Setting the BPM, or beats per minute, when creating a GarageBand session is one of the first things you should do. The BPM of a GarageBand session will determine the tempo of the song. This in turn affects the speed in which it is played. This tempo will be reflected by the speed in which the metronome operates, the layout of the editing grid, and the speed in which the virtual instruments are played in GarageBand.
Open GarageBand.
Click the “New Music Project” button to create a new GarageBand session.
Type a name for the GarageBand session into the “Save As” box.
Type the desired BPM into the box next to “BPM.” This will determine the BPM of the GarageBand session. The default BPM of a new session will start out at 120 BPM.
Click the “Create” button. A GarageBand session will be created with the BPM you specified.
Modify the BPM of a GarageBand session after you have created it by clicking the “Track Info” button located in the bottom right corner of GarageBand. This button is illustrated by the letter “i” with a circle around it. Drag the “Tempo” slider in the menu that appears to manipulate the BPM of the song.