The musical term alto, meaning "high" in Italian (Latin: altus ), historically refers to the contrapuntal part higher than the tenor and its associated vocal range. In 4-part voice leading alto is the second-highest part, sung in choruses by either low women's or high men's voices. In vocal classification these are usually called contralto and male alto or countertenor.
Such confusion of "high" and "low" persists in instrumental terminology. Alto flute and alto trombone are respectively lower and higher than the standard instruments of the family (the standard instrument of the trombone family being the tenor trombone), though both play in ranges within the alto clef. Alto recorder, however, is an octave higher, and is defined by its relationship to tenor and soprano recorders; alto clarinet is a fifth lower than B-flat clarinet, already an 'alto' instrument. There is even a contra-alto clarinet, (an octave lower than the alto clarinet), with a range B♭0 – D4.
In choral music for mixed voices, "alto" describes the lowest part commonly sung by women. The explanation for the anomaly of this name is to be found not in the use of adult falsettists in choirs of men and boys but further back in innovations in composition during the mid-15th century. Before this time it was usual to write a melodic cantus or superius against a tenor (from Latin tenere, to hold) or 'held' part, to which might be added a contratenor, which was in counterpoint with (in other words, against = contra) the tenor. The composers of Ockeghem's generation wrote two contratenor parts and designated them as contratenor altus and contratenor bassus; they were respectively higher and lower than the tenor part. From these derive both the modern terms "alto" (and contralto) and "bass".
The contralto voice is a matter of vocal timbre and tessitura as well as range, and a classically trained solo contralto would usually have a range greater than that of a normal choral alto part in both the upper and lower ranges. However, the vocal tessitura of a classically trained contralto would still make these singers more comfortable singing in the lower part of the voice. A choral non-solo contralto may also have a low range down to D3 (thus perhaps finding it easier to sing the choral tenor part), but some would have difficulty singing above E5. In a choral context mezzo-sopranos and contraltos might sing the alto part, together with countertenors, thus having three vocal timbres (and two means of vocal production) singing the same notes. 
The use of the term "alto" to describe solo voices is mostly seen in contemporary (e.g. pop) music, and is rarely seen in classical music outside of soloists in choral works, though there are many terms in common usage in various languages and in different cultures for solo singers in this range. Examples include contralto, countertenor, haute-contre , and tenor altino, among others.
| Voice classification|
in choral music
In SATB four-part mixed chorus, the alto is the second-highest vocal range, above the tenor and bass and below the soprano. The alto range in choral music is approximately from F3 (the F below middle C) to F5 (the second F above middle C). In common usage, alto is used to describe the voice type that typically sings this part, though this is not strictly correct. Alto, like the other three standard modern choral voice classifications (soprano, tenor and bass) was originally intended to describe a part within a homophonic or polyphonic texture, rather than an individual voice type;  neither are the terms alto and contralto interchangeable or synonymous, though they are often treated as such.
Although some women who sing alto in a choir are contraltos, many would be more accurately called mezzo-sopranos (a voice of somewhat higher range and different timbre). Men singing in this range are countertenors, although this term is a source of considerable controversy,[ citation needed ] some authorities preferring the usage of the term "male alto" for those countertenors who use a predominantly falsetto voice production (boys singing in their natural range may be termed "boy altos"  ).
A soprano ([soˈpraːno]) is a type of classical female singing voice and has the highest vocal range of all voice types. The soprano's vocal range (using scientific pitch notation) is from approximately middle C (C4) = 261 Hz to "high A" (A5) = 880 Hz in choral music, or to "soprano C" (C6, two octaves above middle C) = 1046 Hz or higher in operatic music. In four-part chorale style harmony, the soprano takes the highest part, which often encompasses the melody. The soprano voice type is generally divided into the coloratura, soubrette, lyric, spinto, and dramatic soprano.
A countertenor (also contra tenor) is a type of classical male singing voice whose vocal range is equivalent to that of the female contralto or mezzo-soprano voice types, generally extending from around G3 to D5 or E5, although a sopranist (a specific kind of countertenor) may match the soprano's range of around C4 to C6. Countertenors often have tenor or baritone chest voices, but sing in falsetto or head voice much more often than they do in their chest voice.
A tenor is a type of classical male singing voice whose vocal range lies between the countertenor and baritone voice types. It is the highest male chest voice type. The tenor's vocal range extends up to C5. The low extreme for tenors is widely defined to be B2, though some roles include an A♭2 (two A♭s below middle C). At the highest extreme, some tenors can sing up to the second F above middle C (F5). The tenor voice type is generally divided into the leggero tenor, lyric tenor, spinto tenor, dramatic tenor, heldentenor, and tenor buffo or spieltenor.
A contralto is a type of classical female singing voice whose vocal range is the lowest female voice type.
Singing is the act of creating musical sounds with the voice. A person who sings is called a singer, artist or vocalist. Singers perform music that can be sung with or without accompaniment by musical instruments. Singing is often done in an ensemble of musicians, such as a choir. Singers may perform as soloists or accompanied by anything from a single instrument up to a symphony orchestra or big band. Different singing styles include art music such as opera and Chinese opera, Indian music, Japanese music, and religious music styles such as gospel, traditional music styles, world music, jazz, blues, ghazal, and popular music styles such as pop, rock, and electronic dance music.
A mezzo-soprano or mezzo (; Italian: [ˌmɛddzosoˈpraːno]; meaning "half soprano") is a type of classical female singing voice whose vocal range lies between the soprano and the contralto voice types. The mezzo-soprano's vocal range usually extends from the A below middle C to the A two octaves above (i.e. A3–A5 in scientific pitch notation, where middle C = C4; 220–880 Hz). In the lower and upper extremes, some mezzo-sopranos may extend down to the F below middle C (F3, 175 Hz) and as high as "high C" (C6, 1047 Hz). The mezzo-soprano voice type is generally divided into the coloratura, lyric, and dramatic mezzo-soprano.
Falsetto is the vocal register occupying the frequency range just above the modal voice register and overlapping with it by approximately one octave.
A sopranist is a male singer who is able to sing in the vocal tessitura of a soprano usually through the use of falsetto or head voice vocal production. This voice type is a specific kind of countertenor. In rare cases an adult man may be able to sing in the soprano range using his normal or modal voice and not falsetto due to endocrinological reasons, like Radu Marian, or as a result of a larynx that has not completely developed as is allegedly the case of Michael Maniaci.
A bass-baritone is a high-lying bass or low-lying "classical" baritone voice type which shares certain qualities with the true baritone voice. The term arose in the late 19th century to describe the particular type of voice required to sing three Wagnerian roles: the title role in Der fliegende Holländer, Wotan/Der Wanderer in the Ring Cycle and Hans Sachs in Die Meistersinger von Nürnberg. Wagner labelled these roles as Hoher Bass —see fach for more details.
Head voice is a term used within vocal music. The use of this term varies widely within vocal pedagogical circles and there is currently no one consistent opinion among vocal music professionals in regard to this term. Head voice can be used in relation to the following:
Vocal range is the range of pitches that a human voice can phonate. A common application is within the context of singing, where it is used as a defining characteristic for classifying singing voices into voice types. It is also a topic of study within linguistics, phonetics, and speech-language pathology, particularly in relation to the study of tonal languages and certain types of vocal disorders, although it has little practical application in terms of speech.
Passaggio is a term used in classical singing to describe the transition area between the vocal registers. The passaggi (plural) of the voice lie between the different vocal registers, such as the chest voice, where any singer can produce a powerful sound, the middle voice, and the head voice, where a penetrating sound is accessible, but usually only through vocal training. The historic Italian school of singing describes a primo passaggio and a secondo passaggio connected through a zona di passaggio in the male voice and a primo passaggio and secondo passaggio in the female voice. A major goal of classical voice training in classical styles is to maintain an even timbre throughout the passaggio. Through proper training, it is possible to produce a resonant and powerful sound.
SATB is an initialism that describes the scoring of compositions for choirs, and also choirs of instruments. The initials are for the voice types: S for soprano, A for alto, T for tenor and B for bass.
A soubrette is a type of operatic soprano voice fach, often cast as a female stock character in opera and theatre. The term arrived in English from Provençal via French, and means "conceited" or "coy".
In music, an extension is a set of musical notes that lie outside the standard range or tessitura.
A voice type is a group of voices with similar vocal ranges, capable of singing in a similar tessitura, and with similar vocal transition points (passaggi). Voice classification is most strongly associated with European classical music, though it, and the terms it utilizes, are used in other styles of music as well.
Vocal pedagogy is the study of the art and science of voice instruction. It is used in the teaching of singing and assists in defining what singing is, how singing works, and how proper singing technique is accomplished.
There is no authoritative system of voice classification in non-classical music as classical terms are used to describe not merely various vocal ranges, but specific vocal timbres unique to each range. These timbres are produced by classical training techniques with which most popular singers are not intimately familiar, and which even those that are do not universally employ them.
Soprano sfogato is a contralto or mezzo-soprano who is capable — by sheer industry or natural talent — of extending her upper range and encompassing the coloratura soprano tessitura. An upwardly extended "natural" soprano is sometimes called soprano assoluto.
The term "four-part harmony" refers to music written for four voices, or for some other musical medium—four musical instruments or a single keyboard instrument, for example—for which the various musical parts can give a different note for each chord of the music.