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

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.

Is source elevation an auditory distance cue? A preliminary study

“…The sound samples used for the recordings consisted of an exponential sweep (0.02-20 kHz and 20 s long) with which we obtained the binaural room impulse response for both floor and ear level sources at the following distances: 2, 3, 4, 5, 6, 7, and 8 m. The acoustic measurements showed suprathresholds spectral changes dependent on both the height of the source (up vs. down) and their distances, especially for sources located on the ground (see Figure 1 in Supplemental material). In addition, we calculated the binaural intensity and direct-to-reverberant energy ratio as described in Spiousas et al (2017). The binaural intensity for both conditions (ear and floor levels) are plotted as a function of distance on Supplemental Figure 2a.…”

Direct-location versus verbal report methods for measuring auditory distance perception in the far field

“…Auditory stimulus consisted of 500-ms white noise clips (measured bandwidth 0.05-20 kHz) with onset and offset ramped by a 50-ms raised cosine. The stimulus bandwidth (white noise) was chosen to maximize the availability of acoustical distance cues yielding to more accurate responses (Spiousas et al, 2017). The duration of the sound clips was set on 500 ms to have a temporally limited clip (in order to reduce the duration of the procedure and prevent subject fatigue), but long enough to minimize the onset and offset influence.…”

“…Two seconds after the end of the masking sound, the auditory stimulus was presented through the test speaker. See Calcagno et al (2012) and Spiousas et al (2017) for a thorough description of the experimental set-up.…”