Alto Clef

The alto clef (one of the C clefs) is the notation symbol that fixes the third line of the staff as middle C. The clef’s symmetrical center marks the middle line, anchoring the staff to middle C.

The alto clef is used primarily for the viola — the only orchestral string instrument whose normal range is centered around middle C, making the alto clef the most efficient notation for it. Some early-music wind instruments and some vocal parts (particularly alto voice in older scores) also use alto clef.

C clefs are flexible — they can be placed on different lines of the staff to define different notes as middle C. The alto clef places it on the third (middle) line; the tenor clef (used for cello and bassoon in their upper ranges) places it on the fourth line. Reading C clefs requires comfort with the position of middle C on the indicated line.

English, ‘alto’ from Italian alto (‘high’) — referring to the high male voice (countertenor), which traditionally used this clef. ‘Clef’ from French/Latin clavis (‘key’).

On the alto clef staff, the middle line is middle C. Other pitches are read by interval from there: lines below are A, F, D, B; lines above are E, G.