The effect of loudness on the reverberance of music: reverberance prediction using loudness models

A study of the just noticeable difference of early decay time for symphonic halls

The just noticeable differences (JNDs) of room acoustic parameters are important for the design of concert halls and, in general, research of room acoustics. Precise knowledge of JNDs helps the concert hall designer in assessing the impact that changes in the geometry or materials of the hall will have on its perceived acoustics. When designing a concert hall, creating an appropriate feeling of reverberance for the audience is of prime importance. The early decay time (EDT) parameter has proved to be a better predictor of the perception of reverberance than the classical reverberation time (T30), but no studies have been conducted to specifically determine the EDT JND. In the present study, the EDT JND was investigated for broadband conditions and assessed for individual frequency ranges. A subjective study was conducted with 26 subjects with musical training, in which 21 were considered reliable. The participants listened to orchestral music convolved with measured spatial room impulse responses from three concert halls. The stimuli were auralized in an anechoic chamber using third-order Ambisonic reproduction. The obtained values show that the JNDs for the broadband conditions are lower than those for the individual frequency ranges. The EDT JND for the broadband conditions was found to be approximately 18% of the EDT value.

Reverberation strength perceived by normal-hearing listeners predictable based on time-varying binaural loudness

Previous work has explored novel binaural combinations of reverberation and the resulting perceived reverberation strength (reverberance). The present study examines the perceptual effects of additional binaural combinations of reverberation with the goal of explaining reverberance in terms of basic psychoacoustic principles. Stimuli were generated using virtual space techniques simulating a speech source 3 m to the listener's right in a moderately reverberant environment. Reverberant energy at the ears was varied systematically relative to the natural level for the environment (0-dB gain). The method of magnitude estimation was used to estimate reverberance. Four experiments were conducted. Experiment 1 tested monaural listening conditions for both left and right ears at reverberation gains from -21 dB to 0 dB. Experiment 2 tested a binaural listening condition where only reverberant energy at the ear farther from the source was manipulated (-21 dB to 0 dB). Experiment 3 tested two binaural conditions over a wider range of reverberation gains (-18 dB to +24 dB). In one condition, reverberant energy was manipulated for both ears equally. In the other condition, reverberant energy was manipulated only for the ear nearer the source. In Experiment 4, reverberant tails of the stimuli were removed to test whether listeners were able to use ongoing reverberant information to judge reverberance. The results from all experiments were found to be well predicted by a model of time-varying binaural loudness that focused on "glimpses" in time with relatively high reverberant sound energy and low direct sound energy. These findings suggest that the mechanisms underlying reverberance and loudness may be similar.

Assessing the perceived reverberation in different rooms for a set of musical instrument sounds

Previous research has shown that the perceived reverberation in a room, or reverberance, depends on the sound source that is being listened to. In a study by Osses Vecchi, Kohlrausch, Lachenmayr, and Mommertz [(2017). J. Acoust. Soc. Am. 141(4), EL381-EL387], reverberance estimates obtained from an auditory model for 23 musical instrument sounds in 8 rooms predicted a sound-source dependency. As a follow-up to that study, a listening experiment with 24 participants was conducted using a subset of the original sounds with the purpose of mapping each test sound onto a reverberance scale. Consistent with the literature, the experimental reverberance estimates were significantly dependent on the instrument sound being listened to, but on the top of that, the estimates were significantly correlated with simulated reverberance estimates for the test stimuli as well as for the previously reported long-duration sounds.

Artificial enveloping reverberation for binaural auralization using reciprocal maximum-length sequences

Binaural auralization through proper room-acoustic simulation can produce a realistic listening experience as if the listener were sitting in a room with spatial perception, including enveloping reverberance. Based on analysis of experimentally measured binaural room-acoustic data, this paper discusses an approach to creating artificial but natural-sounding reverberation for binaural rendering that can be employed in simulating such an environment in an efficient way. Approaches to adjusting the spaciousness of enveloping reverberance within the context of artificially generated reverberation are investigated via hearing tests. This paper exploits the excellent pseudorandom properties of maximum-length sequences to generate deterministic and controllable decorrelations between binaural channels for artificial reverberation for room-acoustic simulations with high computational efficiency. To achieve natural-sounding enveloping reverberance in an enclosed space, and thereby an immersive environment, the shapes of both the reverberation energy decays and the spatial characteristics are found to be decisive. This paper discusses systematic hearing test results that support the mentioned finding.

Development of a clarity parameter using a time-varying loudness model

The perceived sound clarity is often estimated with the clarity index, which is calculated on the basis of physical acoustic measures that can correlate weakly to the way humans perceive sound for certain test conditions. Therefore, this study proposes a clarity parameter based on a binaural room impulse response processed with a time-varying loudness model. The proposed parameter is validated by calculating the correlation coefficient with subject responses collected from previous listening experiments. Results show that the parameter outperforms the clarity index in most of the tested conditions, but its performance is less robust than parameter for clarity (P_CLA).

Comparison of psychoacoustic-based reverberance parameters

This study compared psychoacoustic reverberance parameters to each other, as well as to reverberation time (RT) and early decay time (EDT) under various acoustic conditions. The psychoacoustic parameters were loudness-based RT (T_N), loudness-based EDT [EDT_N; Lee, Cabrera, and Martens, J. Acoust. Soc. Am. 131, 1194-1205 (2012a)], and parameter for reverberance [P_REV; van Dorp Schuitman, de Vries, and Lindau., J. Acoust. Soc. Am. 133, 1572-1585 (2013)]. For the comparisons, a wide range of sound pressure levels (SPLs) from 20 dB to 100 dB and RTs from 0.5 s to 5.0 s were evaluated, and two sets of subjective data from the previous studies were used for the cross-validation and comparison. Results of the comparisons show that the psychoacoustic reverberance parameters provided better matches to reverberance than RT and EDT; however, the performance of these psychoacoustic reverberance parameters varied with the SPL range, the type of audio sample, and the reverberation conditions. This study reveals that P_REV is the most relevant for estimating a relative change in reverberance between samples when the SPL range is small, while EDT_N is useful in estimating the absolute reverberance. This study also suggests the use of P_REV and EDT_N for speech and music samples, respectively.

Predicting the perceived reverberation in different room acoustic environments using a binaural auditory model

In this paper a binaural auditory model was used to compute reverberance estimates in four simulated halls. For three of the halls different absorption conditions were evaluated. The model estimates (pRev) were obtained using music excerpts of an orchestra consisting of 23 instrument sections and then compared with the room acoustic parameters of reverberation time (T₃₀) and early decay time (EDT) at mid frequencies. Although the results showed that pRev has a higher correlation with EDT rather than with T₃₀, this relationship depends on the properties of the instruments. The simulations show that pRev depends on the presentation level and that for instruments with similar critical-band spectrum, pRev follows a similar trend across acoustic conditions. A computational framework and sound stimuli are provided to encourage the search of experimental evidence of the aspects addressed in this study.

Influence of impedance phase angle on sound pressures and reverberation times in a rectangular room

In most room acoustic predictions, phase shift on reflection has been overlooked. This study aims to quantify the effects of the surface impedance phase angle of the boundary surfaces on room acoustic conditions. As a preliminary attempt, a medium-sized rectangular room is simulated by a phased beam tracing model, after verifying it numerically against boundary element simulations. First, the absorption characteristic of the boundary surfaces varies uniformly from 0.2 to 0.8, but with various impedance phase angles. Second, typical non-uniform cases having hard walls and floor, but with an absorptive ceiling are investigated. The zero phase angle, which has commonly been assumed in practice, is regarded as reference and differences in the sound pressure level and early decay time from the reference are quantified. As expected, larger differences in the room acoustic parameters are found for larger impedance phase angles. Additionally, binaural impulse responses are compared in a listening test for the uniform absorption cases, revealing that non-zero impedance phase angle cases can be perceptually different from the reference condition in terms of reverberance perception. For the non-uniform settings, the change in the impedance phase angle of the ceiling does not affect the acoustic conditions significantly.

Effect of spectral overlap on the echo suppression threshold for single reflection conditions

In performing arts venues, the spectra of direct and reflected sound at a receiving location differ, due to seat dip effect, diffusive and absorptive surfaces, and source directivity. This paper examines the influence of differing lead and lag spectral contents on echo suppression threshold. The results indicate, that for a highpass filtered direct sound and a broadband reflection, attenuation of low frequencies initially results in an increase in echo suppression threshold, while for higher cutoff frequencies echo suppression threshold drastically decreases. For broadband direct sound and filtered reflections, the echo suppression threshold is inversely related to high frequency content.

The role of diffusive architectural surfaces on auditory spatial discrimination in performance venues

In musical or theatrical performance, some venues allow listeners to individually localize and segregate individual performers, while others produce a well blended ensemble sound. The room acoustic conditions that make this possible, and the psycho-acoustic effects at work are not fully understood. This research utilizes auralizations from measured and simulated performance venues to investigate spatial discrimination of multiple acoustic sources in rooms. Signals were generated from measurements taken in a small theater, and listeners in the audience area were asked to distinguish pairs of speech sources on stage with various spatial separations. This experiment was repeated with the proscenium splay walls treated to be flat, diffusive, or absorptive. Similar experiments were conducted in a simulated hall, utilizing 11 early reflections with various characteristics, and measured late reverberation. The experiments reveal that discriminating the lateral arrangement of two sources is possible at narrower separation angles when reflections come from flat or absorptive rather than diffusive surfaces.