VCAs with 2 (or more) CV inputs - discussion

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VCAs with 2 (or more) CV inputs - discussion

Post by Bachelard » Wed Nov 11, 2020 8:50 am

Hi, I've recently began thinking more about VCAs with 2 CV inputs on each channel, which are not often talked about, but there are plenty of them out there. Doepfer, Frequency Central, Nonlinearcircuits, etc. all offer VCAs with 2 CV inputs, and yet most of us go for the Veils and Quad VCAs in our systems. I haven't seen/found a discussion dedicated to exploring what one does with 2 CV inputs on a VCA, so wanted to start one.

One of my initial thoughts are that it introduces the possibility of the kind of "velocity" control of an audio source that one CV input can't do - if you put an envelope into one CV input (typical), and then an LFO or random source into the other (synced or unsynced), you can get much more lively outputs. That's a very basic example. And tremolos and things like that, something to go along with a basic envelope shape.

Of course, I also love using VCAs to modulate my CV sources, and, using gates to get switching behaviour. Having more than 1 CV input opens up so many possibilities for modulation and control of the control sources.

Curious what other creative, unconventional applications folks here have for VCAs with 2 (or more?) CV inputs.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Dave Peck » Wed Nov 11, 2020 4:16 pm

A handy way of creating a more complex modulation signal for whatever is going through the VCA by doing things like combining two asynchronous LFOs, or making one complex EG by combining two different EGs.

It's essentially the same as patching a simple two-channel CV mixer before the VCA, so however I would use that. Mixers placed before CV inputs (any CV inputs, not just VCA CV inputs) can greatly expand the options of a synth. Like all of those CV mixers that are scattered all over an Arp 2600. Without those, it would be a much more limited synth.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Synthacon » Wed Nov 11, 2020 4:22 pm

I'm as passionate about a VCA with multiple CV inputs as I am about modules that have plenty of built in attenuation. Should be the norm not the exception.
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Re: VCAs with 2 (or more) CV inputs - discussion

Post by KSS » Thu Nov 12, 2020 4:36 pm

:agree:
With both Synthacon and Dave Peck.

As DP says, it's essentially the same as having a 2 -or more- input unity mixer for CV built in. Anything which falls into that category becomes reason enough.

Classic modules had three CV jacks and I tend to think of those as root, ofset and modifier. Partly because in the old modules the mixing was not always equal between the jacks and assigning them this way reflected that and kept patches more consistent. Worth paying attention to this fro new modules too.

Since the question really boils down to how to use a unity CV mixer, think about unusual ways that concept might be employed. For example twin or triple identical parallel patching means you have doubling/halving or trebling/thirding of CV by simply adding or removing a plug. This alone can make a patch more 'performable' than using a mixer and changing its knob positions to achieve similar results. It's a quantifiably step-wise change, easily altered.

Patching direct and via an inverter for the parallel cord is another useful choice. Depending on what's done to one or the other path, you get anything from 'switching' via cancelation, to modification via a send-RCV side chain topology.

The ability to go 'off' the main musical idea and yet come right back to the exact same 'place' because the root CV never changed. Only ofset and-or modifier.

None of these are particularly innovative or unique, yet they affect the results more than choosing to use single input VCAs and external modules for the 'equivalent' patches.

it's like the single-multiple switches of a 2500's EGs. Why bother when all they do is join the two inputs of gate and trigger into one? Especially since you can do that exact same circuit result using the matrix switches nearby? Just above the EG module. And here's the reason. Because those single-multiple switches are always in the same physical position, and the location of the gate and trigger associated matrix switch actuator is not. It's always in the same column of 11 or 21 positions, but can't be assumed in a specific one of those. This seems inconsequential, but it may be more important than you think.

Having the two or three CV jacks on a VCA -or VCO, or VCF- in a fixed location relative to the module is the difference that -can- make the difference.
Because while you 'could' put a simple mixer in front of each VCA -or the others- it takes up space, adds visual and physical complexity. And uses more patchcords for no gain otherwise.
------------
Almost everything just said also applies to having VCAs with dual inputs and outputs. Like the moog 902 or the 2600 VCA<--which lacks the inverted output but does have both plain and inverted inputs that many don't realize or notice. Except the inverters you might add to the CV paths are already built into these native signal paths.

With the Behringer 902 so inexpensive and available, it can be part of anybody's euro setup, and would be a good candidate for re-paneling to other formats. You get the multiple CV jacks AND the dual signal IO. If Behringer's not your thing for any reason, other mfrs also offer 902 based VCAs.
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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Arneb » Thu Nov 12, 2020 7:02 pm

My problem with the idea of a multi-CV VCA is that it's unclear whether the CV inputs are summed or applied one after another.

(Then again, I'm way too young to care about the classics and secretly think that the A in VCA stands for "attenuator". Also, the Behringer 902's panel design is completely incomprehensible to me.)

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Bachelard » Fri Nov 13, 2020 9:50 am

Synthacon wrote:
Wed Nov 11, 2020 4:22 pm
I'm as passionate about a VCA with multiple CV inputs as I am about modules that have plenty of built in attenuation. Should be the norm not the exception.
I agree. And thanks KSS for very thoughtful and detailed insight.

You're right, I suppose having multiple CV inputs is like using a CV mixer beforehand. But I wish, like Synthacon said, in the near future, multiple CV inputs become the norm and not the exception. I think we are truly seeing a very very new and different generation of modular users who are quite spoiled by all kinds of digital, menu-heavy, feature-heavy modules and, even though I'm not THAT old, I very much value all that I've learned through patching, not through diving into the menus of battleship modules. That said, I love my Disting, I love my Westlicht Performer, when digital designs are thoughtfully implemented, and necessary.
KSS wrote:
Thu Nov 12, 2020 4:36 pm
Classic modules had three CV jacks and I tend to think of those as root, ofset and modifier. Partly because in the old modules the mixing was not always equal between the jacks and assigning them this way reflected that and kept patches more consistent. Worth paying attention to this fro new modules too.
That is super interesting. I think a LOT about utilities - vcas, switches, mixers, attenuators/verters, analog logic (min/max), all kinds of voltage processors - because to me it's much more interesting (and elegant) to derive additional moduation signals from a few source signals than to have many many LFOs and modulation sources. There's a balance to everything and every kind of practice, of course (or not, depending on the day :hihi: )

Just before I posted the original post I did come across the Behringer and am very intrigued by it. Arneb - if you're unclear about the 902, it is very inexpensive and perhaps worth picking one up and trying it out (because you can never have enough VCAs, right?). I do think it's worth the time to understand everything a VCA can do for anyone who is serious about learning modular synthesis and want to get the most out of it.

If you still find it incomprehensible, I'll buy it off ya. :hihi:

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Synthacon » Fri Nov 13, 2020 10:35 am

Arneb wrote:
Thu Nov 12, 2020 7:02 pm
My problem with the idea of a multi-CV VCA is that it's unclear whether the CV inputs are summed or applied one after another.

(Then again, I'm way too young to care about the classics and secretly think that the A in VCA stands for "attenuator". Also, the Behringer 902's panel design is completely incomprehensible to me.)

All a VCA is IS attenuation of sorts and is pretty much the simplist way to think about them and how to use them.
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Re: VCAs with 2 (or more) CV inputs - discussion

Post by pugix » Sun Nov 15, 2020 12:46 pm

Synthacon wrote:
Fri Nov 13, 2020 10:35 am
Arneb wrote:
Thu Nov 12, 2020 7:02 pm
My problem with the idea of a multi-CV VCA is that it's unclear whether the CV inputs are summed or applied one after another.

(Then again, I'm way too young to care about the classics and secretly think that the A in VCA stands for "attenuator". Also, the Behringer 902's panel design is completely incomprehensible to me.)

All a VCA is IS attenuation of sorts and is pretty much the simplist way to think about them and how to use them.
It's only unclear if the user manual doesn't tell you. For example, Xaoc Tellun has bot exponential and linear CV inputs, which the manual explains can be thought of a being like an exponential VCA followed by a linear VCA.

And, exponential response in a VCA can amplify as well as attenuate. As I've mentioned elsewhere, there is only one linear response, but many different exponential response curves are possible.

Most linear VCAs are used as VC attenuators, with unity gain happening at a stated CV (5, 8, or 10 volts). Yet some linear VCAs can exceed unity gain, too.
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Re: VCAs with 2 (or more) CV inputs - discussion

Post by KSS » Sun Nov 15, 2020 5:08 pm

pugix wrote:
Sun Nov 15, 2020 12:46 pm
As I've mentioned elsewhere, there is only one linear response, but many different exponential response curves are possible.
Quoting this excellent point for emphasis.

Technically, there's only one expo curve too, but the position a given module takes upon it can be experienced as if there were many different curves across different modules. A module whose range is located near the flat portion will still respond exponentially, but will sound and feel much different in use from one located in the more vertical part of the expo curve. Which is also still responding exponentially.

In fact, if the range of a module on an exponential curve is small, it can be perceived and used *as* a linear response! The ARIES VCA is an example of this. The exponential curve is also essentially linear near both of its 'ends'.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by BlinkyLights » Wed Nov 18, 2020 3:53 am

Fascinating discussion.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by pugix » Wed Nov 18, 2020 10:09 am

Duplicate

I hit the silly Quote button, instead of Edit.
Last edited by pugix on Wed Nov 18, 2020 10:12 am, edited 1 time in total.
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Re: VCAs with 2 (or more) CV inputs - discussion

Post by pugix » Wed Nov 18, 2020 10:11 am

Duplicate
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Re: VCAs with 2 (or more) CV inputs - discussion

Post by ronnieb » Wed Nov 18, 2020 10:21 am

I have a Koma Discrete VCA which has two CV ins but they are summed as opposed to the Tallin mentioned above which seems to be in series. I had initially hoped in my modular infancy to use one input as a sort of velocity control but yeah, it didn't work as planned.
This did frustrate me a lot until it made me think of other use cases, such as using two different envelopes, triggered by different sources with varying shapes on the same sound, and hey presto, I love VCAs with 2 CV ins again!

Really would love to pick up a Tallin but I already have 9 VCAs (11 if you count lpgs) in a 6U case and I know, I know but I swear I have enough... for now :goo:

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by dooj88 » Wed Nov 18, 2020 11:03 am

though not directly applicable to OPs question as he does them in series rather than parallel (mixing) this video was great fun to watch and full of tips for more complex VCA applications


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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Bachelard » Thu Nov 19, 2020 5:44 pm

This was a fun exercise I started today, and ongoing. I like the look of the River Crux, which has unipolar and bipolar cv inputs. I like how different modules label/specify (or not label/specify) their cv inputs. https://www.modulargrid.net/e/racks/view/1383220

Also, just having read KSS's first response a bit more closely - there's indeed a lot of wisdom there.

So, my next question is - why have manufacturers abandoned this "norm" for single CV-in VCAs that everybody uses nowadays? All the basic Doepfer VCAs, and MFOs VCAs (and Thomas Henry!) have 2 or more CV ins, if we're talking about older designs, and in some of the aforementioned classic modular systems. And yet, all we really talk about these days, and what most people use in their systems,and what we see at the top of Modular Grid in terms of popularity, are Intellijel Quad VCAs and Veils and Linuxes, and almost exclusively VCAs with a single CV input. I'm curious what the reasons are, whether it's designers wanted to cut a little bit of cost, or whether they think the market doesn't need/demand it, or whether a newer generation of users and designers just collectively shifted the focus and how they've conceptualized (or simplified?) the use of a VCA. Befaco's early Hex VCA (and Quad VCA!) had dual CV inputs on each channel, but their current HexMix VCA has one.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by flashheart » Sat Nov 21, 2020 12:01 pm

Arneb wrote:
Thu Nov 12, 2020 7:02 pm
My problem with the idea of a multi-CV VCA is that it's unclear whether the CV inputs are summed or applied one after another.

(Then again, I'm way too young to care about the classics and secretly think that the A in VCA stands for "attenuator". Also, the Behringer 902's panel design is completely incomprehensible to me.)
If multi CV inputs were applied one after another that'd essentially mean there's multiple VCAs, as each CV would be CV'ing the next (or is it previous?) one, which is of course a VCA :).
I'm not buying a maths though, not my idea of fun...

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Arneb » Sat Nov 21, 2020 12:43 pm

flashheart wrote:
Sat Nov 21, 2020 12:01 pm
Arneb wrote:
Thu Nov 12, 2020 7:02 pm
My problem with the idea of a multi-CV VCA is that it's unclear whether the CV inputs are summed or applied one after another.

(Then again, I'm way too young to care about the classics and secretly think that the A in VCA stands for "attenuator". Also, the Behringer 902's panel design is completely incomprehensible to me.)
If multi CV inputs were applied one after another that'd essentially mean there's multiple VCAs, as each CV would be CV'ing the next (or is it previous?) one, which is of course a VCA :).
Well, yes, indeed. In both cases there's an "invisible" component under the hood - a VCA or polarizer for successively applied CV inputs, an unity mixer for summing CV inputs - and I prefer having that component not being invisible.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by KSS » Sat Nov 21, 2020 4:43 pm

I have not understood your argument against multi-input CVs nor the confusion about what's inside since you first posted it. It's clearly a unity mixer in all that I'm aware of. The original minimoogs have dual cascaded VCAs but those are obviously separately CV'd.

Can you provide an example of a multi-VCA module which has these undetermined summed v sequentially applied CVs?

Right now it seems you just want individual modules rather than the effective integration of a mixer at the CV input of a VCA?

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Xomrys » Sat Nov 21, 2020 6:35 pm

It's good to have one exponential and one linear, also DC coupled operation. Linear, normaled to 'on (+5V), can be strictly for attenuation.
This way, given a pair of VCA you can immediately patch panners/crossfaders with the linear part, while keeping the exponential for sound shaping. Many other uses as well. It's just convenient to have both functions in one place or in a very compact design.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by KSS » Sat Nov 21, 2020 8:35 pm

Using linear for panning will not result in perceived linear panning movement.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Arneb » Sat Nov 21, 2020 9:36 pm

KSS wrote:
Sat Nov 21, 2020 4:43 pm
I have not understood your argument against multi-input CVs nor the confusion about what's inside since you first posted it. It's clearly a unity mixer in all that I'm aware of.
A-132-8. XAOC Tallin. Verbos Amp&Tone.
Can you provide an example of a multi-VCA module which has these undetermined summed v sequentially applied CVs?
What do you mean by "undetermined"? They're obviously not exhibiting undefined behaviour in the programming sense, but in terms of being clear to the user... well, the A-130-1 and A-131 would be a lot better if Dieter had labeled the CV jacks "CV A" and "CV B". The 130 (EDIT: Roland 130, not A-130-1) layout suggests that it's three VCAs going into a mixer when it's actually two mixers going into a single VCA. The 902's CV sect ion is basically three jacks in a blank panel. The Verbos Amp&Tone literally requires you to find an ARP 2600 manual from somewhere just to understand how it does NOT behave.
Right now it seems you just want individual modules rather than the effective integration of a mixer at the CV input of a VCA?
Well, multiple CV inputs can make sense if they're clearly labeled. The A-132-8 panel design is great in that respect. But it's clear that designing a good panel for a single-CV VCA is easier.
Last edited by Arneb on Sun Nov 22, 2020 5:33 am, edited 2 times in total.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by KSS » Sat Nov 21, 2020 11:38 pm

I still don't get it. Each example does what it says.

The panel picture and the words "daisy-chained" for the A-132-8 are pretty clear. Along with this from the description. As you say, there's little left to understand.
Doepfer description wrote:The module features two Default Gain controls (GL, GX), that enable the opening of the first four VCAs (L) and/or second four VCAs (X).
But it's the same for the others too.
PerfectCircuit wrote: XAOC Tallin. Tallin is a dual VCA with overdrive capabilities. Each of its channels are identical and constructed around a discrete VCA core. The module features a particularly unique voltage control orientation that provides simultaneous exponential and linear control over gain via two CV inputs.
Sounds like the ARP 4019 VCA.
Verbos Amp-n-ToneTech Card wrote:The “Amplitude” control sets the initial level of the VCA. From external control voltage, both exponential and linear control can be used at the same time. Both of these inputs have reversing attenuators and unlike other “2600 style” VCAs, either can reduce the gain of the other.
Again, what's left to understand? It even says its like the 2600's 4019 VCA, which I referenced for the Tallin. Supposedly different in having interaction between CVs.
Doepfer description wrote:Modules A-130 and A-131 provide voltage-controlled amplification. For audio signals, you would normally use the exponential VCA (A-131), and for control voltages, the linear VCA (A-130).
As this text and their panels clearly say, one is a linear VCA and the other is an expo VCA. Each type has two summed CV inputs.

My use of the word undetermined was in reference to your saying this:
Arneb wrote:My problem with the idea of a multi-CV VCA is that it's unclear whether the CV inputs are summed or applied one after another.

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Re: VCAs with 2 (or more) CV inputs - discussion

Post by thelowerrhythm » Sat Nov 21, 2020 11:42 pm

All of this aside, my first VCA was a Noise Reap dual VCA, and I found myself using the second CV inputs to wibblewobble so much that I bought like eight more of them.
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Re: VCAs with 2 (or more) CV inputs - discussion

Post by jamos » Sun Nov 22, 2020 12:09 am

Majella VVCA.

'nough said. Just sayin'. Word to the wise.
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Re: VCAs with 2 (or more) CV inputs - discussion

Post by Arneb » Sun Nov 22, 2020 6:20 am

KSS wrote:
Sat Nov 21, 2020 11:38 pm
But it's the same for the others too.
PerfectCircuit wrote: XAOC Tallin. Tallin is a dual VCA with overdrive capabilities. Each of its channels are identical and constructed around a discrete VCA core. The module features a particularly unique voltage control orientation that provides simultaneous exponential and linear control over gain via two CV inputs.
Sounds like the ARP 4019 VCA.
It's not. Well, not according to the 2600 and Tallin manuals - they unambiguously state that, when one CV input is zero and the other isn't, the 2600's VCA does not close fully while the Tallin VCA does.
Verbos Amp-n-ToneTech Card wrote:The “Amplitude” control sets the initial level of the VCA. From external control voltage, both exponential and linear control can be used at the same time. Both of these inputs have reversing attenuators and unlike other “2600 style” VCAs, either can reduce the gain of the other.
Again, what's left to understand? It even says its like the 2600's 4019 VCA, which I referenced for the Tallin. Supposedly different in having interaction between CVs.
Idk, I feel it just says that it's not like the 4019 VCA... anyways, having interaction between the CVs would be rather different behaviour from summing; I'd interpret it as a poorly-worded attempt to describe an A-132-8/Tallin-like behaviour.
jamos wrote:
Sun Nov 22, 2020 12:09 am
Majella VVCA.
That one applies two linear CVs sequentially, rather than summing them like in the A-130 and (presumably) the Noise Reap one. Another data point.

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