Multichannel Playback issues - no sound from surrounds

Core Machine

Intel NUC 815BEH running ROCK with 16GB - 2TB SSD storage

Network Details

Gigabit switch wired connection with ASUS RT-AC5300 running ASUSWRT Merlin on a 1GB wired fiber connection

Audio Devices

Sonos ARC via HDMI with 2 Sonos Fives and 2 Sonos Subwoofers in surround mode using a Vertex2 from HDMI fury for switching between AppleTV and ROCK NUC

Description of Issue

I am not getting any sound from the surround channels when playing stereo files with the Channel layout set to 7.1, 5.1, or 2.0. The subwoofers appear to be active. I’ve tried “Downmix as needed” and “Channel Mapping only”, and swapping rear/surround channels.

If I play a 7.1 (or 5.1) channel FLAC file, I get discrete sound from the rear channels with 7.1 (or 5.1) Channel layout in settings.

If I use Airplay instead of HDMI for Stereo files, I get good sound from the rear channels, just not discrete. Obviously, this must be a SONOS feature as it works with music this way when playing anything Stereo thru Sonos.

Please help me get some sound from my surrounds.

The setting you made only determine the format of the output; it does not upmix the stereo/2 channel music to fill the other channels. You need to deal with the procedural (and other) filters to redistribute the music.

Thanks for the reply.

Isn’t that a choice to make as = “Downmix as needed” — if it’s a 2 channel source, I would expect this would downmix to 2 channels?

This is how it works for me in other Zones. For example from my PC to a Sonos Playbar also using Roon.

Why does it not work the same way (no sound from surrounds) from a a NUC ROCK to a Sonos ARC?

How can you downmix a 2 channel source to 2 channels when it is so already? Does not make sense to me. FWIW, I know nothing at all about Sonos stuff but I suspect that it is a Sonos issue.

I assume that you have a Mch source file and your equipment can receive Mch sound and process it.
Do not select : send stereo as 5/7 ch
Play Stereo. Go into the DSP, select procedural EQ, add a Mix and start sending your left channel to surround left or try other combinations. That should get you started with troubleshooting.
HDMI Mch licenses need to include more layers of security and fees.

Thanks Joachim_Strobel!

Yes, my equipment plays and supports multichannel. Your recommendation seems spot on. I figured that there was something that could be tweaked in Roon to get surround sound from 2.0 channel sources. With Airplay and RATT to Sonos API these seem to be handled properly, probably by Sonos. With Roon RAAT via HDMI it does not…

I will try and report back.

That is interesting. I do get a strange Mch from my Raspi HDMI fed by Roon’s Raat. May be there is a problem with Raat and Mch via HDMI.


I was able to solve this based on a suggestion from @mitr and @Joachim_Strobel to use the Procedural EQ and manually map the L/R channels to Surround L/R and Back L/R. Good stuff, thank you guys! Very happy!

Roon - It does seem like the “send stereo content as 5.1” does NOT work as expected.

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