What can go wrong during the main working phase? Let us count the ways.
On slower Macs, you may experience an annoying lag between the time you press a key on your instrument and the time the sound comes out of the Mac’s speakers. That’s latency, baby, and there’s one—and only one—step you can take to solve it.
See page 617 for the details.
If GarageBand doesn’t seem to be “hearing” anything from your microphone or line input, the problem is usually that the Mac hasn’t been taught to “listen” to the right audio source. Review the setup steps, including visiting System Preferences and choosing the correct input in the GarageBand → Preferences panel.
Otherwise, double-check these points:
Make sure that you’ve clicked a blue Real Instrument track. If a green Software Instrument track is selected, GarageBand ignores your microphone or instrument.
Also make sure you haven’t muted this track, or soloed another one. (The speaker icon in your track’s header should be lit up in blue, and no other instrument’s headphones icon should be blue.) While you’re at it, make sure that the track’s volume slider isn’t set to zero.
It’s possible that GarageBand is set up to listen to the wrong channel (mono instruments). Double-click the track header and check the Input pop-up menu and Format (mono/stereo) buttons.
Are you getting any sound from GarageBand? That is, is your Mac’s speaker turned up? ...