State of investigations and possible further developments in the field of adaptive echo cancellers

A systematic representation of the basic designs of echo cancellers is offered. Gradient methods for the automatic adjustment of the transversal filters of echo cancellers are reviewed. The roles of the step width factor K, of the adjustment signal, of noise and of time-variant echo paths in adaptive filter design are investigated. The possible future use of the Kalman filter as an adjustment strategy and the use of a recursive filter structure are discussed together with the feasibility of applying differential PCM to echo canceller signal processing.