1. Yamaha WX7, courtesy of dannychesnut.com

    A device that resembles a traditional wind instrument, and generates a set of control signals depending on different aspects of wind-instrument playing technique.  Generally, a pitch signal is generated based on the operation of thumb and finger levers that are arranged in a manner similar to an instrument such as a clarinet or a saxophone.  A pressure sensor generates a second signal corresponding to how hard the performer blows into it; this might be used to generate a gate signal or determine the sending of MIDI note on and note off signals, as well as generating an additional control signal. Depending on the device, additional signals might be sensed based on factors such as lip position on the mouthpiece.  These serves as alternatives to keyboard playing, allowing a brass or woodwind player to play a synth without having to learn keyboard.  The Lyricon was a well-known breath controller; others include the Yamaha WX7 and the Akai EVI.  
  2. A MIDI Controller message, type 2 (and optionally type 34), is generated by the device corresponding to how hard the performer blows into the mouthpiece (as measured by a pressure or flow sensor). This message is referred to as "breath controller" in the standard. The sound parameter that this controller message is supposed to control isn’t specified by the standard; most synths that accept this message use it control either volume or a filter setting.
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