Digital and analog Theremins have differing waveforms. Low tone generation is very important to the quality of a Theremin design. Not only can you see the difference but you can also hear it!

Some Digital Theremins are advertised as Analog! Analog Theremins will have oscillator coils. Digital and Optical 'Theremins' that show a nice looking wave form are simply audio oscillators. It is the combination of two radio frequency signals that create a complex and musically rich wave that will NOT sound harsh or 'sterile'.