It all depends on what the noise/background and the sturcture of the recording is... If the noise is something constant like hiss you're best to use a tool like the noise reduction filter in cooledit/adobe audition. This lets you select a profile of the noise you want to remove [basically you grab a selection of the noise on its own near to the vocal] and then remove it from the whole recording.
Hope this is making sense so far...
If the vocal is recorded in the centre and nosie/background is say instrumental and panned you can have a stab at removing the vocal using some slightly more cunning jiggery pokery have a look here :
http://www.sonicspot.com/guide/vocalremoval.html
http://www.ethanwiner.com/novocals.html
... this isnt perfect but sometimes does the trick !
Its worth noting that noise reduction is never going to be perfect and you're probs gonna have to accept that theres always gonna be some there...
As NDY says u can also try eq'ing but this generally relies on being able to isolate the frequencies that the vocal lies in and noise doesnt. You can try playng around with a parametric eq to surgically remove the noise around the vocal or remove the vocal itself by making a notch at around 1khz [or wherver u think the vocal fundamentally lies] then subtract this filtered wave from the original.
Another technique is to use expansion [the opposite of compression] to increase dynamic range and reduce the noise floor tho this is getting fiddlier by this point ! If you're interested in knowing more I can highly recommend "Mastering Audio - The Art and the Science" by Bob Katz ... Chap12 has some good stuff on noise reduction - its focused ad cd mastering and stuff but the theory and psychoaccoustic bizness is equally relevant.
After you've got rid of noise u might find the vocal is left sounding phasey - u can try to phatten the vocal up using reverb/delay type effects - or alterntaively remove less noise! From a psychoaccousitc point of view leaving some noise in is preferable as the listener will tend to focus on the music/vocal itself [the ear naturally tries to filter noise - especially picking out vocals which our ears are tunes to picking out] - also experiment with placing your vocal over different synths/sounds to mask the noise or shift the listeners focus.
phew! Hope this has made some sense / is useful !
peace + good luck!,
marc
. It won't get rid of incidental noise though (eg a car door) so you'll have to try to eq that out which could be pretty difficult since a car door closing would have a wide frequency range (ie: some frequencies would be in the same range as the voice freqs). You'd do best to place a kick drum over the door shutting!!!
