Just a few thoughts:
As several people have statet, there is nothing such as
applying fast envelopes to a signal without any click.
You will get this with an ideal VCA, and with ideal
conditions - it's a law of nature.
It's most prominent when you're gating a signal with low
frequency, and low harmonic contents.
You can reduce this by choosing a slightly slower attack
time. Some VCAs are "cheating", as they apply a little bit
of filtering to the CV input. Thus, even when you apply
an ultra-fast Attack on the CV input, the actual VCA core
doesn't see this fast Attack anymore. This is certainly
a constraint. The 190 doesn't have this - you choose the
attack time, and this is fed to the VCA core. If you want
a click, you get it (Hammond anybody?). If you don't want
it, set the attack slightly slower. That's what some other
VCAs do internally, without telling you.
To give you an extreme example: I've built this PS-3200
clone some time ago. There, both the VCF and the VCA have
a terrible amount of CV feedthru (or internal DC offset).
Consequently, the ADSR voltage is smoothed/filtered with a
rather high time constant. Obviously, in a 48-voice polyphonic
monster, you can't make this parametric. It's a choice of
one capacitor value, one fixed CV slew rate. As you now
have two time constants (one in the ADSR, one in the VCA),
this even results in what I'd call a "two pole attack",
giving that trademark Polykorg sound. It's foolproof
and rather click-free, too. But you certainly don't want to
have such a fixed configuration in a modular synth, where
you want the widest range of sounds.
To emulate this effect, you can always run the ADSR thru
a VCLAG and experiment with various (low) settings.
If you want a cheap way to emulate this, make a special cable
with a 5.1k series resistor and a 220nF shunt capacitor in
the plug that goes to the VCA input. (Values just out of
my head - experiment!)
But all this are just some hints for getting an "extra".
The 190 VCA is pretty much an "ideal VCA", just as it is.
In addition to that, *excessive* clicks will occur when you
have a DC component at the input which is high compared to
your audio input. Again, this is a law of nature.
And again, you will find VCAs that strip off any DC component
off the input signal by AC coupling.
The obvious downside is that with such a VCA, you cannot process
"slow" signals, like scaling CVs with controillers, etc.
DC in the audio signal isn't always a bad thing either:
AFAIK the ARP 2600 had 50% DC offset on some VCO outputs,
and DC-coupled VCAs. That was part of its sound.
If you have annoying clicks that change over time, you may
have a strong subsonic component in your input signal.
If you have a DC offset of, say, some Millivolts, on
the input of an "ideal" VCA, the clicks will obviously become
(relatively) louder when you have a low input signal level.
So it's a good thing to carefully choose the input level
of a VCA. On "cheap" VCAs you are forced to do this anyway,
in order to avoid drowning in noise. A VCA that is closer to
ideal is more forgiving in that respect, tempting to work with
lower input signals, or not to care much about input level
in general. And this is fine as long as you don't have a DC
component.
If you are determined to work with low level signal sources
that have a high DC offset, you can do some external AC coupling.
Make a cable with a 4.7uF non-poarized capacitor instead of
a straight connection. Do *not* use an electrolytic here.
Again, this is not a fix for the VCA, but for the signal source.
I hope this is of some help,
JH.
> My 190 doesn't click, at least not anymore than my SH-2 does. or any
> other synth I own. I'm running through a Soundcraft Spirit board into
> Mackie monitors. It's certainly not anything that's making bass
> sounds difficult, if I'm using really low freq I just move the attack
> up just slightly on the 800 and the click ceases completely and I get
> really snappy smooth bass.
>
> - Michael nil-x
> - Pressure : Penetration
>
> --- In motm@yahoogroups.com, "Paul Wagorn" <pwagorn@p...> wrote:
> > It's not the 800 envelope generator, it's the VCA. We've been
> through this
> > many times. (now *I* am gritting my teeth)
> >
> >
> >
> > I have a ton of other vca's that do not exhibit the same behaviour
> (Doepfer,
> > moog, etc). of course they will 'click' at superfast attacks & low
> freq
> > waveforms, but nothing like the MOTM vca.
> >
> >
> >
> > If you remember Paul, the problem was never solved. $10,000 scope
> or not.
> >
> > "The *same file* makes *no clicks* on my Event 20/20s." buloney.
> Play the
> > file I sent you a year ago.
> >
> >
> >
> > paul
> >
> >
> >
> >
> >
> > _____
> >
> > From: Paul Schreiber [mailto:synth1@a...]
> > Sent: Thursday, April 07, 2005 5:19 PM
> > To: motm@yahoogroups.com; Jim Carlile
> > Subject: Re: [motm] Re: Clicking VCA
> >
> >
> >
> > (grits teeth):
> >
> > a) there is NOTHING WRONG with the '190 VCA.
> >
> > b) I've sold over 180 '190s, perhaps 4 people have said something.
> >
> > c) I've looked at the outputs with my $10,000 digital scope looking
> for
> > obvious
> > 'spikes' or DC shifts. Nope. I've run FFTs. I've
> duplicated "clicking" by
> > hand-editing waveforms in SoundForge and playing them back on
> crappy PC
> > speakers. The *same file* makes *no clicks* on my Event 20/20s.
> >
> > d) What you may want to try is increasing C9 on the '800 to like
> 10uf
> > non-polar.
> > This will increase the overall ADR times, and you may find that on
> the lower
> > end
> > of the scale (from 0 to 2) it's easier to find an Attack time that
> is more
> > 'forgiving'.
> >
> > e) you may find that Sines and Triangle will 'click less' than
> pulses or
> > saws.
> >
> > Paul S.
> >
> >
> >
> >
> > _____
> >
> > Yahoo! Groups Links
> >
> > * To visit your group on the web, go to:
> > http://groups.yahoo.com/group/motm/
> >
> > * To unsubscribe from this group, send an email to:
> > motm-unsubscribe@yahoogroups.com
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> >
> > * Your use of Yahoo! Groups is subject to the Yahoo!
> > <http://docs.yahoo.com/info/terms/> Terms of Service.
>
>
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>
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>
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>
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