Doepfer

--- In Doepfer_a100@yahoogroups.com, achtung_999 
<heinrich.himmelwasser@g...> wrote:
> Never mind Ingo, I'm really busy too this week..
> No hurry..
> 
> Greetings,
> 
> Ernst


hello ernst,

unfortunately i'm still unable to record some
ems/diode filter examples. i'm in the middle
of a remix project, actually the modular is
in heavy use  and i cannot remove the patches
until the recordings are finished. sorry.

but maybe i can give a description of the
differences between a102 and rs500e.
both filters are weird in some ways.

the quirks on both filters:
increasing the resonance leads to a massive
level drop of the input signal, the input signal
starts to disappear almost completely. this can
be worked out by increasing the level of the
input signal, but this will also introduce
distortion to the filtered signal.
the resonance is frequency-dependent and the
tracking is bad, both is not good if you want
to use these filters as sine vco's or when
exact key-tracking is required.

thoughts about the a102:
this is one of the most extreme filters.
the input sensitivity is very high and
the filter starts to oscillate with the
resonance knob at 9 o'clock position.
this means that approximately 60 percent of
the knob range is outside the usual limits,
leaving plenty of room for those
supernasty overdriven sounds.
the a102 has lots of bass when the resonance
is set to zero. increasing the resonance 
somehow attenuates the low bass frequencies.
the filter output can be very loud.

thoughts about the rs500e:
the signal input is still sensitive, but not
as extreme as on the a102. the filter starts
to oscillate with the resonance knob at
2 o'clock position. this is much more common
than the knob scaling on the a102.
to my ears the rs500e sounds warmer and rounder
than the a102, and also a bit fatter with more
bass when the resonance is turned up.
on the other hand the rs500e cannot go into
the same extreme territories like the a102.

to some extent both filters share the same
sound characteristics, but they are still
different from each other.
the rs500e offers a sound very similar to
the original ems filter, while the a102
sounds a bit harsher and more aggressive.

it is also important to know about the tolerances
of the diodes. the selection of almost identical
diodes is a horror. you probably have to test a
hundred diodes until you find one really matching
pair of two diodes, and you need more than two for
one filter. the result is that, due to the tolerances
of the diodes, each filter has a slightly different
sound. anyway this is a fact for many other filter
designs too, so it is nothing to worry about.

best wishes

ingo