That's a very open-ended question, whose answer might depend on several factors, including the nature of the signal (frequency spectrum, sampling rate, general appearance including symmetry) and what you hope to get out of it (what do you really mean by "envelope"). I take it you are not an electrical engineer (neither am I, but I know of several ways to do this, depending on a more precise specification of the problem) and have never had any exposure to Signal Theory ...
Do you have a picture (I generally hate pictures in the Forum, but here I'll make an exception) of a signal, along with a time base, to provide some answers to "what does the signal look like"?
Bob Schor
