Digital Computer Simulation of a Sampled-Data Voice-Excited Vocoder

Abstract

A sampled‐data system representing a 10‐spectrum channel voice‐excited vocoder (VEV) has been simulated on an IBM 7090 digital computer. This type of simulation permits studying readily the effects of changes in major vocoder parameters, such as excitation, analyzing filter bandwidth, etc., without the lengthy waiting periods required for equipment changes. Programming for the simulation was accomplished by the use of a program compiler that allows specification of a sampled‐data system in functional‐block form. The system represented by the simulation was, in general, determined by finding sampled‐data equivalents (z transforms) of the filters and circuits used in an analog VEV. The derived z transforms were then used to realize functional‐block representations for the sampled‐data filters and circuits. However, to prove economically the feasibility of simulating an entire vocoder, the great number of bandpass filters needed were synthesized initially by using a unique and computation timesaving design. Speech processed by this simulated sampled‐data system is of excellent quality and often is better than that processed by some analog VEV's. The computer program requires about 172 sec to analyze and resynthesize 1 sec of recorded speech.