A robust realtime pitch extraction from the ACF of LPC residual error signals

A robust and low cost realtime pitch extractor is presented in this paper. The algorithm uses long-term prediction with two prediction coefficients calculated from the autocorrelation function (ACF) of LPC residual error signal. This pitch extractor has worked successfully in a narrow band realtime LPC vocoder operating in highly noisy environments, where a conventional AMDF (Average Magnitude Difference Function) pitch extractor failed to provide satisfactory results. The algorithm requires some extra arithmetic operations in addition to the ACF calculations of LPC residual error signals. But, it is implemented in realtime with the programmable microcomputer chip NEC uPD7720. This chip can multiply and accumulate in parallel with the ALU operation during a single machine cycle allowing pitch detection with multiplies.