On Sun, 9 Jun 2002, Olin Lathrop wrote:

> > Well, my youngest just bought himself a bass guitar.
8< snip...

> It would help to look at the pickup output on a scope before designing the
> circuit to receive it.  I'm not familiar with guitar pickups so I have no
> idea what level this signal is.  I always assumed it was a low level signal
> like a microphone, but that wouldn't get thru the circuit you described.
> Apparently a full signal is a volt or two peak to peak, probably from an
> amplifier built into the guitar somewhere.

No amp in the guitar, just the mag pickups.  The signal when the string is
first plucked is surprisingly strong, up to a couple Volts with no load.
Needless to say it varies a LOT.

> In any case, you want to find the fundamemtal frequency of an audio signal.
> This signal can be up to a volt or two in amplitude and may contain
> significant harmonics.  You do not just want to detect zero crossings,
> because the harmonics can create extra zero crossings causing exactly the
> symptom you describe.  What is the frequency range of the fundamental
> signals you want to measure?

Well, it's a 4-string bass, so they range from 41 to 98 Hz.

> This is a simple approach that has a chance of being good enough.  There are
> more fancy ways of doing this that are more robust, but I would start with
> this and see what it gets you.

Thanks, that pretty much agrees with the other responses I've seen.  I'll
hack around a bit to try to add some LP filtering to the input, and maybe
integrate some of the other suggestions as well.  I am mostly a digital
guy with just enough RF knowledge to keep me out of trouble, but I very
seldom do anything with audio, so I'm partly lost in this area.  Learning
quickly, though.

Dale

PS - Of course I'll be posting complete code & schematics once I get this
working perfectly...

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