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From: grayt@Software.Mitel.COM (Tom Gray)
Newsgroups: comp.dsp,sci.electronics
Subject: Re: 180 deg phase shift
Message-ID: <7894@halligan>
Date: 10 May 91 12:42:32 GMT
References: <5781@media-lab.media.mit.edu.MEDIA.MIT.EDU> <1991May8.222501.19572@syd.dms.CSIRO.AU> <1991May10.003817.5593@milton.u.washington.edu>
Organization: Mitel. Kanata (Ontario). Canada.
Lines: 43

In article <1991May10.003817.5593@milton.u.washington.edu> whit@milton.u.washington.edu (John Whitmore) writes:
:In article <1991May8.222501.19572@syd.dms.CSIRO.AU> steveq@syd.dms.CSIRO.AU (Stephen Quigg) writes:
:>In article <5781@media-lab.media.mit.edu.MEDIA.MIT.EDU> cas@media-lab.media.mit.edu (Scud) writes:
:>>In article <1991May5.233533.18783@ux1.cso.uiuc.edu> frerichs@adsl.ece.uiuc.edu (dfRERICHS) writes:
:>>>Does anyone know the algorithm that would take a stream of sampled sound
:>>>,shift it 180 deg in phase and spit it back out again?
:>>

:>deg. Phase shifting moves a waveform along the time axis: it stays the same
:>way up. Try it on an oscilloscope.
:
:
:	That's wrong.  The inverter is a perfectly good 180 degree
:phase shifter, and if you test it at ANY frequency you will see
:180 degrees of phase shift; the phase shift versus frequency is
:EXACTLY what was asked for.
:	Your 'assymmetric waveform' has a lot of Fourier components,
:and time-shifting it as you seem to be describing is NOT a
:well-defined operation.  You have to find some particular frequency,

Not trying to be impudent but just trying to expand on the
idea which Mr. Whitmore put forward.

Time shifting is a well defined operation. A time shift in the
time domain is equivalent to multiplying the frequency domain
function by e**(-jwT) (where T is the magnitude of the time
shift). Remember the requirment in linear systems for a
linear phase response. Well this is where it comes from.

A time delay will not cause a constant phase change for all
frequencies. Instead the it will produce a linear relationship
betweem phase and frequency.


---------------------------------------------------------------
Tom Gray
-------------------------------------------------------------- 
:derive a time delay from THAT ONE FREQUENCY COMPONENT, and apply
:that time delay to get the time-shift, and that is NOT the correct
:phase shift for any frequency component except the one you
:chose as 'most significant'.