Just as you can change a song's pitch, you can also adjust its tempo (or speed). By default, all new GarageBand tunes are configured to play at a speed of 120 beats per minute (BPM). You can adjust that tempo for the entire tune by entering a different tempo when you first create the project or by clicking and dragging up or down on the tempo in GarageBand's LCD.
But if you want the tempo to change over time you can do that as well by choosing Track > Show Tempo Track. This track will appear near the top of the GarageBand window and will have an adjustment line of its own. Double-click where you want the tempo to change to create an adjustment point. Then drag that point up or down to increase or decrease the song's tempo respectively. (Alternatively, hold down the Command key and click where you want the point to appear.)
Mixing your music
GarageBand doesn't have a separate track mixer as does Logic Pro X, but that doesn't mean you can't automate your GarageBand tracks over time. Again, say what!?
What I mean is that with GarageBand's automation controls you can configure your piano track to be quiet for the verse, increase in volume for the chorus, and then drop back down to a pleasant pianissimo for the second verse.
To do that choose Mix > Show Automation (or press the Mac's A key). Each track will fatten up a bit and display a pop-up menu that's labeled, by default, Volume as well as an automation button. Click that button and a yellow line appears within the track's timeline.
You can now click on that line to add adjustment points. Drag those points up or down to change the parameters of the item selected in the track's pop-up menu (again, which is volume by default). When you play back the track it will follow the automation you've configured.
Click on one of these pop-up menus and you'll discover that you can change a variety of things about the sound. You can change all tracks' volume and pan (where the sound sits in the stereo field) as well as individual smart control parameters specific to the track type. For instance, if I've selected a Steinway Grand Piano track I can automate the instrument's low and high frequencies, compression, delay, and reverb settings.
About the Master track
Some of you may take this as "Aw geez, man, does that mean I have to draw in an automation curve for every single track just so that all the instruments in my tune fade out together?" The answer is No.
Sign up for CIO Asia eNewsletters.