# How to MI Attenuverters Work?

Hi,

I’m new to modular and have experimented with sending modulation to my MI Rings and Plaits, but I’m having a hard time conceptualizing and controlling how it works with the latter’s built-in attenuverters. I understand (theoretically) how attenuverters work in general (e.g., decrease signal/range of LFO [0-5V–>0-2.5V or whatever] and then reverse the polarity if needed).

BTW: I’m trying to think through this in terms of the way modulating guitar pedals works (which is what I’m more familiar with). Sorry if that’s a bad analogy to start with!

If I’m sending an LFO to Rings’ Damping CV-in and I use the built-in attenuverter:

(1) does the Damping knob set the maximum value the dampening can go, even with the LFO at maximum? So the LFO would only ‘wiggle’ between fully CCW and its de facto value?

And (2) does the ‘+’ on the attenuverter correspond to an attenuation without polarity switching and the ‘-’ correspond to an attenuation with polarity switching? So if I increase the value of the attenuverter on the ‘+’ side will it effectively increase the rate of how fast the LFO will wiggle between fully CCW and the de fact value?

I’m a little lost, so any sage advice would be much appreciated!

You’re understanding it wrong, so we’ll have to go back to the beginning!

The first thing I have to explain is that LFOs are sometimes unipolar (say they’ll wiggle between 0V and 10V) or bipolar (they wiggle between -5V and +5V). How to know if your LFO is bipolar or unipolar? It’s usually explained in its manual, but you can also check the colors on its output LEDs, or when you patch it through a module like Shades!

You’ll also see that sometimes, LFO modules have a lower range (say unipolar between 0V and 5V).

The main knob (eg: DAMPING on Rings) controls what is called an offset (between 0 and 5V). Think of it as a “base setting”, ie, what setting you’d get with a flat (null) modulation signal.

If your LFO is bipolar, the parameter will wiggle around this base setting. If your LFO is unipolar, it’ll wiggle between this base setting and a value further CW.

How wide will it wiggle around this base value? You decide with the attenuverter. In its central position, there’s no wiggling. Turn the attenuverter further away from the central position and the wiggling amplitude increases, up to 1.5x the amplitude of the LFO (why 1.5x? Because some modulation sources can have a lower amplitude, so it’s good to be able to amplify them). On the “+” side, the modulation keeps its polarity. On the “-” side the modulation’s polarity is reverted.

Let’s take an example…

You have a ramp (sawtooth with an increasing slope) bipolar LFO going from -5V to +5V. If you want to sweep the parameter from its minimum value to maximum value, you need to set the knob to its central position (offset of 2.5V), and the attenuverter around 2 o’clock to get a gain of 0.5. When the LFO is at the minimum, the module will receive 2.5 + 0.5 x -5V = 0V (minimum position of the knob) ; when the LFO reaches its maximum, the module will receive 2.5 + 0.5 x 5V = 5V (maximum position of the knob).

Now you have a unipolar LFO going from 0V to +10V, and you want to sweep the parameter from its maximum value to its medium value. You set the knob to its maximum value (offset of 5V), and the attenuverter around 11 o’clock to get a gain of -0.25. When the LFO is at the minimum, the module will receive 5 -0.25 x 0 = 5V (maximum value of the knob). When the LFO Is at the maximum, the module will receive 5 - 0.25x10 = 2.5V (medium value of the knob).

Last thing to keep in mind: the minimum value is mapped to 0V, the maximum value is mapped to 5V. It’s easy to go below or above these values with some modulations and some knob configurations. Nothing bad will happen, the wiggling will just be constrained to remain within those bounds. For example, unipolar LFO going from 0V to +10V, knob at the minimum (0V), attenuverter to the maximum. The modulation will go from 0 + 1.5 x 0 = 0V (minimum position of the knob) to 0 + 1.5 x 10 = 15V. This means that for 2/3 of the course of the LFO (when the sum goes from 5V to 15V), we’ll just stay at the maximum position of the knob.

And for accuracy’s sake: on most digital modules, this maths is done digitally, so nowhere in the module there’s an actual voltage of 15V!

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Wow. Incredible help pichenettes!

I’ve been searching for this kind of info on YT and online for a while now, but nothing compares to this breakdown.

This’ll help me frame my experiments now.

I can’t thank you enough!

You can try this:

https://www.desmos.com/calculator/fzx3oyitny

Green curve: LFO. You can adjust its minimum and maximum value with lmin and lmax.

a: position of the attenuverter.

k: position of the knob.

Purple curve: how your parameter evolves, from minimum (0) to maximum (5).

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