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In Western musical notation, the staff, or stave, is a set of five horizontal lines and four spaces that each represent a different musical pitch—or, in the case of a percussion staff, different percussion instruments. Appropriate music symbols, depending upon the intended effect, are placed on the staff according to their corresponding pitch or function. Musical notes are placed by pitch, percussion notes are placed by instrument, and rests and other symbols are placed by convention.
The absolute pitch of each line for a non-percussive stave is determined by the placement of an appropriate clef symbol at the appropriate vertical position on the left-hand side of the staff. For example, the treble clef, also known as the G clef, is placed upon the second line (counting upwards), fixing that line as the pitch first G above 'middle C'.
The lines and spaces are numbered from bottom to top; the bottom line is the first line and the top line is the fifth line.
The musical staff is analogous to a mathematical graph of pitch with respect to time. Pitches of notes are given by their vertical position on the staff and notes to the left are played before notes to the right. Unlike a graph, however, the number of semitones represented by a vertical step from a line to an adjacent space depends on the key, and the exact timing of the beginning of each note is not directly proportional to its horizontal position; rather, exact timing is encoded by the musical symbol chosen for each note in addition to the tempo.
The vertical position of the notehead on the staff indicates which note to play: higher-pitched notes are marked higher on the staff. The notehead can be placed with the center of its notehead intersecting a line (on a line), or in between the lines touching the lines above and below (in a space). Notes outside the range of the staff are placed on or between ledger lines—lines the width of the note they need to hold—added above or below the staff.
Exactly which staff positions represent which notes is determined by a clef placed at the beginning of the staff. The clef identifies a particular line as a specific note, and all other notes are determined relative to that line. For example, the treble clef puts the G above middle C on the second line. The interval between adjacent staff positions is one step in the diatonic scale. Once fixed by a clef, the notes represented by the positions on the staff can be modified by the key signature, or by accidentals on individual notes. A clefless staff may be used to represent a set of percussion sounds; each line typically represents a different instrument.
A single vertical line drawn to the left of multiple staves creates a system, indicating that the music on all the staves is to be played simultaneously. A bracket is an additional straight line joining staves, to show groupings of instruments that function as a unit, such as the string section of an orchestra. A brace is used to join multiple staves that represent a single instrument, such as a piano, organ, harp, or marimba. Sometimes, a second bracket is used to show instruments grouped in pairs, such as the first and second oboes, or the first and second violins in an orchestra. In some cases, a brace is used for this purpose instead of a bracket.
When music on two staves is joined by a brace, or is intended to be played at once by a single performer (usually a keyboard instrument or the harp), a great stave (BrE) or grand staff (AmE) is created. Typically, the upper staff uses a treble clef and the lower staff has a bass clef. In this instance, middle C is centered between the two staves, and it can be written on the first ledger line below the upper staff or the first ledger line above the lower staff. Very rarely, a centered line with a small alto clef is written, and usually used to indicate that B,C, or D notes on the line can be played with either hand (ledger lines are not used from a center alto as this creates confusion). When playing the piano or harp, the upper staff is normally played with the right hand and the lower staff with the left hand. In music intended for the organ, a grand staff comprises three staves, one for each hand on the manuals and one for the feet on the pedalboard.
Early Western medieval notation was written with neumes, which didn't specify exact pitches but only the shape of the melodies, i.e. indicating when the musical line went up or down; presumably these were intended as mnemonics for melodies which had been taught by rote.
During the 9th through 11th centuries a number of systems were developed to specify pitch more precisely, including diastematic neumes whose height on the page corresponded with their absolute pitch level (Longobardian and Beneventan manuscripts from Italy show this technique around AD 1000). Digraphic notation, using letter names similar to modern note names in conjunction with the neumes, made a brief appearance in a few manuscripts, but a number of manuscripts used one or more horizontal lines to indicate particular pitches.
The treatise Musica enchiriadis (AD 900) uses Daseian notation for indicating specific pitches, but the modern use of staff lines is attributed to Guido d'Arezzo (AD 990-1050), whose four-line staff is still used (though without the red and yellow coloring he recommended) in Gregorian chant publications today. Five-line staves appeared in Italy in the 13th century, and staves with four, five, and six lines were used as late as 1600.