The clef is a musical symbol which is placed at the beginning of the staff to fix the pitch of one note, and thus, the relative pitches of all the other notes. Of the many different clefs that once existed, three are used to this day: the G clef, which is based on a gradual change; the letter G; the bass clef, which is derived from the letter F; and the alto clef which is a variation of the letter C.
Prior to the Baroque period, all three clefs could occur in various positions on the staff. Today the alto clef is the only movable one.
In the following example, the relative pitches of the different pitches can be seen. As you can see, the G clef indicates that the note which is written on the second line of the higher staff is g1, while the F clef indicates that the note which is written on the
fourth line of the lower staff is f. The C clef is usually used in two positions: when its center is on the third line (called alto or viola clef), the note on this line is c1; and when it is on the fourth line (called tenor clef), the note on this line is c1.
The different clefs are used in order to avoid too many ledger lines.
