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IDProjectCategoryView StatusLast Update
0009636ardourbugspublic2024-02-18 22:01
ReporterBleuzen Assigned Tox42  
Status resolvedResolutionfixed 
PlatformGNUOSLinuxOS Version(any)
Product Version8.2 
Summary0009636: First Stereo Plugin on Mono Flexible-I/O track affects right channel more than left channel
DescriptionHi, if a Stereo plugin is on a Mono track in Flexible-I/O mode, it does do more to the right channel than the left channel and thus breaks the Stereo Balance.
For example if Ardours Stereo Compressor is put on a Mono track:
- Balance is fine if Compressor is set up to do nothing (Ratio: 1)
- If Compressor reduces the gain it affects both channels differently and after the plugin the left channel is loader than the right channel
This only happens for the first Stereo Plugin on a Mono track. Other Stereo plugins after that handle the balance fine. Also not all plugins are affected but most I tested so far.
The issue can be worked around if "Manual Config" is enabled in Pin Configuration of the first Stereo Plugin on the track.
Steps To Reproduce1.) Create a Mono Audio Track in Flexible-I/O mode
2.) Record something on it for testing
3.) Add a Stereo Plugin to the track, for example "ACE Compressor (stereo)"
4.) Make sure the plugin is the first on the track
5.) Set up the compressor to compress the signal
6.) Look at the stereo balance of the output (should be centered - but it is not - left channel is now louder than right channel)
Additional InformationThis issue likely appeared at some point within the last 13 months. I noticed in an older project of which I still have an export from January 2023. If I play back or export the same project again, without any changes, but with the latest Ardour version, the stereo balance of some sounds is noticeably different compared to the export from last year.
TagsNo tags attached.



2024-02-18 17:22

administrator   ~0028507

Fixed in ACE comp 8.2-148-g9386847cc9


2024-02-18 17:57

reporter   ~0028511

cool, however since you only mentioned ACE comp, does the fix also apply to other plugins?
because it also happens with x42 eq and comp and some reverb plugins for example


2024-02-18 18:10

administrator   ~0028512

Those plugins do not correctly handle stereo in-place processing then and need fixing.


2024-02-18 18:15

administrator   ~0028513

Ardour could be changed to provide two separate input buffers to work around issues in plugins. but in plugins are expected to handle this.

Here: left input buffer is identical to left output buffer.

So for the issue at hand, the plugin processes the left channel writes to the left output and thereby modifies the input.
When the right channel is processed. changes already applied to the left channel are used as input.


2024-02-18 18:25

administrator   ~0028514

Thanks for the heads up, x42-eq v8.8-1 fixed. I'll investigate more plugins

But let's take a step back. What are you actually trying to accomplish here?


2024-02-18 21:38

reporter   ~0028515

> What are you actually trying to accomplish here?

well I hope for this to 'just work':
If a track is planned to output Stereo, I tend to use Stereo plugins on it, even if the input is Mono - because mixing Stereo and Mono plugins on the same track can cause some pain when changing the plugins order later (like loosing pin connections or breaking the stereo balance due to switching between single/multi-instace mode...).

Also I would like my old sessions to sound the way they were intended without having to re-do the pin configuration on every affected track again.
Did Ardour have a workaround for this in the past? Because I do not hear this problem in my older exports.


2024-02-18 22:01

administrator   ~0028517

A quick search shows that this optimization was added in 6.0, specifically git revision 00ecc545bc6

Issue History

Date Modified Username Field Change
2024-02-09 22:40 Bleuzen New Issue
2024-02-18 17:22 x42 Note Added: 0028507
2024-02-18 17:22 x42 Assigned To => x42
2024-02-18 17:22 x42 Status new => resolved
2024-02-18 17:22 x42 Resolution open => fixed
2024-02-18 17:57 Bleuzen Note Added: 0028511
2024-02-18 18:10 x42 Note Added: 0028512
2024-02-18 18:15 x42 Note Added: 0028513
2024-02-18 18:25 x42 Note Added: 0028514
2024-02-18 21:38 Bleuzen Note Added: 0028515
2024-02-18 22:01 x42 Note Added: 0028517