Abstract: An average peak slope companded delta codec for converting an analog signal to a corresponding digital signal and vice versa includes a comparator which receives an analog signal and a variable reconstruction signal and converts the analog signal into a digital data bit stream. A detector is provided for detecting the presence of preselected sequences of bits in the digital bit stream. An attack/decay signal is generated wherein the signal increases upon the occurrence of the preselected sequence and decreases upon the non-occurrence of the preselected sequence with the ratio of the increase to decrease of the attack/decay signal being in the range of 30:1 to 500:1. A converter means receives the attack/decay signal and generates a compand signal which is substantially an anti-logarithmic function of the attack/decay signal wherein the rate of increase of the compand signal is in the range of 0.75 dB/bit period to 3.0 dB/bit period.

Abstract: An apparatus for suppressing background noise in a companded delta modulated telephone system. The apparatus includes a comparator for comparing a signal related to the analogue input signal to an encoder of the system with a reference signal. The comparator provides an output to reduce the rate of occurrence of a succession of bits which cause companding within the encoder when the reference signal exceeds the other signal to the comparator. This is achieved by altering the step size of a feedback signal within the encoder or modifying the output from the encoder by removing or inverting one of the compand bits. The reference signal is higher than a signal generated by background noise and consequently for signals below the reference signal the decoder reconstructs an analogue signal which is lower in level than the input signal. A method for achieving the result is also claimed.