posted 27 May 2013 13:19            

New Kyma user here -- loving it so far, but I have so, SO much more to learn. Please bare with me whilst I barrage the forums with rudimentary questions.

Anyway, I've just built myself a quick little 1OP FM patch and I have a question about what is going on with the "MaxMI" field of my Oscillator (which I have setup for FM, with another osc feeding it, as per usual). The help panel says:

"This is the value of the modulation index when the Modulator is at its full amplitude."

Okay, that makes sense, fine and dandy. My question is, what does the modulation index do, and how does it do it (e.g., what domain)? I can hear that the effects of the FM become much more dense when the MaxMI value is greater, but how is it achieving this? Where is the number (20, for example) placed in the math of all this?

Thanks in advance for your insight. I'm having a blast with the Kyma!

Cheers,

posted 28 May 2013 09:26            

"Modulation index

The amount of modulation or volume level we apply to the second oscillator is commonly known as the modulation index. It's difficult to calculate the actual spectrum of the resulting sound from the modulation index, this involves mathematics with Bessel-functions, but the rule of thumb is that the more modulation you apply the brighter the sound gets, resulting in noise if the modulation index is very high. If we increase the modulation index of a sinewave modulating another sinewave, the resulting waveform changes from a sinewave at modulation index 0, through an increasingly more complex and brighter waveform, to noise at a very high modulation index. The change into noise is quite sudden and this can be used in many creative ways."

That, in combination with the wiki on MI, I think I understand it a little better.

FYI, for anyone coming to the forums on a similar quest!

[This message has been edited by atiller (edited 28 May 2013).]

posted 28 May 2013 17:48            

The modulation input is a sound module working at sample rate and hence is limited to value +/-1. The MaxMI is a scaling factor (that you set up before hand) that determines what the +/-1 represents.

With a value of 2 Pi in MaxMI, the phase of the oscillator will be shifted by -180 deg to + 180 deg with an input of -1 to +1.

Don't forget that FM synths like the DX7 and Synclavier (as well as the modules in Kyma) are really Phase modulation, because it is the phase is being controlled by the mod input. It becomes frequency modulation as an aside, but a fix modulation amplitude, will swing the phase by a fixed amount. The actual frequency modulation produced will be determined by both the frequency and the amplitude of the modulating signal.

I hope this makes sense

Pete

posted 29 May 2013 08:55            

I think that does make sense, yes. Thanks for taking the time to explain that to me.

Cheers,