Apple TV 4K will only out PCM Audio to Onkyo Receiver TX NR686

I fixed the issue for myself but not sure if it will fix yours.

I have a 82 inch Samsung 4k TV and Samsung has a feature called “UHD” that you can enable or disable for each HDMI port. If I enable UHD on the HDMI port that my receiver is plugged into, it disables Atmos and Dolby Digital and triggers the PCM only audio. When I disabled the UHD it enabled Atmos.

So long story short, UHD enables HDR and Dolby Vision for video but disables Atmos Audio. You can’t have both HDR and Atmos. Don’t ask me why. Hopefully a firmware update fixes that.

I found that when there is both AAC and AC3 encoding on a video file that it will only play stereo. I used an application called "remux" that allows you to strip off the AAC encoding and leaving only the AC3 encoding. Then all of my movies started playing 5.1 surround again. This was not a problem with the AppleTV2 but was introduced in the AppleTV4K.

Apple prepared a support document for the set up:
Play audio in Dolby Atmos or surround sound on your Apple TV - Apple Support

Notice the last line, that describes what might prevent Dolby Atmos:
“You can't play sound in Dolby Atmos if Quick Start is turned off in Settings. To check, go to Settings﹥Apps﹥iTunes Movies and TV Shows﹥Quick Start.”

I have slightly different receiver, but seems to be doing something similar.

I checked that Quick Start , it was not turned off.

I appears that the receiver just doesn't light up that it's receiving Dolby , when I use the info button on my receiver it shows PCM 2 ch.

I have sort of the same issue. I just upgraded my AV system with the latest Apple 4K TV running tvOS 12.1 and an Atmos receiver, Onkyo TX-RZ630. I used the highest speed Amazon HDMI 2.0 cables that do support 18 Gbps and when playing 4K movies in iTunes that are rated for Dolby Vision/Dolby Atmos I can verify that the receiver is set to Dolby Atmos and I can hear the difference of all the surround channels working including the subwoofer. I can also verify that the input to my TV is coming in at the expected 3840 x 2160/59.9 Hz UHD resolution and color space is set BT.2020 at 30 bits/4:2:0. So all good here and the picture looks amazing.

Issue that I have is that as soon as I exit movie playback and I'm back to the regular app UI my receiver is saying that the audio coming out of the Apple TV is a mere PCM 2.0, i.e. not even a subwoofer channel! So my receiver converts that to 5.0, but again no subwoofer channel is activated. All playback in the YouTube app stays like that which is highly disappointing. Clearly, my HW can handle the extra channels including the subwoofer so what gives? Why would Apple TV revert to such low audio settings when navigating around lesser apps that iTunes movie playback??

dimace wrote:

All playback in the YouTube app stays like that [2.0] …

YouTube and other content providers outputting a stereo audio signal, is something you should take up with each of them. It is not a device limitation, but a 3rd party service limitation. Try uploading a 5.1 clip to YouTube, then try playing back from there using any media player: converted to 2.0.

Thank you. So you're saying that the audio tracks and how many of them are embedded in the playback are encoded on the content side. I get that. However, you'd think that the HW inside the Apple TV would convert ANY audio track to at least PCM 2.1, i.e. include a subwoofer channel.

I'm mostly a video guy so audio standards are not my forte but I'm sure you're aware that a lot of clips in YouTube and other apps are NOT natively captured in UHD/4K. Despite that, at the device level, Apple TV upscales all of them to 3840 x 2160 when you choose that setting in the Audio/Video settings. You'd think that something equivalent would happen on the audio side of things, i.e. all audio tracks despite of how they were authored on the source content side are re-encoded to 5.1 DD Surround by the Apple TV audio HW or something along those lines. I guess that's not the case. Again, I get it but it's not any less disappointing. I was hoping there was an audio setting I missed somewhere under System settings but I guess not.

Be sure to use HDMI 2.0 cables (Premium High Speed, 18 Gbps) and HDMI 2.0 ports. If the equipment needs more than 8 Gbps, then the High Speed HDMI cable won’t be enough.

Have the same problem with a Pioneer LX79, it is displayed to me only PCM. Otherwise I have never had problems and with the XBOX ONE it runs without problems with Atmos

Has anyone solved this problem? I’m having the same issues and don’t know what to do. I’ve tried everything and no luck.

I just had the same issue with a similar tv. I turned off the UHD setting and it worked. My cables are all hdmi 2.0 or 2.1. Neither worked with the UHD setting on.

That's interesting and good to know. We should log a support ticket for this as 4k + Dolby Atmos is what we've paid all the big $$$ for! That sounds like a setting you're changing on your TV though?