Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!motcsd!lance
From: lance@motcsd.csd.mot.com (lance.norskog)
Newsgroups: comp.dsp
Subject: Re: phase of complex number
Message-ID: <3132@motcsd.csd.mot.com>
Date: 7 Mar 91 01:49:48 GMT
References: <21901@unix.SRI.COM>
Organization: Motorola CSD, Cupertino CA
Lines: 24

shimizu@unix.SRI.COM (Dan Shimizu) writes:

>I'm attempting to do an analysis of a multi tone signal using a AT&T
>DSP32c chip and accompanying algorithims.  I'm most interested in the
>phase relationships between the tones.  To accomplish this I'm performing
>a 64 point real fft and then calulating the phase angle of the bins of
>interest.  The problem: the phase calculation is taking too long.

I think you should look up Walsh and Hartley transforms.  These are
alternatives to the Fourier transfrom from the temporal to spectral
domains.  A recent issue of the "Journal of Embedded Systems Development"
(something like that) had an article with example source code for the
Walsh transform.  These transforms operate in integer arithmetic, not
floating point.  Plus, they don't build up floating point round-off error.

The article did not coherently state that Walsh transforms decompose an
arbitrary waveform into sine waves; but they definitely decompose a
waveform into a uniform building block.  They're definitely worth
investigating for real-time applications where you need to extract
a few interesting facts from a waveform over and over again.

I'm obviously ignorant; would a knowledgeable person please comment?

Lance Norskog