ATV 4K + Sonos Playbar: DTS 5.1 source displaying Dolby Digital 5.1

I am using Infuse on an Apple TV 4K to play Bluray/DVD rips with DTS and DTS-HD audio streams. Soundbar is a Sonos Playbar which only accepts Stereo PCM, Dolby Digital, and DTS.

When I select a DTS stream in Infuse the Playbar reports it is receiving a Dolby Digital 5.1 signal. My question is where in my signal chain this re-encode is taking place? I am assuming the Apple TV, but troubleshooting steps would be helpful. The J Tech documentation states it does not decode DTS/Dolby so I don’t think it’s happening there.

Setup:

  • Apple TV 4K (Infuse + Plex)
  • Sonos Playbar
  • J Tech Audio Extractor (JTD18G-H5CH)

Connections:
Apple TV 4K (HDMI) → J Tech (Optical) → Sonos Playbar

Settings:

  • Apple TV
    • Audio Format: Auto
    • Audio Output: TV Speakers
  • J Tech
    • EDID switch: 5.1

The Apple TV can re-encode audio to DD 5.1 if it detects the connected device is not capable of lossless (PCM) audio. This is done at the system level, after the audio has left Infuse.

In your case, I believe the limiting factor is the optical connection as this will be limited to 5.1 channels of lossy audio (EG Dolby Digital) or 2.0 channels of lossless (PCM).

I believe optical supports DTS 5.1. I read somewhere that the Apple TV won’t play DTS, so it transmits multichannel PCM, which obviously the Playbar cannot handle.

So my question is how does the Apple TV know to re-encode to Dolby Digital 5.1 rather than attempting to send multichannel PCM? I might be wrong, but I don’t think the Playbar can report to the Apple TV over optical, “hey don’t send me multichannel PCM.”

The J Tech extractor supports multichannel PCM so I don’t think the Apple TV is getting info there instructing it to re-encode.

If you’re using the optical connection on the J Tech the Apple TV would be able to detect that.

Since the Apple TV doesn’t support passthrough, there is no way to get lossy DTS 5.1, so the Apple TV will re-encode the PCM audio sent from Infuse to lossy Dolby 5.1 before sending it to your device.

Also, since the Playbar doesn’t support multi-channel PCM, I think the best option you can have in this scenario is Dolby Digital 5.1 which is what you are seeing now.

Got it. So the Apple TV recognizes that it’s connected to an optical output that cannot handle multichannel PCM and then transcodes the multichannel PCM to Dolby Digital 5.1.

I agree without updating my equipment this is the best I can do. Just curious as to how the Apple TV could know to re-encode.

I may sub a Blu-ray player in place of the ATV at some point to see if I get DTS on the Playbar. Thanks!

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A Blu-ray player should be able to send DTS 5.1 which is also supported over optical.

The requirement of sending Dolby 5.1 (and not DTS 5.1) is on the Apple TV itself.

Just thought of one more question. I think optical supports LPCM 5.1. If DTS 5.1 from Infuse is converted in the Apple TV to LPCM 5.1, any thoughts why the ATV wouldn’t attempt to send LPCM 5.1 to the Playbar?

I don’t want it to because the Playbar couldn’t play it, but trying to learn.

Optical maxes out at 2.0 channels of PCM. :confused:

Got it. I think the J Tech manual has an error then. It states optical out supports LPCM 5.1.

That may be so. 5.1 LPCM is definitely not supported over optical (toslink).

TOSLINK does not have the bandwidth to carry the uncompressed versions of Dolby TrueHD, DTS-HD Master Audio, or more than two channels of PCM audio.

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