Vizio + Roku Ultra + Playbar = audio weirdness

  • 28 January 2019
  • 11 replies
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Userlevel 2
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I have:

A brand new Vizio P55-F1 television
A Roku Ultra connected via HDMI
A Sonos Playbar+surrounds+sub connected to the Vizio by optical cable

On my previous TV - a Vizio E420i - I set the Roku into forced Dolby D+ mode, and the TV transcoded it down to Dolby Digital. I got proper surround sound out of all Roku apps - Plex, Netflix and Prime Video.

Here is the issue I am seeing with my new Vizio. The Roku can be set to Auto or Dolby D+ and I will get these same results. If I start playing a video in Plex with an AC3 5.1 track, it plays fine all the time. But if I play a video in Plex with a TrueHD or DTS track, I get no audio between the Roku and the Vizio. If I then open the Vizio settings and change the audio away from Bitstream (ie: to PCM or Dolby D), audio will start playing. I can then change it BACK to Bitstream and the audio will work properly. At that point I can verify that the TV is transcoding the incoming audio to DD, and that I’m getting proper 5.1 sound out of the Sonos setup (both in the Sonos app and with my ears).

So this is definitely *not* a format transcoding issue. It seems like it’s some sort of handshake issue… the Roku isn’t communicating to the Vizio that the audio format has changed, but switching the Vizio’s audio setting renegotiates the audio settings and everything comes back to life.

One other question: Is “Dolby D” on the Vizio audio settings to *allow passing* of Dolby D audio? Or is it to *force* a transcode to Dolby D audio? The manual says that you must use Bitstream to pass >2 channels, but any mode other than “PCM” seems to allow that.

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11 replies

Userlevel 7
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Hi radiocolin

The Playbar will not interpret a DTS signal, only DD5.1, stereo or PCM.
Userlevel 2
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Hi radiocolin

The Playbar will not interpret a DTS signal, only DD5.1, stereo or PCM.


Yes, I understand that. The Vizio transcodes these formats to DD before passing them to the Playbar. The issue seems to be happening between the Roku and the TV. This isn't a transcoding or audio format issue.

Did you read my post at all?
Userlevel 7
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Yea...I read your post. This is a Sonos forum...not a Vizio or Roku forum. If you have questions concerning how those products handle the signals they receive then you should be asking the questions on those forums. I don't go to a restaurant and ask the chef to explain the principles of the magnetron in his microwave.
Userlevel 2
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You very clearly did not read my post, because it said that this is not an audio format issue and that the TV is transcoding it to DD.

Since the Sonos is involved, and these are popular home theater products, I thought someone else here may have encountered this issue and have a solution. I've cross-posted this to forums for the other products involved as well.
Where does it say that the Vizio is transcoding from DTS to DD? I'm looking at the Vizio website, and see nothing about that feature, at least on the Specs page.

https://www.vizio.com/tvs/p55f1.html

What am I missing?

I'm thinking about buying one of these, such a feature would be most interesting, and to my knowledge, this would be the only TV maker that would do transcoding, if true.
Userlevel 2
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Where does it say that the Vizio is transcoding from DTS to DD? I'm looking at the Vizio website, and see nothing about that feature, at least on the Specs page.

https://www.vizio.com/tvs/p55f1.html

What am I missing?

I'm thinking about buying one of these, such a feature would be most interesting, and to my knowledge, this would be the only TV maker that would do transcoding, if true.


I haven't been able to find that written anywhere, but that's the only thing I can deduce is happening. I don't believe the Roku transcodes, and if I pick something higher than DD - like a DTS speaker mapping test file and I verify that it's not playing the AC3 core track - everything still comes out of the correct channels. Netflix ONLY outputs DD+, and their test patterns are in the correct channels as well.

I have seen the opposite: that brands like Samsung and LG don't handle this properly.
Interesting. I'd have thought that if in fact the Vizio did any transcoding, that would be a feature that their marketing department would be trumpeting.

I'm guessing that when you're using DD+, it's similar enough to DD that you're getting the 90% similar data, and dropping any of the + data, since DD+ is only an extension of DD. But I'm not an engineer, so I'm not 100% sure. But that would explain why DD+ is working, and DTS and TruHD tracks aren't.
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Just an update for those who may find this thread in the future: someone else in another forum confirmed that they also had a similar issue with audio formats between Vizio and Roku, with the Vizio not properly switching until you toggle the audio mode. I'm going to try just using the built-in apps, which work fine and are able to output DD over the optical to the Playbar.
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Update to the update: When I turn off display refresh rate switching under advanced settings, this problem goes away entirely.
Fascinating. Thanks for the updates. I'm going to have to expand a lot of skull sweat trying to figure out why the heck that makes any difference at all.
Userlevel 2
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Right? It's wild. My guess is that the Vizio doesn't like something the Roku does to change the refresh rate and drops the audio.

Here's what I've found to be optimal settings:

Roku - HDMI audio mode set to to DD+ (no DTS. Seems the TV won't step that down, unfortunately). Refresh rate switching off under advanced.
Vizio - Audio set to bitstream.

Now I have sweet sweet surround sound out of my P55-F1 regardless of the incoming format.