Convert from Ardour 4 to Ardour 6.9 - some tracks only play on left channel

I’ve noticed that when I import and convert old files from Ardour 4, some tracks will only play on the left channel and the Left-Right slider of the mixer is stuck in the middle. All tracks were recorded in mono in Ardour 4. When I right click on the tracks and select “Outputs”, I can see “L” (left) “R” (right) and “1”, which seems to be a “port”.

Any idea how to fix this?


L + R + 1, usually indicates MIDI tracks with a synth (the 1, being a MIDI output), odd though.

Could you upload the original session file (Ardour 6 should have made a backup of that, named something like “the_session_name.ardour-3002” ?

Do you need only this one file? How do I upload it?

Yes, just the one file should be sufficient to investigate.

You could try if it fits on otherwise perhaps google-drive, drop-box or similar service… If you do not have access to any of those services, you could attach it to a bug report at (but that requires a dedicated account)

Here is the link to the file. The lead guitar only plays in the left channel when converted into Ardour 6.9.

Also, why is the Left-Right slider stuck on that track?


This indicates a stereo track, you first have to reduce the width, before you change the center – The Ardour Manual
Alternatively right-click and change it to a stereo-balance control.

I see, you have loaded a stereo plugin onto the mono track. Specifically Calf Reverb. I expect you have not only updated Ardour, but also Calf plugins. Recent Calf adds a MIDI output, which explains why you’re seeing the “1” in addition to L+R.

The easy solution remove the plugins from each track.

Then add a stereo bus, load a revert plugin there, and use sends to the reverb-bus.

It is usually preferable to use a single Reverb, that ties the mix together like it was recorded in a single room. Individual reverb effects on tracks do not necessarily achieve that.

Another solution is to enable “strict i/O” (context menu of the mixer-strip header)

This prevents plugins from adding ports and the mono track will remain mono. However I do not know if that works well with Calf Stereo Reverb.

To elaborate… your original session had a setup like

Calf’s Left input is fed by the Mono track, but the right-input is no connected:

But the plugin produces stereo audio (green) and MIDI (red) output.

Thank you very much for your help, Robin!

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