Modulating synth VCA

Polyphonic Analog Synthesizer
Post Reply
Iaamusic
Posts: 75
Joined: Fri Oct 28, 2016 12:26 pm

Modulating synth VCA

Post by Iaamusic » Sat Jul 27, 2019 3:07 pm

I was wanting to fade in synth 2 on one of my lead patches with the expression pedal or mod wheel. I hit the mod switch moved the VCA 100% positive but it doesn’t raise the VCA? If I do it negatively it reduces the volume. What am I missing??

User avatar
SandyS1
Posts: 6
Joined: Tue Jun 04, 2019 12:25 am

Re: Modulating synth VCA

Post by SandyS1 » Sun Jul 28, 2019 5:00 pm

Iaamusic wrote:I was wanting to fade in synth 2 on one of my lead patches with the expression pedal or mod wheel. I hit the mod switch moved the VCA 100% positive but it doesn’t raise the VCA? If I do it negatively it reduces the volume. What am I missing??

When you have it set to 100% positive, is the default 0 volume or somewhere less than full?

donwp
Posts: 2
Joined: Wed Jun 19, 2019 11:31 am

Re: Modulating synth VCA

Post by donwp » Sun Jul 28, 2019 11:19 pm

The problem is that modulation sources like the expression pedal or mod wheel only produce positive voltages, namely 0.0 to 5.0 volts. Digital synths can simply multiply all the controller values (envelope, velocity, expression pedal, volume setting, etc.) together and produce the expected gain control with an expression pedal. But the Moog One behavior indicates that the control voltages are summed, with programmable weighting factors. Adding more positive voltage with the expression pedal has almost no effect other than affecting the effective decay time if the the VCA gain is already saturated, and in the off position you don't get anything close to silence. As you point out, having the pedal set to a negative weighting diminishes the volume because it creates a negative control voltage, but the pedal action is reversed, which is awkward for performance. It would be nice if you could recalibrate the pedal to produce -2.5V to +2.5V, which would likely solve the problem, but no such offset is available in the pedal menu.
Fortunately, there is a workaround. One of the mod matrix control sources is called "constant," which I assume Moog engineers included for biasing purposes like this case. Add Constant to the matrix with a negative weighting of about -85% if you want something close to silence with the pedal or wheel in the off position. Limit the EXP weighting to +50% or less if you want the volume to respond over the full range of the pedal travel.
Unfortunately, this is not a global solution; you have to edit every preset by adding two mod sources to each one that you want to have expression pedal control of.

Iaamusic
Posts: 75
Joined: Fri Oct 28, 2016 12:26 pm

Re: Modulating synth VCA

Post by Iaamusic » Mon Jul 29, 2019 5:12 am

0 volume. I then want to apply 100% positive modulation to fade that synth in.

Iaamusic
Posts: 75
Joined: Fri Oct 28, 2016 12:26 pm

Re: Modulating synth VCA

Post by Iaamusic » Mon Jul 29, 2019 10:01 am

Many thanks for that, will try. I did drop a note to Moog support too.

paddy ryan
Posts: 23
Joined: Sun Feb 24, 2019 4:08 pm

Re: Modulating synth VCA

Post by paddy ryan » Tue Jul 30, 2019 12:55 pm

Also worth noting, the Expression Pedal(s) do not behave properly as controllers (yet...?!).

With any other controllers, when you assign a mod. destination and amount, the resulting modulation is based on the position of that controller. For example, if the controller is at 0, the resulting mod amount is 0. If the controller is a 50%, the mod amount is 50% of whatever you set it to.

With the ONE expression pedals, when you assign a mod. destination and amount, the modulation amount is immediate, in spite of the fact that the pedal is at 0 (or even unplugged for that matter!). Moving the pedal just adds to the mod amount, instead of controlling it starting from 0 to whatever you set it at. All the other ONE mod. sources work properly... its just when assigning expression pedals that this happens.

So bottom line, if you set the VCA to 0, and assign the pedal to control it, and set the mod amount to anything, the vca will go up by that amount without any pedal. If you set a TINY mod amount, it won't start at 0 any more, but you may be able to come up with a useable volume pedal solution.

In any case, it does need to be fixed!

synthguy
Posts: 91
Joined: Wed Sep 17, 2014 7:37 pm

Re: Modulating synth VCA

Post by synthguy » Wed Jul 31, 2019 5:12 pm

I haven't used the expression pedal to modulate the VCA yet, I'll try checking that out after work. I've used them on other stuff with no problems.

Are you using an expression pedal that has a TRS (stereo) output jack with a TRS cable to the expression pedal inputs? That's how the jacks are wired (they provide a 5V source which goes to the expression pedal pot on the ring connection, and is returned on the tip, IIRC). If you just use a mono cable to connect the pedal, you're basically just slowly shorting the 5v output which doesn't work nearly as well (weird pedal taper) and may not go to zero, depending on your pedal. I have a Moog expression pedal that works properly, and I also sometimes use a couple of old Ernie Ball volume pedals that I've wired to work with the ONE, and they work nicely as well.

A very useful trick for setting up stuff to work how you want it to is to apply the CONSTANT (last in the Mod Sources list) to your destination. Think of it as a fixed voltage that you can apply positively or negatively to that desination to fine tune where it sits. So if you assign the pedal, turn the VCA panel knob all the way down, pull the pedal all the way up and the VCA is still turned on, you can apply a negative CONSTANT amount until the VCA level is set where you want it. Then you can push the pedal all the way down and adjust the expression pedal amount in the Mod Matrix to set the volume level you want.

This works great for other stuff too, like setting filter amounts so that the Cutoff knob is centered for easy live tweaking, etc.

Edit:
I got a chance to try this tonight, and it does work, although Not Quite in the way I expected.
Here's how to do it:
Set the VCA level panel control to 12:00 (halfway up).
Assign the CONSTANT source to the VCA Level destination, and set the amount to about -90%, until the sound of a held note just shuts off.
In the Mod Matrix, assign the expression pedal source to the VCA Level destination, at about 30%, or until the held note volume just quits increasing with the pedal all the way down.

Your expression pedal should now control the VCA level!

It would seem that the pedal is modulating the total level amount dialed in with the front panel VCA level knob, which I didn't expect, but it appears to work quite well this way. Unexpected Grooviness!!

Depending how you adjust the CONSTANT modulation levels, you can also have the pedal just reduce, but not completely shut off the output level however you want (preset your pedal levels, anyone?) and increasing the pedal modulation will sort of affect the curve of the pedal, with it reaching full volume earlier in its travel.
Swap the modulation levels and polarities on a different layer, and you can continuously cross-fade between them with the pedal.

Keep in mind if you are using the master effects, (which are mixed in parallel with the dry signal) they will remain even when the VCA level is set to zero with the pedal, which can be a nice effect, but maybe not what you're after. The synth effect, which is in series with the voice will be turned down with the pedal.

I LOVE how customizable this instument is! (Once you learn its hidden secrets, of course!) :mrgreen:


Hope this helps!
Visit my synthblog...Moogs and more!
Www.synthguy.com

Post Reply