On Sun, 29 Jun 2014, danwgrace@gmail.com wrote:   
      
   > I have a Moog Voyager synth and it has an LFO with a rate setting.  It   
   > is some sort of exponential scaling.  On the front panel it goes from   
   > 0.2 to 50Hz, with 3Hz in the middle.  These three values correspond with   
   > with the A to D values 0, 254 and 131 respectively on the LCD display.   
   > I was wondering if there is a likely equation that describes the circuit   
   > so I can approximate the rate (Hz) for each digital setting.  I tried to   
   > fit an exponential curve and a quadratic curve to the values but neither   
   > worked out.  Any ideas?  In the meantime I may try a cubic spline.   
   >   
   Well, three points determine a quadratic so there isn't enough for a   
   cubic. The quadratic would be   
   .00142x^2-.16464x+.2   
   but   
   .2*16 = 3.2 ~=3   
   3*16=48 ~=50   
   so something like   
   .2*256^(x/256) =.2*2^(x/32)is suggested   
   for this   
   0->.2   
   131->3,414   
   254->49.03   
   and   
   127->3.13   
   maybe the 256s should be 255s or something but I'll bet   
   it's exponential and the marks are approximate. can you measue the LFO?   
   --record it AM modulating and look at the distance between peaks.   
      
   Ron   
      
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