Real-time linear-predictive coding of speech on the SPS-41 triple-microprocessor machine

The autocorrelation method for linear-predictive coding of speech [1] has been implemented in real time on the SPS-41, a commercially available system composed of three dissimilar microprocessors working in parallel. Using user-written microcode, one processor performs I/O and master control, the second handles loop indexing and counting, and the third does the actual arithmetic on data. Such parallelism allows 2 × 10⁶I/O operations and 4 × 10⁶multiplications/s, but actually realizing this potential requires fresh approaches to some old algorithms. Most important is a new autocorrelation scheme with several valuable properties. Using 16-bit fixed-point single-precision arithmetic to accumulate autocorrelation sums and invert the autocorrelation matrix presents problems which have been solved reasonably well. The present program converts frames of 256 16-bit samples into 14 coefficients and then into 128 points of logarithmic power spectrum at 100 frames/s.