Bell Telephone Laboratories

David A Berkley

James Edward West

Ilene J Busch-Vishniac

Robert L Wallace, Jr

Olga M Mitchell

An electret transducer comprises an electrostatically charged electret foil (10) superimposed directly over a selectively metalized rough surface (16) of a backplate (18). Selective metalization is realized by depositing a thin metal layer (20), the contour of which is defined by a predetermined relationship, over the rough surface (16). The sensitivity of the electret transducer at any point thereon is directly proportional to the width of the metal layer on the backplate. The response characteristic of the electret transducer comprises a main lobe and a plurality of sidelobes below a preselected threshold.

Electret transducer with a selectively metalized backplate

A system is disclosed for automatically reducing reverberation in typical voice telecommunications systems. This system uses center clipping levels adaptive to the level of reverberation input speech. In one configuration, the voiceband is divided into two sub-bands and center clipping occurs only for the lower band; costs are reduced with surprisingly little transmission quality sacrifice. Clipping-level holdover circuitry with exponential decay appears to work well for a large variety of reverberant enclosures.

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New York, NY, United States of America

David A Berkley