Re: The Reese bass
When the detuned waves combine, there is constructive and destructive interference and there are areas where the resulting waveform is louder and where there is cancellation. since this happens so fast it changes the waveform shape besides just tremolo.
With the pulse-width modulation, the sound is similar because the "gaps" are like cancellations and summings happening on both sides of the zero line. It's just that it's been reduced to the lowest "resolution", almost like a bitcrushed version of the detuned version.
The thing about audio hearing is that the configuration of a waveform almost doesn't matter. What matters is the mathematical power sum and power distribution along the activated hair cells in the inner ear. It's almost like pouring water into different vessel shapes. The vessel volume (length x width x height) is more important than the shape. Our ears are kinda like that too... many different paths to the same result.
It's amazing how many different types of waveforms all sound like the same supersaw.