Along with being a multi-track audio production system (aka DAW – digital audio workstation) SoundtrackPro is a pitch and tempo correcting Loop Sequencer. This means that loop samples with Pitch and Tempo Metadata can be arranged to produce musical parts and sondtacks that are automatically corrected to be in key and in time

Despite the fact that Apple insist on calling these loops ‘Apple Loops’ there is nothing special or Apple specific about the loops that Apple uses. They are more commonly referred to as ‘Acidized Loops’ named after the first major software to use the technology – Acid Pro made by Sony.

This means that any wav or aiff audio file with pitch and tempo metadata can be used in SoundtrackPro just a it can in any multitrack loop sequencer (Acid, Audition, Cubase, Logic, FL Studio, Reaper, Digital Performer). Doing a Google search for ‘Acidized Loops’ will reveal a wide array of free and low-cost loop sample libraries. 

Here’s a list of some of the good Free Acidized loop collections availible online which will greatly open up the musical and sound design possibilties for your films.

http://www.platinumloops.com/free_loops.shtml

http://www.looperman.com/loops.php

http://www.acidplanet.com/tools/8packs/

http://www.playinmusic.com/Free_Loops.htm

http://www.loopasonic.com/

http://free-loops.com/

http://www.freeacidloops.net/downloads.html

And here’s some that go by the name of Apple Loops (but can be used by any loop sequencer)

http://www.macloops.com/

http://www.macidol.com/downloads.php