this is an old technique, i havent tried it myself, im pretty sure it'll work.
this is from
the-breaks, posted by leroy:
"i'm sure that happened to you before: you found a very nice break, but there are vocals or something else on it and you can't use it. now if you are lucky, the drums are mixed louder on one (left or right) channel, which is often the case in the early seventies and the voice or whatever is on both channels. what you do now is to split the sample into left and right and make two mono channels out of it. the pan must be in the middle and volume settings must be the same on both channels. now take the channel with the less drums and invert the phase of the channel (you can do this with almost every audio software). if you play now both channels, the voice disappears. all is left, is the hall of it (because it "was" stereo). ATTENTION: the more drums you have on the inverted channel, the more it will take bad effect to the result. if there's any latency on one channel the effect will not work!
i prepared a little example with a famous new birth break:
snippet 1: left channel of the sample, panned in the middle
snippet 2: right channel of the sample, panned in the middle, phase inverted
snippet 3: both channels played at same time
http://rapidshare.de/files/2224108/GGANex.mp3.html
try it yourself...
"