How could I do what Inertia does ?

I am looking for a way to patch something to approach one use of this module :

What I would like is something that can get a CV input and follows it loosely, overshoots it when it changes direction, and oscillates a little before stabilizing when it stops changing (“it” being the signal it is following).

My first hunch is to do something with a basic physic equation, mass / spring sort of thing, but what module could do that ? Any other idea on how to do that ?

And of course, if someone feels inspired to do a module that does just that, it would be wonderfull !!

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I had one in my rack for a while. (For myself, I decided it was at its most interesting when used as an audio filter, but I had plenty of filters; for modulation purposes it wasn’t something I wanted frequently enough to justify owning it. Would be cool to have something like it in VCV for occasional use though…)

It’s a 100% analog module. I tried to figure out how to patch something similar and couldn’t work it out. Granted, calculus is “here there be dragons” territory for me so when people talk about integrators and whatever it doesn’t entirely make sense to me. There is a very detailed manual which might be helpful to someone more knowledgeable.

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Well I sure would like to try one someday too… In the meantime, I found the idea really compelling and would love to have this “simple” building bloc in VCV…

I remember using a lot of those “attraction / repulsion” modules in Sensomusic Usine about 12 years ago, it was a xy pad where you could enter the number of balls that could follow the object they were reacting to, and parameters like mass, friction, attraction (quantity and to what), repulsion (quantity and to what)… It was brilliant, it made the most natural movements for volume and panning when doing semi generative granular stuff for exemple…

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Maybe it’s overkill, but the new DC-coupled circuit in the Cytomic CF100 can do something like this. When frequency is turned down low and resonance is turned up, the LP outputs will do the overshoot-oscillate-stabilize thing at sub-audio rates. I don’t know which other filter modules also work on DC signals, but I would guess that there must be some.

EDIT: played around with some other filters, and Alright Devices Zzzorb seems to be the best of the free options for dealing with DC signals. It seems to be a bit lighter on the CPU than the CF100, too. The cutoff control only goes down to 20 Hz, but it can be pushed lower with CV if you need slower oscillations:

Other, even lower CPU options are the SKF and SPF filters by docB, though those don’t always stabilize to the right value. There’s sometimes just a small offset, which may or may not be important, I guess, depending on what you’re trying to do.


Does the Sapphire Elastika module do the ‘mass spring’ technique by cosinekitty? Wouldn’t that what you are asking about?

A mass spring system and a filter are the same thing, actually.

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So please tell me more! How does the mass spring go about filtering the audio?

The same way that a spring reverb would.

You use a transducer to turn an electrical signal into a vibration in one end of the spring. And then another (or possibly the same) transducer turns the vibrations of the spring back into signal

For a spring/needle, you would apply impetus to the needle and measure it’s position.

There are direct analogues between inductors/capacitors/resistors and inertial mass/spring/friction and also acoustic spaces (tubes/boxes/turbulence)


Indeed ! And yet none of the filters I tried reacted to a CV changing direction in a way that would come anything close to the elasticity I’d expect from a mass / spring system, I got some interesting results but nothing close to were I was trying to go to… So I am guessing but, maybe fine tuning the parameters of the system may be crucial ?

On a side note I think modules oriented to patch programming, like lower level building blocks, could be fun too. If I want to patch something that is just giving me the sin(x) I can use a phasor based oscillator, but it will surely have a lot more parameters and a GUI completely polluting the patch… I for one would love lower level building blocks ! Or maybe they exist and I haven’t been able to find them, it is really possible. :slight_smile:

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Good call, I will try that !! Thank you.

A similar question came up in a different thread. This was my half-baked answer.

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The fun part of Inertia is how it’s simultaneously covering both function generator and filter (and oscillator) territory. Most function generators don’t have resonance, and most filters don’t give you separate cutoff frequencies for rising and falling. :slight_smile: Also there’s a clever switch that lets the first two knobs swap between rise/fall time, and rate/skew, so it makes some amount of intuitive sense regardless of how you’re using it.

Also you can get some interesting results (including highpass filtering) by mixing the 1st and 2nd order outputs.

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Exactly !! (hysteresis on a cutoff, whaaaat ? )

I think this modules offers something unique, and that is no small feat in the middle of the 11209 modules that are right now present on modulardgrid (not that this is the start and end of everything you know, just to take a rather absurd step back).

I keep looking, I have found funky looking ways of shaping CV with mixes of filters and mixers, but still nothing elastic, alive. I still have to try @StochasticTelegraph 's proposition with code though, and it looks like a really interesting possibility for sure.

Inertia is related to acceleration

unit for acceleration is [metre per second squared]

Meter per second,per second

How is the progression of speed…in the time

In the algorythm,you have to put a threshold to stop the movement when the speed is near zero…Floats are not perfect on computer

Are you a real person ?


Probably not what you’re looking for, but I was reminded of the bouncing balls idea.

I have done an algorythm in Blitz3d in the past…something simple (not more than 75 lines I think) that could add inertia effect via analog stick on a shoot them up…

I have lost the code

But I have some remembers

Thanks for the suggestion !

I have spent quite some time with the CF100 in that kind of configuration and you are right that it kind of works for certain kinds of CV signal. It does not work with less abrupt slope changes though, I could not get that kind of reaction to a classic function generator à la Rampage with slow rise and fall :

I wonder if @AlliewayAudio Cartoon Running might get you in that ballpark - on some settings. It’s very chaotic and unruly, but with a CV input some of its behaviors might do what you want.

VCV Library - AlliewayAudio CartoonRunning

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That is a great suggestion, I thought about it and went to try other things… Off to try that !

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