1) yeah, normal mixers don't usually have a crossfade, which you use to go between decks
2) i don't know about that. i guess it depends on what kind of mixer. sure, there are mixers with crappy preamps, and therefore, noisy. and there are also mixers with decent preamps.
3) again, depends which mixer.
i don't have a dj mixer, but i do have a Behringer Eurorack MX 1604A, that i use as my main mixer to record on my G4. and i have it hooked up the crappiest way possible: using the analog in on the mac. honestly, this setup works fine. noise? no, not much, and if there is, that's what eq is for. i like the behringer stuff, it's reasonably priced, and they are pretty rock solid. i'm not familiar with their DJ mixers, or if they even make any. but i don't think you can really go wrong with behringer.
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