Anne Guthrie

Headphone- and loudspeaker-based concert hall auralizations and their effects on listeners' judgments

Room impulse responses were measured in a wide variety of concert and recital halls throughout New York State using a spherical microphone array and dummy head as receivers. These measurements were used to create auralizations for second-order ambisonic playback via a loudspeaker array and headphone playback, respectively. The playback methods were first evaluated objectively to determine how accurately they could reproduce the measured soundfields with respect to spatial cues. Subjects were then recruited for listening tests conducted with both reproduction methods and asked to evaluate the different spaces based on specific parameters and overall subjective preference. The results were examined in order to determine the degree to which judgments of the different parameters were affected by the playback method.

The use of multi-channel microphone and loudspeaker arrays to evaluate room acoustics

Most room acoustic parameters are calculated with data from omni-directional or figure-of-eight microphones. Using a spherical microphone array to record room impulse responses can yield more information about the spatial characteristics of the sound field, including spatial uniformity and the directions of individual reflections. In this research, a spherical array was used to measure room impulse responses on stage and in the audience in a wide variety of concert halls throughout New York State, with both the microphone array and an artificial head. The results were analyzed using beamforming techniques to determine spatial information about the sound field and compared to the results of geometrical acoustics and binaural localization models. Of particular interest was how the spatial data can help to differentiate between different spaces or listener positions that exhibit similar values for conventional metrics. Auralizations were created using both headphone playback and second-order ambisonic playba...

The effect of playback method on listeners' judgments of concert hall auralizations

Previous studies of the perception of concert hall acoustics have generally employed one of two methods for soliciting listeners’ judgments. The first is to have listeners rate the sound of a hall while physically present in that hall. The second is to record the acoustics of a hall and later simulate those acoustics in a laboratory setting. While the first method offers a completely authentic presentation of the concert experience, the second allows for more direct comparisons between different spaces and affords the researcher greater control over experimental variables. Higher-order spherical microphone arrays offer a way to capture the spatial components of a concert hall’s acoustics, which can then be reproduced using a loudspeaker array. In this study, eight different concert and recital halls were measured using both a spherical microphone array and binaural dummy head as receivers. Listeners were then presented with auralizations of the halls using an ambisonic loudspeaker array and headphones, and asked to rate the halls based on subjective preference and on similarity to one another. The responses were analyzed using multidimensional scaling methods in order to examine the effect of the auralization system on the listeners’ judgments.

Perceptually evaluating ambisonic reproduction of room acoustics

Spherical microphone array technology allows for the recording of auditory scenes in three dimensions by decomposing a soundfield into its spherical harmonic components. The performance of the array is affected by certain factors in its design, including the size of the array, whether an open or a rigid sphere configuration is used, and the number of sensors and their placement scheme. Ambisonics is a system designed to reconstruct a soundfield from its spherical harmonic components. The process of ambisonic decoding determines the signals that are fed to each loudspeaker in the array to simulate a given soundfield. Such systems have certain accuracy constraints, particularly at higher frequencies, and different decoding methods can be used at those frequencies to recreate more accurate spatial cues, particularly ILD cues. This paper examines how to develop a decoding scheme that addresses the constraints in both the recording and playback phases, and uses binaural modeling to determine its efficacy. Reco...

Using spherical microphone array beamforming and Bayesian inference to evaluate room acoustics

The most well-known acoustical parameters - including Reverberation Time, Early Decay Time, Clarity, and Lateral Fraction - are measured using data obtained from omnidirectional or figure-of-eight microphones, as specified in ISO 3382. Employing a multi-channel receiver in place of these conventional receivers can yield new spatial information about the acoustical qualities of rooms, such as the arrival directions of individual reflections and the spatial homogeneity. In this research, a spherical microphone array was used to measure the room impulse responses of a number of different concert and recital halls. The data was analyzed using spherical harmonic beamforming techniques together with Bayesian inference to determine both the number of simultaneous reflections along with their directions and magnitudes. The results were compared to geometrical acoustic simulations and used to differentiate between listener positions which exhibited similar values for the standard parameters.

Comparison of headphone- and loudspeaker-based concert hall auralizations

In this research, a spherical microphone array and a dummy head were used to measure room impulse responses in a wide variety of concert and recital halls throughout New York State. Auralizations were created for both headphone playback and second-order ambisonic playback via a loudspeaker array. These two systems were first evaluated objectively to determine the level of accuracy with which they could reproduce the measured soundfields, particularly with respect to important binaural cues. Subjects were then recruited for listening tests conducted with both reproduction methods and asked to evaluate the different spaces based on specific parameters and overall subjective preference, and the results of the two playback methods were compared.

Explorations of room acoustics using a second‐order ambisonic microphone.

Most room acoustic parameters are calculated with data from omni‐directional or figure‐of‐eight microphones. Using an ambisonic microphone to record room impulse responses can open up several new areas of inquiry. It can yield much more information about the spatial characteristics of the sound field at the points of interest, including the diffuseness of the sound field and the directions of individual reflections. In this research, a 16‐channel, second‐order ambisonic microphone is designed, built, and tested with both simulations and simple, controlled sound events. Room impulse responses are then measured for a wide variety of different concert halls located throughout New York state. The results are analyzed using beamforming techniques to determine spatial information about the sound field. This method has allowed for determining the directions of individual early reflections and to characterize the spatial evolution of the sound field over the course of the impulse response. This new dimension of d...

Using a spherical microphone array to analyze stage acoustics.

A spherical microphone array, capable of beamforming, has been constructed to measure sound fields using second‐order ambisonics. The design of the microphone is based on the work by Duraiswami et al. using equations for scattering off a rigid sphere. The 16‐channel array was used to measure nine different concert‐hall stages around the state of New York, with multiple positions recorded to analyze their acoustical behavior. Additional measurements with an omnidirectional microphone were obtained to determine A.C. Gade’s stage support parameter for comparison purposes. Based on the measurements, alternative methods will be discussed to obtain better descriptors to quantify stage acoustics based on the additional spatial information the spherical microphone provides. Additionally, the work by Dammerud in developing geometric parameters based on comparisons between omnidirectional measurements and architectural dimensions will be utilized. A comparison between parameters by Dammerud and information extracte...

Using a spherical microphone array to analyze concert stage acoustics

A 16 channel spherical microphone array has been designed and constructed to measure high order Ambisonic sound fields, based on equations for scattering off of a rigid sphere. This microphone has been used to capture and characterize the acoustics of nine different concert hall stages around the state of New York. Musicians have been invited to perform in real-time in auralizations of each hall and participate in a subjective preference test based on their experience. The preference tests have been analyzed using multi-dimensional scaling methods and compared with acoustical data derived from a beamforming analysis of each stage. Additional comparisons with A.C. Gades omnidirectional parameters (stage support, early ensemble level) and geometric parameters described by J. Dammerud are performed.