I am playing with a 10K digital potentiometer to allow for an adjustable sidetone level.  I have connected a 2.2K resistor from the wiper to ground to approximate an audio taper.  Right now I am controlling it with another nano which is also being used to control a SOTABEAMS Vari-Beam DSP audio filter.  Eventually I will replace the Raduino with a Teensys 4.0 adaptor board and my own software to control both devices.

  Digital Potentiometer