Why has audio range FM (via X-Mod) an instable tuning ?

Why has audio range FM (via X-Mod) an instable tuning ?
« on: October 17, 2020, 04:26:56 AM »

When using audio Range FM via Poly-Mod (target is "Freq 1" and both oscillators operating in audio range) it is possible to create great "metallic" sounds.
But when doing that every voice has a noticeable different beat frequency and the "octave purity" gets worse with increasing modulation level.
Therefore it is not possible to play melodic lines over a few octaves or even chords, without sounding "wrong" and out of tune.
Imho this form of FM can just be used for non-melodic effects or monophonic operation.

To be said: Slop and Detune are set to 0. The device is tuned (in the range of a few cents, checked with a tuner)  and also it sounds in tune when played without FM

Is there a reason why the P6 (and also the OB6) behaves in this way ?
Or should that not be the case and I have a non properly working device ?



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Re: Why has audio range FM (via X-Mod) an instable tuning ?
« Reply #1 on: October 18, 2020, 02:46:07 PM »
I believe this the nature of exponential FM, whereas linear FM can be more stable but generally requires the digital domain to pull off successfully.
Kijimi, Xerxes mk2, OB6D, P6D, Prophet 5D (expanded), OB-X8D, Hydrasynth, Pro 3, Wavestate, MS20D, A4mk2, ARmk2, MC202, Avalon, Syntakt, Octatrack, NLDR, H9000, Digitone, Deckard's Dream mk2, Isi-Nin, Roland System 500 + other Eurorack