DETERMINING THE SOURCE OF COHERENCE REDUCTION USING PLAYBACK LEVEL OF M-NOISE

Coherence is reduced by uncorrelated noise, distortion, and reflections which occur outside the analysis window. A procedure has been proposed for measuring the Max Linear SPL of loudspeakers which has both a frequency response compression criterion and a coherence reduction criterion. The purpose of the coherence criterion is to detect the onset of distortion anywhere in the system under test. It is usually possible to find an acoustic environment whose background noise is low enough to start with high coherence. However, it is often useful to be able to be able to do measurements in a non-anechoic environment which has some coherence reduction due to reflections and reverberation. A technique will be demonstrated for determining which phenomenon is the cause of coherence reduction in a given test environment.