Keyboard

A musical keyboard is the set of adjacent depressible levers or keys on a musical instrument, particularly the piano. Keyboards typically contain keys for playing the twelve notes of the Western musical scale, with a combination of larger, longer keys and smaller, shorter keys that repeats at the interval of an octave. Depressing a key on the keyboard causes the instrument to produce sounds, either by mechanically striking a string or tine (piano, electric piano, clavichord); plucking a string (harpsichord); causing air to flow through a pipe (organ); or strike a bell (carillon). On electric and electronic keyboards, depressing a key connects a circuit (Hammond organ, digital piano, synthesizer). Since the most commonly encountered keyboard instrument is the piano, the keyboard layout is often referred to as the "piano keyboard".

Description:

The twelve notes of the Western musical scale are laid out with the lowest note on the left;the longer keys (for the seven "natural" notes of the C major scale: C, D, E, F, G, A, B) jut forward. Because these keys were traditionally covered in ivory they are often called the white notes or white keys. The keys for the remaining five notes which are not part of the C major scale (namely C♯/D♭, D♯/E♭, F♯/G♭, G♯/A♭, A♯/B♭) (see Sharp and Flat) are raised and set back. Because these keys receive less wear, they are often made of black colored wood and called the black notes or black keys. The pattern repeats at the interval of an octave.
The arrangement of longer keys for C major with intervening, shorter keys for the intermediate semitones dates to the 15th century. Many keyboard instruments dating from before the nineteenth century, such as harpsichords and pipe organs, have a keyboard with the colours of the keys reversed: the white notes are made of ebony and the black notes are covered with softer white bone. A few electric and electronic instruments from the 1960s and subsequent decades have also done this; Vox's electronic organs of the 1960s, Farfisa's FAST portable organs, Hohner's Clavinet L, one version of Korg's Poly-800 synthesizer and Roland's digital harpsichords.
Some 1960s electronic organs used reverse colors or gray sharps or naturals to indicate the lower part(s) of a split or 'broken' keyboard: one which is divided into two parts, each of which produces a different Registration or sound. Such keyboards allow melody and contrasting accompaniment to be played without the expense of a second manual and were a regular feature in Spanish and some English organs of the renaissance and baroque. The break was between middle C and C-sharp, or outside of Iberia between B and C. Broken keyboards reappeared in 1842 with the harmonium, the split occurring at e4/f4.
The reverse-colored keys on Hammond organs such as the B3, C3 and A100 are latch-style radio buttons for selecting pre-set sounds.

Size and historical variation:

The chromatic compass of keyboard instruments has tended to increase. Harpsichords often extended over five octaves (61+ keys) in the 18th century, while most pianos manufactured since about 1870 have 88 keys. Some modern pianos have even more notes (a Bösendorfer 225 has 92 and a Bösendorfer 290 "Imperial" has 97 keys). While modern synthesizer keyboards commonly have either 61, 76 or 88 keys, small MIDI controllers are available with 25 notes. Organs normally have 61 keys per manual, though some spinet models have 44 or 49. An organ pedalboard is a keyboard with long pedals which are played by the organist's feet. Pedalboards vary in size from 12 to 32 notes.
In a typical keyboard layout, black note keys have uniform width, and white note keys have uniform width and uniform spacing at the front of the keyboard. In the larger gaps between the black keys, the width of the natural notes C, D and E differ slightly from the width of keys F, G, A and B. This allows close to uniform spacing of 12 keys per octave while maintaining uniformity of seven "natural" keys per octave.
Over the last three hundred years, the octave span distance found on historical keyboard instruments (organs, virginals, clavichords, harpsichords, and pianos) has ranged from as little as 125 mm to as much as 170 mm. Modern piano keyboards ordinarily have an octave span of 164–165 mm; resulting in the width of black keys averaging 13.7 mm and white keys about 23.5 mm wide at the base, disregarding space between keys. Several reduced-size standards have been proposed and marketed. A 15/16 size (152 mm octave span) and the 7/8 DS Standard (140 mm octave span) keyboard developed by Christopher Donison in the 1970s and developed and marketed by Steinbuhler & Company. U.S. pianist Hannah Reiman has promoted piano keyboards with narrower octave spans and has a U.S. patent on the apparatus and methods for modifying existing pianos to provide interchangeable keyboards of different sizes.
There have been variations in the design of the keyboard to address technical and musical issues. The earliest designs of keyboards were based heavily on the notes used in Gregorian chant (the seven diatonic notes plus B-flat) and as such would often include B♭ and B♮ both as diatonic "white notes," with the B♮ at the leftmost side of the keyboard and the B♭ at the rightmost. Thus, an octave would have eight "white keys" and only four "black keys." The emphasis on these eight notes would continue for a few centuries after the "seven and five" system was adopted, in the form of the short octave: the eight aforementioned notes were arranged at the leftmost side of the keyboard, compressed in the keys between E and C (at the time, accidentals that low were very uncommon and thus not needed). During the sixteenth century, when instruments were often tuned in meantone temperament, some harpsichords were constructed with the G♯ and E♭ keys split into two. One portion of the G♯ key operated a string tuned to G♯ and the other operated a string tuned to A♭, similarly one portion of the E♭ key operated a string tuned to E♭, the other portion operating a string tuned to D♯. This type of keyboard layout, known as the enharmonic keyboard, extended the flexibility of the harpsichord, enabling composers to write keyboard music calling for harmonies containing the so-called wolf fifth (G-sharp to E-flat), but without producing aural discomfort in the listeners (see: Split sharp). The "broken octave," a variation of the aforementioned short octave, similarly used split keys to add accidentals left out of the Other examples of variations in keyboard design include the Janko keyboard and the chromatic keyboard systems on the chromatic button accordion and bandoneón.
On electric and electronic keyboards, there is an electric switch under each key. Depressing a key connects a circuit, which causes the tone generation mechanism to be triggered. Most electronic keyboards use a matrix circuit in which the rows and columns are made up of wiring. Without a matrix circuit, a 61-key keyboard would have to have 61 wires into the integrated circuit of the keyboard. With the matrix circuit, the entire keyboard can send signals to the integrated circuit with two matrices of eight wires that are conceptually arranged into columns and rows. The keyboard controller scans all of the columns, to determine if a key has been pressed. If a key in the column has been pressed, then the controller scan the rows, to determine which row has been activated. In a manner analogous to the children's board game "Battleship!", the keyboard controller determines which key has been pressed, and then closes the switch for that key's note. This entire process takes place so quickly that the performer is not aware of the delay.

Playing techniques:

Despite their apparent similarity, keyboard instruments of different types require different techniques. For instance, a piano will produce a louder note the faster the key is pressed. On the other hand, the volume and timbre of the sound on the pipe organ are dictated by the flow of air from the bellows and the stops selected by the player; in the harpsichord the strings are plucked and the volume of the note is not perceptibly varied by using a different touch on the keyboard. Players of these instruments must use other techniques to color the sound. The arranger keyboard uses preset drum rhythms that respond to chords played in the left hand by the instrumentalist, with other buttons and switches used to change rhythms and even the voice of the instrument.

A typical piano keyboard.
Playing a keyboard instrument can prove to be a challenging task; even though the layout is quite simple and all notes are easily accessible, some music puts high demand on the performer's skills to play accurately and in tempo, and beginners will often struggle to produce a passable rendition of a simple piece due to technique deficiency, which takes training to improve. The sequence of movements executed by the playing hand can be almost arbitrarily complicated, with some possible problems being wide-spanned chords, which can be problematic for people with small hands, chords that require unusual hand positions which can initially be uncomfortable or even painful, and also fast scales, trills and arpeggios.
Playing instruments with dynamic keyboards (i.e. ones that respond to varying force with which the key is struck) may require independence of the fingers so that some fingers are able to strike harder while others play more softly. Players need to learn to coordinate two hands and use them independently. Most music is written for two hands; typically the right hand plays the melody in the treble range, while the left plays an accompaniment of bass notes and chords in the bass range. There exist pieces of non-trivial music written for the left hand alone, e.g. several of the Godowsky's 53 Studies on Chopin's Etudes and Ravel's Piano Concerto for the Left Hand. In music that uses counterpoint technique, both hands play different melodies at the same time.