[sdiy] pitch tracking

[amokan]

Thanks. I'll dig up the schem for that and check it out.

On 12/18/05, harrybissell <harrybissell at prodigy.net> wrote:
>
> Pitch tracking might be one of the most difficult processes to make
> work.
> There are two types... Tachometer (like the MS-20) that always take a
> large
> number of pulses to get the correct result... and Ramp/Hold types that
> usually
> work in one, or two cycles.
>
> The Tachometer circuit is probably the easiest. The MS-20 is a VERY good
>
> example of how to do this. I would clone the circuit if you are
> interested. It should
> be easy, excpet for the four-gang potentiometer which will be hard to
> find.
>
> Three of the potentiometer stages form a low pass filter on the input,
> the fourth is
> a low pass filter on the output (lag).  You set the filter to the
> expected input frequency
> range. Higher frequencies can use less delay ... low frequencies need
> more, much more.
>
> The idea is a pulse is produced for every input cycle...and these charge
> a capacitor.
> The more pulses, the higher the voltage.  There will be ripple in the
> output, something
> that makes driving a VCO and tracking pitch almost impossible.
>
> The ramp/hold types are much quicker, but MUCH harder to design and
> build. I made
> a board of this type some years ago, which was distributed by EFM. It
> was based on a
> design by Bob Moog (although he was not the first or last to use the
> technique). This
> board was intended for use with the Etherwave theremin, and could give a
> V/oct output
> that can be used to slave a VCO.  OTOH, the theremin has a continuous
> wave output.
>
> Your 'drum' is probably untrackable. The non-harmonic tones in a drum
> would almost
> guarantee that is IS not pitch to track. You might perceive a 'pitch' to
> the drum but it proabably exists only in your mind :^P   A circuit is
> unlikely to read that (oh how I wish !!!).  You will probably get
> garbled gook out of the converter... or maybe you will read
> a voltage proportional to the number of drum events (a drum roll would
> be a higher voltage than a single hit).
>
> Tom Gamble (retired of EFM) proposed a clone of the MS-20 using active
> filter (OTA)
> stages to replace the four-gang pot.  I don't know if he ever built it.
> The MS-20 design is really very clever, and worth your effort in trying.
>
> H^) harry
>
> amokan wrote:
>
> > Is there a modern version of the pitch tracking circuit in the MS20? I
> > know the MS20 wasn't all that accurate, but I actually like the
> > inaccuracies the most for things like drums and whatnot.
> >
> > Just wondered if there is a module out there that I'm overlooking.
> >
> > Thanks.
>
>
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