Mapping auditory phase sensitivity with timbre discriminations
Roy D. Patterson · The Journal of the Acoustical Society of America · 1986
A flat-spectrum periodic sound composed of 31 equal-amplitude harmonics was used to investigate the effects of phase on timbre. Listeners discriminated a pulse train, wherein the harmonics start in cosine phase from (1) nonmonotonic alternating-phase waves wherein successive harmonics have fixed phases p and q, and (2) monotonic, decelerating-phase waves wherein successive harmonics are phase shifted by an ever decreasing amount. Both phase manipulations produce detectable timbre changes for pulse rates below 400 Hz but monotonic phase increments have to be much larger than alternating phase differences for equivalent performance. For periodic sounds, the output of an auditory filter with center frequency above the fourth harmonic is a modulated sine wave and the modulator's characteristics appear to determine performance. Alternating-phase waves produce a local maximum in the modulator trough which enables the discrimination to be made within each frequency channel. (These waves sound an octave above the pulse train.) Monotonic-phase waves produce strictly sinusoidal modulators and so the discrimination requires detecting modulator phase differences across filters which is more difficult. (These waves sound like damaged pulse trains.)