If they both ran into a UA-5, why stretch and not just shift? They should be all on the same clock which is the big problem related to stretching/shrinking. If it's just delay, then shift it.
^ what he said. Unless two different recorders were used to capture, with two different internal clocks, you should NEVER stretch...only shift.
There will always be some
delay between SBD and AUD tracks, even if the mics were on stage, due to the differences in distance between the AUD mics and the sound sources and the inputs/mics used by the FOH engineer and sound sources. The direct inputs will be at the speed of electricity and stage mics used by the FOH will be within an inch or two of the sound sources for the SBD feed, while even stage lip mics will be a minimum of a few feet from any sound source and room mics much further back. This
delay is corrected by shifting the SBD track(s) later in time until they match up with the AUD track(s).
Drift ALWAYS occurs (though it may be minimal in rare cases and not need correction) when you use two different digital recorders with different internal clocks that are not synced together. The different clocks have a slightly different a level of accuracy in keeping time, and that difference results in increasing
delay at a constant rate over the course of a recorded track. Stretching one of the sources is the best way to accurately correct the
delay that results from the
drift between the clocks. The chop and re-align approach many use is sloppy and inaccurate, and does not actually fix the
delay at the end of each chopped segment. This results in the end of tracks being off, and parts being potentially out of phase with comb filtering effects as the drift of the clocks brings the two sources out of sync during the course of each segment.