Albert Goodwill wrote:
> Is there any PIC based project on the net to measure (main) frequency of
> a musical instrument's sound to determine which note it play?
>
> Any suggestion how to do a fast-responce musical tuner ?

Strobe wheel tuners are 'fast' (instantaneous).
Basically a 6" disk spinning at a fixed rate (synchronous motor) and a
neon bulb driven by the audio.
They worked well because the harmonics of a tone didn't need to be
filtered out. You can still find them in some music store's junk rooms.

If you really want to do it electronically I would suggest using
a zero crossing approach and 'pic' the longest period you find
as your fundamental. A voltage controlled bandpass filter might
be a nice addition to get you higher accuracy. If you want overkill,
how about a FFT with adjustable sample rate so you can optimize the
resolution?