Your right I don't think people would work out what key exactly it is just by listening to it. Especialy because of the pitch control, you could be half way between two semitones and not in any key.
But if beatnik16 has the time and wants to learn, he/she could learn to discern between minor and major. I personally think it would be a waste of time but hey, it's up to him/her.

key matching is pretty impossible.. i know music because i played various instruments throughout growing up (from percussion to strings and brass), although this is not necessary to be able to notice key differences unless you are tone-deaf.. anyhow, i do not believe this is necessary. mainly because of what has been said, by adjusting the pitch, u are changing the speed, well pitch actually, and thus, the notes will change too, so unless you are mixing two songs that were made in the same or compatible keys and are the same bpm, u will not be able to match the keys unless u decide to not beatmatch. unless, u have a mixer that can adjust tone w/o speeding up the record, if i'm not mistaken, the djm600 can do this but i don't remember because i never played with that particular effect.. so basically, if u are mixing two songs that really conflict harmonically, try fading in during the beats and cut the first track out before any musical notes start playing from the second tune.

the vestax pdx2000 has this feature. it has a second slider that changes the tempo without affecting the pitch. which means that keys are not affected either...

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yeah but those features make the record sound like a train wrek. And you've only got one record one. Imaging having both at the same time with key control. lol.

Hmm you guys have some points, but theory differs from practical use quite often.
Take two tunes that have the same key at nominal speed (so when those tunes are at their 0%). But one tune is slower than the other.
Theory says that when pitching up/down tunes, a difference of 5.9% will mean a difference of one semitone (for the guys that know nothing of music, picture a piano, hit one key, the key next to it is a semitone).
Theoretically when you calculate, this means that at (roughly) 3%, the difference will be a quarter tone. Two tunes at a quarter tone will sound pretty crappy, in theory...
But from experience I can tell it will still sound good. Up to say 4.5-5% it will still be good enough to call it an harmonic mix.
Once you go over that, you're better off to take another record (either same key at roughly the same speed, or a semitone difference if the speed difference is high).

I agree, harmonic mixing isn't required to make good mixes. Harmonic mixing is an extra. I just found that mixes needed something more, and harmonic mixing has that little extra. When you know the keys, it's much easier to make perfect blending mixes whereever you want (no clashing basslines, and don't tell me use the EQ, you'll still perceive it as wrong, and no boring intro-outro mixing). But it gets even funnier if you try mixing more than two records. Mixing in chords. It's very very difficult with melodical trance, because so much is going on. But knowing your keys makes it a whole lot easier, and when you're able to pull of such mixes, believe me, you'll be happy you did.

You'll notice, though, that if you use a setup that adjusts speed without affecting pitch that it causes strange clipping effects on synth pads. It's not super noticeable in all cases, but on some songs it sounds wierd.

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