Keeping 2 audio files in perfect sync

[Andrew Robinson]

A bit of an odd question, but someone might have an idea about how to do
this...

I've got 2 high res (24bit 96Khz) files. They are the vocal and
instrumental versions of a classic 80s pop song. I'm fiddling about with my
own remix, and I'd love to do the 'subtract one for the other to get an
acapella' trick. This usually works really well on digital files,
especially when the mixes are otherwise identical as these are. The problem
with these ones is that they are not quite digitally identical, but have
each been through an analogue tape stage, which has introduced a *tiny* bit
of speed instability, inaudible, but enough to make digital subtraction a
nightmare as the files drift away from each other by up to about 50 samples
per bar. I can match up .2 to .5 second bits perfectly and get a tiny
snippet of crystal clear acapella, but what I really need is a way of
either automatically phase-locking the files, making almost imperceptible
pitch bends, or automating very very short delay changes.

Logic Pro is frustratingly hopeless at this, it provides a sample accurate
delay plug in, with sample accurate automation on the delay times... but
the automation can only be set in massive clunky increments, and I can't
find any way at all to adjust it precisely.

Any ideas, folks?

- Andy_R
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