The effect of modulation rate on the detection of frequency modulation andmistuning of complex tones

Experiment 1 measured frequency modulation detection thresholds (FMTs) for harmonic complex tones as a function of modulation rate. Six complexes were used, with fundamental frequencies (F0s) of either 88 or 250 Hz, bandpass filtered into a LOW (125-625 Hz), MID (1375-1875 Hz) or HIGH (3900-5400 Hz) frequency region, The FMTs were about an order of magnitude greater for th e three complexes whose harmonics were unresolved by the peripheral auditor y system (F0 = 88 Hz in the MID region and both F0s in the HIGH region) tha n for the other three complexes, which contained some resolved harmonics. T hresholds increased with increases in FM rate above 2 Hz for all conditions . The increase was larger when the F0 was ss Hz than when it was 250 Hz, an d was also larger in the LOW than in the MID and HIGH regions. Experiment 2 measured thresholds for detecting mistuning produced by modulating the F0s of two simultaneously presented complexes out of phase by 180 degrees. The size of the resulting mistuning oscillates at a rate equal to the rate of FM applied to the two carriers. At low FM rates, thresholds were lowest whe n the harmonics were either resolved for both complexes or unresolved for b oth complexes, and highest when resolvability differed across complexes. Fo r pairs of complexes with resolved harmonics, mistuning thresholds increase d dramatically as the FM rate was increased above 2-5 Hz, in a way which co uld not be accounted for by the effect of modulation rate on the FMTs for t he individual complexes. A third experiment, in which listeners detected co nstant ("static") mistuning between pairs of frequency-modulated complexes, provided evidence that this deterioration was due the harmonics in one of the two "resolved" complexes becoming unresolved at high FM rates, when ana lyzed over some finite time window. It is concluded that the detection of t ime-varying mistuning between groups of harmonics is limited by factors tha t are not apparent in FM detection data. (C) 2000 Acoustical Society of Ame rica. [S0001-4966 (00)05207-3].