giuliomoro any reason why you used ADC level = -12dB at the same time as PGA = 12dB ?
This was the final experiment exploring the relationship between ADC level and input impedance.
I was doing several experiments combining ADC level and gain to see what changed what. I just posted a graph from the final experiment in the series.
As the ADC level 0 dB lowers the input impedance toward 20k, and the 3 dB cut-off moves up toward 80 Hz.
This isn't a configuration I would actually use unless I needed the low-end bandwidth and gain. I confirmed behavior is consistent with the datasheet where the ADC level changes input impedance independently from PGA gain.
For completeness, here's a comparison. Note these graphs are normalized so you only see the change in frequency response, and not the gain.
This is the root of the hardware issue I opened. The input coupling capacitors in Bela should be 1uF to guarantee full-bandwidth operation at 0 dB.
For my guitar usage I run the ADC level at -12 dB and PGA gain of 0dB. ADC level -12 dB gets the higher input impedance AND this is about where the level is correct: on the scope I can see it barely clip if I strum like somebody trying to break a string.