What is the difference between alto and mezzo-soprano in voice?
“Alto” is used more often when discussing parts in choral siging, such as SATB or SSA. In fact, boys can sing alto and men called “countertenors” who sing in falsetto can sing alto parts. Some mezzo-sopranos will sing alto and some mezzo-sopranos will sing second soprano. The real term for the woman’s voice part that is lower than mezzo-soprano would be “contralto”. True contraltos are much rarer than mezzo-sopranos. A contralto would do most of their singing in the lower part of the range and the sound would be rich. They would need to be able to sing passages that spend a lot of time below middle C and just above middle C. Mezzo-sopranos can have a similar range to sopranos, but would spend more of their time singing in the lower part of their range than a soprano would, and a soprano would spend more of their time singing in the higher part of their range than a mezzo would. Mezzo-sopranos can have light voices or heavy voices.
