The role of amplitude modulation in auditory distance perception

Abstract

The ratio of direct to reverberant sound energy (D/R) has been shown to be a primary acoustic cue to perceived sound source distance. Because it is unclear exactly how D/R might be encoded in the auditory system, a variety of more physiologically plausible correlates to D/R have been identified, including: spectral variance, interaural correlation, and temporal cues. Here, following recent neural work by Kuwada and Kim [ARO, 2014], we describe a new correlate to D/R and perceived distance related to the amplitude modulation (AM) depth of the signal at the listener's location. This cue is caused by the change in the modulation transfer characteristics of the room as a function of source distance. Results from an apparent distance estimation task confirm the efficacy of this AM depth cue in a reverberant soundfield (approximate broadband T60 = 3 s), when level cues are made ineffective. Distance estimates to near sources (≤ 2m) were found to be more accurate when the source signal (1-octave band of noise centered at 4 kHz) had AM (32 Hz, 100% depth), and this facilitation was only observed in reverberation. The facilitation was most evident for monaural input, indicating that the AM depth cue is likely processed monaurally.