Garage band lets you shorten Real Instrument loops by moving the start and/or end point. This works for the end point with Software Instruments but not the start point. It seems immovable. I found a simple way to beat this using another feature of GB for cutting loops. - Place the loop (whose start position you want to change) on the timeline (let's call it LoopA). -Listen to and identify where you want to start LoopA from. - Get any other SI loop (let's call it LoopB) drag and drop LoopB onto the LoopA's track on the timeline away from LoopA. (You need this step so GB will show you LoopB's endpoint in the next step) - Now drag and drop LoopB onto LoopA so that the endpoint of LoopB matches the new start point you want for LoopA. - Discard LoopB and any other remnants of LoopA.