by support »
Hello,
Loopbacks can occur at two levels, in principle: Directly by the audio chip or in software.
It's easy to check on the latter: Turn off pulseaudio (with "pulseaudio --kill" and verify that the /dev/xillybus_audio file can be written to directly, so it's not taken by Pulseaudio). If loopback still exists, it's by the audio chip.
In this case, you need to set up its registers to disable the loopback. I suggest taking a look on /usr/local/bin/zedboard sound setup.pl, which is where the default values are set.
Regards,
Eli