Yeah, this is the issue alright. Congested vs. Clear. Fizzy vs. Glassy. Boxy vs. Depth.
When the issue surfaces the congestion I hear seems as if it is something in the upper mids or lower top end. Something about the gain structure or crunch end, hard to describe. But when it surfaces it's almost always the same theme. There's also something in the lower/lower-mid area in a depth sense. To me the end result is KPA sounds more boxy and fizzy in comparison whereas the amp sounds glassy and 3d dimensional. It is almost as if the amp has a slight Sonic Maximzer or Aural Exciter type of thing compared to the KPA. Has anybody tried running KPA tracks through a Sonic Maxizier to see if it might get closer to the original amp? Anyway, yeah, this is basically the issue alright. It ends up giving the perception of congestion. And the overall effect is just enough that it causes it to not sound as convincing as a real amp IMO for direct recording, especially when placed next to real amp tracks. That upper mid/top-end crunch as sweetness is a HUGE part of what separates a tube amp from an imitation.
Still, we don't know how widespread/common this is, or if this is a profiling technique issue or rather a KPA issue (hardware or software) or just WHAT is really going on. But we do know this problem is real, it occurs more than just rarely, and it is definitely not trivial for recording purposes in most of instances where it surfaces.
The ultimate bottom line question: Is this fixable / correctable or not ??
Sonic