[sdiy] XOR as 'digital' ring modulator

[David G. Dixon]

> So what am I missing?!

A perfect 4-quadrant multiplier uses one wave to modulate both the amplitude
and polarity of the other wave, without fundamentally altering the content
of either wave.

If the modulating wave is a square wave, then only the polarity is being
modulated, not the amplitude.

If the signal wave is also a square wave, then there is no amplitude to
modulate.

I believe this latter situation describes a digital ring mod.

Whether the square waves have 50% duty cycles or not is immaterial, as it is
based purely on combinatorial logic (i.e., time is not a factor).

Hence, Tom, you are right and Chamberlin is wrong.