Clefs define the pitch range, or tessitura, of the staff on which it is placed. A clef is usually the leftmost symbol on a staff. Additional clefs may appear in the middle of a staff to indicate a change in register for instruments with a wide range. In early music, clefs could be placed on any of several lines on a staff.
|G clef (Treble clef)
The centre of the spiral defines the line or space on which it rests as the pitch G above middle C, or approximately 392 Hz. Positioned here, it assigns G above middle C to the second line from the bottom of the staff, and is referred to as the "treble clef". This is the most commonly encountered clef in modern notation, and is used for most modern vocal music. Middle C is the first ledger line below the staff here. The shape of the clef comes from a stylised upper-case-G.
|C clef (Alto, and Tenor clefs)
These clefs point to the line (or space, rarely) representing middle C, or approximately 262 Hz. As illustrated here, it makes the center line on the staff middle C, and is referred to as the "alto clef". This clef is used in modern notation for the viola. While all clefs can be placed anywhere on the staff to indicate various tessitura, the C clef is most often considered a "movable" clef: it is frequently seen pointing instead to the fourth line and called a "tenor clef". This clef is used very often in music written for bassoon, cello, trombone, and double bass; it replaces the bass clef when the number of ledger lines above the bass staff hinders easy reading.
Until the classical era, the C clef was also frequently seen pointing to other lines, mosly in vocal music, but today this has been supplanted by the universal use of the treble and bass clefs. Modern editions of music from such periods generally transpose the original C clef parts to either treble (female voices), octave treble (tenors), or bass clef (tenors and basses). It can be occasionally seen in modern music on the third space (between the third and fourth lines), in which case it has the same function as an octave treble clef. This unusual practice runs the risk of misreading, however, because the traditional function of all clefs is to identify staff lines, not spaces.
|F clef (Bass clef)
The line or space between the dots in this clef denotes F below middle C, or approximately 175 Hz. Positioned here, it makes the second line from the top of the staff F below middle C, and is called a "bass clef". This clef appears nearly as often as the treble clef, especially in choral music, where it represents the bass and baritone voices. Middle C is the first ledger line above the staff here. In old music, particularly vocal scores, this clef is sometimes encountered centered on the third staff line, in which position it is referred to as a baritone clef; this usage has essentially become obsolete. The shape of the clef comes from a stylised upper-case-F (which used to be written the reverse of the modern F)
Used for pitchless instruments, such as some of those used for percussion. Each line can represent a specific percussion instrument within a set, such as in a drum set. Two different styles of neutral clefs are pictured here. It may also be drawn with a separate single-line staff for each untuned percussion instrument.
Treble and bass clefs can also be modified by octave numbers. An eight or fifteen above a clef raises the intended pitch range by one or two octaves respectively. Similarly, an eight or fifteen below a clef lowers the pitch range by one or two octaves respectively. A treble clef with an eight below is the most commonly used, typically used for guitar and similar instruments, as well as for tenor parts in choral music.
For stringed instruments it is possible to notate tablature in place of ordinary notes. In this case, a TAB sign is often written instead of a clef. The number of lines of the staff is not necessarily five: one line is used for each string of the instrument (so, for standard 6-stringed guitars, six lines would be used). Numbers on the lines show which fret to play the string on. This TAB sign, like the percussion clef, is not a clef in the true sense, but rather a symbol employed instead of a clef. Similarly, the horizontal lines do not constitute a staff in the usual sense, because the spaces between the lines in a tablature are never used.