ASA 127th Meeting M.I.T. 1994 June 6-10

4aPP5. Time-interval patterns in damped and ramped sinusoids.

MRC Appl. Psychol. Unit, 15 Chaucer Rd., Cambridge CB2 2EF, UK

When a sinusoid with a temporally asymmetric envelope is reversed in time, the power spectrum of the sound does not change but the timbre often does. When the envelope is a repeated, damped exponential, the forward and backward versions are discriminable over a wide range of carrier frequencies (400--4800 Hz) and half-lives (1--64 ms) [R. D. Patterson, J. Acoust. Soc. Am. 93, 2293 (A) (1993)]. The earlier experiment has been replicated with a fixed number of carrier periods per envelope period to test the hypothesis that the sound of a sinusoid is more closely related to the number of phase-locked time intervals at the carrier-period than it is to the energy in the carrier channel. Time-interval histograms were calculated from auditory-image representations of the stimuli. The ramped stimuli generate more carrier-period activity in cases where the ramped stimulus is identified as more sinusoidal. Much of this activity is in channels well above and below the carrier channel indicating the time-interval models will probably provide a better basis for timbre perception than spectral models. [Work supported by the UK Medical Research Council and DRA Farnborough.]