Some lucky fucker just scored an AK on fleabay for just shy of £500.
It wasn’t me… 
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there’s one for sale in Ireland for €750 European beans at the moment. on my local classifiedz. no use to the UK posse but 
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I just tried another. Bit more subtle. Tracking better.
[Free patch further down.]
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Phase modulation is just FM for a digital waveform. If you picture a wave that’s just, say, 256 samples, adjusting the “phase” of the wave by 90° just means starting at sample 64. Now if you imagine advancing the phase of the wave forward as it’s being played, you might be in a situation where instead of sample 1, you get sample 2. And then instead of sample 2, you get sample 4, etc. essentially skipping every other sample. What you would end up with is playing all the samples of a wave with the exact same shape, just in half the time — in other words, it would be twice the frequency. So in digital, phase modulation is the same as frequency modulation. Just, because it’s all samples and numbers, it’s easier to do with math, and thus is much more precise (and less CPU intensive than trying to do all that floating point stuff with DSP).
For analog, I think you just want to stick with frequency. Especially as “phase”, when it comes to the osc of the A4, tends to mean that “pulse-width” skew thing it does with the waves that aren’t pulses.
Totally! And I experimented a bit with this to great results (note that your LFO has to modulate the cutoff frequency of the filter directly, not the osc pitch. It’s “key” tracking, not “pitch” tracking 
). The biggest thing that held me back is the unstable tuning of the self-oscillating filter. Elektron says a TRK of 32 ought to map to the keyboard, but I can’t get it to stay in tune across more than an octave. But maybe this is my unit and I need to tune it up with some trim pots or something? If anyone else is getting stable tuning self-oscillating filter, let me know.
EDIT: Just thinking it through to write this, I thought “what about filter 2? It’s digital, right?” And yeah, it’s key tracking is rock solid. You can get some truly great FM sounds using a self-oscillating filter2 and Sine LFO modulating FILT:F2 Frequency. Playing with this now!
EDIT of the EDIT @Jeanne points out below that all the filters of the A4 are analog, even the multimode ones in filter 2. My bad!!
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If you’re looking for a very clean waveform use the sub osc set to 1 oct with osc turned off and pitch an octave up for compensation. Now using filter 2 in low pass or peak can give you the cleanest sine-like shape you can get out of the A4 afaik. Works better in lower registers, though.
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Wow!! This is easily one of the coolest sounds I’ve heard from the A4!! Very well done. I’m just about to fire up my A4 and start exploring this stuff.
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Thanks! Makes me very happy, you like it. Can upload the patch later, if you’re interested.
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I have noticed that too with mine, the VCF 1 doesn’t track well across a broad range.
Definitely diving into this now as well.
Going to explore the mod envelope modulating the lfos phase and depth although it might not work the way I think it might.
Thanks for clarifying the stuff about digital phase modulation. I’m a total noob with FM and this was all new info for me.
I would love that!!
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nice 
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Thank you! 
Here you go …
SY ELECTRIKPI.afsnd (666 Bytes)
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Thank you!!
The second filter is tracking v well through the freq range so maybe that’s where the confusion comes from.
I remember hearing/reading both, it being analog and it being digital but likely what is written on the manual is the truth.
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Just a little snippet of the filter 2 used as the sound source and frequency modulated with the lfo. Not the best example of flawless tracking or much of a shot at a piano sound but still something I’m very pleased with as I haven’t really done stuff like this with the A4 before, amazingly enough.
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Love my A4MK2 was first real synth but OT has more complexity.
Here I undergo a real harassment.
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Right you are! Thanks so much for the correction. The multimode filter is even marked as analog in the block diagram, so I feel foolish. Geeze, I this box is full of goodies.
Man, I can get close. But still little instabilities getting in the way. It starts getting pretty inharmonic higher up in the range (which is where FM pianos shine, IMHO). Also, while the multimode filter seems to track the keyboard much more accurately, I can’t seem to dial in a cutoff exactly equal to whatever frequency the tuning-fork-LFO is locked to, so everything goes flat in the sustain. And, because we have to use the multimode flt as the osc, we only get one carrier, which robs us of some complexity.
All in all, when I do this again, I’ll probably stick to the sync method unless I figure out something I’m missing (again ). Still, good times. Thanks for the weekend challenge!
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