DTS-HD MA audio tracks on my Google TV with passthrough enabled play with crackling/popping sounds

Plex Players Smart TVs
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Server Version: 1.23.5.4801
Player Version: 8.20.0.26605 (781d3db5)

I have the new Sony A90J TV, and an old Sony CT780 Soundbar. I’m currently using Plex installed on the Google TV, the Soundbar is connected to the TV through the ARC/eARC port, and the “passthrough” option in the Plex Android app is set to “HDMI”.

Here’s the audio formats supported by my Soundbar:
image

When I play a video file with TrueHD, Plex transcodes this to AAC, because the TV itself can’t passthrough TrueHD to the Soundbar (apparently no TV in the market can). So far so good, but… When I play a video file with DTS-HD MA, the audio is constantly cracking/popping. I don’t think this is supposed to happen.

In an attempt to debug/fix the issue, I’ve changed the “passthrough” option in the Plex Android app to “Disable”, and I no longer have crackling/popping sound for DTS-HD MA audio streams; however, Plex changed from Direct Play to Direct Stream. Not a dealbreaker for me, but the interesting thing here is that there is no transcoding, not even for the audio track.

So, I’ve disabled passthrough, Plex uses Direct Stream, but sends both the audio and video tracks to the Soundbar/TV without any transcoding whatsover, and the DTS-D MA tracks plays without issues.

If Plex isn’t transcoding when passthrough is disabled, shouldn’t it be able to play the DTS-HD MA audio track with passthrough enabled without any crackling/popping sounds? What am I missing?

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Output via HDMI and output via ARC is not the same thing. You can’t pass DTS-HD (and it’s variants) through ARC, that’s only possible with eARC. Plex does not support eARC.

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Output via HDMI and output via ARC is not the same thing.

I keep hearing this, but I can’t understand why… I mean, here’s the two scenarios:

  • External Player → HDMI → TV → HDMI-ARC → Soundbar
  • TV → HDMI-ARC → Soundbar

In both cases, isn’t the audio going through the HDMI cable connected to the ARC ports in the TV/Soundbar? Why do they differ?

You can’t pass DTS-HD (and it’s variants) through ARC, that’s only possible with eARC.

I don’t understand why… In both cases (with and without passthrough enabled), transcoding is not happening, the DTS-HD MA track is being sent directly from the TV to the Soundbar, why does one play correctly, while the other doesn’t?

Please note that I still hear the audio track in both cases, it’s just that one of them has constant crackling/popping sounds.

Plex does not support eARC.

Just curious, is this something that Plex might support in the future?

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Really? If it doesn’t support eArc, then how does Plex on nVidia Shield output TrueHD and DTS HD?

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Keep in mind that the hdmi ports on a TV are typically meant to be for input, not output. ARC allows that specialized port to be used for output if needed. This is the opposite of the hdmi port on your external player, it can only do output. You can connect another player to it and use it for input. Because of this limitation, when using the normally input hdmi port for out (ARC) there are restrictions.

What type of audio is going through when you hear this? Does your soundbar have a way of showing what it’s input is?

Possibly, but it will take quite a bit of work. It’s not just a flag to turn on.

See my comment at the top of this comment about hdmi output vs ARC.

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Keep in mind that the hdmi ports on a TV are typically meant to be for input, not output. ARC allows that specialized port to be used for output if needed. This is the opposite of the hdmi port on your external player, it can only do output. You can connect another player to it and use it for input. Because of this limitation, when using the normally input hdmi port for out (ARC) there are restrictions.

I’m sorry, I must be really dumb, because I still can’t understand the difference…

Scenario 1)

  • External player
  • HDMI port outputs video/audio to the HDMI input port on the TV
  • The TV plays the video signal received from the HDMI input
  • The TV sends the audio signal received from the HDMI input through the HDMI-ARC port to the Soundbar HDMI-arc port

Scenario 2)

  • TV built-in player
  • The TV plays the video signal received from the built-in player
  • The TV sends the audio signal received from the built-in player through the HDMI-ARC port to the Soundbar HDMI-arc port

The only difference is the source of the audio signal, but both are going through the HDMI-ARC port on the TV to the HDMIC-ARC port on the soundbar, right? So, where’s the restriction that you speak of? Is this a software or hardware limitation?

What type of audio is going through when you hear this? Does your soundbar have a way of showing what it’s input is?

Just checked on this, and here’s what I found:

  • With passthrough set to HDMI in Plex:
    • Soundbar reports LPCM (sound plays, but crackles all the time)
    • Plex direct plays the video file (no transcoding)
  • With passthrough disabled in Plex
    • Soundbar reports DD+ (sound plays just fine)
    • Plex direct streams the video/audio tracks (no transcoding)

Then I noticed my TV audio settings also has a “passthrough” option, which was off, and I’ve enabled that:

  • With passthrough set to HDMI in Plex:
    • Soundbar now reports DTS (sound plays, no crackling, but is constantly dropping, like half a second of silence)
    • Plex direct plays the video file (no transcoding)
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It’s just literally not supported. It’s a direct limitation of ARC.

Taken from What Is HDMI ARC? | Tom's Guide :

The ARC standard was designed specifically to replace S/PDIF digital audio outputs (also called TOSLINK), and thus supports every audio format that would normally pass through S/PDIF: Dolby Digital, DTS and PCM audio. It can handle both the TV’s regular two-channel audio and 5.1 surround sound without any trouble.

But it also has the same limitations as the S/PDIF standard it replaces. Namely, it can’t send HD or high-bit-rate audio used by standards like Dolby Atmos and DTS:X. This is especially irritating because downstream audio over HDMI can carry the signal with no problem; it’s purely a limitation of the ARC spec.

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@rfgamaral - There are a couple of things going on here that need to be clarified.

1. HD Audio via Internal Apps:

There is currently not TV on the market that supports HD audio formats using the internal apps that are installed directly on the TV. This includes DTS-HD and Dolby TrueHD.

There is no disputing this, it is just not supported and therefore will not work.

It doesn’t matter how you try to output, it just won’t work.

2. HD Audio via ARC:

The HD audio formats (DTS-HD and Dolby TrueHD) are lossless, and therefore the audio tracks are at a much higher bitrate and require more digital bandwidth.

Because of this, the ONLY way to transport the HD audio formats is over HDMI or eARC (Enhanced Audio Return Channel)

And therefore, HD audio formats are NOT supported over ARC.

Again, there is no disputing this, it just doesn’t work.

It is likely that the TV is “trying” to send something down the ARC channel, and the soundbar is “trying” to do something with it, and that is the reason you are hearing “something”. But this solution will never work.

Ultimately, it is likely you are going to need to replace your Soundbar for one that supports both eARC, and the HD audio formats.

I hope this clarifies things for you :smiley:

2 Likes
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@axemanuk666 Thank you for making such detailed post, things are clearer for me, but I’m still intrigued by a couple of things:

1. HD audio via internal apps, still goes through the HDMI-ARC cable, right? Just like HD audio via an external player goes through the same HDMI-ARC cable, right? So, where exactly is the limitation on the internal apps? Is this a software issue? Probably not, because otherwise some TVs would have fixed this by now. So, what’s the hardware limitation with the internal apps?

In other words, when I play a DTS-HD or TrueHD format on an external player, such as the Shield TV, the audio goes from the external player HDMI connection to the TV, and then to the Soundbar through the HDMI-ARC connection, and it plays just fine. When I check the format that the Soundbar is actually receiving, I see DD+ when playing TrueHD, and DTS when playing DTS-HD. So, something is transcoding the HD audio to the core audio, correct? What is this “something”, and why can’t the internal apps use it as well?

I’m not disputing this, I’m just trying to understand how everything works, that’s all.

(The following point is not directly related to your point 2 above)

2. If I have passthrough disabled on the Plex app, my Soundbar reports that a DD+ track is being played when playing a TrueHD video file, and a DTS track when playing a DTS-HD track. But the same does not happen when I have passthrough enabled, because Plex tries to passthrough the HD audio formats, and it can’t, because it needs eARC, which I don’t have.

I’m wondering, is it possible for Plex to be smarter, and somehow detect that it can’t passthrough and instead play the TrueHD/DTS-HD tracks just like passthrough was disabled (as explained in the previous paragraph)? In other words, could Plex do something on the software side, and try to play the core audio tracks when the HD audio ones can’t be played because of hardware limitations?

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Yes, but this ain’t a “cable” thing…

Yes and No… Don’t get hung up on the fact that something is transported down the same cable. This is not a cable limitation.

Think of ARC and eARC as a protocol. As a means to “communicate” when a specific condition is met. They are strictly designed to transport the sound from the TV itself (internal apps or the TV tuner) to an external sound device.

However when you use an external player, such as a game console, BlueRay player, or the NVIDIA Shield, the TV is aware that the input is via one of the HDMI ports, and therefore does NOT implement the ARC / eARC protocols, and simply passes the audio through to the sound device.

Again, don’t necessarily get hung up on the cables themselves.

Maybe… The likelyhood is that TV manufacturers make the assumption that all internal apps will be used with streaming services, none of which stream with HD audio, and therefore choose not to bother in development time.

An example of that is the fact that you cannot currently find any TV on the market with a Gigabit LAN port, although that might start to change as more 8K TVs get developed.

Maybe, but in all honesty that’s starting to get a little deep, and all I can say right now is… It all currently works, as long as you have the right equipment.

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@axemanuk666 I think I got it now, thank you :slight_smile:

1 Like
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Your old sound bar doesn’t support EARC.

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