On the localization of high-frequency, sinusoidally amplitude-modulated tones in free field

Abstract

Previous headphone experiments have shown that listeners can lateralize high-frequency sine-wave amplitude-modulated (SAM) tones based on interaural time differences in the envelope. However, when SAM tones are presented to listeners in free field or in a room, diffraction by the head or reflections from room surfaces alter the modulation percentages and change the shapes of the envelopes, potentially degrading the envelope cue. Amplitude modulation is transformed into mixed modulation. This article presents a mathematical transformation between the six spectral parameters for a modulated tone and six mixed-modulation parameters for each ear. The transformation was used to characterize the stimuli in the ear canals of listeners in free-field localization experiments. The mixed modulation parameters were compared with the perceived changes in localization attributable to the modulation for five different listeners, who benefited from the modulation to different extents. It is concluded that individual differences in the response to added modulation were not systematically related to the physical modulation parameters themselves. Instead, they were likely caused by individual differences in processing of envelope interaural time differences.

Wave interference at the contralateral ear helps explain non-monotonic envelope interaural time differences as a function of azimuth

“…3 ), with comparable results observable in other HRTF databases as well (data not shown; e.g., Denk and Kollmeier, 2020 ). These findings imply that while there appears to be little discussion of non-monotonic ENV-ITD-azimuth functions in the literature (to our knowledge, only one other study has reported them; Macaulay et al, 2017 ), such non-monotonicities evidently occur and could potentially impact perception. Furthermore, they imply conventional time-independent models of binaural cue generation may fail to capture more complex and time-dependent interactions of real signals propagated around the head.…”

A framework for testing and comparing binaural models

“…Interaural group delay is an additional physical cue complementing the IPDs. It is used to describe interaural cues in acoustic waveforms at the ears prior to processing by the auditory system (Macaulay et al, 2017).…”