AW: Fwd: Nice Analysis of Minimoog Filter and Oscillators

[Haible Juergen]

	>A year ago, I experimented with a v.c. state variable filter.
This is
	>a completely different filter design, but the same applys:  The
	>observation is that increasing resonance "steals" volume at the
bottom
	>in lowpass-mode.  (The same happens in every filter with
feedback, only
	>frequencys at Fc are boostet, the rest is decreasing).  My idea
was to
	>insert a simple RC highpass filter (Fc ~ 100 Hz) into the
feedback loop
	>(a better idea is to use a cap/pot for tuneable bass).  Of
course, this
	>decreases resonance at the low end, and it also enhances the
bass
	>frequencys.  Before the filter had the typical "thin" or "airy"
sound,
	>after insertion of hp there was a "fat bottom". WOW!

Oh well, this would completely make sense - and if memory serves,
is designed into the TB-303-filter, and maybe other synths as well -
*if* you would not be speaking of s SVF design.
SV filters either have *no* bottom loss at high resonance, or they have
a very significant loss in order to prevent overload, just depending on
which point of the filter you feed your input signal.
But that's completely different from other filter designs - remember the
resonance feedback loop on a SVF does just the opposite of other
filter's feedback loops.

JH.