Interesting Paper available on Moog VCF

[Erik of zo]

About the cap: sigma-delta conversion is based on very small changes in the
signal. Not the actual signal but the difference between two signals is
'sampled'. So only small voltages can be sampled. The cap is probably just
needed for decoupling of the input-signal. I don't really know whether it
must be in for the sampling. It should work both ways. It'll just kick the
offset away.

Don't know about that other question (don't even know the question anymore).

Erik