Keyboards Keyboards are by far the most common type of MIDI controller. These are available in sizes that range from 25-key, 2-octave models, to full-sized 88-key instruments. Some are keyboard-only controllers, though many include other real-time controllers such as sliders, knobs, and wheels. Commonly, there are also connections for sustain and expression pedals. Most keyboard controllers offer the ability to split the playing area into zones, which can be of any desired size and can overlap with each other. Each zone can be assigned to a different MIDI channel and can be set to play any desired range of notes. This allows a single playing surface to control a number of different devices. MIDI capabilities can also be built into traditional keyboard instruments, such as grand pianos and Rhodes pianos. Pedal keyboards can operate the pedal tones of a MIDI organ, or can drive a bass synthesizer. Wind controllers Wind controllers allow MIDI parts to be played with the same kind of expression and articulation that is available to players of wind and brass instruments. They allow breath and pitch glide control that provide a more versatile kind of phrasing, particularly when playing sampled or physically modeled wind instrument parts. A typical wind controller has a sensor that converts breath pressure to volume information and may allow pitch control through a lip pressure sensor and a pitch-bend wheel. Some models include a configurable key layout that can emulate different instruments' fingering systems. Examples of such controllers include Akai's Electronic Wind Instrument (EWI) and Electronic Valve Instrument (EVI). The EWI uses a system of keypads and rollers modeled after a traditional woodwind instrument, while the EVI is based on an acoustic brass instrument, and has three switches that emulate a trumpet's valves. Simpler breath controllers are also available. Unlike wind controllers, they do not trigger notes and are intended for use in conjunction with a keyboard or synthesizer. Drum and percussion controllers Keyboards can be used to trigger drum sounds, but are impractical for playing repeated patterns such as rolls, due to the length of key travel. After keyboards, drum pads are the next most significant MIDI performance controllers. Drum controllers may be built into drum machines, may be standalone control surfaces, or may emulate the look and feel of acoustic percussion instruments. MIDI triggers can also be installed into acoustic drum and percussion instruments. The pads built into drum machines