Frequncy deviation in the VST interface?

I have tried using different LUFS plugins(VST2) with Audacity but don´t get the expected results.

This is my primary setup:

  • Audacity 3.1.0 64-bit
  • Youlean Loudness Meter 2 - V2.4.3
  • Windows 10 Enterprise 21H2

Test files:
25Hz Expected 23 LUFS:
100Hz Expected 23 LUFS:
500Hz Expected 23 LUFS:
1kHz Expected 23 LUFS:
2kHz Expected 23 LUFS:
10kHz Expected 23 LUFS:

When I run YouLean on these files I get the following results: -15,9, -20,4, -23,0, -22,9, -23,1 and -23,0
Not correct for 25Hz and 100Hz.

But hey… Maybe it is the YouLean plugin? Nope. I have tested the same version of YouLean on the following hosts for the same files:

  • Youlean standalone app
  • Ocenaudion 3.10.13 64-bit
  • Adobe Audition

ALL these shows 23 LUFS for all frequencies!! I have also tried Audacity with FinalLoud3 (3.0.12) which gives the following results: -15,9, -20,3, -23,1, -22,9, -23,2 and -22,9. Almost identical to Audacity+YouLean.

My conclusion is that there is a bug in the VST interface, signals below 500Hz are lower they should be.
Can this be fixed??

IMO that sounds like they are incorporating equal loudness curves to compensate for the peculiarities of human hearing.

Due to license restrictions, Audacity has not been able to use the Steinberg VST2 headers and has had to rely on unofficial open source headers instead.
Fortunately, Steinberg have released VST3 headers under an open source license (GPL v3), and it is hoped that Audacity will be able to use these in the future.
Because of this, I doubt there will much work (if any) on Audacity’s current VST2 support, but if all goes according to plan, Audacity will have much better VST support when VST3 is adopted.

In short, don’t expect too much in the short term, but all being well there is much better VST support on the way.

@Trebor: My point here is that it is the combination Audacity + any LUFS plugin that gives this deviation, the same LUFS plugins with ANY other host gives correct values.

@Steve: That makes sense. Roughly, when can we expect VST3 support?

Not all LUFS plug-ins give this deviation. Ebumeter works fine for me on Linux, and there was another one that I tried on Linux that I don’t recall the name of which worked fine (neither of them are “VST” plug-ins).

The problem may be with VST LUFS meters, but I’ve only tried a couple of them (I rarely use VST plug-ins).

I don’t know as I’m not privy to the management / development team’s schedule, but I’ve seen that work has begun on sorting out the relevant licensing issues.