Objective and Subjective Evaluation of the Use of Directional Sound Sources in Auralizations

Omni-directional sources are often used in room acoustic computer simulations, as opposed to directional sources, since measured directivity data are quite limited and difficult to obtain. The purpose of this study is to investigate the objective and subjective significance of adding more complex directivity to the sources used in computer simulations and auralizations. A simple hall was used as the modelled space in the software program ODEON. Three source positions on stage and three receiver audience positions were chosen. Impulse responses (IRs) were calculated for the nine source/receiver combinations, using (a) an omni-directional source, (b) a highly directional source beaming in a sixteenth-tant of a sphere, and (c) three realistic sources: piano, singing voice and violin. The directivity data for the three realistic sources, obtained from the Physikalisch-Technischen Bundesanstalt website, were available in octave bands from 1 kHz – 4 kHz for the piano and violin, and from 125 Hz – 4 kHz for the singing voice. The objective measures evaluated were Sound Pressure Level (SPL), Reverberation Time (T60) and Clarity Index (C80). In general, there is at least 5% difference in T60 data between the omni-directional source and the realistic directional ones. Differences in SPL and C80 are more irregular across frequency bands and appear to be more apparent for sources with higher directivity index. For select source/receiver combinations, the IRs resulting from each source directivity have been convolved with anechoic musical recordings of piano, singing and violin to produce auralizations. Subjective testing revealed a noticeable difference between the omni-directional and the sixteenth-tant sources, but not with the realistic sources

A Comparison Of Late Lateral Energy (GLL) and Lateral Energy Fraction (LF) Measurements Using a Spherical Microphone Array and Conventional Methods

Late Lateral Energy Level (GLL) and Lateral Energy Fraction (LF) are two room acoustics measures that have both been shown to correlate with certain aspects of the spatial impression of a listening space. In order to obtain these quantities, the lateral energy must be measured, which is typically carried out using microphones with a figure-of-eight (figure-8) polar pickup pattern. However, most commercially available figure-8 microphones are intended for use in audio recording applications, and are not laboratory-grade or designed for room acoustics impulse response (IR) measurements. Such microphones may suffer from non-ideal frequency response and/or directivity patterns. This study compares measurements that were taken in a 2500 seat auditorium using an omni-directional and studio-grade figure-8 microphone pair versus the omni-directional and dipole components extracted from a 32 element spherical microphone array. The results show that the two measurement methods agree in the 500 Hz and higher octave bands, but differ at low frequencies due to differences in the directivity patterns. The difference of the LF average from 125 Hz to 1 kHz for the two methods was between 0.59 and 1.81 just noticeable differences (JNDs) at the six receiver locations. The difference of the GLL average from 125 Hz to 1 kHz for the two methods was between 0.02 and 0.48 JNDs (applying the JND for strength of 1 dB). It was also found that repeatability error was present at one of the six receiver locations for the LF measurements, but was very small for the GLL measurements

Objective and Subjective Evaluation of the Use of Directional Sound Sources in Auralizations

Omni-directional sources are often used in room acoustic computer simulations, as opposed to directional sources, since measured directivity data are quite limited and difficult to obtain. The purpose of this study is to investigate the objective and subjective significance of adding more complex directivity to the sources used in computer simulations and auralizations. A simple hall was used as the modelled space in the software program ODEON. Three source positions on stage and three receiver audience positions were chosen. Impulse responses (IRs) were calculated for the nine source/receiver combinations, using (a) an omni-directional source, (b) a highly directional source beaming in a sixteenth-tant of a sphere, and (c) three realistic sources: piano, singing voice and violin. The directivity data for the three realistic sources, obtained from the Physikalisch-Technischen Bundesanstalt website, were available in octave bands from 1 kHz – 4 kHz for the piano and violin, and from 125 Hz – 4 kHz for the singing voice. The objective measures evaluated were Sound Pressure Level (SPL), Reverberation Time (T60) and Clarity Index (C80). In general, there is at least 5% difference in T60 data between the omni-directional source and the realistic directional ones. Differences in SPL and C80 are more irregular across frequency bands and appear to be more apparent for sources with higher directivity index. For select source/receiver combinations, the IRs resulting from each source directivity have been convolved with anechoic musical recordings of piano, singing and violin to produce auralizations. Subjective testing revealed a noticeable difference between the omni-directional and the sixteenth-tant sources, but not with the realistic sources

Room acoustics computer modelling: Study of the effect of source directivity on auralizations

Auralizations are very useful in the design of performing arts spaces, where auralization is the process of rendering audible the sound field in a space, in such a way as to simulate the binaural listening experience at a given position in the modeled space. One of the fundamental modeling inputs to create auralizations is the source directivity. Standard methods involve inputting the measured source directivity, calculating the impulse response and convolving it with a single channel anechoic recording. An initial study was conducted using this method and the results showed significant differences in reverberation time and clarity index when using a directional versus omni-directional source. Further research was conducted focusing on an alternative method of modeling source directivity that involves multi-channel anechoic recordings to create auralizations. Subjective tests were conducted comparing auralizations made with one, four and thirteen channels, with three different instrument types and subjects rated differences in realism. An analysis of variance (ANOVA) was carried out to determine the effect of the number of channels and instrument on realism. The primary result from this study was that subjects rated the auralizations made with an increasing number of channels as sounding more realistic, indicating that when more accurate source directivity information is used a more realistic auralization is possible

Investigations of incorporating source directivity into room acoustics computer models to improve auralizations

Room acoustics computer modeling and auralizations are useful tools when designing or modifying acoustically sensitive spaces. In this dissertation, the input parameter of source directivity has been studied in great detail to determine first its effect in room acoustics computer models and secondly how to better incorporate the directional source characteristics into these models to improve auralizations. To increase the accuracy of room acoustics computer models, the source directivity of real sources, such as musical instruments, must be included in the models. The traditional method for incorporating source directivity into room acoustics computer models involves inputting the measured static directivity data taken every 10° in a sphere-shaped pattern around the source. This data can be entered into the room acoustics software to create a directivity balloon, which is used in the ray tracing algorithm to simulate the room impulse response. The first study in this dissertation shows that using directional sources over an omni-directional source in room acoustics computer models produces significant differences both in terms of calculated room acoustics parameters and auralizations. The room acoustics computer model was also validated in terms of accurately incorporating the input source directivity. A recently proposed technique for creating auralizations using a multi-channel source representation has been investigated with numerous subjective studies, applied to both solo instruments and an orchestra. The method of multi-channel auralizations involves obtaining multi-channel anechoic recordings of short melodies from various instruments and creating individual channel auralizations. These auralizations are then combined to create a total multi-channel auralization. Through many subjective studies, this process was shown to be effective in terms of improving the realism and source width of the auralizations in a number of cases, and also modeling different source orientations. In addition, this approach was applied to modeling an entire orchestra with individual sources, in three different configurations, for the first time. This method shows great promise as a new technique for auralizing both solo instruments and an entire orchestra

Investigations of incorporating source directivity into room acoustics computer models to improve auralizations

Room acoustics computer modeling and auralizations are useful tools when designing or modifying acoustically sensitive spaces. In this dissertation, the input parameter of source directivity has been studied in great detail to determine first its effect in room acoustics computer models and secondly how to better incorporate the directional source characteristics into these models to improve auralizations. To increase the accuracy of room acoustics computer models, the source directivity of real sources, such as musical instruments, must be included in the models. The traditional method for incorporating source directivity into room acoustics computer models involves inputting the measured static directivity data taken every 10° in a sphere-shaped pattern around the source. This data can be entered into the room acoustics software to create a directivity balloon, which is used in the ray tracing algorithm to simulate the room impulse response. The first study in this dissertation shows that using directional sources over an omni-directional source in room acoustics computer models produces significant differences both in terms of calculated room acoustics parameters and auralizations. The room acoustics computer model was also validated in terms of accurately incorporating the input source directivity. A recently proposed technique for creating auralizations using a multi-channel source representation has been investigated with numerous subjective studies, applied to both solo instruments and an orchestra. The method of multi-channel auralizations involves obtaining multi-channel anechoic recordings of short melodies from various instruments and creating individual channel auralizations. These auralizations are then combined to create a total multi-channel auralization. Through many subjective studies, this process was shown to be effective in terms of improving the realism and source width of the auralizations in a number of cases, and also modeling different source orientations. In addition, this approach was applied to modeling an entire orchestra with individual sources, in three different configurations, for the first time. This method shows great promise as a new technique for auralizing both solo instruments and an entire orchestra

Investigations of Multi-channel Auralization Technique for Various Orchestra Arrangements, with Phase-Shifted String Sections

An orchestra can be simulated in room acoustics computer modelling using a variety of methods, ranging from a single omni-directional source to individual sources of all instruments. This study utilizes the method of individual sources for each instrument, but with reduced source representation for the string sections. The anechoic recordings used in this investigation are five-channel recordings, which capture the source directivity of the individual instruments. For each string section, the individual anechoic recordings were phase shifted several times, up to 23 ms, and combined to create a single recording for use in the simulations. An orchestra was simulated in three different configurations – American (first and second violins adjacent), European (first and second separated) and a completely random arrangement. For each configuration, auralizations were created using a single channel and five-channel representation for each instrument or section and for both a Brahms and Mozart symphony. Listening tests were conducted to determine if subjects could detect differences in auralizations created using the three different orchestra configurations. Preliminary results from this pilot study show subjects can detect differences between some of the configurations, particularly the American versus Random, and European versus Random, with more of an effect with Brahms than with Mozart

Investigations of Multi-channel Auralization Technique for Solo Instruments and Orchestra

Computer modeling of room acoustics is a useful tool in the design of acoustically sensitive spaces and an important outcome from these programs is auralizations. This study examined the perceived changes in realism and source width when listening to multi-channel auralizations compared to single channel auralizations for both solo instruments and a full orchestra. The first experiment, which examined subjective judgments of auralizations made from solo instruments, showed that perceived realism increased as the number of channels was increased from one to four to thirteen, while the relationship between source width and number of channels was less clear. In the second experiment, an orchestra was auralized in four different ways: individual instrumental sections with (i) one channel each and (ii) five channels each; and the entire orchestra emanating from (iii) a single omni-directional source and (iv) a surface source. Listeners’ judgments comparing all of the auralizations showed improved perceived realism with the multiple sources (i, ii) compared to the surface source, and wider source width with the multiple sources compared to the single omni-directional source. No improvement in either realism or source width was found as the number of channels was increased from one to five for the individual sources