Using MIDI ModulationModulation in GarageBand is a way to manipulate the vibrato in a recording. This vibrato sound is the way a note is held while the pitch jumps up and down quickly or slowly. It's common in vocal tracks, but can be applied to other instruments as well.
Modulation in Track Editor
To edit your modulation, first select the track you want to work with. It helps to click theSolo button so that you only hear this track. Then open up the track editor window by clicking on the Track Editor button.
On the left side of the track editor window, find the View bar. Click the bar and scroll to the Modulation View option.
Points of Modulation
Click the Apple key to get the pen tool. Using the pen tool, click a point on the graph where you want to begin your audio modulation. A small dot will appear where you clicked, marking the start of the modulation.
Use the pen tool to select the high point of your modulation. When you click the second point, a line will automatically connect the two points.
Use the pen again to select the end of the modulation. A second line will automatically connect the second and third dots.
You can change the points of modulation by clicking and dragging the dots on the graph. The modulation peak will create a shake in the pitch of your audio.
If your track contains more than one loop, GarageBand will automatically repeat the modulation in each loop.