Are there any free music editors that can open mp3 files and seperate the singing from the background music/beat?
You can't mp3 slice 100%
There are ways to change the frequency of mp3's around, but you can never completely remove vocals or a beat or whatever (because things are always on different frequency's.. unless the performer is very very very very very horrible).
Ya mp3's are divided into two signals, one for the right, and one for the left.
Not different signals for each instrument.
What you would have to do is simply get an audio player, input a signal that is the exact opposite of only the singers voice, and play it at the same time. The tough part is finding which frequencies the singers are, and which are instrumentals.
But there are some programs that does a decent job of it..
The one I used is called "Karaoke Anything!"
Also, the artists skill and talent of their voice (their ability to sing in different frequencies) is a huge factor in splicing music..