There is only one file type that uses the .KT3 extension:
Battery 3 Drum Kit File
File used by Battery 3, a program that uses drum audio samples to create drum rhythms and sounds; contains descriptions and sound samples for different drum kit types, such as a Jazz Kit or Rock Kit; includes kit sound samples for snare drum, bass drum, toms, hi-hats, and cymbals.
|Native Instruments Battery 3|
Updated: November 2, 2009