Hi @barritia.

Thanks for reaching out and I appreciate your detailed post here, I’d be glad to help.

HDMI-eARC is required to play lossless Dolby Atmos audio using the Dolby TrueHD codec. 

The main benefit of eARC is greater bandwidth and speed, which enables hi-res audio formats like Dolby Atmos.

Arc supports HDMI ARC and eARC connections, while Sonos Amp uses HDMI ARC.

If you connect to a TV with eARC, the Dolby audio formats supported include Dolby Atmos, TrueHD, MAT, Dolby Digital Plus, and Dolby Digital.

If you connect to a TV using ARC, the Dolby audio formats supported are dependent on your TV model and manufacturer. The TV may be capable of sending Dolby Atmos, Dolby Digital Plus, and Dolby Digital. An ARC connection cannot support TrueHD or MAT.

You can find more information in this support article which outlines the main factors that determine if your Sonos Arc can play Dolby Atmos audio.

If you have any other questions or concerns, don’t hesitate to reach out, we’re always here to help.

Thanks Annazel but I think you are misunderstanding my question. Basically if I am getting True HD Atmos to my Arc speaker and I add my a Sonos Amp into that group so I can run the floor standers and extra subwoofers what format is being sent to the Amp. The system info only shows Atmos True HD on the Arc but nothing for the Amp. Basically am I also getting the Atmos True HD through the Amp because it’s in that group or does Sonos compress that Audio that sent to the Anp when it’s added to the Arc group. 

Hi @barritia.

Thanks for your response.

You’re getting the Dolby Atmos True HD on Sonos Arc because it is compatible, and getting the right codec or signal directly from the audio source.

You can group the Sonos Amp with your Arc to play music in sync and play TV audio (with a slight delay), but Amp cannot play specific audio channels for your home theater.

If you have any questions or concerns, please feel free to let us know, we’d be glad to help.

Yes I know I’m getting Atmos True HD to the Arc the app tells me that. But am I getting True HD to the Amp because it’s in the same group as the arc. The app does not show anything not even stereo or am I getting a lower resolution  audio to the amp when it’s in the Arc group. 

Hi @barritia.

Thanks for the response.

No, you’re not getting the same Doly Atmos True HD on Sonos Amp even if it is grouped to Arc because it has no direct connection on the TV.

When the Sonos Amp is grouped with the Sonos Arc it only generates a stereo signal regardless of the source since it is set up as a music device.

The Sonos Amp will be able to generate surround audio when added as surrounds as it will only receive surround audio from the main home theater speaker connected to the TV.

Supported home theater audio formats

• PCM Stereo
• Dolby Digital/AC3

Sonos Arc only

• Dolby TrueHD (Dolby Atmos)
• Dolby Digital Plus (Dolby Atmos)

If you have any questions, please feel free to let us know, we’re always here to help.

Ok I still don’t think you are getting what I’m saying. I am using the Amp to power a extra stereo pair of speakers and 2 subwoofers in combination with the Arc so a stereo pair plus subwoofer. It’s has a separate subwoofer output so I assume it’s not just pulling the bass from the left and right pair. The Amp can obviously be used as surrounds for Atmos rear surrounds but is the Amp receiving the audio in a HD format. Kind of defeats the purpose of having Dolby TrueHD Atmos if the Arc can’t supply this high bitrate format to the rear speakers. But if it can is it also giving a HD audio to the amp setup as fronts from the Arc. 
 

basically is the Arc sending a HD stereo signal to the rears and if it is then is it also sending that HD signal to my fronts on Sonos amp. If not what bit rate of audio is being sent to the Amp from the Arc. 

Hi @barritia.

Thanks for the update here, my apologies for the delayed response.

To better understand your system/setup, kindly submit a diagnostic report through the Sonos app, and reply with the confirmation number.

To clarify, the Sub is the only speaker ‘bonded’ on the Arc as a home theater but the Dolby Atmos is just from the Arc, while the Amp is set or named as another ‘room’, and in order to play the same sound on 2 ‘rooms’, they need to be ‘grouped’ together. If the Amp is added or bonded to Arc, it will work as surrounds to enhance the sound but it will not get the Dolby Atmos signal from the Arc, the same thing if the Amp is ‘grouped’ with the Arc to play TV audio, Arc will not send a Dolby Atmos signal to Amp but you will get the most out of the Amp which is ‘stereo’.

Most S2 compatible players support 24 bit audio. For the select few that don’t, they will automatically downmix any 24-bit audio to 16-bit when streaming. If your grouped speakers do not support 24-bit audio, they will automatically downmix to 16-bit audio. Speakers that support 24-bit audio will stream 24 bit when grouped. At this time 24-bit support is limited to local playback from Music Library, NAS shares, or playing music from your Android phone or tablet.

If you have any other questions or concerns, don’t hesitate to reach out, we’re always here to help.

Ok so basically when the Amp is grouped on the arc as a front stereo pair and subwoofer it’s not receiving HD audio from the Arc to the fronts or the rear surrounds. 
 

thanks that’s all I needed to know. 

Hi @barritia.

Thanks for the immediate response and confirmation.

If you have any questions, please feel free to let us know, we’re always here to help.

You are always welcome here in the community.

Cheers!