The Musical Staff
The musical staff is a set of five horizontal lines and four spaces that represent musical pitches. The absolute pitch of each line is indicated by a clef symbol at the beginning of the staff. The treble clef, for example, fixes the second line as the first G above "middle C". Notes are placed on the staff according to their pitch, with higher notes positioned higher on the staff. Ledger lines can be added above or below the staff to represent notes outside its range.
Staff Positions
The vertical position of a notehead on the staff determines the note to be played. Notes can be placed on a line or in a space. The interval between adjacent staff positions is one step in the diatonic scale. The notes represented by the staff positions can be modified by the key signature or accidentals on individual notes. A clefless staff may be used to represent percussion sounds, with each line typically representing a different instrument.
Ensemble Staves
Vertical lines and braces are used to group staves. A system, indicated by a vertical line, shows that the music on multiple staves is played simultaneously. Braces connect staves representing instruments played by a single performer, such as a piano or harp. Brackets can be used to show groupings of instruments functioning as a unit, such as the string section of an orchestra.
Grand Staff
When two staves are joined by a brace, a grand staff is created. The upper staff typically uses a treble clef, and the lower staff a bass clef. Middle C is centered between the two staffs. In piano or harp music, the upper staff is played with the right hand, and the lower staff with the left hand.
History
The modern musical staff evolved from medieval notation, which used neumes to indicate melodic contours. The use of lines to represent pitches emerged in the 9th century, and the four-line staff is attributed to Guido d'Arezzo in the 11th century. Five-line staves became common in the 13th century. Staves with varying numbers of lines were used until the 17th century, when the five-line staff became standardized.