An adaptive non-uniform sign clipping preprocessor (ANUSC) for real-time autocorrelative pitch detection

In its nature, the autocorrelation function (ACF) is well suited to periodicity detection. As exemplified by the SIFT algorithm, and discussed by Sondhi in a classic paper, the success of ACF pitch detection is very much dependent on the availability of an efficient preprocessor. Often, the combination of low pass Filtering and Uniform Sign Clipping (FUSC) is chosen as a preprocessor because it yields an algorithm which is easily implemented in real-time. A disadvantage of using FUSC is that one does not obtain a reliable V-UV decision from the ACF alone. Also, FUSC algorithms often fail when successive pitch pulses vary widely in amplitude (at the onset and termination of voicing, or when the vocal cords of the speaker vibrate anomalously). Adaptive Non-Uniform Sign Clipping (ANUSC) is introduced as a means of coping with these problems while achieving the same computational advantages as with FUSC.