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From: todd@appmag.com (Todd Day)
Newsgroups: comp.dsp
Subject: Re: 180 deg phase shift
Message-ID: <1991May8.022953.781@appmag.com>
Date: 8 May 91 02:29:53 GMT
References: <1644@fs1.ee.ubc.ca> <1991May7.152409.3933@njitgw.njit.edu>
Organization: R&D, Applied Magnetics, Goleta, CA
Lines: 21

%Well, sure, you all can say how easy it is, but you're stopping shy of the
%hard part. Can't implement a transfer function without getting it into the
%form of a difference equation! That's the challenge...

Well, I can see you guys are having fun with this, but let me make a
few comments.

First of all, 180 deg phase shift is not the same as simply inverting
the signal.  A phase shift implies a time delay of some sort.

Second of all, he *may* have meant a 180 deg phase shift for each of the
frequencies that add up to his composite signal.  The output signal will
definitely NOT look much like the input signal.  You can prove this to your
self by drawing a time axis and delaying a 100 Hz and 50 Hz signal by 180
degrees.  What you can see is similar to what happens in a typical speaker
system when an impulse sound like a drum hit is reproduced.  Most of the
time, it doesn't sound quite right because of the "phase smearing" that
results...

-- 
Todd Day  |  todd@appmag.com