All audio streams converted to LPCM on AppleTV 4K Gen1

Hi everyone,

As I just changed my sonos Beam to a Beam2, I took the occasion to plug an AppleTV 4K gen1 to use Infuse on my TV (previously KODI/Videostation)

I’m aa bit confused, as on my main HC install (Sonos ARC + Arkana HDFury + AppleTV 4K Gen2), all audio streams are converted to PCM, excepts Dolby AC3 and Dolby E-AC3 (with Atmos metadata).

On this new installation (Sonos Beam2 + TV Sony A9S eARC + AppleTV 4K Gen1), all streams are converted in LPCM, including the dolby’s ones. Results, I lose the Atmos data (while it works perfectly with Disny+/Netflix), and also the LPCM sounds pretty flat. (I A/B Test on Thor Love and Thunder with many audio formats and platforms, and the LPCM from Infuse to Beam2 sounds flat, and low in volume).

All parameters on AppleTV 4K seem correct (keep stream original, and match quality/frequency for video). Any guess on that issue?

Thanks all!

This is due to limitations of the Apple TV, as Atmos is only supported when using E-AC3 audio tracks.

More info on the available audio options can be found here.

Thanks James.
But All dolby AC3 and E-AC3 are converted in LPCM (including Atmos files over E-AC3).
For TrueHD files (as well as DTS files), I understand it’s transcoded to LPCM due to Apple limitations.

But for the AC3/E-AC3, any idea?

That’s correct, everything gets sent as LPCM.

However, if you play an E-AC3 file with Atmos this will be sent as LPCM + Atmos. The same can be seen with other ATV apps (ATV+, Netflix, etc…).

Thanks James.

Another question: the PCM output from Infuse is less dynamique and loud that the same audio from other apps (benchmark of Thor Love and Thunder in EAC3=>LPCM on Infuse, EAC3=>ECA3 on Disney+, but same with other movies).

Any idea why the bitstream is better than LPCM?
It would be great to be choose in Infuse if we want, for Dolby AC3/EAC3, to choose between bitstream vs. LCPM…

Most likely it is something your Sonos is doing. On a traditional receiver you can set up specific profiles on a sound format basis. So maybe it is treating bitstream different from lpcm. Not familiar with that device though or how you configure it

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