noob question on .vca

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noisetheorem
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noob question on .vca

Post by noisetheorem » Mon Mar 21, 2011 8:26 am

I got this as part of a deal that scored me a BAM as well, which I really like. I am having some not expected results with my the other item I got, the .vca.

I was running a patch, using an envelope as the control, with audio as the signal input, and even when the envelope was fully closed, I was hearing some audio pass. I was thinking it might have something to do with the position of the DC/AC switch, but I dont remember where that switch was set. I have another patch going now that has a CV on both the Control and Signal inputs, and it seems to be working fine...

So my very basic noob question is this, simply, does the .vca work for audio? and what does the DC/AC switch actually do? When should I engage one over the other.

Sorry for the (possibly dumb and obvious) question, but I'd rather err on the side of looking a little foolish than blowing something up.
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e-grad
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Post by e-grad » Mon Mar 21, 2011 8:33 am

Don't know this module but I'm quite sure that switch allows you to choose whether you process audio signals (AC) or controll voltages (DC).

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felix le chat
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Re: noob question on .vca

Post by felix le chat » Mon Mar 21, 2011 7:10 pm

Hello,

The .vca is the only VCA I have currently (if I except using filters as VCAs). In my system it works for both audio and control without any problem.
noisetheorem wrote:I was running a patch, using an envelope as the control, with audio as the signal input, and even when the envelope was fully closed, I was hearing some audio pass.
This is not normal and I did not experience it. Which envelope are you using? Are you sure the envelope is fully closed? To put it differently, does your envelope really produce zero Volt when fully closed?

Another problem could be (wild guess): the audio you are sending to the VCA has such a high level that the VCA cannot attenuate it completely. But I'm afraid it would require a huge level that is not possible inside a modular system.
I was thinking it might have something to do with the position of the DC/AC switch, but I dont remember where that switch was set.
Normally the switch should not have anything to do with this.
In DC mode, output_signal = input_signal * control_signal, which is the regular behaviour of linear VCAs.
The AC mode adds DC filtering: constant values (or DC offsets) are suppressed at the output. This mode is usually not recommended for attenuating control signals with the VCA.

Sorry it's all I can tell, and M. Suitandtieguy who makes this module should give you some more technically-accurate explanations if you need it.

Best,
Flc

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suitandtieguy
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Post by suitandtieguy » Tue Mar 22, 2011 5:40 am

Felix was kind enough to answer your questions better than i could.

i too am curious what envelope you were using.
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Post by noisetheorem » Sat Mar 26, 2011 2:21 pm

It is the Doepfer A140. Whats really weird is it seems to have stopped doing this. I have no idea if it was something I was doing in that patch, or if ive got some gremlins running round the inside of my case....but if it happens again, Ill post again with more exact details.

Very happy with it btw. I kinda got it on a whim because I wanted the .bam and the guy had a .vca he was selling too.
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felix le chat
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Re: noob question on .vca

Post by felix le chat » Fri Feb 26, 2021 12:31 pm

felix le chat wrote:
Mon Mar 21, 2011 7:10 pm
Hello,

The .vca is the only VCA I have currently (if I except using filters as VCAs). In my system it works for both audio and control without any problem.
noisetheorem wrote:I was running a patch, using an envelope as the control, with audio as the signal input, and even when the envelope was fully closed, I was hearing some audio pass.
This is not normal and I did not experience it. Which envelope are you using? Are you sure the envelope is fully closed? To put it differently, does your envelope really produce zero Volt when fully closed?

Another problem could be (wild guess): the audio you are sending to the VCA has such a high level that the VCA cannot attenuate it completely. But I'm afraid it would require a huge level that is not possible inside a modular system.
I was thinking it might have something to do with the position of the DC/AC switch, but I dont remember where that switch was set.
Normally the switch should not have anything to do with this.
In DC mode, output_signal = input_signal * control_signal, which is the regular behaviour of linear VCAs.
The AC mode adds DC filtering: constant values (or DC offsets) are suppressed at the output. This mode is usually not recommended for attenuating control signals with the VCA.

Sorry it's all I can tell, and M. Suitandtieguy who makes this module should give you some more technically-accurate explanations if you need it.

Best,
Flc
Hello,

I was wrong in 2011 (see the quote above). I guess I tested with other envelopes at that time (including software generated envelopes that I calibrate manually). Then I almost always used the .VCA for CV, which explains why I discovered it only recently. And of course, a little audio signal bleed is easily masked in a mix so I may have missed it several times (for example: when also using a ride cymbal)

But yesterday I tested the STG .VCA and the Malekko mVCA as amplitude VCAs with the following control envelopes:
Doepfer A-140
Makenoise Maths (1st version)
Malekko/Richter/Wiard Envelator (old and new versions)
Analogue Systems RS-60
Serge/Elby VCS
Frequency Central X-Envelope (dual version)

Here are the results
(Y = works: the envelope closes to silence)
(N = does not work: the envelope lets some audio pass even when closed)

1) With the .VCA (AC or DC mode)
* A-140 (L): Y
* A-140 (M): N
* A-140 (H): N
* Maths (trigger input): Y
* Maths (audio input): N
* Envelator: N
* old Envelator, with DMOD = fully CCW: Y
* RS-60: N
* VCS (AC output): Y
* VCS (DC output): N
* X-Env: N

2) With the mVCA (linear mode, level fully CW)
* A-140: Y
* Maths (trigger input): Y
* Maths (audio input): N
* Envelator (all modes): Y
* RS-60: Y
* VCS: Y
* X-Env: Y

Measuring with a multimeter, very few of these envelopes outputs do close to about 0.000V, but as you can see there is something else going on.

What should I do?

Thanks

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felix le chat
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Re: noob question on .vca

Post by felix le chat » Mon Mar 08, 2021 3:30 pm

^ This story continues here:
viewtopic.php?f=16&t=245788

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