Steady State Delay as Related to Aperiodic Signals
R. V. L. Hartley · Bell System Technical Journal · 1941
The concepts of phase and envelope delay, as applied to any linear system, rather than only to a medium, are discussed. Criteria are set up for the time of occurrence of that part of an aperiodic signal which corresponds to a small segment of the spectrum. The original spectrum of the signal gives the time of entry and this spectrum as modified by the phase characteristic of the system gives the time of exit.