Why can't I hear my instrument in GarageBand?
First, check to make sure you are connected properly. Your headphones or speaker cable should be plugged into the front headphone jack on StudioConnect. Second, make sure the gain level on StudioConnect is high enough to return sound and that the volume on your instrument is high enough to send sound. You can use the dial on the right side of StudioConnect to adjust the gain. Finally, make sure you tap the instrument cable icon in GarageBand (usually middle left side of the instrument you have chosen) and turn the Monitor setting ON.