The CS-synthesizer mystery - what is responsible for that smooth
sound ? (;->).
I've been thinking about the CS-60 filter quite some time now.
My *temporary* conclusion is that the *circuit* may be less special
than many people tend to think. What is it - a series connection of
two State Variable VCFs (as in the Oberheim SEM, or in a forthcoming
MOTM module I have designed earlier this year.)
I have recently bought two extra CS-80 voice cards, so I can make
more detailed tests / measurements, but I don't expect too many
surprises.
It's clear that most of the CS-synths' "warmth" comes from its VCOs.
(I just wanted to state that before I go on to filtering.)
Now what is IMO special about the CS-60 filters ?
(1) Limited Resonance Range
The front panel sliders were apparently designed to fit a range that was
intended to emulate acoustical instruments rather than harsh electronic
sounds. Emulate it with SEM-style filters ? Refrain from setting Q to
the extreme ...
(2) Limited parameters for the HPF / LPF pair. You can set the cutoff
frequencies manually to different values, but all the keyboard tracking,
After Touch and ENV modulation is the same for both. This is an
obvious limitation, but it has two pleasant side effects: The combination
of both VCFs will always have a certain "character", rather than providing
unlimited variety. And, more important: If the VCF combination does not
produce harsh sound at the initial setting, it won't during the whole
ENV cycle.
For comparison: With two separate, freely programmable VCFs, you can
have the first stage (resonant HPF) emphasising a certain harmonic, but
not distorting yet, and when the cutoff frequency of the second stage
(resonant LPF) crosses the the cutoff of the first one - bang, overload.
This can hardly happen on a CS-60. Which is better ? Both options
have their benefits. The Korg MS-20 is a prominent example for the
other option. (no SV filters here, but a resonant HPF / LPF pair, too)
(3) The 3rd VCF in the CS-60.
Yes, you're not dreaming. There's a 3rd VCF in the CS-synths. It is
Vactrol based (!) and it is called Expression Circuit. (;->)
The Expression pedal of the CS-60 does not simply work as a VCA.
It's a kind of "loudness correction" circuit which will reduce
the treble at lower volumes. I don't have an original pedal for
my CS-synths, neither for the C-50 nor the CS-60, so I can't really
tell how it behaves with these. But the pedal CV input is normalized
to a certain value, and this is *not* a "neutral" position for all
I know. In fact, for my taste the CS-60 sounds too "dark" as it
is (without the pedal). Yesterday I clipped out the capacitor in
question to get more high end. (This can easily be reduced by
outboard devices - I'm running the CS-60 thru a leslie emulator
at times, which cuts off everything above 5kHz.)
Bottom Line:
I really think you can emulate the CS-60 VCF with a pair
of these forthcoming MOTM SEM-style filters, by just
using the same CV (and same CV attenuation) for modulation
inputs, and by keeping the discipline to limit the resonance
range below a certain position.
As Peter Forrest so wisely stated in his A-Z book:
"The CS Polyphonics are one of these very few types of synth
that can rival the sound of an electric guitar ..."
And I'd like to add, it has limited parameters but immense
immediate control and "expression" from the player - and it's
that "freedom within borders" that's the secret of the CS.
Comments / discussion invited.
JH.
-----Urspr\ufffdngliche Nachricht-----
Von: <perpetual@...>
An: <motm@egroups.com>
Gesendet: Montag, 18. Dezember 2000 19:06
Betreff: [motm] CS-60 future MOTM filter?
Show quoted textHide quoted text
> got my cs-60 on friday and man do i love it. it was three hours
> before i even remembered it had a filter input. so, as with
> everything, i pulled out my trusty 606 filter test vehicle and ran it
> in. what strangeness ensued! that thing's filter is completely
> unlike anything else i've got in my rack right now. what i can't
> understand is why we see a couple ms-20 inspired filters, the prophet
> 5 inspired MOTM 440, even JH's wasp filter. why no cs-60(or 80)
> filters from anybody? this thing is really weird and has this raspy,
> yet bubbly persona that i love. juergen, i know you've got your's on
> the bench as we speak. can we look forward to a JH, and maybe MOTM
> cs filter in the future? sure would save me from having to lug this
> coffin around to gigs...
>
> alex "more off-topic than you" dickey
>
> p.s. - this question mainly goes out to JH and jim who i know just
> got their's. is it my imagination or is that input also an envelope
> follower? seems like if you switch it to effect the VCO or VCA, it
> would have to be, right? imagine an MOTM envelope follower/cs filter
> with a switch that sets it to either be filter, or go to CV/gate
> outs. i'm getting waaaay too carried away here....
>
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