Halt! What is it about that deep but sensual, powerful, but subtle voice that unsettles us in that way? Ladies and gentlemen, let me introduce the contralto (alto).
The situation can be like this. You were a listener without further pretensions, then Amy Winehouse delivers a blues from the bottom of her soul that shakes, not your senses, but the complete meaning of things.
Technically, the tessitura of those who sing as alto goes from F4 to F6 (considering that the number 4 corresponds to the central scale on a piano keyboard). A pure alto is a rara avis since only 2% of women would have that voice, which is surprising due to its range and strength of intonation.
Opposite to the cliché of female singing high-pitched, which is associated with the sopranos, an alto brings sonority when moving smoothly across the deep register. It can confer the works a direct emotional touch, without any artifice.
Apart from solo performances, a choir is usually made up of mixed voices: two female –soprano and alto— plus two male —tenor and bass. The alto line often gives support and expression, thus completing the harmonic spectrum to enhance polyphony. However, given the limited number of singers with a real alto voice, that line is often taken on by mezzo-sopranos.
Through technique and practice, a man may also sing like an alto, then becoming what is known as a countertenor. While still being women, there are other types of altos: the buffa and the dramatic alto. As seen in the name of these subclasses, the contralto voice allows for expressing extreme feelings with authenticity: from comicality to the most profound tragedy.
Maybe this is why Amy Winehouse makes us get gooseflesh (not just the flesh; also the bones). Like all good losers do.