Source
r/modular•
Earhacker

Looking for modulation that can change direction on a trigger

I've made the mistake of falling in love with a modulation idea that might not exist, but hopefully you guys can help me out with a solution.

Say you have a saw ramp down, which I'll represent with numbers:

9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 9, 8, 7, 6...

The level is read from the ramp over time:

[9], 8, 7, 6, 5...
9, [8], 7, 6, 5...
9, 8, [7], 6, 5...
9, 8, 7, [6], 5...

(This is a continuous thing, not a sample & hold discrete thing)

So far so good. But then the device receives a gate, and the level changes direction, walking back up the ramp:

9, 8, 7, [6], 5...
9, 8, [7], 6, 5...
9, [8], 7, 6, 5...

Another gate, and the direction changes again:

9, 8, [7], 6, 5...
9, 8, 7, [6], 5...
9, 8, 7, 6, [5]...

I bought Xaoc Zadar, and it's an awesome module that I've got 101 uses for. But it doesn't do this one thing I'm looking for. When you hit Reverse on a looped envelope in Zadar, it changes the direction of the wave, but the level wiper stays at the same position. So something like:

9, 8, 7, [6], 5, 4, 3, 2, 1, 0
# reverse
0, 1, 2, [3], 4, 5, 6, 7, 8, 9

...which isn't wasn't I'm looking for here.

Like I say, this should be a continuous thing, not a stepped group of levels. And if there's waves more complex than a ramp down then excellent. Anyone know of a module or combination of modules that would get me what I'm looking for?

Posted Apr 23, 2022, 8:45 PM UTC

518
hafilax•

I believe that the triangle wave of a CEM3340 based VCO will do this with a trigger to the sync input. Many of them have an LFO mode.

4
x2mirko•

Yes, some other vcos that offer soft sync will also do this (e.g. dixie/rubicon).

3
hafilax•

Another way you could do it is by sending the output of a flip flop through a slew limiter. Each trigger of the flip flop would switch the slope.

2
Agawell•

set 1 channel of zadar going forwards and another identically set up one going backwards and instead of triggering reverse use a sequential switch to switch between them

4
EarhackerOPhttps://www.modulargrid.net/e/racks/view/1913432•

Nice idea, but I think I’ll still get a big jump on the switch, same as reversing a single wave.

1
marcedwards-bjango•

Add a slew limiter in the path as well?

EuroPi could do it, if you’re willing to write the code.

https://www.allensynthesis.co.uk

5
Agawell•

Thinking about it you are right…

Do you have any modulation modules with open source code (mutable digital modules - tides, frames etc) if you do you could do it in that though

You’d either have to keep track of the position in the interpolation table and then on reverse set the position to be (number of interpolation points - current position) or possibly just switch the direction of movement through the table…

It’s been a while since I looked at the code … but shouldn’t be too difficult

Don’t think there’s a module that does this currently… maybe zadar source code is open source - can’t remember but there were some alt firmwares for batumi so maybe..

Another way to do it would be only reverse at 1 or 0…

1
fearsome_crocostimpy•

This plus a slew limiter is how I'd do it.

1
dvanzandthttps://www.modulargrid.net/e/racks/view/1923758•

I’d think you could do it with the maestro, build a chained envelope you like and use a second channel with a different divider to create the rest? Just a thought

3
HrottiHrottalegi•

I guess you could use a skewable lfo like WMDs modbox or 4ms quad pingable lfo where you can control the skew amount with cv, running a gate in to the skew shape will reverse the saw shape. Then you could use a sequencer or a stepped lfo or something with a vca to control amplitude

Also something like ILM Kermit could probably do something like this with wavetables

2
kafkametamorph2•

You can do something very similar using the x-n input of the Mimetic Digitalis. You can step through the sequence with a triangle wave into an attenuator, and whenever it hits a peak it would switch the direction of the sequence.

This would work well if you aren't trying to keep time. Otherwise you could put that into a sample and hold.

It's convoluted, but I think you could get there.

2
synthdadmusic•

Easily done with Ornament and Crime in Sequins sequencer mode. Just dial in a stepped ramp in the steps of the sequencer. Set the play mode to forward and map one of the Trigger inputs to reverse play direction. Then when you send the trigger the play head reverses and your output reverses. Patch into a slew limiter to smooth out the steps.

2
EarhackerOPhttps://www.modulargrid.net/e/racks/view/1913432•

Oh now that’s interesting. To be honest I had wanted to go into o_C (Quantermains) but I never thought of using o_C itself. Thanks!

Buying a second o_C has just got a little closer.

1
Selig_Audio•

A flip flop controlling a polarity inversion would work for the ramp example.

1
EarhackerOPhttps://www.modulargrid.net/e/racks/view/1913432•

But inverting the polarity would cause a big jump like Zadar does, no?

2
Selig_Audio•

Yea, didn’t think it all the way through. Another possibility is controlling a step sequencer’s direction, providing it can ramp smoothly between steps (such as the Minibrute 2s).

1
dfpratt09•

I believe, with modulation you can do exactly this with the new (and probably the old) Toppobrillo Sport Modulator. It’s basically two slew limiters with CV control of the amount of slew. This is a fairly in-depth tutorial of the v1 module, but I’m pretty sure that they go though (with an oscilloscope) this exact thing.

1
Efficient-Matter5509•

I haven’t tried this yet, but cd you use soft sync on a triangle LFO to achieve this? Trigger in on soft sync to reverse direction of wave?

1