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 Forum index » Clavia Nord Modular » Nord Modular G2 Discussion
Logic gate/switch
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Afro88



Joined: Jun 20, 2004
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PostPosted: Mon Apr 11, 2005 7:42 pm    Post subject: Logic gate/switch Reply with quote  Mark this post and the followings unread

I was wondering if there are any logic boffins that can help me out with this...

I want to build some kind of struture that lets a signal pass only while you're moving a knob. So lets say you have a constant value knob. If you leave it alone no audio will pass. As soon as you start moving it, the logic structure maybe sends out a gate to let the envelope let audio/signal through.

I thought maybe getting the difference between the current knob position and the one 10ms ago using logic and delay modules could work... So I mucked around with some compare modules, but they're all >= and not just > so I can't get the difference between the current knob position and the knob position 10ms ago. I know I'm missing something here...

edit: I abandoned the compare modules idea, and went for the sum of the original signal, plus the original signal inverted and delayed. This works if I move the knob anti-clockwise, but not clockwise... why?? Mad


Gate.pch2
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experimental gate

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Last edited by Afro88 on Mon Apr 11, 2005 7:54 pm; edited 1 time in total
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Blue Hell
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Joined: Apr 03, 2004
Posts: 20473
Location: The Netherlands, Enschede
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PostPosted: Mon Apr 11, 2005 7:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

The basic idea is good.

I's more convenient to subtract the signal and it's delayed version in a mixer/mix2-1b module with one input set to invert. When you then route this through a shaper/rect with the 3rd button pressed it will work for both knob directiions and then you're nearly there.

Jan.
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Afro88



Joined: Jun 20, 2004
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PostPosted: Mon Apr 11, 2005 7:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry, I edited my post then saw yours. I added in the rectifier module on double positive and it works for negative values but not positive ones. I'm happy with this, but is there any way I could make it work with positive ones as well?


Gate2.pch2
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gate2

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Blue Hell
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PostPosted: Mon Apr 11, 2005 8:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

There seems to be some audio rate racing going on, don't understand it but using a s&h to slow things down seems to do the trick.

Sorry hadn't tried it, just used some old NM knowledge.

Jan.


gate2-1-1.pch2
 Description:
knob movement detection

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davep



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PostPosted: Mon Apr 11, 2005 9:45 pm    Post subject: Re: Logic gate/switch Reply with quote  Mark this post and the followings unread

Afrokid wrote:
I was wondering if there are any logic boffins that can help me out with this...

I want to build some kind of struture that lets a signal pass only while you're moving a knob.Mad


Aaahh, you're sooo close Smile

This puzzle came up a while ago in the old NM list. Try this:

Assign the knob to a "Level" module knob ("Constant" module in NM1 speak).
Now patch this knob signal to one input of a mixer, and also patch it to the input of a portamento or lag module.
Now patch the lag output to another input of the same mixer, and invert this input. This will result in a momentary "bump" of DC signal when the knob is moving, because the two signals won't exactly cancel out while the knob is moving.
Now, connect the mixer output to a rectifier, set to "full pos" (two positive humps). This will make the DC bump go positive, regardless if the knob is moving up or down.
Now patch the output of the rectifier to the input of a "Compare to Level" module, set so that it generates a pulse whenever this input is greater than zero.
Tadaa ! Now you can use this pulse to trigger or switch stuff automatically whenever the knob is moving!

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Dave Peck
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Afro88



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PostPosted: Tue Apr 12, 2005 5:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Fantastic, thankyou very much guys Very Happy. Both solutions work! I'm gonna go post this into the building blocks...
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Blue Hell
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PostPosted: Tue Apr 12, 2005 9:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Afrokid wrote:
I'm gonna go post this into the building blocks...


Thanks for doing so.

Jan.
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ian-s



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PostPosted: Tue Apr 12, 2005 3:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have been using davep’s solution for a long time (thanks Dave), not for knob movement, but other applications like triggering on a random value change etc.
This thread made me think what the circuit did to audio rate changes so I looked and it is just a differentiator or high pass filter, so I tried using the simple 6dB highpass set to max frequency and it supplies a neat, 1 module solution to the problem. Although it uses only one module, the other two solutions offer better efficiency dsp & zero page memory wise.


knobgate3.pch2
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more cat skinning

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