and other approaches have been adopted to reach a real time solution. The implemented fixed-point decoder and synthesizer run at 11.3 MIPS on the average and occupy 1246 words of program memory, 1338 words of table ROM and 814 words of RAM in a 40 MHz TMS320C50 DSP chip. The results indicate the possibility to implement the whole vocoder with low cost fixed-point DSP.