You can also edit "real instrument" tracks (tracks where you record an instrument or microphone connected to your Mac). You can, for example, split, trim, and rearrange them. (Another feature called Flex Time allows you to change a real instrument track's "feel" but it's obscure enough that I'm not going to get into it.)
Making music is really no mystery. All you have to do is play the right notes, play them at the right time, and play them the right way. There's a feature called quantization that can help with the second task.
The idea is pretty simple. When you quantize software instrument notes you force them to align with rhythmic values on a grid. Say what!? Try this example on for size.
You're playing a bass part and you want to play the note E on the four counts of a measure — so, play on exactly beats 1, 2, 3, and 4. But your timing wasn't perfect and you hit beat 1 but slop over a bit with the remaining beats. You can fix this by quantizing the measure.
Just select the track, expose the Edit pane, and select those four notes. From the Time Quantize pop-up menu choose 1/4 Note. Like magic (or a bit like musical chairs) the selected notes will move to the nearest quarter note. When you play back the measure, the notes will fall exactly on beats 1, 2, 3, and 4.
Choosing 1/4 Note is pretty strict. If you do that with all your music you'll find that it's very measured and static (and some of the fast notes you played between the beats will simply disappear). Fortunately you can choose finer values — the range is 1/1 Note to 1/64 Note. (You can also choose Triplet, Tuplet, and Swing values but, again, I'm venturing into music nerd territory.)
Transpose your tune
You've recorded all the instruments for your master work, you place your microphone in front of you with the idea of delivering the perfect vocal, you press Play and... holy smokes, that's high! No worries (mostly).
Software instrument tracks can be moved up or down in pitch (called transposing) with ease. Just choose Track > Show Transposition Track and a new track will appear at the top of the GarageBand window. Click on the orange line that appears in this track where you'd like to change the tracks' pitch and drag the line up or down. The software instrument tracks will adjust accordingly.
Real instrument tracks, however, are more challenging. You can change one of these track's pitch by selecting it, exposing the edit pane, and dragging the Transpose slider up or down. Note, however, that these tracks can sound funky (in a bad way) if you transpose them too much. Drag the slider too far to the right and the sound can get chipmunky. Drag it to the left and it sounds like Darth Vadar is playing the track. You can somewhat safely move up or down by three or four increments, but beyond that the sound will venture into the territory of the unnatural. This is not something to chide Apple over. It's just what happens when you make extreme pitch adjustments.
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