I have two identical tracks, one with vocals and one without, I would like the isolate the vocals and was wondering if this is possible using the instrumental track.
I tried using the noise removal effect but its really noisy, even with the maximum amount of smoothing.
There might be a minimal difference in the tracks due to compression, but looking at the spectogram it really is minimal.
So if anyone knows please let me know 
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I tried it once or twice, you have to align both tracks at an accuracy of sample per sample, and then invert one of them.
However there is no warranty of a perfect result.
Did you try straight, simple cancellation? Select the instrumental track and Effect > Invert. That will make all the “Up” waves in one “Down” waves in the other.
Play both. You can use any of he volume tools and The Time Shift Tool (two sideways black arrows) to shift the tracks sideways and up and down until they exactly match and cancel.
If either or both of them were MP3 files, you’re stuck. MP3 gets it’s tiny, convenient files by re-arranging musical tones and leaving some out. It decides what to do by the content. So if your two files sound different (one has a vocal), their overall compression will be different.
Post back if you get one to work.
Koz