Multiplex communications – Wide area network – Packet switching
Patent
1988-12-28
1990-12-18
Ng, Jin F.
Multiplex communications
Wide area network
Packet switching
379406, 379388, 379390, H04M 908
Patent
active
049791630
ABSTRACT:
An adaptive speakerphone employs an echo suppression arrangement which compensates for a reverberant effect that occurs during operation of the speakerphone in a near full or full duplex mode. This reverberant effect allows the far-end party to hear his or her own echo from the near-end location. The arrangement includes an echo suppression process which compensates for this effect by inserting loss in the transmit path of the speakerphone as appropriate. Operation of this process is such that whenever the speakerphone is in the receive state, the levels of a transmit and receive speech signal in the speakerphone are monitored. By monitoring these speech signal levels, the process determines when speech into a microphone in the speakerphone is being coupled from a loudspeaker also in the speakerphone and when the transmit speech signal level exceeds a predetermined threshold. If this threshold is exceeded, then loss that tracks an envelope of the receive speech signal is inserted in the transmit path. This loss increases and decreases with the speech envelope after a 1 millisecond to 5 millisecond delay. Once the transmit speech signal level drops below the predetermined threshold, any loss previously inserted by this process is removed.
REFERENCES:
patent: 4571461 (1986-02-01), Uno et al.
patent: 4715063 (1987-12-01), Haddad et al.
patent: 4796287 (1989-01-01), Reesor et al.
Erving Richard H.
Ford William A.
Miller, II Robert R.
AT&T Bell Laboratories
Augustus Jhancy
Ng Jin F.
Williamson Samuel R.
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