exponential mod-amount knob

[tomtakestooth]

Hi guys. I am trying to recreate some patches from my old nord micromodular in NI Reaktor. One of the main things I've been struggling with is trying to recreate the mod-amount knob properly.

From the nord manual:

[TYPE II]
The mod-amount knob attenuates the incoming signal in an exponential fashion. A setting of 127 (max-
imum) leaves the incoming signal unaffected, a setting of 64 attenuates the incoming signal by a factor
considerably less than 0.5 (leaving less than half of the level of the incoming signal to modulate). A setting
of 0 shuts off the modulation completely. The pitch mod-input on the various oscillators are examples of
Type II attenuation.

My maths isn't great, but i understand that the knob works exponentially. I've managed to find create a knob that is very close but not exact. Does anyone know what the mathematical function is for this knob. I'm assuming it's something like x=a^b, where a is a range between 0 and 1.

Please excuse my lack of proper math terminology....

If anyone knows what I'm trying to get at and can help, that would be very much appreciated.

As I don't have the micromodular to do tests with, it's become quite difficult to work this out... all i can go by is recordings I've done with it...

-T

[Electromagnetic Wave]

Hi tomtakestooth,

I think you can have a look to the "Bessel-functions". I'm not 100% sure.

[tomtakestooth]

thanks for the tip. Unfortunately that was a bit beyond my maths knowledge.

I managed to get around it, but running a constant to the pitch mod of an oscillator both in the nord modular and in reaktor, and run them both through tuners, and working out the numbers for each step (0-127) where both oscillators were in tune.

It took a while, but at least it worked. I would still like to know the real answer to this question though. I emailed Clavia, but never got a reply.

-T