Use the Transform Pad
GarageBand includes a set of patches that use a powerful new synthesizer engine. When one of these patches is selected, the Transform Pad appears in the Smart Controls pane. You can adjust the sound of the patch by dragging the rectangular framing box around the Transform Pad.
Each of the eight sections (called snapshots) of the Transform Pad represents a complete group of settings controlling the sound of the patch. When the framing box is over one snapshot, you hear the sound of that snapshot. When the framing box partially covers multiple snapshots, the sound of those snapshots is transformed to create a new sound. The amount which each covered snapshot contributes to the sound is determined by how much of the framing box covers the snapshot.
Control the sound of a patch using the Transform Pad
To play using a single snapshot: drag the framing box over the snapshot.
To transform the sound between multiple snapshots: drag the framing box so that it partially covers the snapshots.
Patches using the Transform Pad include Deep Synth Bass, Classic Techno Lead, and Celestial Voices.