Effects of signal-to-noise ratio on the frequency discrimination of complex tones with overlapping or nonoverlapping harmonics

Abstract

Frequency difference limens for multiple-component complex tones (DLCs) were measured using an adaptive two-interval, two-alternative forced-choice task. The tones were presented either in quiet or in pink noise at various noise levels. The tones to be discriminated either had all harmonics in common, or no common harmonics. DLCs for the tones with no common harmonics were generally, but not always, larger than those for complex tones with common harmonics. For the former, performance did not worsen monotonically with increasing noise level, but tended either to stay constant or improve at first, only worsening when the tones were almost completely masked by the noise. For the latter, performance tended to worsen monotically with increasing noise level, although, again, large changes only occurred when the tones were almost completely masked by the noise. Even at the highest noise level used, DLCs for complex tones with no common harmonics were usually larger than DLCs for tones with common harmonics. The results suggest that the worse performance for tones with no common harmonics does not result from internal noise in the channels conveying information from the periphery to the mechanism determining residue pitch. Rather, spectral differences between tones with noncoincident harmonics appear to have a distracting effect that impairs pitch discrimination.