Graph in UI for Invada Compressor LV2 plugin does not match parameters

[pablomme]

Binary package hint: invada-studio-plugins-lv2

If I insert the Invada Compressor LV2 plugin (mono or stereo) in a track in Ardour, I'm presented with a very nice interface to configure its parameters, where I can see a graphical representation of the effect of the compressor (an output vs input dB plot). This plot has the usual straight-line shape with a sharp kink at the threshold, as expected. However the right portion of the curve is incorrect. For example:
- set threshold to -10dB
- set ratio to 2:1
I would expect that a make-up gain value of 5dB would make the output 0dB at an input of 0dB. But it doesn't. You need a make-up gain of about 3dB to make the curve hit (0dB,0dB). Similarly for other values.

I haven't tried to figure out what the actual connection between the graph and the parameters is, or whether it is the slope or the offset that is wrong, but it would be easy to find out.

Note that I'm using Ardour 3.0 alpha 4, I can re-test with Ardour 2.8 from the repositories if necessary. I've been assured that the problem lies with the plug-in, though, since it renders its own UI.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: invada-studio-plugins-lv2 1.2.0-1
ProcVersionSignature: Ubuntu 2.6.38-8.41~ppa1-lowlatency 2.6.38.2
Uname: Linux 2.6.38-8-lowlatency x86_64
NonfreeKernelModules: nvidia
Architecture: amd64
Date: Sat Apr 9 01:25:19 2011
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Alpha amd64 (20110326)
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: invada-studio-plugins-lv2
UpgradeStatus: No upgrade log present (probably fresh install)

[pablomme (pablomme)]

Attached is a screenshot of the problem as described above. On the left side is the Invada compressor, and on the right side is the Calf compressor with (approximately) the same parameters, whose graph looks exactly as it should.

[pablomme (pablomme)]

Attached is a patch that fixes the problem. Also fixed is an off-by-one-pixel issue on the left-hand side of the compressor curve.

[pablomme (pablomme)]

...and finally a screenshot of the fixed plugin.

[pablomme (pablomme)]

I could not find a way to report this problem directly to the original authors (the latest changes are from over 2 years ago, so I'm not sure if they are still maintaining it). I also notice that Ubuntu currently does not maintain any patches against this package, but Debian does. Any help in upstreaming this patch to Debian would be much appreciated.