Abstract: A controllable-gain amplifier is connected between the transmitter and receiver of a telephone set and is controlled in response to the level of the telephone user's speech so as to provide an increase in gain when the user speaks too loud and a decrease in gain when the user speaks too low. This results in a sidetone which causes the user to change his or her voice level to obtain an acceptable level of sidetone. A better-controlled user voice level is thus achieved.

Abstract: An error reducing arrangement is provided for a signal receiver wherein a sequence of received signals is divided into groups and each group is partitioned into subgroups. A signal representative of the deviations among the signals of each group and a signal representative of the deviations among the signals of each subgroup of said group are generated. Responsive to a subgroup deviation signal exceeding its group deviation signal, the subgroup signals are altered to reduce the subgroup deviations. In this manner errors are reduced without affecting error free signals.

Abstract: Ideally, when a signal is quantized, the range of the quantizer should be matched to the power of the signal. Disclosed herein is adaptive quantizer apparatus which utilizes a particular quantizing scheme for those communications where the power of the signal to be quantized is unknown, but remains constant for the duration of a communication. The amplitude range of an adaptive quantizer is adjusted during an initial training period to a value appropriate to the power of the applied input signal. This is accomplished by successively altering the amplitude range by a multiplicative quantity that depends upon the amplitude of the quantizer output signal and upon the time elapsed since the onset of the training period.