Abstract: This invention relates to digital devices for spectral analysis.Signal x(t) of spectrum X(f), sampled at frequency 1/T and encoded, is processed by a temporal digital filter having a width NT followed by one or more perfect digital resonators in parallel, each tuned to a specific predetermined frequency f.sub.p and possessing two outputs, one being the "sine" output and the other being the "cosine" output on which the digital signals X(f.sub.p) sin 2.pi.f.sub.p kT and X(f.sub.p) cos 2.pi.f.sub.p kT are obtained after time NT, from which the value X.sup.2 (f.sub.p) can be formed by conventional digital processing.Application to encoded multifrequency signal receivers used in telephone switching.

Abstract: The invention relates to methods and apparatus for demodulating a differentially phase-modulated digital input signal to produce an output signal representing the digital signal corresponding to the transmitted message.The process comprises memorizing the last two digital samples of the input signal received, computing the series of digital sample phases of the input signal, before and after the last change of the input signal's initial phase, and then substituting for the difference between two phases having the same order number, the corresponding group of output signal bits.Applicable in differentially phase-modulated signal transmission systems.