[sdiy-interim] PLL (4046) for pitch tracking?

[Scott Gravenhorst]

torpedo at demadrid.com wrote:
>Has anyone tried a PLL (4046, for example) for pitch tracking? 
>Maybe to make a pitch to CV converter for a theremin or a mono 
>played guitar (I understand it might go crazy if you try to use 
>it with a guitar while playing chords). Any comments about how 
>fast is it or about ripple? 
>
>I have read on the internet, in guitar and synth forums, lots of 
>people talking about the possibility of such a use, but have not 
>seen any reports on how it actually tracks the pitch. 

I have some experience in this regard, not as a CV generator, but definately as a
"tracker".  

Please see:
http://home1.gte.net/res0658s/fatman/4046pll.html

This is a PLL frequency multiplier with outputs at 1x 1.5x 2x 3x 4x 6x and 12x the
input frequency.  The loop filter I use is very simple and includes a pot to allow
variable damping.

In my opinion as a user of this technology, it works for music, quite well in my
view.  I understand that there is a delay, however, magnitude is everything.  The
damping control on my loop filter does allow intentionally extending the delay as
well as adjustment to fit the size of the pitch excursions you will actually use
in any given piece to reduce to minimum this delay.  In my music work, the delay
has not been objectionable, or even noticable if I so adjust the loop filter
damping.  I think if you do 5 (or more) octave pitch changes, you may notice a bit
of portamento - but I've never tried that.  The music I do has parts which tend to
stay within a fairly small set of octaves.  Given such caveats, I find this device
works quite well and the perfect 5th generation it does is interesting.

Also note that I use this device attached to a sythesizer, not a guitar.  Guitars
will not have the nice easy to track constant amplitude of a synth, nor do they
like to output one negative going zero crossing per wave cycle.  In my view, 
these factors will make PLL tracking of a guitar a challenging design experience.

Theremin would be more like a synth and thus would be easier to do.  It would be
best to attach the PLL input to the internal VCO output and before any filter or
VCA, it really likes a large input signal (rail to rail is actually best).  You
can always VCA and filter it using control signals already in the theremin.


-- ScottG

---------------------------------------------------------

-- Someday is not on the calendar.

-- Scott Gravenhorst
-- Xilinx Spartan-3E Based Music Synthesizers
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/



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