Bobby E. Gibbs

Modulation masking and glimpsing of natural and vocoded speech during single-talker modulated noise: Effect of the modulation spectrum

Compared to notionally steady-state noise, modulated maskers provide a perceptual benefit for speech recognition, in part due to preserved speech information during the amplitude dips of the masker. However, overlap in the modulation spectrum between the target speech and the competing modulated masker may potentially result in modulation masking, and thereby offset the release from energetic masking. The current study investigated masking release provided by single-talker modulated noise. The overlap in the modulation spectra of the target speech and the modulated noise masker was varied through time compression or expansion of the competing masker. Younger normal hearing adults listened to sentences that were unprocessed or noise vocoded to primarily limit speech recognition to the preserved temporal envelope cues. For unprocessed speech, results demonstrated improved performance with masker modulation spectrum shifted up or down compared to the target modulation spectrum, except for the most extreme time expansion. For vocoded speech, significant masking release was observed with the slowest masker rate. Perceptual results combined with acoustic analyses of the preserved glimpses of the target speech suggest contributions of modulation masking and cognitive-linguistic processing as factors contributing to performance.

Explaining intelligibility in speech-modulated maskers using acoustic glimpse analysis.

Intelligibility was measured in speech-modulated noise varying in level and temporal modulation rate (TMR). Acoustic analysis measured glimpses available above a local signal-to-noise ratio criterion (LC). The proportion and rate of glimpses were correlated with intelligibility, particularly in relation to masker level or TMR manipulations, respectively. Intelligibility correlations for each metric were maximized at different analysis LCs. Regression analysis showed that both metrics measured at -2 dB LC were required to best explain the total variance (R2 = 0.49) for individual sentence intelligibility. Acoustic conditions associated with recognizing speech in complex maskers are best explained using multidimensional glimpse metrics.

The intelligibility of glimpsed speech: Effect of competing amplitude modulation

The present study investigated how amplitude modulation of an interrupted noise influences the intelligibility of glimpsed speech. Prior studies have demonstrated that amplitude modulation can aid speech intelligibility when speech is periodically interrupted. This study used a competing talker to define high-intensity and low-intensity speech glimpses that were used to interrupt the target speech. These interrupted intervals were filled by one of five different types of amplitude modulated noise; each noise was presented at two different presentation levels. Silent interruption was also examined. This resulted in 22 different experimental conditions. The results indicated effects of glimpsed speech level, noise modulation, and noise level. In agreement with previous studies using periodic interruption, significant benefit was obtained when the noise was amplitude modulated by the missing speech segment, but only when the modulation came from high-intensity speech segments. In contrast, amplitude modulati...

The independent contribution of glimpse properties to speech recognition in speech-modulated noise

During fluctuating noise, temporal speech fragments (i.e., glimpses) at sufficient signal-to-noise ratios (SNRs) contribute to speech recognition. Different acoustic properties of these glimpses, related to rate and proportion, reflect the temporal distribution of available speech cues. Glimpse metrics may be used to define different aspects of this temporal distribution. However, these measures are often highly correlated, limiting interpretation of how different glimpse properties contribute independently to speech recognition. The present study investigates how the local SNR cutoff (LC) influences the correlation between glimpse metrics and affects related associations with speech recognition. Speech recognition was assessed in the presence of speech-modulated noise that was temporally manipulated through time compression and presented at different SNRs. Optimization analyses identified LCs that yielded glimpse metrics that were most correlated with the perceptual data. Stimulus manipulations of the no...

Glimpsing Predictions for Natural and Vocoded Sentence Intelligibility During Modulation Masking: Effect of the Glimpse Cutoff Criterion.

This study varied the signal-to-noise ratio (SNR) cutoff criterion for acoustically defining usable perceptual glimpses that contribute to speech intelligibility. Criterion-dependent effects were determined by examining the correlation of three different acoustic glimpse metrics with intelligibility. Glimpse properties change depending on the acoustic interactions between the speech and competing noise. Therefore, these measures were investigated with different rates of competing speech that were varied using time compression or expansion. Finally, effects of temporal modulation masking and spectral segregation were examined by comparison between unprocessed (natural) and vocoded speech. Results revealed a range of SNR cutoffs that were associated with correlations between the different acoustic glimpse metrics and intelligibility. Changing the glimpse criterion strongly influenced the associations between intelligibility and two of the acoustic glimpse metrics for the different masker modulation rates. However, the proportion of target speech above the SNR cutoff was less affected by altering the cutoff criterion. These results suggest that intelligibility models should account for the perceptual contribution of different glimpse metrics or limit glimpse cutoff criteria to an SNR region (1-3 dB based on this data) that captures the perceptual utility of multiple glimpse mechanisms.

Defying the physical: Acoustic design as a medium for reimagining space and recontextualizing expression

Just as the physical laws of light are both an inspiration and a point of departure for visual artists, the canvas of acoustic design is not aesthetically bound to real spaces. Using findings from venue visits, interviews and an interactive virtual auditory exploration, we will discuss the bricolage of physical space and cultural expression inherent in the dissemination of a unique musical genre. In particular, we will explore how experimental improvisers preserve and subvert spatial cues to create aural experiences that are at once intimate and illusive.

The impact of visual cues on perceived intimacy in an acoustic ecology.

Crossmodal studies of the effects of visual cues on the perceived acoustics of a performance space have suggested the inextricable relationship between vision and audition. When designing a building or virtual environment for music, critical attention must be paid to a visual aesthetic to ensure a desired level of intimacy between the audience and performer. This visual aesthetic is ordinarily left entirely to the main architect or visual artist. However, given the body of research suggesting crossmodal influences on the human auditory system, it is clear that acousticians must also carefully consider the visual effects of their recommendations for acoustic improvement. The objective of this study is to establish the effects of various visual cues on audition as pertaining to intimacy in an ecological context. This study uses digital compositing (bluescreen) techniques to place a musical performance in various virtual environments, and employs real time audio‐video processing to create an interactive, cro...

Converging evidence in evaluating acoustical intimacy

Previously, we presented a novel interactive pilot experiment in which participants modified parameters in a virtual acoustical environment so that they corresponded to three intimacy settings: low, medium, and high. Additionally, participants were asked to rank the ‐‐ yet unknown ‐‐ parameters (volume, direct‐to‐reverberant energy ratio, frequency attenuation, and room size) in terms of the importance in making their judgments. Based on a larger body of data, the direct‐to‐reverberant energy ratio emerges as the strongest acoustical correlate of intimacy. A repeated‐measures test revealed that the “preservation” of this parameter (the degree to which a participant changed the value from an optimum setting) varies the least across intimacy levels and across levels of previous training. Additionally, this parameter is consistently ranked as being the most important in the ranking portion of the test. We also found that salience of some of the other parameters varied significantly across intimacy levels, po...

Interactive acoustical intimacy exploration

A novel methodology to explore salient cues for acoustical intimacy is presented. Subjects are instructed to modify a set of sliders in a virtual acoustical environment to correlate with three intimacy settings: low, medium, and high. As the experiment proceeds, subjects are allowed to audition their choices and make modifications to achieve what they feel to be optimal settings. At the conclusion of the interactive phase, subjects are instructed to rank the (as yet unknown to them) parameters in terms of their overall effect on intimacy. Unknown to the subjects, each slider correlates to an acoustical parameter: direct‐to‐reverberant energy ratio, high‐frequency attenuation, room size, and volume. Results from the experiment are discussed relative to concert‐hall acoustics and virtual spaces.

Intimacy in performance venues: Towards a socioecological methodology

Intimacy can be subjectively defined as the feeling of closeness to performance. Intimacy has been widely correlated with the initial time delay gap, the delay between the direct sound and early reflections in a venue [Beranek, Concert and Opera Halls: How They Sound (Acoustical Society of America, New York, 1996)]. Contemporary research suggests that visual stimuli have considerable bearing upon intimacy perception [e.g., Cabrera and Nguyen, J. Acoust. Soc. Am. 116, 2475 (2004)]. Building upon paradigms of ecological psychology, the author hypothesizes that social affordances, perceived offerings of social propinquity in a venue, will significantly enhance the auditory impression of intimacy. A socioecological approach to weigh the hypothesis is proposed wherein auditory perception is evaluated in the context of both the physical and the social environment. The methodology will employ interviews, ethnographic analyses, field studies, and laboratory tests. The research results will likely have immediate r...