Turn on input monitoring for audio tracks
You can hear, or monitor, input from an instrument or microphone in GarageBand while you play and record. When you turn on monitoring for a track, you hear the sound from the musical instrument or microphone connected to the track’s input. Monitoring lets you hear yourself play so that you can hear the part you want to record as well as the rest of the project. This is useful for setting audio levels or practicing parts before you record.
Turn on input monitoring for an audio track
Click the Monitoring button in the track header.
Click the Monitoring button again to turn off input monitoring for the track.
You should usually turn off monitoring when you’re not playing or singing. When monitoring is turned on, your computer can pick up output from your speakers or monitors, causing unwanted feedback. Using headphones rather than speakers to listen to your projects can help eliminate feedback.
If you select your computer’s built-in microphone as the audio input (in the Audio/MIDI pane of GarageBand preferences), monitoring is turned off for all Electric Guitar tracks to avoid unwanted noise.