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From: asd@cbnewsj.att.com (Adam S. Denton)
Newsgroups: sci.electronics
Subject: Re: DSP project
Message-ID: <1991Apr17.194724.14349@cbnewsj.att.com>
Date: 17 Apr 91 19:47:24 GMT
Organization: AT&T
Lines: 24

In article <8078@uceng.UC.EDU> schriste@uceng.UC.EDU (Steven V. Christensen) writes:
>And let me tell you, that it is mucho difficult to quantify a vibrating 
>guitar string without resorting to DSP technology (we were using strict
>analog).

I bet you 100 capacitors of your choice that you didn't try a phase-locked
loop, or did not try one correctly.  A PLL, properly designed, will
do EXACTLY what you want, and do extremely well.  You toss the raw
harmonic-infested string sound to the input, and out comes a nice,
clean fundamental square/triangle/whatever wave to go to your F2V.
The PLL can also do F2V but is typically not as accurate as a circuit
designed specifically for that purpose.

>It was basically a mic, and amp, a filter to get rid of hi-freq garbage,
>and then the most futile attempt at a half-a-dozen methods to get a good
>signal to send to a freq-voltage converter (to determine if a string is
>in tune or not).

If you insert a properly-designed PLL in between, you'll succeed.  Trust me.
Begin with the (LM, uA, NE, ...) 565 data sheet and associated application
notes.  Signetics has about a zillion (+/- a few) of them on the 565.

Adam Denton
asd@mtqua.att.com