Blind estimation of sound coloration in rooms using chi-square distributions of damping constants

Depending on the room type and various other assumptions, the damping distribution of a room will follow a specific "reference distribution," i.e., any deviation from the distribution should indicate sound coloration. In this paper, sound coloration will be caused by the acoustic feedback when operating sound reinforcement systems at relatively high gain settings. A sound reinforcement system based on measured impulse responses as well as an "emulated" system are studied using two speech and two music samples with system gains ranging from low to just before instability. Using one microphone placed in the audience area, blind estimation of sound coloration is achieved by computing decay times of non-harmonic components in the time-frequency domain. The results show that the computed damping distributions agree well with the chi-square distributions at low system gains. As the system gain increases, the distributions are shifted toward lower damping constants, and their shapes deviate more and more from the reference distribution, thus, giving a clear indication of sound coloration. The suggested objective measures show that deviations from the reference damping distribution can be detected at substantially lower system gains compared to results of related listening tests where audible coloration is evaluated.