M. Torben Pastore

The influence of signal type on perceived reverberance

Currently, architectural room acoustic metrics make no real distinction between a room impulse response and the auditory systems internal representation of a room. These metrics are generally based on impulse responses, and indirectly assume that the internal representation of the acoustic features of a room is independent of the sound source. However, while a room can be approximated as a linear, time-invariant system, auditory processing is highly non-linear and varies a great deal over time in response to different acoustic inputs. Listeners were presented with various signals (clicks, long-duration noise, music, and speech) convolved with impulse responses consisting of Gaussian noises with different rates of exponential decay. Listeners were asked to adjust the reverberation time of one of the signals to match the other. Analyses of the data show that the source signal has a significant influence on perceived reverberance. Also, listeners were less accurate when matching reverberation times between different signals than they were with identical signals, suggesting that predicting subjective measures of reverberance from room impulse responses faces severe limitations that cannot be neglected. Results further suggest that the auditory system does not have a well-developed temporal representation of the diffuse reverb tail.

Sound source localization identification procedures: Accuracy, precision, confusions, and misses

Rakerd and Hartmann (1987) provided a useful set of equations that can describe listener performance in sound source localization identification tasks requiring listeners to identify which loudspeaker presented a sound. The data from such identification tasks can be presented in confusion matrices in which one dimension is the actual sound source locations and the other dimension is the reported/perceived sound source locations. This presentation describes how Rakerd and Hartmann’s measures relate to estimates of sound source localization accuracy, precision, confusions, and misses. We will describe some of the advantages and limitations of these measures of performance in sound source localization identification tasks, especially in conditions involving sound sources located around an entire azimuth circle. [Partially support by a grant from the National Institute on Deafness and Other Communication Disorders, NIDCD.]

Binaural detection of a Gaussian noise target in the presence of a lead/lag masker

Masked detection thresholds were measured for a noise target in the presence of a masker composed of (1) a lead/lag noise pair with the lead interaural time difference (ITD) set the same or opposite to the target, (2) a diotic masker, and (3) a dichotic pair of decorrelated noises. If the precedence effect actually eliminates a second, later arriving stimulus, a spatial release from masking would be expected when the lead ITD is opposite that of the target. Results for a range of lead/lag delays suggest that the precedence effect is not the result of a perceptual removal of the lag.

Vertical sound source localization when listeners and sounds rotate: The Wallach vertical illusion

In addition to testing his prediction that listeners would use changes in binaural cues relative to listeners’ self-induced head movements to disambiguate front-back confusions, Wallach (1939) also tested his calculations that the relative rate at which these binaural cues change could be used by listeners to determine the elevation of the sound source. Wallach was able to induce the illusion that a sound source rotating along the azimuth plane was perceived as though it were above the listener. We sought to replicate and expand upon Wallach’s study. We rotated listeners in a specialized chair at constant velocity. We presented filtered Gaussian noises at bandwidths of one-tenth octave, two octaves, and broadband, using center frequencies of 500 Hz and 4 kHz from a ring of 24 azimuthal loudspeakers located at pinna height. Sounds could also be presented from loudspeakers elevated relative to pinna level. The relative rates of sound and listener rotation around the azimuth plane were varied according to th...

Sound source localization as a multisensory process: The Wallach azimuth illusion

An auditory spatial illusion, introduced by Wallach (1939, 1940) and recently revisited by Brimijoin and Ackeroyd (2012), occurs when both listeners and sounds rotate. Rotating a sound, around the listener in the azimuth plane at twice the rate of listeners’ head turns, can elicit the sensation of a static sound source located either in front of the listener when the sound is originally presented from behind, or behind the listener when the sound is originally presented in front. We investigated this auditory illusion when listeners were rotated at constant velocity in a rotating chair with eyes open, for bandpass noises presented from an azimuthal ring of 24 loudspeakers. For noises that were likely to generate front-back confusions, the illusion of a stationary sound was robust, especially for low-frequency sounds. On the contrary, for noises that were unlikely to produce front-back confusions, listeners reported the sound rotating around them on the azimuth plane. These observations are predicted by a ...

The import of within-listener variability to understanding the precedence effect

The purpose of this study was to gather behavioral data concerning the precedence effect as manifested by the localization-dominance of the leading elements of compound stimuli. This investigation was motivated by recent findings of Shackleton and Palmer [(2006). J. Assoc. Res. Otolaryngol. 7, 425-442], who measured the electro-physiological responses of single units in the inferior colliculus of the guinea pig. The neural data from Shackleton and Palmer indicated that processing of binaural cues like those relevant to understanding localization dominance is greatly affected by internal, neural noise. In order to evaluate the generality of their physiological results to human perception, the present study measured localization dominance so that behavioral responses within and across sets of samples (i.e., tokens) of frozen noises could be compared. Conceptually consistent with Shackleton and Palmers neural data, the variability of perceived intracranial lateral positions produced by repeated presentations of the same tokens of noise was greater than the variability of intracranial lateral positions measured across different tokens of noise. This was true for each of the four individual listeners and for each of the 72 stimulus conditions studied. Thus, measured either neuro-physiologically (Shackleton and Palmer, 2006) or behaviorally (this study), the import of within-listener variability appears to be a general, intrinsic aspect of binaural information processing.

How well do measures of the precedence effect based on clicks predict performance for long-duration stimuli?

Despite multiple reflections off nearby surfaces, listeners often localize sound sources based primarily upon the first arriving, direct sound. This is called the precedence effect. Much has been learned about the precedence effect using transient clicks, but the vast majority of everyday sounds are relatively long in duration. Recently, Pastore and Braasch (JASA, 2015) tested the effects of increased lag intensity on localization dominance for longer, 200-ms duration stimuli with 20-ms cosine-squared ramps. Assuming that interactions at the onset of lead-lag stimuli are primarily responsible for the precedence effect, it has been suggested that the binaural cues important to the precedence mechanism are the same for clicks and longer-duration noise stimuli. To test this hypothesis, we presented lead-lag stimuli composed of 1-ms, rectangular clicks, as well as 41-ms and the previously used 200-ms long noise bursts. Five, lead-lag delays between 1 and 5 ms were tested for lead/lag level differences of 0-, ...

Investigating the effect of arrival time of diffuse reflections on listener envelopment

Listener Envelopment (LEV) is a quality of diffuse sound fields, and a highly sought after attribute of performance venues. However, the ability for an enclosure to achieve ideal, diffuse sound field is often difficult, and varies from space to space. Thus, a rigid transition time between early and late energy is an insufficient way of evaluating LEV. Current theories on listener envelopment focus on the arrival time of the reflections within the impulse response, but typically disregard the diffusivity of these reflections, building on the fact that the impulse response generally becomes more diffuse over time. An alternative model is proposed, where the listener envelopment is determined by both the diffusivity and the arrival time of reflections. The model disregards the current 80-ms criterion and also allows reflections earlier then this to contribute to LEV. A 64-channel wave field synthesis system is used to perceptually evaluate the effects of spatially and temporally diffuse sound components as a function of arrival time.Listener Envelopment (LEV) is a quality of diffuse sound fields, and a highly sought after attribute of performance venues. However, the ability for an enclosure to achieve ideal, diffuse sound field is often difficult, and varies from space to space. Thus, a rigid transition time between early and late energy is an insufficient way of evaluating LEV. Current theories on listener envelopment focus on the arrival time of the reflections within the impulse response, but typically disregard the diffusivity of these reflections, building on the fact that the impulse response generally becomes more diffuse over time. An alternative model is proposed, where the listener envelopment is determined by both the diffusivity and the arrival time of reflections. The model disregards the current 80-ms criterion and also allows reflections earlier then this to contribute to LEV. A 64-channel wave field synthesis system is used to perceptually evaluate the effects of spatially and temporally diffuse sound components as a...

The addition of a second lag to the lead-lag precedence effect paradigm for temporally overlapping noise stimuli

In reverberant conditions, humans routinely perceive sound sources in the direction of the first wavefront despite competing directional information presented by a host of reflections arriving soon after—the so-called “Precedence Effect.” This is often tested over headphones using a “direct sound” (lead) with a single delayed copy (lag) serving as a modeled reflection. Previously, we employed this common experimental paradigm to investigate the lateral extent of the precedence effect using temporally overlapping noise stimuli. The current study extends this inquiry towards the multiple reflections encountered in room-acoustic scenarios by presenting a second lag. Lead and lag stimuli are 200-ms Gaussian noise (500-Hz center frequency, 800-Hz bandwidth) presented dichotically with a programmable amount of delay for both lags. Relative to the intensity of the lead, the two lags are presented at 0, −3, and −6 dB. The lead is presented at the midline, with an ITD of 0 μs. The two lags are delayed by between 1...

The influence of signal type on the internal representation of a room in the auditory system

Currently, architectural acousticians make no real distinction between a room impulse response and the auditory system’s internal representation of a room. With this lack of a good model for the auditory representation of a room, it is indirectly assumed that our internal representation of a room is independent of the sound source needed to make the room characteristics audible. In a perceptual test, we investigate the extent to which this assumption holds true. Listeners are presented with various pairs of signals (music, speech, and noise) convolved with impulse responses for different rooms. They are asked to evaluate the differences between rooms and disregard differences between the source signals. Multidimensional scaling is used to determine the extent to which the source signal influences the internal representation of the room and which room acoustical characteristics are important/perceivable for each sound type.