Digital multiplex telephone transmission system using statistical properties of speech

A digital multiplex telephone transmission system is proposed, which should achieve a smaller bandwidth than conventional pulse-code modulation by using the statistical properties of speech waveforms. Each frame of transmitted pulses only contains a coded sample for a channel if the sample differs from the previous one from that channel. The frame can thus contain fewer time slots than there are channels, if there is a high probability of baseband signals changing by less than one quantising level during the frame period.