pitch bend wheels, sustain pedals, pitch sliders, buttons, knobs, faders, switches, ribbon controllers, etc., alter an instrument's state of operation, and thus can be used to modify sounds or other parameters of music performance in real time via MIDI connections. Some controllers, such as pitch bend, are special. Whereas the data range of most continuous controllers (such as volume, for example) consists of 128 steps ranging in value from 0 to 127, pitch bend data may be encoded with over 16,000 data steps. This produces the illusion of a continuously sliding pitch, as in a violin's portamento, rather than a series of zippered steps such as a guitarist sliding their finger up the frets of their guitar's neck. The original MIDI specification included 128 virtual controller numbers for real-time modifications to live instruments or their audio. MIDI Show Control (MSC) and MIDI Machine Control (MMC) are two separate extensions of the original MIDI spec, expanding MIDI protocol to accept far more than its original intentions. Common products The most common MIDI controllers encountered are various sizes of MIDI keyboards. A modern controller lacks internal sound generation, instead acting as a primary or secondary input for a synthesizer, digital sampler or a computer running a VST instrument or other software sound generator. Many have several user-definable knobs and slide controls that can control aspects of a synthesizer's sound in real time. Such controllers are much cheaper than a full synthesizer and are increasingly equipped with Universal Serial Bus, which allows connection to a computer without a MIDI interface. Despite not using MIDI directly, software applications recognize such controllers as a MIDI device. In most cases, a USB-equipped controller can draw necessary power from USB connection, and does not require an AC adapter when connected to a computer. Keyboards range in size from 88 weighted-action keys to portable 25-key models. References Computer peripherals Electronic musical instruments MIDI