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From: truman@zabriskie.berkeley.edu (Tom Truman)
Newsgroups: comp.dsp
Subject: Re: 180-deg phase shift -- A study in Usenet technical advice
Message-ID: <14014@pasteur.Berkeley.EDU>
Date: 7 Jun 91 17:33:30 GMT
References: <51184@prls.UUCP>
Sender: news@pasteur.Berkeley.EDU
Reply-To: truman@zabriskie.berkeley.edu.UUCP (Tom Truman)
Organization: U.C. Berkeley VLSI for DSP group
Lines: 19


With all of the commotion caused by a simple question regarding 180 deg.
phase shift, I can't resist posting this one:

" Suppose that a certain telephone channel can be characterized by
a frequency response H(f) = exp(j * P(f)), where P(-f) = -P(f).

Because P(f) may be a complicated function of frequency, such a channel may
have serious distortions.  It has been suggested (rather impractically) that
the signal on the recieving end be recorded on tape, flown by fast jet back
to the transmitting end, played backwards through the original channel a second
time, and recorded again on tape.

The signal on this second tape, if played backwards, should (it is claimed)
be the original signal, independent of P(f).

Would this work ?"

tom truman.