Exponential FM?

I know it's not the "correct" way to do FM due to the pitch-shifting effect, but I'd like to emulate the FM sounds I've gotten from analog synths with exponential CV inputs.

I want this to be full audio range, so I'd like to use the F input.

I briefly tried sticking an Expo module before the F input, but didn't hear what I expected.

Can someone explain the math necessary for this conversion in simple terms?

Thanks in advance,
Greg
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Hmmm,
In hardware synth terms, what I would need here is an "expo converter," so I guess maybe the Expo module is correct and I just wasn't multiplying my modulator by the right range?

 

You have to use Power module (Math) where X is 2 and Y is your input (value -1..1). The formula is: F * x^y (where F is frequency). This formula will modulate frequency in that way (exponential frequency modulation). For example, 440 * 2^1 will raise it by 1 octave (880 Hz) or 440 * 2^(-1) will lower it by 1 octave (220 Hz). Is that what you've been looking for?

 

Yes, thanks! Can't wait to go home and try it.

That makes sense when I think about it in terms of octaves doubling the frequency.

 

Okay, glad it helped. I didn't know that either, but I googled it and implemented it in Reaktor (for me it works). There is also other way of controlling your FM - linear. That would be like X+Y instead of X^Y. The process itself is called "Chirp". Here is theory:

http://en.wikipedia.org/wiki/Chirp

Good luck!

 

FYI, the power module did the trick and it sounds great. It seems easier to find the weird sounds with expo FM than with linear.

Thanks!

 

OK, glad it worked for you as well. I will store this in my Reaktor folder then.