Sound Spectrum Influences Auditory Distance Perception of Sound Sources Located in a Room Environment.

Ignacio Spiousas,Manuel C Eguia,Ramiro O Vergara,Pablo E Etchemendy,Ezequiel Abregú,Esteban R Calcagno

doi:10.3389/fpsyg.2017.00969

Abstract

Previous studies on the effect of spectral content on auditory distance perception (ADP) focused on the physically measurable cues occurring either in the near field (low-pass filtering due to head diffraction) or when the sound travels distances >15 m (high-frequency energy losses due to air absorption). Here, we study how the spectrum of a sound arriving from a source located in a reverberant room at intermediate distances (1–6 m) influences the perception of the distance to the source. First, we conducted an ADP experiment using pure tones (the simplest possible spectrum) of frequencies 0.5, 1, 2, and 4 kHz. Then, we performed a second ADP experiment with stimuli consisting of continuous broadband and bandpass-filtered (with center frequencies of 0.5, 1.5, and 4 kHz and bandwidths of 1/12, 1/3, and 1.5 octave) pink-noise clips. Our results showed an effect of the stimulus frequency on the perceived distance both for pure tones and filtered noise bands: ADP was less accurate for stimuli containing energy only in the low-frequency range. Analysis of the frequency response of the room showed that the low accuracy observed for low-frequency stimuli can be explained by the presence of sparse modal resonances in the low-frequency region of the spectrum, which induced a non-monotonic relationship between binaural intensity and source distance. The results obtained in the second experiment suggest that ADP can also be affected by stimulus bandwidth but in a less straightforward way (i.e., depending on the center frequency, increasing stimulus bandwidth could have different effects). Finally, the analysis of the acoustical cues suggests that listeners judged source distance using mainly changes in the overall intensity of the auditory stimulus with distance rather than the direct-to-reverberant energy ratio, even for low-frequency noise bands (which typically induce high amount of reverberation). The results obtained in this study show that, depending on the spectrum of the auditory stimulus, reverberation can degrade ADP rather than improve it.

Highlights

Perceiving accurately the location of a sound source is an essential capability of the human hearing system, enhanced through selective pressure due to its survival value
Cumulated evidence shows that, for near-field sources located outside the median plane, auditory distance perception (ADP) relies on low-frequency interaural level differences, an acoustical cue that rapidly increases its relative importance when the source approaches within 1 m of the listener’s head (Brungart, 1999; Brungart and Rabinowitz, 1999; Brungart et al, 1999; Kopco and Shinn-Cunningham, 2011)
Once the direct and reverberant fields were separated, we calculated the direct-to-reverberant energy ratio (DRR) by convoluting each portion of the binaural room impulse response (BRIR) with the filtered noise bands, and computing the ratio between the total energy contained in the two portions

Summary

Introduction

Perceiving accurately the location of a sound source is an essential capability of the human hearing system, enhanced through selective pressure due to its survival value (when the source is out of view or occluded, the auditory modality often plays a crucial role on assessing the location of the source). Cumulated evidence shows that, for near-field sources located outside the median plane, auditory distance perception (ADP) relies on low-frequency interaural level differences, an acoustical cue that rapidly increases its relative importance when the source approaches within 1 m of the listener’s head (Brungart, 1999; Brungart and Rabinowitz, 1999; Brungart et al, 1999; Kopco and Shinn-Cunningham, 2011). In order to assess if it was our case we calculated the cumulative energy decay functions (Schroeder, 1979) for pink noise (Figures 2B,C for the left and right ear, respectively) In these curves, even for the worst case (farthest source distance), the energy decays almost 40 dB before flattening.

Methods

Results

Conclusion