The KAT Percussion MalletKAT GS Express 3-Octave Keyboard Percussion Controller has a fresh audio board design with an optimized line level output. There are two TRS (balanced) 1/4" stereo audio outputs on the back of the unit, and the left channel can also act as a summed-mono channel. The front panel features a 1/4" phone jack with a dedicated rotating knob for headphone volume adjustment. There is also a dedicated reverb knob on the front panel. The MalletKAT GS also has 1/4" stereo inputs that will merge its audio with the MalletKAT, allowing you to practice with other players or play with CD's and hear it on your headphones or remote speakers. The huge sound library features chromatic percussion, Latin percussion, world percussion and more, including the typical sounds you are used to getting such as pianos, keyboards, organs, basses, guitars, ethnic stringed instruments, brass and woodwinds, strings, accordions, choir effects, and synthesizer pads and effects. A complete GM (General MIDI) sound library that can be accessed by any MIDI instrument via the malletKAT's MIDI IN connection. The sound module can be updated with a simple flash stick that plugs into the USB input on the back of the malletKAT GS.