Pitch -> CV conversion

gstopp at fibermux.com gstopp at fibermux.com
Wed Mar 12 19:22:14 CET 1997

     I made one of those - I'm sure it's in the archives.... I used an 
     exponential tri-square VCO of the Electronotes variety (excellent 
     tracking, MAT-03 matched pair, all that) plus a home-built phase 
     comparator made from a quad NAND gate. I just made up the comparator 
     design out of my head, tried it, and it worked great first time so I 
     didn't do any further research. The loop filter was likewise designed 
     by sheer fumbling around with various parts. My findings were that the 
     best tracking and response happens when there is *no* loop filter at 
     all (!) but the CV is un-useable for controlling an external synth. I 
     ended up with a compromise between good tracking and clean CV. As you 
     note, since the VCO in the PLL is exponential, the CV to an external 
     synth is 1V/oct.
     It worked amazingly well over the audio range, with my wife playing a 
     flute into the mic and the CV controlling a Minimoog. The VCO idles 
     between notes at a couple of hertz so short release times worked best.
     - Gene
     gstopp at fibermux.com

______________________________ Reply Separator _________________________________
Subject: Re: Pitch -> CV conversion
Author:  chordman at concentric.net at ccrelayout
Date:    3/12/97 7:27 AM

On Wed, 12 Mar 1997 13:07:44 GMT, you wrote:
>On Wed, 12 Mar 1997 08:20:48 +0100 (MET), you wrote: 
>>Ok, why not using an external VCO together with the 4046 phase comparator. 
>>Somebody reported some time ago that this works pretty good, even
>>if the ext. VCO is exponential. The waveforms may be a bit distorted, 
>>due to the  permanent phase modulation.
Let's assume that you want to create a CV to drive a VCO of type 
'XYZ'.  If you build a PLL using the same type of VCO, it's linearity 
curve will very closely match the VCO you are trying to drive.  In 
otherwords, the CV produced should allow the driven VCOs to track the 
input signal rather well.  Using the 4046 comparator circuitry, you 
have two different comparators to choose from, both with different 
characteristics.  The drawback of pitch->CV conversion using a PLL is 
the built-in portamento and overshoot, depending on the loop filter 
characteristics.  This can, however, produce interesting results.

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