Thanks Lokki for the feedback and klangFM for the schema.
I forgot to push to github the correct Makefile.
It now compiles fine.
I attached the firmware of this adcIn branch.
USE IT AT YOUR OWN RISK !!!
For technical info, a timer interuption and some DMA mechanism sample automatically the 4 analog pins.
It is done 4 times per block for each analog pins.
The final value is the average of those 4 samples to get rid of sample noise.
The final sampling rate is one value per 32 samples so arround 1200Hz. External oscillator as fast as 500Hz should work, wich leads to modulation much faster than the internal lfo.
I only tested with variable resistor pot plugged between 0v and 3.3v as analog source.
So let me know if some of you succed in using real analog hardware.