Effects of landscape and distance in automatic audio based bird species identification.

The present work focuses on how the landscape and distance between a bird and an audio recording unit affect automatic species identification. Moreover, it is shown that automatic species identification can be improved by taking into account the effects of landscape and distance. The proposed method uses measurements of impulse responses between the sound source and the recorder. These impulse responses, characterizing the effect of a landscape, can be measured in the real environment, after which they can be convolved with any number of recorded bird sounds to modify an existing set of bird sound recordings. The method is demonstrated using autonomous recording units on an open field and in two different types of forests, varying the distance between the sound source and the recorder. Species identification accuracy improves significantly when the landscape and distance effect is taken into account when building the classification model. The method is demonstrated using bird sounds, but the approach is applicable to other animal and non-animal vocalizations as well.

Investigation of the seat-dip effect using finite-difference time-domain simulations.

The seat-dip effect (SDE) occurs when low-frequency sounds propagate through the seating area of a performance space. The physical aspects governing the effect still puzzle acousticians mostly due to the large variety of seating configurations. In this study, the SDE is investigated in three parameterized hall models using the finite-difference time-domain method to simulate a large number of seat configurations in order to quantify the contribution of different geometric properties related to the seating area. The results show that the step size defining the inclination angle of the seating area and the opening underneath the seats (or underpass) are significant factors contributing to the SDE, whereas the stage height and the source position are found to be less important. The results also demonstrate that with an underpass greater than the step size, the first frequency dip occurring between 80 and 100 Hz is mitigated regardless of the hall type considered. The phenomenon is also found to be predominant in the early part of the room response. Visualizations of spatial and time-frequency evolution in the halls are also provided for the cases where the seat properties are found to visibly affect the magnitude spectrum.

Chamber music hall acoustics: Measurements and perceptual differences.

This study investigates the room acoustics of seven chamber music halls of various modern and historical architecture by means of objective room acoustic measures and a subjective listening experiment. The acoustic measurements were performed with heavy cloth covering the audience areas to simulate occupancy in the halls. A loudspeaker quartet was used for auralizations, which were reproduced in a surrounding loudspeaker array. The perceptual differences between the halls were evaluated in terms of envelopment, warmth, clarity, proximity, and preference by using a paired comparison paradigm. The subjective evaluations were conducted in two different laboratories and latent class analysis was used to study the agreement between laboratories and the emergence of different listener groups in the ratings of each attribute. Concerning preference, the emergence of two groups found in the study of large symphony halls was confirmed, where one group prefers rich, enveloping sound and one group prefers high clarity. The perceptual ratings were not clearly associated with a specific hall shape, but rather depended on the distribution of early and late sound energy. Thus, the distinction between rectangular and non-rectangular floor plans previously found for large symphony halls was not observed with these smaller halls.

Perceptual detection thresholds for numerical dispersion in binaural auralizations of two acoustically different rooms.

Room acoustic simulations using the finite-difference time-domain method on a wide frequency range can be computationally expensive and typically contain numerical dispersion. Numerical dispersion can be audible and, thus, constitutes an artifact in auralizations. There is a need to measure perceptual thresholds for numerical dispersion to achieve an optimal balance between computational complexity and audibility of dispersion. This work measures the perceptual detection thresholds for numerical dispersion in binaural auralizations of two acoustically different rooms. Numerical dispersion is incorporated into measured binaural room impulse responses (BRIRs) by the means of filters that represent the dispersion that plane waves experience, which propagate in the simulation in the direction of the worst-case dispersion error. The results show that the perceptual detection threshold is generally lower for the most reverberant room and greatly depends on the source signal independently of the room in which the threshold is measured. It is the most noticeable in the pure BRIRs, i.e., with an impulse as source signal, and almost unnoticeable with speech. The results also show that there was no statistical evidence that the perceptual thresholds for the conditions where numerical dispersion was present or absent in the direct path of the BRIRs be different.

Clearly audible room acoustical differences may not reveal where you are in a room.

A common aim in virtual reality room acoustics simulation is accurate listener position dependent rendering. However, it is unclear whether a mismatch between the acoustics and visual representation of a room influences the experience or is even noticeable. Here, we ask if listeners without any special experience in echolocation are able to identify their position in a room based on the acoustics alone. In a first test, direct comparison between acoustic recordings from the different positions in the room revealed clearly audible differences, which subjects described with various acoustic attributes. The design of the subsequent experiment allows participants to move around and explore the sound within different zones in this room while switching between visual renderings of the zones in a head-mounted display. The results show that identification was only possible in some special cases. In about 74% of all trials, listeners were not able to determine where they were in the room. The results imply that audible position dependent room acoustic rendering in virtual reality may not be noticeable under certain conditions, which highlights the importance of evaluation paradigm choice when assessing virtual acoustics.

Perceptual roughness of spatially assigned sparse noise for rendering reverberation.

Multichannel auralizations based on spatial room impulse responses often employ sample-wise assignment of an omnidirectional response to form loudspeaker responses. This leads to sparse impulse responses in each reproduction loudspeaker and the auralization of transient signals can sound rough. Based on this observation, we conducted a listening test to examine the general phenomenon of roughness due to spatial assignment. First, participants assessed the roughness of both Gaussian noise and velvet noise, assigned sample-wise to up to 36 loudspeakers by two algorithms. The first algorithm assigns channels merely by selecting random indices, while the second one constrains the time between two peaks on each channel. The results show that roughness already occurs when few channels are used and that the assignment algorithm influences it. In a second experiment, virtualizations of the test were used to examine the factors contributing to increased roughness. We systematically show the effect of spatial assignment on noise and conclude that besides time-differences, level-differences caused by head-shadowing are the principal cause for the perceived roughness. The results have significance in spatial room impulse response rendering and spatial reverberator design.

An exploratory investigation of speech recognition thresholds in noise with auralisations of two reverberant rooms.

OBJECTIVE: Speech-in-noise tests are widely used in hearing diagnostics but typically without reverberation, although reverberation is an inextricable part of everyday listening conditions. To support the development of more real-life-like test paradigms, the objective of this study was to explore how spatially reproduced reverberation affects speech recognition thresholds in normal-hearing and hearing-impaired listeners. DESIGN: Thresholds were measured with a Finnish speech-in-noise test without reverberation and with two test conditions with reverberation times of ∼0.9 and 1.8 s. Reverberant conditions were produced with a multichannel auralisation technique not used before in this context. STUDY SAMPLE: Thirty-four normal-hearing and 14 hearing-impaired listeners participated in this study. Five people were tested with and without hearing aids. RESULTS: No significant differences between test conditions were found for the normal-hearing listeners. Results for the hearing-impaired listeners indicated better performance for the 0.9 s reverberation time compared to the reference and the 1.8 s conditions. Benefit from hearing aid use varied between individuals; for one person, an advantage was observed only with reverberation. CONCLUSIONS: Auralisations may offer information on speech recognition performance that is not obtained with a test without reverberation. However, more complex stimuli and/or higher signal-to-noise ratios should be used in the future.

Recognizing individual concert halls is difficult when listening to the acoustics with different musical passages.

This article presents a listening experiment in which the listeners' task was to recognize the acoustics of a seat in a specific concert hall. Stimuli included two short passages extracted from a Beethoven symphony and samples of a solo violin auralized to four real concert halls. In each trial, listeners were presented with a reference and four alternatives with one correct match. In the "same" condition, the reference and the alternatives contained the same source sound. In the "different" condition, the source sounds were different musical passages but always of the same sound type, that is, symphonic music or solo violin. Results show that on average listeners could recognize the halls when the task was performed with the same source sound but had difficulty when listening to different sounds. The patterns of erroneous responses exhibited confusion between particular hall pairs and corresponded well to the values and just-noticeable-differences of the traditional objective room acoustic parameters. While the type of music is previously well known to influence the perception of concert hall acoustics, the present results indicate that even minor changes in the source sound content may have a strong impact on the ability to recognize the acoustics of individual halls.

Perception of loudness and envelopment for different orchestral dynamics.

One of the main factors that makes listening to live concerts emotionally engaging is the dynamic changes in the music. Recent research has shown that concert hall acoustics can affect the perception of orchestral dynamics, but hardly any listening tests have focused on this interplay between the dynamics in music and hall acoustics. In this study, the influence of the orchestral dynamics is assessed with auralizations of musical excerpts of different dynamics (from pianissimo to fortissimo) in two listening positions within four different concert halls. Pairwise comparisons were made in terms of loudness and envelopment which are among the main perceptual factors of concert hall acoustics. The subjective results show that the loudness and envelopment can depend on the musical dynamics. Therefore, in future research on concert hall acoustics, much more attention should be paid to the dynamically varying spectrum of the stimulus signal and the listening level, not only to linear impulse responses used for computing objective parameters.

Perception and preference of reverberation in small listening rooms for multi-loudspeaker reproduction.

An experiment was conducted to identify the perceptual effects of acoustical properties of domestic listening environments, in a stereophonic reproduction scenario. Nine sound fields, originating from four rooms, were captured and spatially reproduced over a three-dimensional loudspeaker array. A panel of ten expert assessors identified and quantified the perceived differences of those sound fields using their own perceptual attributes. A multivariate analysis revealed two principal dimensions that could summarize the sound fields of this investigation. Four perceptual constructs seem to characterize the sensory properties of these dimensions, relating to Reverberance, Width & Envelopment, Proximity, and Bass. Overall, the results signify the importance of reverberation in residential listening environments on the perceived sensory experience, and as a consequence, the assessors' preferences towards certain decay times.

Concert halls with strong lateral reflections enhance musical dynamics.

One of the most thrilling cultural experiences is to hear live symphony-orchestra music build up from a whispering passage to a monumental fortissimo. The impact of such a crescendo has been thought to depend only on the musicians' skill, but here we show that interactions between the concert-hall acoustics and listeners' hearing also play a major role in musical dynamics. These interactions contribute to the shoebox-type concert hall's established success, but little prior research has been devoted to dynamic expression in this three-part transmission chain as a complete system. More forceful orchestral playing disproportionately excites high frequency harmonics more than those near the note's fundamental. This effect results in not only more sound energy, but also a different tone color. The concert hall transmits this sound, and the room geometry defines from which directions acoustic reflections arrive at the listener. Binaural directional hearing emphasizes high frequencies more when sound arrives from the sides of the head rather than from the median plane. Simultaneously, these same frequencies are emphasized by higher orchestral-playing dynamics. When the room geometry provides reflections from these directions, the perceived dynamic range is enhanced. Current room-acoustic evaluation methods assume linear behavior and thus neglect this effect. The hypothesis presented here is that the auditory excitation by reflections is emphasized with an orchestra forte most in concert halls with strong lateral reflections. The enhanced dynamic range provides an explanation for the success of rectangularly shaped concert-hall geometry.

Perceptual significance of seat-dip effect related direct sound coloration in concert halls.

In concert halls, the spectrum of direct sound (here 0 to 15 ms) is influenced by the seat-dip effect that causes selective low frequency attenuation. The seat-dip effect has been considered to be detrimental to the acoustic quality of halls, yet there is little evidence about the perceptual significance of the effect. This paper studies the discrimination and preference of seat-dip effect related changes in the direct sound, with realistic auralization of multichannel anechoic orchestra recordings in halls measured with the loudspeaker orchestra. Comparisons are made with a free-field direct sound and direct sound magnitude changes typically associated with the seat-dip effect. Overall, the differences were not significantly audible, except with a subgroup of participants in one out of four halls, and two out of three comparisons. Furthermore, participants' preference for the uncolored direct sound was significant in the halls with less reflected energy, but non-significant in the halls with more reflected energy. The results imply that for most seats in adequately reverberant halls, typical seat-dip effect related coloration in the direct sound can be perceptually negligible.

Perceptual aspects of reproduced sound in car cabin acoustics.

An experiment was conducted to determine the perceptual effects of car cabin acoustics on the reproduced sound field. In-car measurements were conducted whilst the cabin's interior was physically modified. The captured sound fields were recreated in the laboratory using a three-dimensional loudspeaker array. A panel of expert assessors followed a rapid sensory analysis protocol, the flash profile, to perceptually characterize and evaluate 12 acoustical conditions of the car cabin using individually elicited attributes. A multivariate analysis revealed the panel's consensus and the identified perceptual constructs. Six perceptual constructs characterize the differences between the acoustical conditions of the cabin, related to bass, ambience, transparency, width and envelopment, brightness, and image focus. The current results indicate the importance of several acoustical properties of a car's interior on the perceived sound qualities. Moreover, they signify the capacity of the applied methodology in assessing spectral and spatial properties of automotive environments in laboratory settings using a time-efficient and flexible protocol.

Concert halls with strong and lateral sound increase the emotional impact of orchestra music.

An audience's auditory experience during a thrilling and emotive live symphony concert is an intertwined combination of the music and the acoustic response of the concert hall. Music in itself is known to elicit emotional pleasure, and at best, listening to music may evoke concrete psychophysiological responses. Certain concert halls have gained a reputation for superior acoustics, but despite the continuous research by a multitude of objective and subjective studies on room acoustics, the fundamental reason for the appreciation of some concert halls remains elusive. This study demonstrates that room acoustic effects contribute to the overall emotional experience of a musical performance. In two listening tests, the subjects listen to identical orchestra performances rendered in the acoustics of several concert halls. The emotional excitation during listening is measured in the first experiment, and in the second test, the subjects assess the experienced subjective impact by paired comparisons. The results showed that the sound of some traditional rectangular halls provides greater psychophysiological responses and subjective impact. These findings provide a quintessential explanation for these halls' success and reveal the overall significance of room acoustics for emotional experience in music performance.

Perception of music dynamics in concert hall acoustics.

Dynamics is one of the principal means of expressivity in Western classical music. Still, preceding research on room acoustics has mostly neglected the contribution of music dynamics to the acoustic perception. This study investigates how the different concert hall acoustics influence the perception of varying music dynamics. An anechoic orchestra signal, containing a step in music dynamics, was rendered in the measured acoustics of six concert halls at three seats in each. Spatial sound was reproduced through a loudspeaker array. By paired comparison, naive subjects selected the stimuli that they considered to change more during the music. Furthermore, the subjects described their foremost perceptual criteria for each selection. The most distinct perceptual factors differentiating the rendering of music dynamics between halls include the dynamic range, and varying width of sound and reverberance. The results confirm the hypothesis that the concert halls render the performed music dynamics differently, and with various perceptual aspects. The analysis against objective room acoustic parameters suggests that the perceived dynamic contrasts are pronounced by acoustics that provide stronger sound and more binaural incoherence by a lateral sound field. Concert halls that enhance the dynamics have been found earlier to elicit high subjective preference.

Concert hall acoustics: Repertoire, listening position, and individual taste of the listeners influence the qualitative attributes and preferences.

Some studies of concert hall acoustics consider the acoustics in a hall as a single entity. Here, it is shown that the acoustics vary between different seats, and the choice of music also influences the perceived acoustics. The presented study compared the acoustics of six unoccupied concert halls with extensive listening tests, applying two different music excerpts on three different seats. Twenty eight assessors rated the halls according to the subjective preference of the assesors and individual attributes with a paired comparison method. Results show that assessors can be classified into two preference groups, which prioritize different perceptual factors. In addition, the individual attributes elicited by assessors were clustered into three latent classes.

Investigation of auditory distance perception and preferences in concert halls by using virtual acoustics.

Virtual acoustics with multichannel sound reproduction was used to study auditory distance perception in four concert halls with multiple sound sources on stage. Eight subjects reported apparent auditory distances in five seating positions from 10 to 26 m to the middle of the sources on stage. The distance estimates were collected by absolute distance estimation procedure as well as a free modulus estimation procedure including both within and between halls evaluations. In addition, pairwise preferences were collected for two positions within each hall and for one position between halls. Results reveal that the perception of distance is dependent on the hall acoustics and show how the strength factor G and direct-to-reverberant energy ratio covary in relation to perceptual distances in these halls. The results also indicate that in such large spaces the overestimation of short distances may continue up to and further than 10 m from the sound sources. Preference results show that closer seats were liked more than further ones and that the strength of this preference is associated with the difference in perceptual distances.

Identifying concert halls from source presence vs room presence.

Identification of concert halls was studied to uncover whether the early or late part of the acoustic response is more salient in a hall's fingerprint. A listening test was conducted with auralizations of measured halls using full, hybrid, and truncated impulse responses convolved with anechoic symphonic music. Subjects identified halls more reliably based on differences in early responses rather than late responses, although varying the late response had more effect on acoustic parameters. The results suggest that in a typical situation with running symphonic music, the early response determines the perceptual fingerprint of a hall more than the late response.