First formant location determination and removal from speech correlation

Abstract

A vocoder system and method for estimating the pitch of a speech signal. The speech signal comprises a stream of digitized speech samples. The speech samples are partitioned into frames. For each frame of the speech signal, the following processing steps are performed. First, an optimal order-two inverse filter is determined based on the samples of the speech frame. Second, a dominant formant frequency is calculated from the coefficients of the optimal order-two inverse filter. Third, an autocorrelation function is calculated on the samples of the speech frame. The autocorrelation is performed for a range of time-delay values over which the pitch period and its multiples might be expected to occur. Fourth, the peaks of the autocorrelation function are analyzed incorporating the knowledge of the dominant formant period (which is the inverse of the dominant formant frequency). Normally, the dominant formant is the first formant. Thus, the dominant formant period defines the expected time-delay for the first formant peak in the autocorrelation function. As such, any peak in the autocorrelation function occurring with a time-delay equal to the dominant formant period is treated with increased caution before being accepted as the pitch period.