Abstract: An echo canceler-suppressor speakerphone arrangement effectively addresses the limitations of regeneration and reverberant return echo inherent in the design of speakerphones. The tendency for regeneration is eliminated by employing adaptive echo cancellation in the receive path of the speakerphone arrangement to cancel speakerphone talker echo across a hybrid and thereby reduce the local loop gain to below unity. And the generation of a reverberant return echo to the far-end party is avoided by employing adaptive echo suppression in the transmit path of the speakerphone arrangement. Near-full and full duplex operation are regularly achieved since the receive path remains open at all times and the transmit path has its gain reduced only to the level necessary to suppress excessive reverberant return echo.

Abstract: An improved switched-loss, adaptive speakerphone dynamically adjusts its switching thresholds and other performance parameters based on an analysis of acoustic environment and telephone line conditions. To access these conditions, the speakerphone utilizes a computer with associated firmware. As part of a calibration process, the speakerphone computes its thresholds before each use to compensate for possible variations in hardware circuitry therein. This is achieved by passing a first and then a second level of a test tone signal through the hardware circuitry and measuring the resulting response. The speakerphone also measures the acoustics of the room in which it operates as part of the calibration process. For this measurement, a tone burst signal is generated through a loudspeaker in the speakerphone and measured by a microphone also in the speakerphone. A time-domain acoustic response of the room is obtained which provides to the computer the amplitude of the return signal and the duration of its echo.

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.