Syncing audio tracks


Mac OS X.

I’m new to podcasting and am having trouble me with syncing the tracks. I recorded my podcast with one other who was not on location. It was conducted over the phone, with each of us recording our own tracks. Me on a zoom h4n, and the second person on his computer using audacity. We both counted to 3 and clapped to make syncing the two tracks in audacity later on easier. I synced both tracks, and the beginning sounds fine. But about 20 min into the podcast, we are out of sync again even though nothing has been moved or changed. As it goes on it gets worse. I even fixed the latency issue.
What can cause this issue, and is there any way of fixing it? Any input would be very helpful. Thank you

Two independent recording devices will never run at exactly the same speed. Better quality recording equipment is likely to run closer to the “correct” speed, but it will never be absolutely exact.

In order to bring the tracks back into synchronisation, you will need to use the “Change Speed” effect to either slow down the quicker (shorter) track, or speed up the slower (longer) track.

For your current project, finding the right amount to change the speed by will be a bit hit or miss - you will need to experiment a bit, and may need to apply an approximate correction to the entire track, then smaller corrections to parts of the tracks to keep the synchronisation close enough. This is the current “Change Speed” effect:

For future projects, do the clap thing at the start and at the end. If it is a long recording, do the clap thing every 20 minutes or so. The next version of Audacity has an enhanced Changed Speed effect that allows you to set the exact length that your require a selection to be. This will make the adjustment much easier. The new version is due out in a matter of weeks. Details of the new version can be found in the alpha manual here: