Massive audio bug with tvOS 14.5 and Apple TV 4k: loud plops!

Just an update to this thread, to inform everybody, who might come across this post, how I have been able to solve it.

First of all, I contacted the amazingly helpful Apple support, which got back to me One to One by telephone, so I could fully and technically elaborate on the issue.

I finally was able to sort out a HDMI active extender cable as the culprit.

My 4K TV is on Marantz’s main HDMI output, my JVC D-ILA projector on HDMI output #2.

Since the JVC only supports 1080p, output #2 in Marantz’s settings is not activated, I do TOGGLE between output 1&2 as needed. Activating both outputs at the same time would have led to a permanent 1080p SDR setting.

So, even with only output #1 being active, still, obviously the active components of the extender cable must have had some “backwards” influence to the Marantz / the ATV 4k and its new firmware.

Once I disconnected the 5V power adaptor from the extender cable and ran it in “passive” mode, all sync issues were gone.

A few additional hints, that I got from Apple and Marantz support in case you might come across problems:

• set your Apple TV 4K to 4k 30 Hz HDR. They said, it’s a good overall setting.
• Marantz suggests in case of sync issues to use the HDMI inputs closest to the outputs - this minimizes any influences of longer internal signal-paths

i_rina

thanks for trying to help.

I have already done all those steps you suggested. There is currently no way to improve the situation. Getting rid of the AV amp is no solution - it has worked flawlessly for the past 2 years with my ATV, so the problem is not my setup, but the tvOS 14.5 update.

Since these burst happen twice a second, here is my guess, what’s happening:

initially, ATV is set to HDR 50Hz and syncs to the AV preamp/TV

since ATV settings are set to „adjust framerate“, ATV does just that, when I play a movie form f.e. Netflix: it syncs everything to 24fps (which works)

the moment I stop the movie and ATV goes back to its main screen, it syncs back to 50Hz - that’s when the audio bursts start twice per second

now, divide 50Hz by 24? Yes, roughly 2!

My guess: video framerate gets synced back to 50, audio framerate cannot sync and stays at 24 - with the effect of producing these burst. Just an educated guess…

I would have loved to test it by setting the ATV to default to HDR 24Hz, but this previously available option was cut from tvOS 14.5 - so there‘s no way to check my theory, if the frame rate ALWAYS stays at 24fps

I can disable automatic frame rate adjustment, though, and the issue is gone! But since Apple discarded the 24fps HDR default setting, I can only choose HDR 50 or 60 Hz - and I am not willing to watch the mostly 24fps content with a jittering picture…