Originally Posted by Faint Brouhaha
He should put the NI plug into VST Plugin Analyser and look at the phase distortion and the THD levels.
This graphic above linked from recording.de shows the VPA harmonic distortion graph for the UAD Massive. It exhibits just two significant harmonics, 2 and 3, with the second order harmonic dominant, consistent with expected tube circuit behaviour. The NI Passive when tested by me exhibits multiple cascading harmonics, arguably more typical of a coloured compressor's behaviour than a mastering EQ's, and has the third (and subsequent odd) order harmonics dominant, consistent with unexpected transistor circuit behaviour.
Secondly, the UAD emulates all the characteristics of the original hardware, including the analogue input stage's requirement for professional levels, to the point where levelling down before, and levelling back up after, is considered standard operating practice when running hot. Driving the UAD (or indeed the real thing) much above EBU levels is certain to drive the Massive into inharmonic distortion. So the earlier 'run it hot' test seems a bit misleading to me.
NI Passive may or may not be a good equalizer, it certainly doesn't seem to me to have a lot in common with the UAD Massive emulation.
I don't remember exactly the harmonic content of the massive passive (I've ran some sine sweeps, impulses and static tones through it) but when driven moderately hard it has TONS of harmonics and interesting things going on. Indeed if the UAD model only shows a few it must be completely wrong.
The massive passive is not what I would call a transparent EQ either. It has a certain "manley" mojo which is awesome on a lot of material. There's a good reason why the EQ is used so often in mastering but it is most definitely not due to it's transparency. There are other much more transparent options available.