[sdiy] How does 3320 sound as hipass/bandpass

[jh.]

Right. I think that's how I learned it at school: "filter" means a linear,
time invariant system. So both, distortion and envelope generators, would
make a circuit something different than a filter.

And I'm almost sure that Bob Moog would have used the CEM3320's
brilliant linearized multiplier technology rather than the ladder circuit,
if
he had had the choice. But then again, the Jazz guitarists who wanted to
be as loud as the drummer (is that how the story goes ?), would rather have
chosen a modern HiFi amplifier than a nonlinear tube amplifier, if they had
had the choice. In retrospect, I'm glad that neither of them had this
choice,
and we have a multitude of distorting guitar amps and distorting "filters"
to choose from today. And some non-distorting ones as well when we need
them.

Personally I like distorting LP-filters, and I think it makes a difference
whether
the distortion happens in front of a filter or inside a filter. It can be
better or
worse: The distortion in the mixer *before* my Prophet 5's filter is much
better than distortion inside the 3320 (note: The stock P5 was designed to
have
no distortion at all - both were experiments of mine with increasing level
either in the mixer stage - 3280's - or in the filter - 3320.), but it does
not
come close to the distortion that happens *inside* a Moog filter or SSM2040
filter. So my personal "selection tree" would be:

Want a distortion free filter ?
Yes: CEM3320, Vactrols, any modern VCAs as building blocks.
        BUT avoid overdrive by all means then.
No: So you want a "nonlinear filter". Do you have to use linear
       building blocks? (because you're making modifications, and
       3320's are already there, for instance)
       Yes: Put a nonlinear circuit in front of the filter. Make sure
               that the distortion unit's output never ever exceeds the
               filter's linear input range.
       No: Ah, freedom of choice. Do you want a filter that also
              sounds good without overdrive?
              Yes: You need high quality components, because you
                       want to run the same circuit with much lower
                       input levels than *with* distortion. SNR is an issue
!
                       (SSM2040 is my own favorite here.)
              No: Do you want a "classic" sounding filter?
                     Yes: Choose any one you like. Moog ladder,
                              SSM2040, SSM2044, the various Korg
                              and Roland filters, EMS diode ladder,
                              they all distort, and each one in a different
                              way. A matter of taste, and some will only
                              be satisfied when they have them all !
                      No: This is your chance to create your own
                             "classic" filter (;->) (Many of the above
                              classics were created by avoiding other
                              circuits. Sure, not all of them became
                              classics themselves.)

HPF's are a different story: the harmonics from overdriving the 1st
filter stage are *not* filtered here (as in a LPF), so I think it's a good
choice
to design a HPF quite distortion free, using a CEM3320 with limited
input level. BPF's are more like LPF when it comes to distortion: harmonics
can be filtered, and dynamics are rather high, so choosing a filter with
"good" internal nonlinearities is recommended.

JH.



-----Ursprüngliche Nachricht-----
Von: Grant Richter <grichter at asapnet.net>
An: <owner-synth-diy at dropmix.xs4all.nl>; <synth-diy at dropmix.xs4all.nl>
Gesendet: Samstag, 1. September 2001 20:07
Betreff: Re: [sdiy] How does 3320 sound as hipass/bandpass


> > I have never liked the 3320 as an lpf and since
>
> Now here is a perfect example of personal taste in action.
>
> I personally prefer the CEM3320 to the transistor ladder type. The CEMs
are
> more linear and do not produce distortion like the ladder type. If I want
> distortion, I prefer to add it deliberately and not be stuck with it.
>
> By definition, a filter is supposed to be a linear device. If they add
> significant distortion (non-linearity), they should be called a "frequency
> shaping distortion device" and not a filter ;^)
>
> In practice, musicians prefer a filter with more distortion, so they say
> they are "better". An engineer would consider a filter with more
distortion
> as "worse".
>
> That has confused me for a long time.
>
>