Patent ID: 7003096

Claim:
A full duplex telephone set, comprising: a receiver; a transmitter; a first filter arranged to filter substantially all line echo and conventional side tone signals from a signal received by the receiver; a second filter arranged to filter substantially all acoustic echo signals from a signal transmitted by the transmitter; a third filter arranged to match the level of the filtered transmitted signal to about that of the filtered received signal and to combine the two signals to form a modified received signal; and, a fourth filter arranged to enhance the modified received signal by effecting at least one of amplification, compression, and soft limiting thereof, and wherein the third filter comprises: means for detecting first periods during which the filtered transmitted signal is zero and the filtered received signal is non-zero; means for detecting second periods during which the filtered received signal is zero and the filtered transmitted signal is non-zero; means for measuring the level of the enhanced received signal and for storing the levels measured during the first periods; and, means for increasing or decreasing the level of the filtered received signal during the second periods such that the level of the enhanced received signal matches that of the enhanced received signal during the first periods.