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Author Topic:   MaxMI parameter in Oscillator
trotz
Member 		posted 18 December 2009 07:18         Edit/Delete Message   Reply w/Quote
I'm happy to report some progress in my Kyma learning experience. I just finished reading (twice) the Kyma Revealed book and I'd like to start building some simple Sounds froms scratch rather than getting lost modifying complex Sounds in the Library.

I have come across a small question that eludes me.


I can't find in the documentation the units of the parameter MaxMi in the Oscillator. Shouldn't it be a (unitless) factor of the Modulator input?. It sounds like it is an absolute value in hz but I don't understand the advantages of that.

Is there a way to get a constant relative modulation depth across the audible spectrum using MaxMi? Let's say, an octave?

I know this is possibly some really simple beginner question... but I'd prefer to fully understand the most used modules before trying more advanced subjects.

Thanks a lot in advance!

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SSC
Administrator 		posted 18 December 2009 14:43         Edit/Delete Message   Reply w/Quote
Right, the modulation index, MI, is a unitless value. The (very rough) rule-of-thumb for frequency modulation is that MI is approximately equal to the number of side-bands that you hear. And that (also unitless) c/m ratio (Carrier frequency / Modulator frequency) determines which sum and difference frequencies comprise the side band frequencies.

MaxMI is the peak value that MI will reach when the modulator's amplitude is at unity gain. So, for example, if the modulator's amplitude is 0.5, then the actual MI will be MaxMI * 0.5. Of course, the interesting timbre changes traditionally associated with FM occur when you have an amplitude envelope on the modulator so the number of side bands changes dynamically.

It's fun to drag a SpectrumAnalyzer to the right of an FM Sound and experiment with different c/m ratios and MIs.

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trotz
Member 		posted 18 December 2009 18:43         Edit/Delete Message   Reply w/Quote
Very interesting. Thanks!

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