Technique for transmission of voice communications and apparatus useful therein

In the transmission of communications one or more signals is sampled by a sampler 414 with sampling period t. Every n + 1 th sample is transmitted via a switch 415 and transmitter 416 and the intermediate samples are extrapolated from the (n + 1)th sample, n being an integer such as 5 or 10. The sampled amplitude of the signal at a time T is stored in a computer 426, and updated every (n + 1)th sample. The computer performs the extrapolation and sends corrections via the transmitter. Frequency modification apparatus 422 translates higher frequencies to lower frequencies. Transmission by differential encoding is described with the number of coding bits adapted to the sizes and signs of amplitude changes in a plurality of signals.