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Soprano sfogato ("Vented" soprano) is a term which, in the art of singing, designates a contralto or mezzo-soprano who is capable—by sheer industry or natural talent—of extending their upper range and being able to encompass the coloratura soprano tessitura. An upwardly extended "natural" soprano is sometimes called soprano assoluto. 
In the early 19th century as well as in the baroque and classical periods, distinctions between voices were not based so much on the range as in the tessitura and color of the voice. There were two main groups: soprano and alto. Their range was often blurred, relying more on tessitura to cast different roles in opera. In Italian bel canto, the soprano did not have extremely high notes actually written (often just to B5 or high C♭) and it was not until the "nightingale" type of sopranos such as Jenny Lind, Fanny Persiani, Adelina Patti and her imitators that ending the cabalettas in a climactic high E or E♭ became traditional as it was in the French grand opera which became so popular when Rossini moved to Paris. Singers however did ornament higher than high C but in a light and fast way as it was done still in the classical and baroque periods. Virtuosity was shown by quick-silver agility, changes in register and tessitura, perfect control of dynamics and tonal coloration, not by whistle-like high notes.
For contraltos on the other hand, they started to be more used in Rossini's bel canto operas for example, and to assume roles replacing the castrati who by that time were almost extinct, and composers demanded a range often going as high as B below high C. This change in demand of the voice would give birth to the soprano sfogato or assoluta
These voices had in common with those of the greatest castrati the ability to sing widely contrasting tessituras, segments well into the contralto and segments in high soprano.
By definition, the soprano sfogato is linked to the contralto. It possesses a dark timbre with a rich and strong low register, as well as the high notes of a soprano and occasionally a coloratura soprano. Those voices are typically strong, dramatic and agile, supported by an excellent bel canto technique and an ability to sing in the soprano tessitura as well as in the contralto tessitura with great ease, such as was said of Giuditta Pasta.
Testimonies of the time tell us that the main flaw of the soprano sfogato was the lack of homogeneity in the voice, something so prized in Mozart's time. It not be confused with the mezzo-soprano, lies between the soprano and the contralto voice, without covering both voices in tessitura and vocal color. But currently, the mezzo-soprano sings the part of contralto roles made for "sfogato soprano" already that scarce the true contraltos.
The term soprano sfogato appeared in the bel canto era of the Nineteenth Century, the time when its greatest exponents were performing. They included: Isabella Colbran, Giuditta Pasta, Maria Malibran, Giuseppina Ronzi de Begnis, Wilhelmine Schröder-Devrient, Mary Ann Paton (Mrs. Wood), Giuseppina Strepponi, Emma Calvé, Marianne Brandt, Félia Litvinne among others. Another example was Pauline Viardot, who alternated roles of soprano and contralto.
In the 20th century, the main exponent of this voice category was Maria Callas. However, she did sing excerpts of roles for mezzo-soprano, including Cenerentola and Dalila in the original keys and also many of the roles associated with the soprano sfogato, such as Médée, Armida, Norma, Anna Bolena, Amina, Abigaille and Lady Macbeth; using an overall a range of three octaves with high notes, until E6. Other likely assolutas of the 20th century were Marisa Galvany and Leyla Gencer.
The common requirements for the roles associated with this voice type are:
- widely varied tessitura throughout the role, extended segments lying well into the low mezzo or contralto tessitura and segments lying in high soprano tessitura
- a range extending down to at least low B and at least up to high B with at least one whole tone required at either end
- fioratura (coloratura) singing in the most intricate bel canto style
- florid singing combined with heroic weight
- a heavy or dense sound in the lower range
- vocal power over energetic orchestral accompaniment
The major exponents of the soprano sfogato vocal type were able to sing both soprano and contralto roles: Giuseppina Ronzi de Begnis was the first Elisabetta in Devereux, and she also performed Bellini's Romeo as well as Norma; Isabella Colbran sang both Armida and Desdemona in Rossini's Otello as well as the contralto role of Paisiello's Nina and Mozart's soprano heroines; Giuditta Pasta originated Anna Bolena, Norma and La Sonnambula as well as singing La Cenerentola, Tancredi, Arsace, Cherubino and Romeo.