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As for the ramp/hold type roland used this in the GR-300 guitar synth
(which some claim was the first playable guitar synth). There's a bit
of explanation about the ramp and it's reset at this link<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.joness.com/gr300/patent.htm">http://www.joness.com/gr300/patent.htm</a><br>
<br>
in the "square wave to sawtooth" section. This is describing the hex
distortion circuit, but I'm nearly positive the same ramp is used for
the pitch CV. It's split into two paths - one for the distortion
circuit (clipper) and one to a sample and hold. There's also a link
from that page to the roland patent which gives more detail into the
structure the GR-300. The microsecond pulses shown at (c) in the
diagram are actually triggered by another one shot. So you have a
chain. The first one shot gates the sample/hold to catch the voltage
at the top of the ramp, then the second triggers to reset the wave.
The patent shows this pretty clearly.<br>
<br>
Dave<br>
<br>
amokan wrote:
<blockquote
cite="midf86a98e60512181147x7df22f10hd1d197a9a22fd6c4@mail.gmail.com"
type="cite">Thanks. I'll dig up the schem for that and check it out.<br>
<br>
<div><span class="gmail_quote">On 12/18/05, <b
class="gmail_sendername">harrybissell</b> <<a
href="mailto:harrybissell@prodigy.net">harrybissell@prodigynet
</a>> wrote:</span>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Pitch
tracking might be one of the most difficult processes to make<br>
work.<br>
There are two types... Tachometer (like the MS-20) that always take a<br>
large<br>
number of pulses to get the correct result... and Ramp/Hold types that<br>
usually<br>
work in one, or two cycles.<br>
<br>
The Tachometer circuit is probably the easiest. The MS-20 is a VERY
good
<br>
<br>
example of how to do this. I would clone the circuit if you are<br>
interested. It should<br>
be easy, excpet for the four-gang potentiometer which will be hard to<br>
find.<br>
<br>
Three of the potentiometer stages form a low pass filter on the input,
<br>
the fourth is<br>
a low pass filter on the output (lag). You set the filter to the<br>
expected input frequency<br>
range. Higher frequencies can use less delay ... low frequencies need<br>
more, much more.<br>
<br>
The idea is a pulse is produced for every input cycle...and these
charge
<br>
a capacitor.<br>
The more pulses, the higher the voltage. There will be ripple in the<br>
output, something<br>
that makes driving a VCO and tracking pitch almost impossible.<br>
<br>
The ramp/hold types are much quicker, but MUCH harder to design and
<br>
build. I made<br>
a board of this type some years ago, which was distributed by EFM. It<br>
was based on a<br>
design by Bob Moog (although he was not the first or last to use the<br>
technique). This<br>
board was intended for use with the Etherwave theremin, and could give
a
<br>
V/oct output<br>
that can be used to slave a VCO. OTOH, the theremin has a continuous<br>
wave output.<br>
<br>
Your 'drum' is probably untrackable. The non-harmonic tones in a drum<br>
would almost<br>
guarantee that is IS not pitch to track. You might perceive a 'pitch'
to
<br>
the drum but it proabably exists only in your mind :^P A circuit is<br>
unlikely to read that (oh how I wish !!!). You will probably get<br>
garbled gook out of the converter... or maybe you will read<br>
a voltage proportional to the number of drum events (a drum roll would
<br>
be a higher voltage than a single hit).<br>
<br>
Tom Gamble (retired of EFM) proposed a clone of the MS-20 using active<br>
filter (OTA)<br>
stages to replace the four-gang pot. I don't know if he ever built it.<br>
The MS-20 design is really very clever, and worth your effort in
trying.
<br>
<br>
H^) harry<br>
<br>
amokan wrote:<br>
<br>
> Is there a modern version of the pitch tracking circuit in the
MS20? I<br>
> know the MS20 wasn't all that accurate, but I actually like the<br>
> inaccuracies the most for things like drums and whatnot.
<br>
><br>
> Just wondered if there is a module out there that I'm overlooking.<br>
><br>
> Thanks.<br>
<br>
</blockquote>
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