Logic Instruments
Synthesizer Basics plus links to information about each of the softsynths in Logic.
The link address is: http://documentation.apple.com/en/logicstudio/instruments/index.html#chapter=A%26section=0%26tasks=true
The link address is: http://documentation.apple.com/en/logicstudio/instruments/index.html#chapter=A%26section=0%26tasks=true