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A MIDI keyboard is typically a piano-style electronic musical keyboard, often with other buttons, wheels and sliders, used for sending MIDI signals or commands over a USB or MIDI 5-pin cable to other musical devices or computers connected and operating on the same MIDI protocol. The basic MIDI keyboard does not produce sounds by itself, as it lacks an onboard sound engine. Instead, MIDI information on keys or buttons the performer has pressed is sent to a receiving device capable of creating sound through modeling synthesis, sample playback, or an analogue hardware instrument.
The receiving device could be: a) a computer running a digital audio workstation (DAW) or a standalone VST/AU instrument (alternatively, the computer could be used to re-route the MIDI signal to other devices); b) a sound module; or c) a digital (digital piano/stage piano) or analogue (synthesizer) hardware instrument with MIDI capability, such as a drum machine. While many digital and analogue hardware keyboards in the aforementioned categories of digital piano, stage piano, and synthesizer can be used as MIDI controllers if they have MIDI capability, they often do not offer the same level of software integration and number of MIDI-mappable controls as a dedicated MIDI keyboard. MIDI keyboards are often utilized by individuals who work with DAWs and software instruments, from hobbyists to professional musicians working in recording studios or concert stages.
Below is an example of possible signal chains for a MIDI keyboard setup, with the goal of producing audio:
MIDI Keyboard -> 5-pin MIDI connector OR USB cable (will need a "B" connector, so "USB A to B" or "USB C to B", depending on computer) -> computer running a DAW or a standalone VST/AU instrument OR a sound module OR a digital piano, stage piano, or synthesizer with MIDI capability -> audio sound device (amplifier and speakers or headphones)
When using a MIDI keyboard with a computer, class compliance must be taken into consideration. Class compliant means, essentially, "plug and play": upon being plugged in (USB or 5-pin) and powered up, MIDI keyboards that are class compliant should be recognized by any computer. MIDI keyboards and MIDI-capable hardware keyboards that are not class compliant require a keyboard-specific software driver to be installed on the computer in order for the keyboard to be recognized.
While most MIDI keyboards produced in the 2010s are bus-powered, meaning their electrical power is supplied through the same USB connection that transfers MIDI data to the computer, some keyboards have the option of, or even require, using external power to operate. If using a traditional 5-pin MIDI connector instead of USB, the MIDI keyboard will likely require external power, as 5-pin MIDI connections cannot send the current needed to power a keyboard. If using a MIDI-capable hardware keyboard as a controller, one will also likely need external power, as most 2010s hardware keyboards rely on external power to function.
The action of a keyboard is the internal mechanism by which the keys work in order to move and produce sound, or, in this case, MIDI data. Two major types of keyboard actions exist: those derived from traditional, European, key-based instruments and non-traditional, contemporary designs that allow for expanded playing possibilities.
MIDI controllers in this category have keys meant to resemble those of a grand piano, pipe organ, or synthesizer. Each of these action types is designed differently from the next, which, in turn, gives the action a particular "feel" to the player and lends it to an ideal usage.
Many examples of the above actions, other than the waterfall keys, will include a small lip that protrudes from the top of the distal end of the white keys. This is emulating a customary design detail found on acoustic piano keys. Keyboards with any type of hammer action are most likely to display this lip.
Most of these traditional key keyboards determine the attack velocity, sustain, and release of a note based on a calculation made between two sensors in each key. Some high-end keyboards now feature triple sensors, claiming improved accuracy in the tracking of key movement, which could translate into a more detailed, and perhaps more expressive, performance.
Some MIDI keyboards are capable of sending aftertouch data, which can be assigned to a variety of effects, including: vibrato, pitch bends, and volume swells. Aftertouch data is generated when a key is depressed further into the keybed after its initial depression (without releasing the key). Keyboards can be equipped with channel or polyphonic aftertouch. The former sends only one aftertouch message, regardless of which key is depressed; the latter sends individual aftertouch messages for each key. Keyboards with every key aftertouch can enable the performer to create aftertouch effects on particular notes, such as emphasizing a melody note by continuing to press it.
Not all MIDI keyboards utilize variations on the traditional piano-style action. One example of a MIDI keyboard with a non-traditional action is the Continuum Fingerboard, which is based on a "fretless" type keyboard interface, enabling portamento style note changes at will during play.
Another unconventional MIDI keyboard is the Tonal Plexus keyboard, which provides for up to 1266 different pitches possible through the TPX6 1266 Keys (Microtonal MIDI Controller).
The Roli Seaboard line of MIDI keyboards has soft, squishy keys. All the above-mentioned MIDI keyboards take the concept of aftertouch to new heights: for instance, the Roli Seaboards can sense left-to-right, front-to-back, downward pressure/depth, and the rate of change in each of these parameters. All that information can then be used to control the behavior of a digital instrument.
MIDI keyboards come in a wide range of sizes and number of keys, each with their own benefits and drawbacks. Generally speaking, some sizes are more common while others are less common, both in online stores and in bricks and mortar music stores.
Most 25-key through 49-key keyboards come equipped with synth or semi-weighted actions. Most 49-key and 61-key keyboards come equipped with semi-weighted actions, but some may be found with hammer actions. Waterfall keys can be found occasionally on some 61-key and 73-key keyboards. Most 73-key through 88-key keyboards come equipped with hammer actions; however, some may be outfitted with semi-weighted actions.
MIDI keyboards are usually full-size keys, like a grand piano. Some smaller keyboards use minikeys, which are smaller. Some tiny keyboards have flat minikeys which are even smaller.
Many MIDI keyboards include control devices (other than the keys), which may allow for manipulation of DAW controls and/or the sound generator (either software or hardware). Provided they are mapped, or mappable, to the correct function, these allow the player to access a DAW or alter the sound of an instrument patch without taking hands off the keyboard.
MIDI keyboards often have the ability to accept foot controllers, of which there are four main types: piano pedals, expression pedals, stomp boxes, and organ-styie foot pedal keyboards.