Eric R. Thompson

Suitable reverberation times for halls for rock and pop music.

The existing body of literature regarding the acoustic design of concert halls has focused almost exclusively on classical music, although there are many more performances of popular music, including rock and pop. Objective measurements were made of the acoustics of 20 rock music venues in Denmark and a questionnaire was used in a subjective assessment of those venues with professional rock musicians and sound engineers as expert listeners. Correlations between the measurements show that clarity, including bass frequencies down to 63 Hz, is important for the general impression of the acoustics of the hall. The best-rated halls in the study have reverberation times that are approximately frequency independent from 0.6 to 1.2 s for hall volumes from 1000 to 6000 m(3). The worst rated halls in the study had significantly higher reverberation times in the 63 and 125 Hz bands. Since most audiences at rock concerts are standing, absorption coefficients were measured with a standing audience from 63 Hz to 4 kHz. These measurements showed that a standing audience absorbs about five times as much energy in mid-/high-frequency bands as in low-frequency bands.

Binaural processing of modulated interaural level differences

Two experiments are presented that measure the acuity of binaural processing of modulated interaural level differences (ILDs) using psychoacoustic methods. In both experiments, dynamic ILDs were created by imposing an interaurally antiphasic sinusoidal amplitude modulation (AM) signal on high-frequency carriers, which were presented over headphones. In the first experiment, the sensitivity to dynamic ILDs was measured as a function of the modulation frequency using puretone, and interaurally correlated and uncorrelated narrow-band noise carriers. The intrinsic interaural level fluctuations of the uncorrelated noise carriers raised the ILD modulation detection thresholds with respect to the pure-tone carriers. The diotic fluctuations of the correlated noise carriers also caused a small increase in the thresholds over the pure-tone carriers, particularly with low ILD modulation frequencies. The second experiment investigated the modulation frequency selectivity in dynamic ILD processing by imposing an interaurally uncorrelated bandpass noise AM masker in series with the interaurally antiphasic AM signal on a pure-tone carrier. By varying the masker center frequencies relative to the signal modulation frequency, broadly tuned, bandpass-shaped patterns were obtained. Simulations with an existing binaural model show that a low-pass filter to limit the binaural temporal resolution is not sufficient to predict the results of the experiments.

An Energetic Limit on Spatial Release from Masking

This study tested the hypothesis that energetic masking limits the benefits obtained from spatial separation in multiple-talker listening situations, particularly for listeners with sensorineural hearing loss. A speech target was presented simultaneously with two or four speech maskers. The target was always presented diotically, and the maskers were either presented diotically or dichotically. In dichotic configurations, the maskers were symmetrically placed by introducing interaural time differences (ITDs) or infinitely large interaural level differences (ILDs; monaural presentation). Target-to-masker ratios for 50 % correct were estimated. Thresholds in all separated conditions were poorer in listeners with hearing loss than listeners with normal hearing. Moreover, for a given listener, thresholds were similar for conditions with the same number of talkers per ear (e.g., ILD with four talkers equivalent to ITD with two talkers) and hence the same energetic masking. The results are consistent with the idea that increased energetic masking, rather than a specific spatial deficit, may limit performance for hearing-impaired listeners in spatialized speech mixtures.

Interactions between listening effort and masker type on the energetic and informational masking of speech stimuli

In most cases, normal-hearing listeners perform better when a target speech signal is masked by a single irrelevant speech masker than they do with a noise masker at an equivalent signal-to-noise ratio (SNR). However, this relative advantage for segregating target speech from a speech masker versus a noise masker may not come without a cost: segregating speech from speech may require the allocation of additional cognitive resources that are not required to segregate speech from noise. The cognitive resources required to extract a target speech signal from different backgrounds can be assessed by varying the complexity of the listening task. Examples include: (1) contrasting the difference between the detection of a speech signal and the correct identification of its contents; (2) contrasting the difference between single-task diotic and dual-task dichotic listening tasks; and (3) contrasting the difference between standard listening tasks and one-back tasks where listeners must keep one response in memory during each stimulus presentation. By examining performance with different kinds of maskers in tasks with different levels of complexity, we can start to determine the impact that the informational and energetic components of masking have on the listening effort required to understand speech in complex environments.

Spatial release from masking as a function of the spectral overlap of competing talkers

This study tested the hypothesis that the reduced spatial release from speech-on-speech masking typically observed in listeners with sensorineural hearing loss results from increased energetic masking. Target sentences were presented simultaneously with a speech masker, and the spectral overlap between the pair (and hence the energetic masking) was systematically varied. The results are consistent with increased energetic masking in listeners with hearing loss that limits performance when listening in speech mixtures. However, listeners with hearing loss did not exhibit reduced spatial release from masking when stimuli were filtered into narrow bands.

Enhancing listener strategies using a payoff matrix in speech-on-speech masking experiments.

Speech recognition was measured as a function of the target-to-masker ratio (TMR) with syntactically similar speech maskers. In the first experiment, listeners were instructed to report keywords from the target sentence. Data averaged across listeners showed a plateau in performance below 0 dB TMR when masker and target sentences were from the same talker. In this experiment, some listeners tended to report the target words at all TMRs in accordance with the instructions, while others reported keywords from the louder of the sentences, contrary to the instructions. In the second experiment, stimuli were the same as in the first experiment, but listeners were also instructed to avoid reporting the masker keywords, and a payoff matrix penalizing masker keywords and rewarding target keywords was used. In this experiment, listeners reduced the number of reported masker keywords, and increased the number of reported target keywords overall, and the average data showed a local minimum at 0 dB TMR with same-talker maskers. The best overall performance with a same-talker masker was obtained with a level difference of 9 dB, where listeners achieved near perfect performance when the target was louder, and at least 80% correct performance when the target was the quieter of the two sentences.

Multicomponent signal detection: Tones in noise and amplitude modulation detection

In order to predict the detectability of broadband acoustic signals, a model must include a means of integrating information across frequencies. There have been several previous studies measuring the detectability of multicomponent signals, but it is still not clear what the best model is when signal components are not equally detectable. Some researchers have proposed that thresholds are driven by the most detectable component (max-d’ model), while others have found that the best model for their data is a statistical summation model, where component sensitivities are combined using a Pythagorean sum. In the present study, detection thresholds were collected in broadband noise for single tones at three frequencies and three signal-to-noise ratios (SNRs) and for all combinations of SNRs for the three tones presented together. Also, amplitude modulation (AM) detection thresholds were measured for a 16-Hz AM signal imposed on 300-Hz-wide noise bands centered at three frequencies at three modulation depths fo...

On a variable broadband absorption product and acceptable tolerances of reverberation times in halls for amplified music

Previous studies have shown that what distinguishes the best from the less well liked halls for pop and rock music is a short reverberation time in the 63, 125 and 250 Hz octave bands. Since a quite long reverberation time in these frequency bands is needed in order to obtain warmth and enough strength at classical music concerts, variable acoustics must address these frequencies in order to obtain desirable acoustics in multipurpose halls. Based on the results of a previous study of Danish rock venues as well as three newly built halls, acceptable tolerances of T30 were investigated. The results suggest that T30 can be at least 1.4 times as long in the 63 Hz octave band as in the 125 Hz band and attain values of +/- 15% at higher frequencies compared to previously determined values. A variable broadband absorption product is also presented. Absorption coefficients are approx. 0.8 in the 125, 250, 500 Hz bands, 0.6 at 1 kHz and decreasing at higher frequencies and in the 63 Hz band when in the ON position. In the OFF position the product attains absorption values between 0.0 and 0.2.

A variable passive low‐frequency absorber

Multi‐purpose concert halls face a dilemma. They can host classical music concerts, rock concerts and spoken word performances in a matter of a short period. These different performance types require significantly different acoustic conditions in order to provide the best sound quality to both the performers and the audience. A recommended reverberation time for classical music may be in the range of 1.5–2 s for empty halls, where rock music sounds best with a reverberation time around 0.8‐1 s. Modern rhythmic music often contains high levels of sound energy in the low frequency bands but still requires a high definition for good sound quality. Ideally, the absorption of the hall should be adjustable in all frequency bands in order to provide good sound quality for all types of performances. The mid and high frequency absorption is easily regulated, but adjusting the low‐frequency absorption has typically been too expensive or requires too much space to be practical for multi‐purpose halls. Measurements w...

Learning-related improvements in auditory detection sensitivities correlate with changes in sensory- and decision-related components of the event-related potential

Listener performance in an auditory detection task can improve with practice (Zwislocki, Maire, Feldman, & Rubin, 1958). This could result from a selective attention process and/or sensory plasticity (e.g., if trained stimuli receive increased cortical representation). Here, listeners were trained to detect either an 861-Hz or 1058-Hz tone (counterbalanced across participants) presented in a noise masker. On the following day, high-density EEG was collected while listeners: 1) attempted to detect 861-Hz and 1058-Hz tones in noise at an SNR of -21 dB, and 2) passively heard the same tones presented in quiet. Listeners were significantly better at detecting tones at their trained frequency. In addition, P3 amplitudes were larger for trained than for untrained tones during the detection task. During passive exposure to the same tones, P2 amplitudes were similarly larger for trained than for untrained tones. The difference in P3 amplitudes suggests that training leads to more efficient decisional processing, ...