Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!oakhill!charlie
From: charlie@oakhill.UUCP (Charlie Thompson)
Newsgroups: sci.electronics
Subject: Audio Spectrum Analyzer
Keywords: FFT
Message-ID: <2017@radio.oakhill.UUCP>
Date: 2 May 89 14:53:10 GMT
Organization: Motorola Inc. Austin, Tx
Lines: 26


 I agree with T.B., the DSP56001 from Motorola will do a 1024 point
complex FFT in < 4 milliseconds.  You can call the Motorola 
bulletin board "Dr. BuB" at 512 891-DSP1 and download an
FFT for the 56001.  I have used this FFT to create a real-time
spectrum analyzer using a Blackman-Harris window and a log
magnitude output display routine.  The program will be operational
at the ICASSP conference in Glasgow, if you're in the area drop by
and take a look. 
 
For good resolution at lower frequencies I believe that a log
scale DFT might be a better approach.  This would give a constant
number of frequency bins per decade as opposed to the linear
frequency scale output from the FFT.  While the DFT is an
N-squared job as opposed to the Nlog(N) of the FFT it would
take a fairly large FFT (with round off errors abounding) to
get the equivalent low end resolution of a brute force N-squared 
log scale DFT. 
 
Has anybody out there done any log scale DFT's? 
 
-Charlie Thompson
 Motorola DSP Operation
 Austin, TX  
 
 NBITS