Big Difference between Real Time (RT) and normal Export

I had become increasingly paranoid that my mixes sounded different when exported to how they sound during playback in Ardour, so I decided to do some null tests…

There was substantial differences as demonstrated by null tests comparing mixes exported using the RT option or not.
Mostly reverbs, but also some entire instruments are very clear and audible in what should be null.
My guess is that this is almost certainly caused by the multiple windows vst plugins that I am using via Carla Rack and Wine.
In one test, a Carla Rack and plugin test caused the phase to invert 180°.

I’d like to be able to figure out which plugins are causing this issue in existing mixes, but I don’t know how to re-import and align the rendered mixdown so that I can use it to do a null test against playback (so that I can switch on and off plugins).
Is there any way to do this, or has anyone got any suggestions?

I’m using Ardour 7.5 on Kubuntu 20.04

I’d suggest a few things…

  • Get the latest Ardour from here and retest, 7.5 is old and missing a LOT of improvements
  • Try your theory on a bare session with just Ardour Plugins if no difference then an outside issue
  • Carla has great merits as a general host but it is not a great Windows VST bridging idea, yabridge and even LinVST are a far better option if you MUST have Win Plugins

Thanks for the suggestions, but I’m in the middle of a big project that will require recalls until next June, so I’m kind of stuck with Carla and 7.5 until then.

I did try the bare-bones session test, and the resulting files null as expected.

BTW, why are yabridge and LinVST better than the Carla Rack plugin?

@robbert-vdh the developer of yabridge is a member here and could probably give you several good reasons and I’m not a programmer per se… yabridge seamlessly makes it like the Windows Plugins are like any other system Plugin… no intermediate host rack, Ardour sees them directly and handles saving the presets et al just like any system Plugin… I would guess yabridge is much more optimized and processes faster than Carla is capable of… Off the top of my head those are a few things… Hopefully Robbert pops by with the really good stuff though! :slightly_smiling_face:

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I wonder if latency compensation is handled properly with yabridge.
If it is, I’ll give it a go on another computer.

Ardour handles that and yabridge is probably as accurate as the Plugin is at reporting it’s latency.

If you don’t mind the download the AV Linux Live ISO has a yabridge environment all set up…

Boot into a live session, launch ‘YADbridge’ and click on ‘Synchronize VST Plugins’ which will automatically set up a small collection of test Windows VST’s that are included for demonstration. Then launch Ardour–>Edit–>Preferences–>Plugins–>VST and manually add the hidden ‘.vst’ folder in your Users home folder and the do a Plugin scan in Ardour. The Windows Plugins will show up after the scan and you can test for yourself how it all works!

*YADbridge screenshot from a development version of AV Linux

@paul @x42 for the love of god please just add ~/.vst to Ardours default list!! yabridge and literally MOST of the 3rd-party native Linux VST2 Plugins out there are expecting to be in that folder I don’t care what the VST2 spec says or doesn’t say… that’s where they are and have been for many years. A User having to manually add that Path on their first run of Ardour is a completely unnecessary and confusing speed bump! Even Reaper has this in their defaults!

If others have been annoyed by this please add your voice to the feature request:

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For the love of $god, if you need Windows VSTs, use Windows, and the sooner VST2 dies the better. VST3 is so much nicer and actually has a spec where plugins are to be installed to.

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Tell that to the numerous Vendors (ie Harrison AVA :open_mouth:) and the huge amount of FLOSS github Plugin developers still providing VST2 in their multi-builds… Sorry, I cannot understand the stubbornness about this issue, it really baffles me… :thinking: both VST2 and yabridge are used by a very large percentage of Ardours Users… What possible harm could adding that Path do…? If you get your wish and VST2 dies you can remove it or leave it as it will simply be unused but I can guarantee you it will be VERY useful for at least a few more years.

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Back on-topic, I don’t believe Carla can inform plugins that Ardour exports faster than realtime. So this can explain the difference.

Then again most plugins are agnostic to the actual speed. Can you pinpoint which plugin[s] cause issues?

Part of the topic was yabridge vs. Carla, I provided a turnkey answer which brought up a related issue with where yabridge was going to end up placing the Plugin files, I see that it is now a closed avenue…

Best of luck @glitterball

Keep in mind that default paths are only applied for new installations of Ardour, so this would have had no effect here (hence I deemed it off-topic).

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I haven’t figured out which plugins cause the issue, that’s why I wanted to know if there was a way to align an exported track in order to do a null test (switching plugins on and off).

I wish that I didn’t have to use Windows VSTs, but in all honesty there still aren’t good-enough algorithmic reverbs available for linux. I haven’t found any Oxford Inflator clones for Linux either.

Unfortunately I am getting a dropout when doing a Real Time export - is there any way for me to avoid these?

I’ve done some more tests, and in a simple session several of the most common VSTs that I use under Carla Rack null just fine in Real Time vs. normal export tests (LoudMax64, PTEQ-x, JS Inflator).
However reverbs do not (OrilRiver, Epicverb), though this is probably to be expected.
I still haven’t figured out why some tracks had their phase inverted in more complex sessions.

The dropout issue is solved by doubling the buffer size, so I will stick to Real Time exports for the moment.

I tried Yabridge, but unfortunately it crashed Ardour with the very first plugin that I tried (JS Inflator).

Do you have tried linvst? Now, 99% i use linux native plugins. But sometimes i need the TDR Nova dynamic eq and for me it works with linvst. I didn’t had any problem with linvst. 3 years ago i managed many windows vst’s with linvst and it works very good!

DragonFly and Aether are supposedly among the better opensource/free linux alternatives, if you haven’t already checked them out.

I have tried both of those:
To my ears, the Dragonfly reverbs don’t even sound as good as the mid-range rack-mount reverb units that I was using in the mid 90s.
The Aether reverb does sound good, but it seems to be lacking some optimisations, as it is very resource hungry - probably 4x what the Orilriver uses via Carla Rack.

You may try the reverbs from Airwindows, some are quite, mmh… specific or more but all (including the abbey) great. Only thing is you must not be a slave to flashy GUIs :wink:
see at

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Any particular Airwindows reverb recommendations for large rooms and halls?

I love Airwindows Verbity, It’s so simple yet so versatile, from drum ambience to big halls it really can do it all… I’ve had a few people walk in while I’m working on a session and ask me what Reverb is that!? When I tell them and show them the UI they are very surprised that it isn’t Fabfilter or Valhalla…

On the proprietary side I recently purchased Eos from Audio Damage and it actually uses some of the Valhalla stuff and it’s hall Reverbs are quite impressive…

As far as Dragonfly, it is excellent as well you just have to dig a bit to get what you want…


I take it back about Dragonfly Hall - I spent the last 30 minutes playing with it, and I was able to get some very decent results - as you said, I just need to dig a bit…

The Verbity reverb is very narrow when fed from a mono source, and has a certain resonant rhythm to it on longer verbs. Verbity2 is also very narrow when fed with a mono source - it does have an interesting effect if you feed it from one side or the other though.