Method and apparatus for reducing the word length of a digital input signal and method and apparatus for recovering a digital input signal

A method and signal processing apparatus for reducing the number of bits of a digital input signal (M.sub.i), includes adding a pseudo-random noise signal (N.sub.a) to the digital input signal (M.sub.i) to obtain an intermediate signal (D.sub.i), the pseudo-random noise signal (N.sub.a) being defined by noise parameters (N.sub.p), and quantizing the intermediate signal (D.sub.i), having a word length of n bits, to a reduced word-length signal (M.sub.e) having a word length of m bits, n being larger than or equal to m. The method further includes quantizing the intermediate signal (D.sub.i) using a first transfer function which is non-linear, the first transfer function being defined by non-linear device parameters (NLD.sub.p).