Signal Processing to Reduce Multipath Distortion in Small Rooms

Abstract

The transmission between a sound source and a microphone in a small hard-walled room is characterized by multiple peaks and sharp valleys. Sound received by such a microphone often is judged to be undesirably distorted or spectrally colored. A technique is described for combining the signals from two or more microphones to produce a single output having less multipath distortion than any of the individual microphone signals. The output from each microphone is filtered to separate it into a number of bandpass signals occupying contiguous frequency bands. The microphone with greatest long-time response in a given frequency band contributes that band to the output. Each microphone, then, is used only for those frequency bands in which its response is greater than any other microphone, so that the combined output contains less spectral coloration than the signal from any individual microphone. The performance of the process was studied by simulation on a digital computer, and sample recordings are included.