Female vocal ranges.
Alto is the female voice type of lowest range. The alto's range is typically from about E3 to about E5, corresponding to a low female or high male voice. An alto's first passaggio occurs around E4 or E4, and her second passaggio around Eb5 or E5. A true alto is rare, and many female altos can be classified as a mezzo-soprano. The term is also used in an instrumental context.
Technically, the alto is the lowest voice in four-part harmony. In classical or operatic music a distinction is drawn between alto and contralto, the latter's range extending below that of an alto.