Abstract: An echo canceller which estimates an echo gain from a reception signal level and a transmission signal level; calculates logarithmically converted power of a reception signal level; calculates logarithmically converted power of a transmission signal level; estimates an echo gain based on the reception signal level and the transmission signal level; adds the estimated echo gain to the reception signal level to obtain an estimated echo level, calculates logarithmically converted power of a residual signal level; and compares the estimated echo level with the residual signal level after echo cancellation; wherein the echo of the reception signal contained in the transmission signal is canceled when the estimated echo level exceeds the value obtained by adding a margin to the residual signal level.

Abstract: The present invention provides a hands-free telephone wherein near-end caller voice detection information is provided with little error, and wherein electric power saving effects are improved, and also wherein the far-end caller does not receive an unnatural impression.

Abstract: A speech coder utilizing previously stored sound source vectors to generate synthetic speech, a distortion computing circuit for computing a distortion of synthetic speech from input speech and a selection circuit for selecting the sound source vector that provides minimum distortion. Sound source vectors are stored within a plurality of reduced size code books rather than a single larger code book. A vector adder adds the sound source vectors respectively output from each of the reduced code books thereby generating a single sound source vector for comparison with the input speech. The distortion circuit computes the distortion for this sound source vector by analyzing the sound source vectors respectively output from each of the reduced code books in addition to the sound source vector output from the vector adder. The computational complexity required to determine the distortion is greatly reduced from the complexity required if a single larger code book of sound source vectors is utilized.