Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!dptg!att!cbnewsc!jgk
From: jgk@cbnewsc.ATT.COM (joseph.g.klinger)
Newsgroups: sci.electronics
Subject: Re: Audio Spectrum Analyzer
Keywords: make one,homebrew,spectrum analyzer
Message-ID: <3002@cbnewsc.ATT.COM>
Date: 7 Sep 89 18:00:57 GMT
References: <3906@mentor.cc.purdue.edu>
Reply-To: jgk@cbnewsc.ATT.COM (joseph.g.klinger,55236,ihp,1c212,312 416 5314)
Distribution: usa
Organization: AT&T Bell Laboratories
Lines: 30

In article <3906@mentor.cc.purdue.edu> aic@mentor.cc.purdue.edu (George A. Basar) writes:
>  Occasionally, I work with bands running sound.  One of the nicer
>pieces of equipment to own is an audio spectrum analyzer, along with a pink
>noise source.
>  I'd like to build one of these beasties(the SA, not the pink noise source)
>to interface with a PC (C64 to be precise).  I've had a few ideas on how

>  Ultimately, it should be 31-band, starting at 20Hz and ending at 20KHz,
>something like a sweepable notch filter connected to an A/D converter.

I built one of those Gold-Line 10 band spectrum analyzers many years back,
it was simply ten parallel notch band filters with a little bit of 
logic to drive a half dozen LEDs per channel.
That's probably the most direct (and conservative) approach to take.
I don't think you can find the I/O bandwidth on a C64 to support 
16 bit (or 12 bit for that matter) A/D at 44 kHz.

One idea, that might save time without too much expense, is to get one of 
those BSR spectrum analyzer/equalizers from DAK ($100 ?).  And use only
the notch filters, case, and power supply.  Using their filter output (TTL ?)
should save a lot of the work.  I would think that the interface logic 
would be strait forward enough.

If you went with the A/D method, you would also have to write an FFT
program, I found one for the C64 (in basic) on a BBS but it is sloooooow.

Joe Klinger
att!iexist!jgk

Disclaimer - yes