It is a midi converter used with Yamaha BC3A Breath Controller (TM). But since Yamaha has stopped producing BC3A, we make our own Mrt Audio headsets. The Breath Controller accepts the BC3A and Mrt Audio headset as input and generates continuous MIDI data corresponding to the amount of breath pressure applied to it. default setting sends CC7 midi volume signals and 1,2,3 midi channel control. The new MRTaudio controller chip has been re-programmed and has new features. First, it has much faster response. Second, it is programmable to send different MIDI controllers and after touch. Mod Wheel (CC 1),Breath Controller (CC 2),Volume (CC 7) and After touch. default setting Volume (CC 7) you can use 1 channel or 1,2 channel and last section 1,2,3 midi channel. default 1,2,3 midi channel BOOST your extra Gain for yamaha bc3 section with yamaha bc3. The Breath Controller will also accept older Yamaha BC2 units. Because you cannot find Yamaha BC3 on the market, you can use MRT Audio Headset instead. You can control three midi channels, 1,2,3 channel..., simultaneously on your keyboard. Mrtaudio Breath Controller works with any keyboard with midi in device. Using Mrt Audio Headset is easier and requires less effort compared to Yamaha BC3A. Mrt Audio is convenient to use in 3 and more hour-long playing. We have tested it with yamaha tyros 4, korg m3, korg pa800, korg pa 500 , korg pa3x ,korg kronos, roland xp30, roland xp50.