Translations:Frequency response of a digital system/46/en

By definition, an all-pass system is a causal system with the property that the magnitude spectrum of the output signal is the same as the magnitude spectrum of the input signal. The energy-delay theorem (Robinson, 1963, theorem 7, p. 204) establishes that an all-pass system has the property that the time structure of output energy is delayed with respect to the time structure of input energy. In other words, an all-pass system differentially delays the return of energy in passing a signal from input to output. An all-pass system is comparable to a bureaucrat who day by day receives written requests on his desk and who holds them and later passes them on in some other order to a subordinate. Nothing in content has changed, but certain requests are delayed with respect to others. In seismic processing, an all-pass system always gives trouble.