Densil Cabrera

Non-auditory factors affecting urban soundscape evaluation

The aim of this study is to characterize urban spaces, which combine landscape, acoustics, and lighting, and to investigate peoples perceptions of urban soundscapes through quantitative and qualitative analyses. A general questionnaire survey and soundwalk were performed to investigate soundscape perception in urban spaces. Non-auditory factors (visual image, day lighting, and olfactory perceptions), as well as acoustic comfort, were selected as the main contexts that affect soundscape perception, and context preferences and overall impressions were evaluated using an 11-point numerical scale. For qualitative analysis, a semantic differential test was performed in the form of a social survey, and subjects were also asked to describe their impressions during a soundwalk. The results showed that urban soundscapes can be characterized by soundmarks, and soundscape perceptions are dominated by acoustic comfort, visual images, and day lighting, whereas reverberance in urban spaces does not yield consistent preference judgments. It is posited that the subjective evaluation of reverberance can be replaced by physical measurements. The categories extracted from the qualitative analysis revealed that spatial impressions such as openness and density emerged as some of the contexts of soundscape perception.

Seeing sound: real-time sound visualisation in visual feedback loops used for training musicians

Musicians in training need to understand the sound they are producing in order to improve its deficient aspects. Verbal feedback from musical masters is the usual method used for attaining this understanding. However, using realtime sound visualisation as a complementary form of feedback allows the large amounts of data typical of real-time acoustic analysis to be employed within training. This improves the efficiency of the feedback loop normally present within musical training and pedagogy. The implementation and effect of such a system is discussed.

PsySound3: a program for the analysis of sound recordings

This paper demonstrates the sound analysis software PsySound3, which was written by the authors. The software currently includes a range of DSP‐based analysis techniques (e.g., spectrum, cepstrum, autocorrelation, Hilbert transform, sound level meter emulator), as well as implementations of psychoacoustical algorithms often associated with sound quality (e.g., loudness, sharpness, loudness fluctuation, roughness, pitch, binaural attributes). In some cases, PsySound3 makes available multiple models of the one auditory attribute ‐ for example it implements dynamic and static loudness models using Erb‐ and Bark‐based auditory filters. The program is extensible, and so has the potential to allow researchers to share their analysis models using a common interface. PsySound3 is written in Matlab, and is also available as a stand‐alone program. The software is freely available from www.psysound.org.

Self-to-other ratios measured in an opera chorus in performance

Four volunteer members of the chorus of Opera Australia, representing four different voice categories, wore binaural pairs of wireless microphones during a penultimate dress rehearsal on the Opera Theater stage of the Sydney Opera House. From the recordings, data were obtained on sound levels and on the self-to-other ratios (SORs). The sound levels were comparable to those found in loud music in chamber choir performance. The average SOR ranged from +10 to +15 dB. Compared to chamber choirs in other types of room, the SOR values were high. On a separate occasion, the stage support parameters ST1 (early reflections) and ST2 (late reflections) were measured over the whole stage area. ST1 was about -16 dB, which is typical for opera stages, and -20 dB for ST2, which is unusually low. It is concluded that the SOR in the opera chorus depends mostly on choir formation, which is highly variable, and that an opera chorus artist generally can hear his or her own voice very well, but little of the others and of the orchestra. This was confirmed by informal listening to the recordings.

Influence of fundamental frequency and source elevation on the vertical localization of complex tones and complex tone pairs

This study investigates the vertical localization of single complex tones (monads) and simultaneous complex tone pairs (dyads), especially as it is affected by their fundamental frequency and source elevation. Two complex tone timbres are considered: one consisting of five low-order harmonics, and the other of all odd harmonics (a square wave). Sound sources were at -15, 0, 15, and 30 deg from the horizontal plane at ear height. For eight subjects, this source array was in the median plane, and for a further nine subjects, it was directly to the subjects left (lateral plane). The subjects localized the angle of the auditory image(s) of one or two complex tones around the vertical plane containing the sound sources. Mean responses for the five-harmonic complex tones show a systematic effect (referred to as Pratts effect) of fundamental frequency on vertical localization--whereby high-frequency complex tones are localized to positions higher than low-frequency complex tones for equivalent source positions. For the square wave, the sound-source position dominates localization, although some effect of fundamental frequency is evident for median plane sources.

The effect of visual and auditory cues on seat preference in an opera theater

Opera performance conveys both visual and auditory information to an audience, and so opera theaters should be evaluated in both domains. This study investigates the effect of static visual and auditory cues on seat preference in an opera theater. Acoustical parameters were measured and visibility was analyzed for nine seats. Subjective assessments for visual-only, auditory-only, and auditory-visual preferences for these seat positions were made through paired-comparison tests. In the cases of visual-only and auditory-only subjective evaluations, preference judgment tests on a rating scale were also employed. Visual stimuli were based on still photographs, and auditory stimuli were based on binaural impulse responses convolved with a solo tenor recording. For the visual-only experiment, preference is predicted well by measurements taken related to the angle of seats from the theater midline at the center of the stage, the size of the photographed stage view, the visual obstruction, and the distance from the stage. Sound pressure level was the dominant predictor of auditory preference in the auditory-only experiment. In the cross-modal experiments, both auditory and visual preferences were shown to contribute to overall impression, but auditory cues were more influential than the static visual cues. The results show that both a positive visual-only or a positive auditory-only evaluations positively contribute to the assessments of seat quality.

Effects of Training on Time-Varying Spectral Energy and Sound Pressure Level in Nine Male Classical Singers

The male classical singing voice is a musical instrument that is very important in western culture. It has many acoustic features which should change and improve over the period in which the singer trains. In this study we compare nine singers in different stages of training, from university level students through to international soloists. Typically, Energy Ratio (ER; a measure of mean spectral slope) and mean sound pressure level (SPL) may be calculated to summarize an entire singing sample. We investigate an alternative approach, by calculating the time-varying ER and SPL. The inspection of the distribution of these descriptors over an arias time period yields a more detailed picture of the strategies for high-frequency energy production used by singers with different levels of training.

Increasing robustness in the calculation of the speech transmission index from impulse responses

There are many factors that can affect the measured values of the speech transmission index (STI), and this paper examines how and why identical inputs into STI calculation software are yielding varying results. The study involved a survey of a number of software implementations of the Indirect Method for computing the STI from an impulse response, one of which was written by the authors. Results are presented for artificial and measured impulse responses, and for signal and noise spectra that were designed to test particular aspects of the STI calculation. While most deviations between implementations were within 0.01 STI, some were not, revealing a need for greater robustness in the design of software and greater clarity in the STI standard (IEC60268-16), including more support for validation. This paper provides some data for such validation.

Long-Term Horizontal Vocal Directivity of Opera Singers: Effects of Singing Projection and Acoustic Environment

Vocal directivity refers to how directional the sound is that comes from a singers mouth, that is, whether the sound is focused into a narrow stream of sound projecting in front of the singers or whether it is spread out all around the singer. This study investigates the long-term vocal directivity and acoustic power of professional opera singers and how these vary among subjects, among singing projections, and among vastly different acoustic environments. The vocal sound of eight professional opera singers (six females and two males) was measured in anechoic and reverberant rooms and in a recital hall. Subjects sang in four different ways: (1) paying great attention to intonation; (2) singing as in performance, with all the emotional connection intended by the composer; (3) imagining a large auditorium; and (4) imagining a small theatre. The same song was sung by all singers in all conditions. A head and torso simulator (HATS), radiating sound from its mouth, was used for comparison in all situations. Results show that individual singers have quite consistent long-term average directivity, even across conditions. Directivity varies substantially among singers. Singers are more directional than the standard HATS (which is a physical model of a talking person). The singers formant region of the spectrum exhibits greater directivity than the lower-frequency range, and results indicate that singers control directivity (at least, incidentally) for different singing conditions as they adjust the spectral emphasis of their voices through their formants.

Variation in Oral-Binaural Room Impulse Responses for Horizontal Rotations of a Head and Torso Simulator

Oral-binaural room impulse responses (OBRIRs) describe the room acoustical response from the mouth to the ears of a head or dummy head. In this study, we measured OBRIRs in ten rooms, ranging from small to large. In each room, a head and torso simulator (HATS) was rotated at 2 degree increments to sample the room response at the selected measurement position. In rotating the HATS, the radiation pattern of the mouth rotates with the reception pattern of ears. This paper characterises the variation in room gain and interaural response of the tested rooms, and in doing so, we consider how OBRIRs can be usefully understood in terms of acoustical parameters.