Some issue in stem export (Ardour 7.4 on Linux)

[atux]

Hi all,

In Ardour 7.4 on Linux, when I export n MIDI tracks, using “stem export”, some audio files that are created, especially those relating to tracks that have the ZynAddSubFX plugin, have very unpleasant constant tone, even where the instrument doesn’t play.
For example it happens with these ZynAddSubFX instruments:

GUITAR → DIST JAZZ GUITAR
SYNTHPIANO → SYNTH_PIANO_2
OLIVERS-100 → EP-MUTED
FANTASY → EMPTYNESS2
COLLECTION → GHOST WHISTLE

What can this be due to?
Thank you,
a.

[peder (Peder Hedlund)]

Does it happen if you mute all the other tracks and just export the one Zyn track?

Does it happen with any Zyn instrument or only a selected few?

[atux]

Does it happen if you mute all the other tracks and just export the one Zyn track?

Yes, nothing changes.

Does it happen with any Zyn instrument or only a selected few?

It doesn’t happen with all Zyn instruments, but only with some of them (like the ones I wrote above).

a.

[x42 (Robin Gareus)]

Does it work if you pick realtime export (Export dialog, timespan tab)?

Perhaps this is an issue with the when doing a faster-than-realtime (freewheeling) export with those instruments.

[atux]

Does it work if you pick realtime export (Export dialog, timespan tab)?

I tried, nothing changes.

[peder (Peder Hedlund)]

Did it use to work fine in older versions of Ardour?
Does it still work if you open your session in an older version?

Try creating a new session with just one Zyn track and see if the problem there as well.

Are you using the same version of Zyn as when it used to work?
I don’t think it’s that likely to be an Ardour problem if there’s only certain Zyn patches that are causing problems.

[atux]

I have to specify that this project was made with Ardour 6.9.0 and now opened with Ardour 7.4. In Ardour 6.9 it runs fine without problems, in Ardour 7.4 it struggles a lot (especially in terms of CPU) and this also causes slowdowns. But this is another topic that I would like to explore further.
Apart from that, I tried to create a project ex novo in Ardour 7.4 with those same Zyn patchs, and this time there is no problem: the exported audio files are good, also with “stem export”.
The version of Zyn I use is always the same.
Thanks,
a.

EDIT:
To reproduce the problem, I tried to build a new project with Ardour 6.9.0 using “those” Zyn patches.
I reopened it with Adour 7.4, I ran the “stem export” and the problems didn’t show up.
All exported audio files are OK.
So I believe that the problem I exposed in my first post is related to “that” particular Ardour project (it’s very large, about 50 MIDI tracks). Executing the “stem export” with Ardour 7.4, as I said, some exported .wav audio files are constant tone from start to finish. I still can’t explain it.