GarageBand for Mac: Set the key and scale
Each project has a key, which defines the central note to which the other notes relate. By default, new projects are in the key of C major. You can choose a new key when you create a project, and change it later while you’re working. When you add Apple Loops to your project, they match the project key.
Set the project key and scale in the LCD
In the LCD, click the key, then choose a key from the pop-up menu.
You can also transpose parts of a project using the Transposition track. For information about the Transposition track, see Transposition track overview.
When you change the project’s scale type from major to minor or vice versa, in some cases the key may change enharmonically (for example, from Db major to C# minor). These changes follow common practice for printed music, and affect only the key as shown in the menu, not the pitch of regions in your project.