The measurement of coloration in electroacoustic enhancement systems

Abstract

The use of electroacoustic systems to enhance the acoustics of concert halls is becoming increasingly prevalent. Regenerative systems are often used for obtaining a source position independent enhancement of reverberation time. However, these systems can produce unnatural acoustics due to the unequal enhancement of the response at different frequencies, a phenomenon termed coloration. Coloration alters the natural Rayleigh statistics of the transfer function magnitudes, and the variation in statistics can be used as a method for quantifying it. This approach avoids the difficulties of examining only the peaks in the transfer function magnitude. A method is developed for measuring the deviation of room transfer functions from Rayleigh statistics. Variance measures are derived. The underlying probability density function is modeled by fitting a three-parameter density termed the generalized gamma function. The maximum deviation of the modeled cumulative distribution from the Rayleigh distribution provides an alternative measure of coloration. The sensitivity of the measures is improved by eliminating the dominant early part of the impulse response, which is largely unaffected by non-in-line systems. An assisted reverberation system simulator is used to simulate the VRA system, which includes a unitary multichannel reverberator in the feedback loop to provide room volume expansion. The simulations show that the coloration measures increase with loop gain as expected, and are independent of other parameters in the system such as the secondary room reverberation time.