PLL Question

[Scott Gravenhorst, Synthaholic]

I have constructed a very nice Phase Locked Loop system that generates 
various harmonics while tracking a VCO output.  This has proven to be 
very much musically valid.

My question:

Has anyone ever tried to put an XOR gate inserted into the loop (in the 
same place one would put a counter for freq mult) so that another 
square wave signal could be injected?

         +---------------------------------------+
         |           PLL                         | 
         |      +------------+  +----> output    |
         |      |            |  |  +----\        |
         +------+phase    vco+--+--|     \       |
synth >---------+comp        |     | xor  >------+
  VCO           +------------+  +--|     /
                                |  +----/
                                |
            'other' >-----------+
            signal  

EG if a low frequency signal were supplied for 'other' like several 
hertz, this would cause the phase of the PLL-VCO to change 180 on each 
half cycle of the 'other' signal.  This phase shift would have to cause 
some kind of change in the PLL-VCO output.

Does anyone know what this would do / sound like?  Musically valid?


-- 
-- Scott G., Synthaholic

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