Nice test, though may I suggest some things.MrM wrote:OK, a small test.
Test with a 1kHz sine wave too, because right now you test only the lowend and most audio effects are aimed to work on the whole frequency content and not just the lowend.
Well, anyway this will tell you that e.g. #4 has still reasonable distortion at 1kHz. Another thing would be sine sweeps to see how they act on the whole spectrum, e.g. here the Cockos ReaComp (default settings, with RMS size set to 0 and threshold so it yields a 6dB GR, but shouldn't matter since it is constant signal level anyway and thus constant GR etc..):
Here you can see the distortion reaches way up to the 20k range, while the Kjaerhus Classic Compressor has distortion/artifacts only in the low end.
So you need to consider what you define as transparent least colored, because as far as I can tell does you're test only ensure least coloration in the lowend, though if an effect is clean in the lowend it should be clean all over the spectrum anyway.
P.S. Before anyone asks the sinesweep picture stuff is explained here: http://www.cockos.com/forum/showthread.php?t=18471
(If anyone wants to add to the sine sweep collection, you're welcome, so when it is done I might trim all the pics and publish them on one site with other test data or if someone else wants to make a site like that take them or whatever.)