Just put this together and thought it sounded decent. Not bad for 7.6% DSP power, eh? I just thought I'd throw this in here for new micromod owners like myself. Also, is it just me, or does the crappy sound of LFO's pretending to be oscillators sometimes actually sound appealing?

Linear FM is possible with the LFOs by multiplying the modulating sine with the grey value through use of a gain controller. The grey input is actually a simple linear frequency input of the V/Hz type. To get control over the modulation index the amplitude of the modulating wave must increase in a linear fashion for the higher frequencies. The grey isganl is exactly the right signal to do that. By crossfading between the nonscaled sine and the sine scaled with the grey value the DX keyboardscale can be implemented.

If the grey value is used directly to scale the modulating waveform the modulation index can be set between 0 and 1, which is not a big range. By increasing the scaled modulating wave with a factor four the index can be set between 0 and 4, which is more useful. This is simply done with two control mixers in a simple 1+1=2 -> 2+2=4 manner.

But as this is plain vanilla textbook linear FM applying feedback will cause a pitchshift. DX type FM is modulation of the phase position and not of the linear frequency parameter, which behaves much better with feedback. Inserting a highpass filter in the feedback loop fixes thing a bit. The disadvantage is however that if the modulation index exceeds 1 the feedback is more than 'unity gain' which causes the HP filter to oscillate even through the FM loop and the whole thing gets unstable. Same reason why the FMB oscillator gets unstable with feedback and a FMB knobsetting exceeding something like 67, 68.

Well, who cares...

Here is a two operator FM patch that has eight voices on the Micro Modular, featuring both FM feedback and keyboard scaling.