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.   
      
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