Re: Recording & Live Performance - Glyn Johns Method
X/Y is valid with any condenser microphones for overheads (or ribbons, but I wouldn't use those live!). A/B is equally valid - it's just a personal preference. Try both and see what happens! With A/B, you just have to make sure that you're placing the mics equidistant from the snare drum or you may end up with phase issues, that's what X/Y was partially designed to eliminate - but you lose the stereo width with X/Y. It's a tradeoff. X/Y is a form of overhead micing, just as Glyn Johns is.
NT5s will work with any method you want to use that require cardioid mics, ORTF,X/Y, A/B, Glyn Johns, etc. All of them are valid for different applications. I only recommended X/Y specifically because of my experience of it and the relative ease of setting it up on a stage. The most popular method for overhead micing is A/B (spaced) for a variety of reasons - both have pro and cons. Try both! See what works! Live I would stick to either X/Y or A/B because they're quick and easy to set up and won't have issues with monitors but again, it's really up to you! In a studio, if you have time you do what you like. Glyn Johns can produce excellent results.
I suggested the NT5s because they're relatively inexpensive SDC mics that can be used in a variety of contexts. They're rugged and reliable, won't topple stands with their weight and can be bought just about anywhere. The AKG Perception mics were the ones that you linked up in the original post and those are the ones that I have extensive experience with. I would prefer to use SDCs live because of the weight issue, that's the only major factor as far as I'm concerned.
Both of those models will produce acceptable results in a studio and good results live. I wouldn't want to get anything more expensive for dual-use because live microphones can take a punishing. Most of the skill in recording is effective placement of the mics and working well within the room you've got. It doesn't matter if you have inexpensive or expensive mics if your placement is off - it'll still sound unacceptable. If you consistently get good results with the 'cheaper' mics, then it's reasonable to upgrade.
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