All things considered, the AT897 and NTG2 are very similar. If you recorded exactly the same source at the same time I think that most people would not hear the difference.
The NTG3 does sound better, even to about half of the “average listeners” out there. The other big difference is that, unlike the AT897 and NTG2 which both can be powered by a battery, the NTG3 can only be powered by external phantom power. So if you are using a budget recorder like the H4n or DR-100 you will go through batteries like crazy; you’ll need fresh batteries about every 90 to 120 minutes. So you will either have to invest in many sleeves of batteries, battery packs, a separate phantom power supply (one more potential problem on the set) or get a new digital audio recorder.
IMHO you would not really hear an appreciable difference between the AT897 or NTG2 and the NTG3 if you are not using at least a prosumer recorder like the HD-P2, FR2 or PMD-661 with their better quality preamps and AD/DA convertors.
All of the technical cow dung aside, quality production sound lies heavily on the skills of the boom-op. If you have a good boom-op you will get solid production sound with even a low budget mic like the AT897 or NTG2; if you’re handing the boom to an inexperienced PA or mounting it on the camera it won’t matter how much you spend on the mic.
Peace,
Bob
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Filmmaking is the art of the invisible;
If anyone notices your work you haven’t done your job right.