UC Irvine

Through a series of experiments, the possible influence of cubic difference tones (CDTs) was investigated in a task traditionally used to investigate the bandwidths of phase sensitivity. In each procedure, estimates of modulation depth necessary to discriminate amplitude modulated (AM) and quasi-frequency modulated (QFM) tones were measured. Threshold functions for the listeners were often non-monotonic, with sharp non-monotonicities observed at higher bandwidths (e.g. above 600 Hz for a 2000 Hz carrier). This is likely due to the generation of a CDT at the site of the lower sideband creating a salient spectral cue. The cue is shown to be degraded by randomizing phase of the carrier frequency (Tabuchi, Borucki, and Berg, 2012). However, when duration is limited, temporal discrimination ability is degraded while a smaller effect is found at the sites of probable distortion product effects. When the intensity of the center frequency is decreased from 80 dB to 40 dB SPL a greater number of non-monotonicities are observed for high modulation frequency conditions, reflecting changes in phase of the CDT that occurs with changes in intensity. Finally, thresholds were measured as a function of the phase of the lower side band; thresholds support a model that suggests listeners discriminate between tone complexes based on the interaction of the CDT with the lower sideband at higher bandwidths.