Software Instrument Loops vs. Audio Loops
There are two types of loops available in GB: audio loops, indicted by the blue audio wave form icon; and software instrument loops (MIDI loops generating sound through a software instrument), indicated by the green music note icon.
The software instrument loops are much more processor intensive than audio loops, because the computer is playing multiple samples, notes and live effects in real time.
Here is a workaround for using those cool software instrument loops. You can let Garageband convert those software instrument loops to audio loops when you drag to the timeline, thus using much less processing power.
1. Use the loop browser to find the software instrument loop you want to use.
2. Create a new track on the timeline. Choose a Real Instrument - Vocals - No Effect - and make sure Stereo is selected.
3. Drag the software instrument loop to your new track and watch as Garageband converts the MIDI info and softare instrument to an audio file.
You can compare the audio file method to the software instrument method by again dragging the software instrument loop to the timeline and letting Garageband create a new software instrument track. Alternate muting the two and watch the playhead.