Editing Double bass (section)

===C extension===
[[File:Double bass C extension.jpg|right|thumb|upright=1.15|A low-C extension with wooden mechanical "fingers" that stop the string at C{{music|#}}, D, E{{music|b}}, or E. For orchestral passages which only go down to a low E, the "finger" at the nut is usually closed.]]
Most professional orchestral players use four-string double basses with a ''C extension''.<ref>{{Cite web |title=What are double bass extensions and how do they work? |url=https://doublebasshq.com/gear_posts/what-are-double-bass-extensions-and-how-do-they-work/ |access-date=2024-09-01 |website=Double Bass HQ |language=en-US}}</ref> This is an extra section of fingerboard mounted on the head of the bass. It extends the fingerboard under the lowest string and gives an additional four semitones of downward range. The lowest string is typically tuned down to C<sub>1</sub>, an octave below the lowest note on the cello (as it is quite common for a bass part to double the cello part an octave lower). More rarely this string may be tuned to a low B<sub>0</sub>, as a few works in the orchestral repertoire call for such a B, such as [[Ottorino Respighi|Respighi]]'s ''The Pines of Rome''. In rare cases, some players have a low B extension, which has B as its lowest note. There are several varieties of extensions:

In the simplest mechanical extensions, there are no mechanical aids attached to the fingerboard extension except a locking nut or "gate" for the E note. To play the extension notes, the player reaches back over the area under the scroll to press the string to the fingerboard. The advantage of this "fingered" extension is that the player can adjust the intonation of all of the [[stopped note]]s on the extension, and there are no mechanical noises from metal keys and levers. The disadvantage of the "fingered" extension is that it can be hard to perform rapid alternations between low notes on the extension and notes on the regular fingerboard, such as a bassline that quickly alternates between G<sub>1</sub> and D<sub>1</sub>.

The simplest type of mechanical aid is the use of wooden "fingers" or "gates" that can be closed to press the string down and fret the C{{music|#}}, D, E{{music|b}}, or E notes. This system is particularly useful for basslines that have a repeating [[pedal point]] such as a low D because once the note is locked in place with the mechanical finger the lowest string sounds a different note when played open.

The most complicated mechanical aid for use with extensions is the mechanical lever system nicknamed the ''machine''. This lever system, which superficially resembles the keying mechanism of reed instruments such as the bassoon, mounts levers beside the regular fingerboard (near the nut, on the E-string side), which remotely activate metal "fingers" on the extension fingerboard. The most expensive metal lever systems also give the player the ability to "lock" down notes on the extension fingerboard, as with the wooden "finger" system. One criticism of these devices is that they may lead to unwanted metallic clicking noises.

Once a mechanical "finger" of the wooden "finger" extension or the metal "finger" machine extension is locked down or depressed, it is not easy to make microtonal pitch adjustments or [[glissando]] effects, as is possible with a hand-fingered extension.

Five-string basses, in which the lowest string is normally B<sub>0</sub>, may use either a two semitone extension, providing a low A, or the very rare low G extension.