A scheme for pitch extraction of speech using autocorrelation function with frame length proportional to the time lag

Although pitch extraction schemes based on the short-time autocorrelation function offer reliable results for most of the speech signal, the autocorrelation peaks indicating fundamental period fluctuate with frame position, causing occasional pitch extraction errors. In order to reduce these errors, a scheme using a new definition of normalized short-time autocorrelation function is proposed. One of the major advantages of the definition over conventional ones is that the frame length changes in proportion to the time lag, and, therefore, the input speech can be analyzed without any knowledge of the fundamental frequency range of the speaker. Two methods are proposed for the normalization, and the one compensating for variations of the short-time power of the waveform is shown to offer better results. A system for pitch extraction is constructed on a workstation, and the validity of the proposed scheme is demonstrated by experiments using the connected speech of male and female announcers