Is a female singer with a range usually extending from the A below middle C to the A two octaves above Middle C (A3-A5). Mezzosopranos generally have a darker (or richer) vocal tone than sopranos, and their voice type sits between the soprano and the contralto. The terms Dugazon and Galli-Marié are sometimes used to refer to light mezzosopranos, after the names of famous singers. A castrato with a mezzosoprano range was called a mezzosoprano castrato.

A contralto is a singer with a vocal range somewhere between a tenor and a mezzosoprano. The term is used to refer to the deepest female singing voice, or the highest male voice. A typical alto will have a range from around the F below middle C to the E a tenth above middle C (F3-E5); at the bottom of their range, altos sound almost like tenors.

Although both men and women may have voices in the alto range, the word is usually used to mean a female singer. However, choirs singing early music frequently include adult male altos, also called countertenors. In English church usage, the term alto is sometimes exclusively used to mean a boy with this range, while contralto is used for a female singer. A few popular music enthusiasts define the contralto and alto separately, as the contralto having an especially dark range, from the D above low C to Tenor C, which is essentially a female of tenor range, while alto is a voice with a range from F below middle C (F3) to the F an eleventh above middle C (F5), and is closer to the mezzosoprano. The majority however define contralto and alto as synonyms, and assign the adjectives light and dark, with a dark alto being a female of tenor range, while a light alto, commonly referred to as simply alto, to include mezzosopranos as well.

The countertenor is a unique and somewhat controversial vocal class for men, being the highest voice class for them. Because of the extensive use of falsetto, which some purists do not view as musical, some view the countertenor as actually being a baritone engaging in "false tenor brillance". Regardless, attempts have been made to assign a "legitimate" fach to this voice class. The prevailing range for a countertenor is D below middle C (D3) to F an eleventh above middle C (F5), although many go much higher.

There are five main class of countertenor: hautcontre, altino, sopranist, baritonic, and falsettist. Hautcontre, a french word for countertenor, is a tenor who can use his falsetto to reach heights well above Tenor C (C5). The altino is a rare voice type, commonly considered the "true" countertenor. This person can sing high without falsetto well above the usual male passagio. Typically, this rare voice has problems reaching depths of even low C unlike most men, and usually has an androgynous tone, even when speaking. The typical altino will speak normally between the range of F# and B below Middle C (F#3-B3), more in keeping a female than a typical male, whose speaking voice settles closer to low C (C3). An even rarer full voice can sing tenor and female contralto (or even mezzosoprano) parts with equal ease.

A baritonal countertenor is an adult male singer who uses the falsetto part of his voice more than usual to sing a higher range than the typical adult male voice. When people think of or hear a countertenor, usually this is the voice they are hearing. A countertenor trains himself to use the whole of the vocal cords as well to produce a rich sound, as distinct from the falsettist who makes a much slighter sound by only using the edges of the cords (or falsetto). What singers term 'onset of tone' (in layman's terms, the beginning of the sound) is perhaps the key to the different usages. A healthy voice uses both the fine edges of the cords and the 'body' of the cords. The difference in onset between, say, a baritone and a countertenor is how much of the edges of the cords are being used at the 'onset' or start. A countertenor will use a huge amount of falsetto in the onset of tone - then expanding into the rest of the cord - while a baritone will use the main part of the cord in onset, whilst having some falsetto present.

A castrato is a male soprano, mezzosoprano, or alto voice produced by castration of the singer before puberty. Castration before puberty (or in its early stages) prevents the boy's larynx from being fully transformed by the normal physiological effects of puberty. As a result, the vocal range of prepubescence (shared by boys and girls) is largely retained, and the voice develops into adulthood in a unique way. As the castrato's body grows (especially in lung capacity and muscular strength), and as his musical training and maturity increase, his voice develops a range, power and flexibility quite different from the singing voice of the adult female, but also markedly different from the higher vocal ranges of the uncastrated adult male.