After you've set up your electric guitar track, plugged in your guitar and received a signal on the track, you can use one of the amplifier combinations that GarageBand provides. There are various combinations to choose from. If none have the perfect sound for your music project, you can manually modify the default settings.
Step 1: Access the Settings
Step 1: Access the SettingsDouble click on the amplifier icon in the right sidebar. The input box below it will switch to the amplifier settings.
Step 2: Make Adjustments
The ten knobs control different aspects of the amplifier's sound effects. They are Gain, Bass, Mids, Treble, Presence, Master, Output, Reverb, Tremolo Rate and TremoloDepth.
Raising the Gain will add more grittiness to your sound, while the Bass, Mids and Treble are EQ settings that control the frequency levels. Changing the Presence will create a different type of tone and the Master knob controls the overall volume.
It's best to experiment with a few of the settings to find the sound you want for your project.