Real-time digital hardware pitch detector

A high-quality pitch detector has been built in digital hard-ware and operates in real time at a 10 kHz sampling rate. The hardware is capable of providing energy as well as pitch-period estimates. The pitch and energy computations are performed 100 times/s (i.e., once per 10 ms interval). The algorithm to estimate the pitch period uses center clipping, infinite peak clipping, and a simplified autocorrelation analysis. The analysis is performed on a 300 sample section of speech which is both center clipped and infinite peak clipped, yielding a three-level speech signal where the levels are -1, 0, and +1 depending on the relation of the original speech sample to the clipping threshold. Thus computation of the autocorrelation function of the clipped speech is easily implemented in digital hardware using simple combinatorial logic, i.e., an up-down counter can be used to compute each correlation point. The pitch detector has been interfaced to the NOVA computer facility of the Acoustics Research Department at Bell Laboratories.