Transmission system using differential pulse code modulation

A digital information transmission system using differential pulse code modulation and comprising an encoder in which the differential PCM signal to be transmitted is formed by quantizing the difference signal between the incoming linear signal and a prediction signal produced by a prediction filter comprising a local decoder receiving the said differential PCM signal, and a remote decoder, the local decoder and the remote decoder comprising filters of the same structure, characterized in that these filters are constructed from one or several filtering sections arranged in cascade, each filtering section being of the purely recursive or non-recursive type with a sole coefficient differing from zero, the roundoff (or truncation) operators which operate in each filtering section and on the incoming linear PCM signal being controlled to realize these rounding (truncating) operations with a quantizing step equal to the quantizing step of the said difference signal, and characterized in that the encoder is preceded by an expansion circuit for converting the compressed PCM signal into a linear PCM signal and the decoder is followed by a compression circuit for converting the linear PCM signal into a compressed PCM signal, the sign of the signal produced by the expansion circuit being changed at the input of the roundoff (or truncation) operator provided between the expansion circuit and the encoder, the initial sign being restored at the output of the said roundoff (or truncation) operator.