My Macbook Pro (2016, 4 thunderbolt 3 ports) has this very annoying problem where something breaks in the audio system, and it stops playing sounds and being able to detect any output devices. It's doesn't seem to be random, but I don't know what causes it.

More specifically, it stops playing any sound whatsoever, regardless of the volume setting and which output device is selected. Then if you try plugging in a new output device in that state, it doesn't recognise it. In this state, if you try clearing audio-related caches, or rebooting coreaudio or AppleHDA, it just loses the output devices it had registered, and still can't detect new ones.

The only action that fixes the problem is reseting the NVRAM. This suggests that it's possible for the NVRAM state to become broken in a way that audio playback stops working, and new audio output devices can't be recognised anymore.

So.. why?

What exactly is stored in the NVRAM that could have this effect? I couldn't find any comprehensive list of what is stored in the NVRAM, instead the only things that are confirmed is that volume and screen aspect ratio are stored there. I still have some hope that by knowing this I may discover the exact actions that cause the NVRAM to get to the broken state, so that I may avoid it. Having to reset the NVRAM often is awful, since it requires a reboot.

  • stored in NVRAM include sound volume, display resolution, startup-disk selection, time zone, and recent kernel panic information. The settings stored in NVRAM depend on your Mac and the devices that you're using with your Mac. – Ruskes Nov 8 '18 at 20:03
  • what audio beside Apple do you use ? does it show your output device in the Sound – Ruskes Nov 8 '18 at 20:19
  • @Buscar웃 that's strange, neither of those should cause the issue I'm having :/. This issue happens with two output devices showing in the Sound preferences: an E2241 DisplayPort (this is my monitor, plugged-in via an HDMI cable with Apple's original adapter for power+hdmi+usb <-> thunderbolt), and my Headphones in the Headphones port. As I've said in the question, they show up even though no sound is produced, they don't disappear from unplugging, and restarting coreaudio makes them disappear forever. – brocoli Nov 12 '18 at 19:30
  • OK, lets open Console in the Utility Folder and Watch it as you plug in the Headphones and plug out. Also in the System Preferences Audio watch the Output switching. – Ruskes Nov 12 '18 at 20:29
  • I don't know precisely how to reproduce the issue. That's kind of the point of the question in the first place. – brocoli Nov 13 '18 at 14:23

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