Basso profondo

Basso profondo (Italian: "deep bass"), sometimes basso profundo or contrabass, is the lowest bass voice type.

While The New Grove Dictionary of Opera defines a typical bass as having a range that extends downward to the second E below middle C (E2), operatic bassi profondi can be called on to sing low C (C2), as in the role of Baron Ochs in Der Rosenkavalier. Often choral composers make use of lower notes, such as G1 or even F1; in such rare cases the choir relies on exceptionally deep-ranged bassi profondi termed oktavists or octavists, who sometimes sing an octave below the bass part.

Bass singer Tim Storms holds the Guinness World Record for the "lowest note produced by a human".

Definition
According to Rousseau (1775): "Basse-contres – the most profound of all voices, singing lower than the bass like a double bass, and should not be confused with contrabasses, which are instruments."

Oktavist
An oktavist is an exceptionally deep-ranged basso profondo, especially typical of Russian Orthodox choral music. This voice type has a vocal range which extends down to A$2$ (an octave below the baritone range) and sometimes to F$4$ (an octave below the bass staff) with the extreme lows for oktavists, such as Mikhail Zlatopolsky or Alexander Ort, reaching C$1$.

Slavic choral composers sometimes make use of lower notes such as B1 as in Rachmaninoff's All-Night Vigil, G$1$ in "The Twelve Brigands", G$1$ in "Ne otverzhi mene" by Pavel Chesnokov, or F1 in "Kheruvimskaya pesn" (Song of Cherubim) by Krzysztof Penderecki, although such notes sometimes also appear in repertoire by non-Slavic composers (e.g. B1 appears in Gustav Mahler's Second and Eighth Symphonies).

In popular culture, several a capella groups have bass singers with an oktavist range, such as Home Free's Tim Foust, VoicePlay's Geoff Castellucci, and Avi Kaplan formerly of Pentatonix, as well as Tony-nominated Broadway performer Patrick Page, each of these being able to reach down to a G$1$ or in some cases even lower, with Castellucci able to hit a B$1$ using subharmonic singing and Foust able to hit a G$1$ using growl.