Comment 1 for bug 837200

Which version of Mixxx are you using, and are you using key lock or vinyl-style pitch control? Versions before 1.10-beta have an older version of the vinyl pitch-scaling code which had a habit of eating samples, causing sync issues. If you're using 1.9, try the 1.10 beta and see if there is an improvement: http://builds.mixxx.org/builds/release-1.10.x/