[neetdeth]

Ok, that's actually a lot more interesting than I was giving them credit for. I assumed they were just overwhelming the LPF or exploiting some side lobe to create aliasing in the audible range, but that's discussed in section 2.

All I can contribute is that nonlinearity in audio systems is also known as distortion, and it's impossible to eliminate entirely because every system, whether electrical mechanical or even digital, goes nonlinear when it reaches its amplitude limits. Some more gracefully than others.

Seems like it would be difficult to tease out the relative contribution of the MEMS element and the preamplifier because the preamps are typically implemented on ASICs in the same package. So that might be speculation on the authors' part.