Built-in audio output emits a loud pop when Apalis iMX8 powered off

When I evaluate “poweroff” on the Linux command line, the Apalis module shuts down and there is a very loud audio pop in the headphone output. Curiously, there is no corresponding pop when the module is powered up.

My guess is that the pop is due to the rapid discharge of the DC bias voltage on the CODEC side of the DC blocking output capacitors.

What can I do in either hardware or software to avoid this (potentially ear and speaker damaging) pop?

Thanks for your help!

Any ideas would be appreciated…

Hi @aunt_enna

I have so far been unable to reproduce this on my local setup. Can you reproduce this on one of our provided carrier boards with the latest prebuilt BSP from TEZI?


Update, after reinstalling my board I am able to reproduce this. I have slightly varying symptoms and (more importantly) volume on different types of SOMS but there is definitely something there. I’ll dig a bit more and respond back.


I was hoping that muting the channel would help but that does not appear to be the case. I’m asking the hardware folks internally and will let you know what I find.

Great, thanks for looking into this!

Hi @aunt_enna

Just wanted to let you know that we are still investigating this. I don’t have any specific update for you at the moment though.


Hello aunt_enna,

Yes there can issues like this arise and this is due to the design. We have the problem that the SGTL audio chip is repeating the last few samples on a reset since the chip does not get any new data and the chip does not go into a real reset since there is no reset input signal to the SGTL chip.
Are you using one of our board or a custom designed carrier ?
is it possible to see the schematic?

Best Regards,