Hi @ImPee 

Welcome to the Sonos Community!

I’m not sure how much I can help you with this. If you ever receive surround audio from your Arc, then things are properly setup/configured. I am unsure as to whether this is what you are saying, however, as you said “results in surround audio on my Arc (Dolby Multichannel PCM 2.0)”, but that is only stereo audio, despite being Dolby.

If you can receive surround audio (Dolby Digital 5.1, DTS 5.1, Multichannel LPCM 5.1/7.1 or Atmos reported in the Sonos app) via apps built into the TV, then I can only recommend you contact Google for support with your Chromecast.

Or, my posting here will get this topic back on the Recently Active list - perhaps someone with a Chromecast will be able to assist.

I hope this helps.

Hi Corry,

Thank you for your feedback. Really very much appreciated.

Up until now, I only saw “ Dolby Multichannel PCM 2.0” and “Dolby Digital Plus 2.0” in the Sonos App. I didn’t knew these are stereo too (should have known as it states 2.0). But, even when these are stereo formats, for me they still sound subjectively way better than “Stereo PCM”. Not sure if this is objectively /technically the case either?

I was hoping someone could point me in the direction where I can find sound samples using Dolby Digital 5.1, DTS 5.1, Multichannel LPCM 5.1/7.1 or Atmos. I will then try to play those samples using apps built into the TV.

Kind regards,

ImPee

Hi @ImPee 

If anything, they should be lower quality due to the use of lossy codecs, but what you are probably hearing is a slight increase in volume - I think compressed formats are boosted in gain slightly as they are decompressed.

I can't really help you there, though I would suggest testing with movies/TV with the sources you are likely to use.

I did do a search on Chromecast and found a page that certainly suggests you should be able to stream surround sound formats to your device: https://developers.google.com/cast/docs/media. It seems likely that it may depend on the device sending the stream, however.

I suggest taking things a step at a time - use the TV’s in-built apps to ascertain whether or not the TV is properly set up to provide surround audio to your Arc, then once that has been verified, move to testing with the Chromecast. Your settings look right, for what it’s worth.

I just now found this on another thread: https://download.dolby.com/us/en/test-tones/dolby-test-tones_7_1_4.mp4. Hopefully, it will be of assistance.

I hope this helps.

Hi Corry,

Thanks for your appreciated input.

The suggested approach sounds very solid to me. Unfortunately, I will only be able to run the tests in the weekend or early next week. Will come back with feedback as soon as possible.

Kind regards,

ImPee.

Hi Corry,

After some additional testing, it turns out I can easily get 5.1 (+ Atmos) when playing content from local apps and Google Chromecast. The rootcause of my original problem was that the media files contained only stereo audio tracks. Stupid mistake - I know . Thx for putting me in the right direction. In the meantime, I learned a bit more on audio formats/codecs and how to check for them in media files.

I do have some additional questions:

1. What is the difference between “Multichannel PCM” and “Dolby Multichannel PCM”?
2. I have episodes of a series with audio codec “MPEG AAC (mp4a)” according to VLC and “AAC 5.1” according to Plex. The audio format as reported in the Sonos app changes when I jump 30s forward while playing the episode with the Plex client on Chromecast. The format switches back and forth between “Stereo PCM” and “Dolby Multichannel PCM 5.1”. In the latter case, it happens often there is no sound at all coming from the surround speakers (One SL). Any idea what this is all about?

Kind regards,

Impee 

Hi @ImPee 

Apologies for the delay - I have been on holiday for a couple of weeks.

Thanks for updating the thread - I’m glad to hear that you found the answer!

As to your additional questions:

1. I think “Dolby Multichannel PCM” may be a misnomer - as an uncompressed stream, there’s nowhere for Dolby compression technology to get involved. “Multichannel LPCM” is the correct term, as far as I am aware. Do you see “Dolby Multichannel PCM” reported in the Sonos app?
2. I would guess that it may be due to Plex transcoding on-the-fly as you play, and when you skip forward you momentarily get the original (unsupported) stream before then getting the converted audio a moment later. Sonos Home Theatre devices do not support AAC coming from the TV, so this would explain the silence. If the format only switches when skipping forwards, then this makes sense. If it changes format while playing normally, this is unusual and I would recommend seeking assistance from Plex support. In my experience, on-the-fly transcoding gets a bit unreliable when sipping through a file (though I should point out that I don’t use Plex).

I hope this helps.

Hi Corry,

Thanks for your feedback. Very much appreciated as always!

I hope you enjoyed your holiday. I’m now also on holiday and will not be able to provide feedback on your follow-up questions. Expect me to come back with more on this in a couple of weeks from here.

Kind regards,

ImPee