Browse Prior Art Database

Crosstalk Elimination

IP.com Disclosure Number: IPCOM000084017D
Original Publication Date: 1975-Sep-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Crider, GD: AUTHOR [+2]

Abstract

Reduction of the level of recorded crosstalk is often required in dictation equipment. In many instances, this requirement is such that intelligent recordings of speech or other signals at levels below 60db at the dictation equipment input terminals are to be eliminated, without degrading a desired audio signal.

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Crosstalk Elimination

Reduction of the level of recorded crosstalk is often required in dictation equipment. In many instances, this requirement is such that intelligent recordings of speech or other signals at levels below 60db at the dictation equipment input terminals are to be eliminated, without degrading a desired audio signal.

A switchable attenuator, a threshold detector, and an integrator are combined in the circuit to prevent attenuation of normal incoming audio inputs. The switchable attenuator is controlled by the threshold detector sensing the magnitude of the incoming audio.

Integration is then performed to convert the detector output into a smooth, continuous drive signal for the attenuator. R1, R2, and Q1 form the switchable attenuator. With Q1 "off" (high resistance), audio passes through unattenuated. With Q1 "on" (low resistance), a resistor divider formed by R1 and R2 provides attenuation.

A comparator along with the reference voltage VR input forms the threshold detector. VR is chosen such that desired audio inputs will trigger the comparator and maintain Q1 in the off state. Audio inputs of such a level as to be defined as crosstalk are too small a magnitude to trigger the comparator. Therefore, Q1 is maintained in the on state.

The integrator is made up of R3, R4, C1, and D1. As audio exceeds the reference threshold, the integrator charges to a negative level and turns Q1 off. The time involved, by design, is reduced in order that clipping...