Mono source not mapped to stereo when a convolution step has been inserted (ref#THJ01O)

Jeffrey_Moore · February 15, 2026, 5:24pm

Hi! What’s not quite right with Roon?

· None of the above quite fits

None of the above quite fits

· None of these quite match

Tell us what's going on

· Mono MP3 not always channel mapped to stereo

Tell us about your home network

· A bunch of UniFi stuff; has been reliable with Roon for years

Support request submission flow only accepts one image (seen above), but comparing these two as below helps clarify the issue.

For this zone, the mono source file gets mapped to stereo before sending to the Lumin U2 Mini, and the sound plays as expected:

For this zone, the mono source file does not get mapped to stereo before sending to the Lumin U2 Mini, something downstream is unable to handle mono digital play, and this zone mutes for the duration of this track:

Both zones use a Lumin U2 Mini as the device, both zones are using a non-USB digital output from the Lumin (so no DAC recognition passed upstream).

So, what should I be looking for in configurations to force the broken zone to require a 2-channel feed?

I could’ve sworn that channel mapping used to be a stage always available for manual setting in zones, but now it just automagically appears… sometimes.

alex_h · February 16, 2026, 9:16pm

Hello @Jeffrey_Moore,

Thanks for reaching out to us with this question.

Regarding your multichannel setup, we recommend reviewing our guide on how Roon handles downmixing and channel mapping here: Roon Knowledge Base: Multichannel Setup & Downmixing

To help us better understand your specific configuration, could you please share screenshots of the following?

Device Setup: The "Device Setup" screen for your Lumin endpoint (accessible via Settings > Audio > Gear Icon).
MUSE (DSP): A screenshot of your MUSE page if you currently have any signal processing or downmixing rules active.

Looking forward to your reply.

Thanks.

Jeffrey_Moore · February 17, 2026, 2:42am

Thanks for looking at my report!

Just to clarify: there is no multichannel action involved in this trouble report. Both zones involved (the one which works and the one which doesn’t) are straightforward stereo zones, each fed via its own Lumin U2 Mini.

The issue is that in one case, a mono source is getting mapped to stereo to match the output device, and plays correctly, while in the other case the mono source is being passed all the way to the Lumin as mono and playback fails for that zone.

Aha! One of the zones, the one not working properly, was set up to run through a convolution step (which I always leave active, because it corrects for the bass issues from this zone’s speakers being too close to the wall behind them).

So I turned off the convolution step temporarily to simplify the comparison I was going to send you… and without that convolution active, the zone automatically maps mono to stereo and plays correctly.

I apologize for not having tried that before opening this ticket! It’s an obvious thing to try; it’s the only major difference between the zones.

It’s such an obvious thing to try that I could swear I already tried it (a few months go, when I first encountered this issue but didn’t have time to file a trouble report). But I guess I must not have.

So. The trouble I’m looking to resolve is now not a mysterious difference between zones, it’s that the automatic mapping from mono to stereo happens if there’s no convolution step, but fails to happen when the convolution step is enabled.

I’ve changed this post’s Subject text to reflect this.

Here’s the main device settings page:

Here are the advanced device options:

Here’s the signal path (WORKS CORRECTLY!) with convolution disabled:

…and here’s the signal path (OUTPUT STAYS MUTED because unsupported mono sent to device) with convolution enabled:

Here’s the MUSE setup with convolution enabled:

Here’s a list of the contents of the Acourate-generated ZIP file for convolution:

Does Roon forget about the need to convert mono to stereo once a convolution step has been introduced?

Is there a way I can force that conversion to happen?

alex_h · February 17, 2026, 7:02pm

@Jeffrey_Moore,

Thanks for confirming those details.

Based on your setup, I recommend using the Procedural EQ to manually map the channels.

Please try the following:

Open your DSP settings.
Enable Procedural EQ.
Add a Mix filter.
Map the channels exactly as shown in the screenshot below.

Let us know please if that helps in your situation.

Thanks.

system · February 24, 2026, 7:03pm

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