Mixing in Key

[loopdon]

That's the thing jeroen, it's all about relative key.

They have to be in-key at the same BPM.

The easiest way to tell this is to beatmatch them and see if it clangs or not.

There really is no point using analytical tools, your ears are your best bet.

Very rarely will a track be in perfect C, or perfect G minor or whatever.

It'll be microtones out.

i think quite a lot of more melodic stuff, esp. made by people with classical training is pretty much spot on when it comes to this. not that i have had that training, mind you.