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Another note: I built a circuit posted at generalguitargadgets.com <br>
<br>
<a class="moz-txt-link-freetext" href="http://www.generalguitargadgets.com/index.php?option=content&task=view&id=175&Itemid=200">http://www.generalguitargadgets.com/index.php?option=content&task=view&id=175&Itemid=200</a><br>
<br>
which is based on 4046 PLLs. I was surprised how well and how fast it
could track. Yes, there's a little glitch at the start of a note, but
you get a long of bang for the buck with the 4046. The circuit
basically LPFs the input then runs it into a opamp with positive
feedback to get a nice square which feeds the PLL (same requirement of
ramp/hold pitch trackers). It also uses the square to gate a sample
and hold (not filtered, gates at audio frequency) in the CV loop of the
PLL - the idea is as long as there's signal the PLL will track, then
hold when the signal stops. In practice, this doesn't work to well on
messy guitar signals; noise or glitchy decays set off the S/H and you
lose your note. Would probably work better with a separate gate
circuit to hold when the input drops below a certain level. The
circuit works much better (int terms of note length) with a
compressor/sustainer in front set to max sustain.<br>
<br>
In general, the circuit sounds pretty dull, very akin to an octave
pedal or bad organ, but could be made more interesting in a number of
ways. VCF would help a lot. Or have PLL number 2 not track, but use
the CV from 1 plus a manual tuning voltage (would probably need to trim
the scale. Often). That would also free up the XOR in PLL2 which could
be used to do psuedo ring mod. Grant Richter's woggle bug schematic
shows how to grab a sawtooth off the timing cap of a 4046 which would
let you do PWM and all sorts of fun things.<br>
<br>
Dave<br>
<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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