Comparison of three fixed point signal processors for waveform coding of speech

Three programmable fixed point single chip processors were compared: the TMS320C25 of Texas Instruments, the DSP56001 of Motorola, and the DSP16 of AT&T. Although the architectures of these processors are already several years old, they still represent the state of the art of fixed point DSPs (digital signal processors). The performance of each DSP is evaluated in the implementation of the adaptive predictor of the lower subband for the SB-ADPCM (subband adaptive differential pulse code modulation) codec. The results are presented both as number of instruction cycles and as execution times including the effect of instruction cycle length. The results seem to favor DSPs with short instruction cycles over DSPs with large complicated instruction sets. The conditional instructions that can replace conditional jumps are found to be essential for the speed of execution