The goal of my guitar tuner project was not to be able to detect notes in
a chord or even to be particularly good at following a single melody
line.  It was just to be able to identify a nice loud, steady pitch and
tell you if the string is sharp or flat.

So far I've never gotten it to work in practice, but I have a plan for
how to make it work.  I tried using an amplifier and schmidt trigger to
eliminate harmonics and give a squared output.  This works, but only for
the first second or so after the string is struck.  If you look on a
scope when you hit a guitar string, you'll see that the fundamental is
reasonably strong initially, but it is soon eclipsed by harmonics.  I
think it's the second harmonic that was the real killer but I can't
remember for sure right now.

Anyway my plan is to detect the frequency the same way I do now, but if I
start seeing that the pitch appears to increase suddenly, I'll just
ignore any transitions that don't arrive near the expected times.  This
should have the effect of discarding the harmonics and yielding a longer
useful tuning time.

It would be interesting to also pursue the generation of MIDI from a
guitar signal, though I think many serious applications would require DSP
horsepower.  My detector is reasonably fast at identifying the pitch.

I have some code that sends MIDI (a nice little subroutine) if anyone is
interested.

Hmm that's two programs I've volunteered to pass around.  What's the best
way to do this?  I can put them up on my web page, in an ftp directory,
post them to the list, or email them to individuals.  How is this best
handled?

David
--
Their address sums up their attitude: One Microsoft Way
        http://www.rt66.com/dthomas/