Calculation of a "narrowed" autocorrelation function

A method of calculating an autocorrelation function with extremely narrow peaks is described. This is done by including terms in the autocorrelation expression corresponding to delays at 2 tau, 3 tau, etc., in addition to the usual term with delay tau. Implications in the frequency domain are explored. Graphs of this autocorrelation function for a number of violin sound samples, including a two-octave scale, vibrato, and glissando, are presented. Graphs of the autocorrelation function for some synthetic sound samples are also included.