My friend and I both have the Tascam DP-24SD Portastudio. We live in different states and exchange files using Dropbox. He gave me a guitar and vocal track at 115 bpm which I downloaded from Dropbox, loaded onto my Portastudio, recorded my drum track, exported my drum track from my Portastudio, and uploaded it to Dropbox. My friend downloaded my drum track from Dropbox and then loaded it onto his Portastudio. The drum track is now at 125 bpm on his Portastudio instead of 115. How is this possible? What could have happened along the way to change the bpm of my drum track? Any insight would be greatly appreciated. We've been working together for years on songs using this exchange method and have never had this issue. It just doesn't seem possible. Thanks.