That’s interesting.
Just to be clear, here are examples of what I’m talking about:
44.1 kHz (clean, except for highest two notes):
48 kHz (artifacts start manifesting themselves already after a couple of octaves):
Recorded directly on Zynthian using the Audio Recorder. Played from a MIDI keyboard transposed up two octaves, so I believe that makes the lowest note played MIDI note 60 (middle C).
(It’s a V4 RPi5 Zynthian, with the original V4 hardware except for the RPi5, with the audio buffer size set to 128).