Vero 4k+, LG CX, Apple TV 4k and Sonos Arc

Bought a Sonos Arc yesterday after I got tired of waiting for the Bose 900 to reach New Zealand!

I’m not an expert by any means but I would have thought that the equipment listed in the thread title is a reasonably common combination. Thanks to the guide at the link below, I think I have managed to get Dolby Atmos up and running so thanks to whoever put that together. It took me a good hour or more of tinkering but I got there.

Audio hardware and software configuration

The online advice suggests that, if your Sonos app displays you are getting Atmos, it is probably true. The “Dolby Atmos” notification which used to appear on the top right of the TV no longer appears. I am guessing that might only appear when you getting the version of Atmos that comes through the TV speakers only – ie. a much lower level of Atmos, if you know what I mean.

One question that I cannot get my head around. I thought the Sonos on its own is essentially a 5.0.2 system – I do not have a subwoofer. Why in “number of channels” on the Vero do I set it to 7.1? Am I losing any sound quality by doing this?

Next step is to add the PS5 into the mix……

You set to 2.0 or stereo, and enable bistream and hd bitstream passthrough. (I don’t know the exact wording of the settings as I am not in front of Kodi right now, but it’s all in the same system/sound settings page) That sounds counter intuitive but it’s the correct way.

Also the CX was downgraded compared to C9 in what it would passthrough through HDMI, but I think it still supports Dolby TrueHD.

The channels settings is the maximum number of LPCM channels Kodi will allow to be output. When your playing something that is in a format that is set to passthrough mode then this channels settings does not come into play since Kodi is just sending along the unmodified bitstream (AC3 transcode and striping down and sending just DTS core depending on settings types of situations excepted). If the connected equipment allows for 8 LPCM channels then one would normally set that to allow for multichannel content that is not Dolby or DTS to be transmitted as surround instead of dumping down to stereo or being compressed with AC3 transcoding. It really depends on the situation as many people may not have any content that this would pertain to in which case it wouldn’t matter.

Yes in a rare usecase where somehow the end user prefers 7.1lpcm that is encoded as 7.1 flac or something. But then I guess you can just check the encode to ac3 instead, which you probably should do anyways since the Arc doesnt support DTS. (I think)

I think you might be misunderstanding things a bit. Audio is sent as PCM or bitstreamed with passthrough. Thus if you have a soundtrack in multichannel FLAC which can’t be sent out as is, then Kodi must transcode it. If you have your settings set to 8 channels then it outputs a signal that is lossless to the original. If you use two channels and AC3 transcode then it is compressed in a lossy format. Same thing with playing a DTS soundtrack when the output device doesn’t support passthrough of that format.

If you AVR/soundbar/TV your passing through/etc. only supports two PCM channels then stereo and transcoding is the likely choice. Otherwise you will get better sound quality by not recompressing the audio.

No I didnt misunderstand anything.

  1. Kodi doesn’t properly downmix from 7.1 to 5.1 LPCM. (but please correct me if I’m wrong as I haven’ followed development for a few years)
  2. Vero 4K doesnt support 5.1 output without it being in a 7.1 container. (please correct me if this has changed or is different in the plus model)
  3. You can’t ouput 7.1 LPCM to Sonos Arc as rear surrounds will be discarded entirely. It only supports 5.1 LPCM.

That leaves the solution I already posted. (I believe the downmixing from 7.1 to 5.1 within AC3 transcoding is done properly) I Wouldn’t worry about reencoded AC3 @ 640kbs. I’ll bet you an arm you wouldn’t be able to hear the difference in a megabuck home cinema. With the Sonos ARC, there’s no chance anyone is gonna hear a difference.

As near as I can tell you are mistaken. I just tested it with a 7.1 TrueHD soundtrack and my AVR shows the input format as 3/2/.1 PCM being received with Kodi set for 5.1 channels and passthrough disabled.

This is also not correct. This question came up recently here…

According to the interwebs the Sonos Arcs with eARC and current firmware support 7.1 LPCM input.

I can, others can’t, some don’t care. Regardless, if one is going to bother tweaking their settings there really isn’t a point in using less than optimal settings.

Of course , but doesn’t contradict what I wrote. It seems you just look at “what does it say on the display” without really answering the question. (And I do welcome being corrected if I’m wrong, it’s not that) Does it properly mixdown 7.1 to 5.1 or are the extra back surround channels just discarded?

I am not sure what to make of the post you linked or even that you understood me right. What I mean is: is the following information from this post from 2018 still valid or has it been fixed (I guess @Chillbo could chime in): 5.1PCM being converted to 7.1PCM - how to stop this? - #4 by Chillbo

As I said, it just discards the surround back channels, even though it “supports it”. The following thread is only 2 months old, so I’m pretty sure it’s still valid: Sonos Arc and 7.1 Downmix to 5.1 | Sonos Community

You are right, that is why I posted the optimal settings. Although I remain somewhat skeptic of your magic ears, let’s agree that for all practical intents and purposes, the ARC isn’t gonna reveal noticeable differences in sound quality regardless of LPCM og transcoded AC3.

I just tested it with a test file that identifies channels. It output the extra two channels into the rear speakers. It did not discard them.

I posted that my AVR was showing as receiving a 5.1 input so clearly that was not being forced into eight channel LPCM wrapper. A lot of changes have happened in the last four years.

I’m really not sure how that thread on Sonos’s site about how that soundbar is doing its processing is relevant here. If a Sonos device is not processing a 7.1 LPCM input in a desirable way then one can just set Kodi to output 5.1 channels and let it do the downmix.

I’m not sure the thread @darwindesign linked is relevant to what you are saying. That was about the number of HDMI channels needed for various passthrough formats.

Regarding LPCM, there is no such thing as a ‘7.1 container’. HDMI has two modes: it carries 4 stereo channels which either contain 4 successive stereo samples or 4 simultaneous ‘stereo’ samples to provide up to 8 channels. I guess you could call that a 7.1 container at a stretch. For 5.1, six channels are carried in three of those ‘stereo’ pairs and one pair is not used. 3/4 years ago we did a lot of work to make sure the spare pair of channels was properly muted because users were getting funny noises on RL and RR when playing 5.1. Maybe that’s what you remember.

Passthrough formats similarly use 4 successive 2-channel samples (DD, DD+, DTS) or all 8 channels (HD audio formats). But that has nothing to do with the number of channels you set in Kodi’s settings unless you want to use the AC3 transcoding option.

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OP here. Thanks for your help. What I have boiled all the replies down to is “mess with the settings a bit and see what sounds right with your ears”. There is no one right answer and experts have differing opinions.

Very simply and clear: This was fixed at the time and it’s been working properly for years. Vero signals the correct PCM output channel layout via HDMI and thus AVRs can do their magic correctly. :+1:t2:

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