How else would they know that the song they're bringing in is at the correct bpm?
How else would they know that the track they're bringing isn't too loud / too soft?
Especially with vinyl & cd's - you need to cue the second track in your headphones to match the bpm with the track in your monitors. If you didn't do that, the crowd would hear off-beats and clashes every time you wanted to bring another track in.
So they can listen and cue the next track without it playing "live" over the track that playing over the pa/club system and sounding awful. Also in terms of beat matching djing it allows the DJ to get the two records in time to create a mix between the tracks without it sounding a train wreck of a mix
Same reason why musicians have in-ear/monitors/drum-fills on stage and why their manager/booking agent have mobile phones and why their nightline driver have glasses and maps and/or GPS and why the blind person (that the driver just almost ran over) have a stick when walking. Same reason why the groupies use mirrors.
When you "dj" with Ableton, you don't need headphones because everything is already beatmatched, and you can even go so far as editing volume/pitch modulations into the tracks ahead of time. But of course, this isn't real DJ'ing, and I was kidding, hoping to push a few buttons maybe. I use and love Ableton, but will concede it isn't in the same league as turntables or even CDJ's
Any respectful DJ will use the headphones just to make sure the tracks are beat matched correctly and that both tunes are at the same noise levels (meaning setting up gain and such to make sure both tracks sound equally loud and clear - quality of tracks varies, especially with mp3's)
Ableton can do quite a bit, don't get me wrong, but you shouldn't take it as gospel and still check what you're doing.
Using Ableton only and no headphones seems a bit cocky and foolish, IMO.
Oh and if you're writing music and you ask why do DJ's use headphones, I would go back to the drawing board and watch some stuff on the art of DJing and turntablism.
Last edited by KaliTheMisfit; 13-01-2013 at 04:54 PM..
Reason: heat of the moment typos