On temporal integration versus frequency-based discrimination of direct-to-reverberant energy ratio

Abstract

The direct-to-reverberant (D/R) energy ratio is considered to be an important cue for sound source distance judgments (Zahorik, 2002; Bronkhorst, 2001). The current experiments investigated the processes that might be involved in D/R energy ratio discrimination. Two basic processes may be responsible: temporal integration and frequency domain changes. Temporal integration cues are available only if the on- and offset times of the stimulus are sufficiently rapid relative to the room reverberation time such that distinct direct and reverberant portions of the stimulus are perceived. Therefore, in the first experiment we compared JNDs for signals that either did or did not contain temporal integration cues by varying on- and offset time. We propose that the frequency-based method relies on the standard deviation of the spectral response in a reverberant room, which increases monotonically from 0 dB to 5.57 dB (Schroeder limit) as the D/R energy ratio decreases from approx. 20 dB to 0 dB. Outside this range, the standard deviation asymptotes and thus should not offer any cues for discrimination. Therefore, in the second experiment we compared JNDs for stimuli with D/R energy ratios inside and outside the range of 0–20 dB. The results from both these experiments will provide evidence for the processes of source distance coding based on the D/R energy ratio by the auditory system.