Microprocessor assisted real-time harmonic analysis by minicomputer

A real-time signal averaging and harmonic analysis technique for low audio frequency waveforms is described that, although based on based on earlier software emulations of lock-in detection instruments, eliminates problems inherent in the earlier systems. Parallel processing is employed between a data acquisition minicomputer (HP-2116B) and a microcomputer (Z-80) to (1) replace an earlier chopper-type lock-in algorithm with a coherent Fourier transform, (2) digitally produce a pure (0.01% THD) modulation sine wave, (3) simplify system tune-up, and (4) produce a high-quality, flicker-free, real-time display of the averaged waveform and its harmonic content.