Does your voice thin out as you go into powerful/screamy or loud & clean type vocals? I ask this because, quite frankly, most people's voices do. And so it's possible that the mic/mic preamp combo may be accurately picking up what you are doing. After all, it's not distorting, right? Are you singing directly into the mic when you do these kinds of vocals, or is it slightly off-axis? What kind of room are you singing these kinds of vocals in?
Personally, when I do these screamo-type vocals (I used to do a lot of hardcore), I'd listen to the voice. If there's a lot of "raspy" top-end stuff going on that might sound shrill, I'd choose a slightly darker combination of mic / mic preamp at first, although I'd probably set up several combinations and test each one, just to be sure.
I don't believe one has to necessarily a tube mic preamp. For example, the Neve Portico does not have a tube, but it does have a lot of girth. I'd choose a microphone that didn't have a lot of "fizz" on the top end (so possibly the NTK might not be the greatest choice for this kind of thing).
I'd also make sure that I put a dynamic mic out there, such as one of the Heils, just to see how that did. Sometimes, there's nothing like a large diaphragm dynamic for really loud screamo or hardcore vocals, and I frequently end up going for one of these. Has some "natural compression" (bear with me, you know what I mean!) when compared to condensers, and sometimes, that's just what's needed.
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I don't have a huge mic preamp or microphone locker, so these following suggestions are what I would do with what I have, not necessarily saying that it'd be "the best" (not that there's any such thing anyway). When I encounter screamo/super loud/hardcore vocals, I usually set up the Neve Portico and Peavey VMP-2 tube mic preamps and the Lawson L251 (just because everything seems to sound damn good through this) and a Heil P40 or whatever the hell it's called (large diaphragm dynamic) and see if those worked, switching mic preamps to see what would happen. Usually one of those combinations is golden. If not, I've got a 421 and a modified AT4060, both of which would be appropriate choices for the task at hand as well.
Great post... and very informative. I appreciate the input!
And yes, the voice does thin out as it gets higher... and as I push it. It's definitely not distorting. At high volumes, I tend to sing off axis where the NTK is notorious for the 's' and 'p' sounds. I have a nice pop filter as well.
I was just wondering if there are any pres/mics combos specific to the loud volume vox. I'll definitely look into your suggestions, and I greatly appreciated the post!