Conference telephone apparatus

Details Conference telephone apparatus Conference telephone apparatus

1984-04-16

1986-02-18

Dwyer, James L.

H04M 160

Patent

active

045714614

ABSTRACT:
The invention provides a circuit for preventing howling responsive to an acoustic feedback between a microphone and a loudspeaker in a hands free telephone or the like. Both a transmit path and a receive path include a variable loss circuit and a level detector circuit which compares the level of a signal picked-up by a microphone with a level of a signal received from another party. Responsive to the comparison, a normal gain is set in one of the communication paths at a level which is higher than the signal level in the path. A loss is inserted in the other communication path. A control circuit compares outputs of the level detector circuits to control the losses of the variable loss circuits. To measure a loss due to the acoustic coupling and to measure a reverberation time, a manual switch is operated to drive a microprocessor type control circuit responsive to an in-band noise which produces a voice-band noise signal from the loudspeaker. The acoustic coupling loss and reverberation time are found by computation and then stored. Signals transmitted and received during conversation are processed to control the variable loss circuits of the communication paths, on a basis of stored signal levels.

REFERENCES:
patent: 3970786 (1976-07-01), Randmere
patent: 4465902 (1984-08-01), Zato
patent: 4490582 (1984-12-01), Munson

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