GarageBand Sound Effects
The Sound Effects are sample based. These cover a number of nature sounds, laughter and applause, and so on.
Volume slider: Sets the overall volume level of the instrument.
Filter Cutoff slider: Allows more (high) or less (low) of the sound through, making it brighter or damping it.
Release slider: Determines the time it takes for notes to fade out after you let go of the keys on your keyboard.