Bolt Beranek and Newman Inc.

Richard A Greiner

Thomas R Horrall

In the masking sound source disclosed herein, easily adjustable but matching acoustic energy spectrums are obtained from different channels by providing, for each channel, a plurality of bandpass filters, each of which is provided with a respective gain-controlled amplifier for selectively adjusting the respective signal level. The bandpass characteristics of each filter are matched to the corresponding filter in each other channel and a common control signal is applied to the respective gain-controlled amplifiers. The filtered and level-adjusted signals for each channel are then summed and applied to respective power amplifiers suitable for energizing loudspeakers. Accordingly, the frequency spectrum applied to all loud speakers will be the same even though the signals applied may be incoherently related within the spectrum.

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Madison, WI, United States of America

Richard A Greiner