[sdiy] pitch tracking

[harrybissell]

In the GR-300... the hex distortion is completely separate from the
tracking
section.  All the hex distortion is, is diode clipping of the hex
preamp.

The ramp section 'is' a ramp/hold converter.  There are two possible
outputs...
one is a sawtooth shaped pulse that is directly generated from the
string pitch.
The other is a quasi-VCO... the reset level for the sawtooth it
generates is the
sample/hold peak voltage of the original ramp. This in effect, allows
you to tranpose
over a small range, without any dividers or expo converters.  Ergo (what
DOES that mean?) ... no temperature tracking problems and very little in
the way of calibration.

otoh... if you do not do the correct filter before the ramp converter,
all is lost !!!
Its not the P/V conversion that is the problem... its

(thanks, Scott)  Multiple zero crosses in a single cycle of guitar

~and~  How to detect that the note is becomming untrackable, before it
really does !

Roland cuts off the sustain when the note becomes untrackable.  In
all... probably
a real good choice.  Getting the fundamental out of the guitar is also
very, very hard.

If you get a good fundamental, PLL tracking is a possibility...

H^) harry

David Moylan wrote:

> 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
>
> http://www.joness.com/gr300/patent.htm
>
> 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.
>
> Dave
>
> amokan wrote:
>
>> Thanks. I'll dig up the schem for that and check it out.
>>  On 12/18/05, harrybissell <harrybissell at prodigynet > 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.
>>
>>