Tuning
The double bass is generally tuned in fourths, in contrast to other members of the orchestral string family, which are tuned in fifths. The standard tuning (low to high) is E-A-D-G, starting from E below second low C (concert pitch). This is the same as the standard tuning of a bass guitar and is one octave lower than the four lowest-pitched strings of standard guitar tuning.
Throughout classical repertoire, there are notes that fall below the range of a standard double bass. Notes below low E appear regularly in the double bass parts found in later arrangements and interpretations of Baroque music. These parts are transpositions of parts written for other bass instruments used before the modern double bass became common and may actually lower the part an octave.
In the Classical era, the double bass typically doubled the cello part an octave below, occasionally requiring descent to C below the E of the four-string double bass. In the Romantic era and the 20th century, composers such as Wagner, Mahler, Beethoven, Busoni, and Prokofiev also requested notes below the low E. There are two common methods for making these notes available to the player. Major European orchestras generally use basses with a fifth string, tuned to B three octaves and a semitone below middle C. Players with standard double basses (E-A-D-G) typically play the notes below "E" an octave higher.
In the United States and Canada, most professional orchestral players use four-string double basses with a C extension, which extends the lowest string down as far as low C, an octave below the lowest note on the cello (more rarely, this string may be tuned to a low B). The extension is an extra section of fingerboard mounted up over the head of the bass. 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 for the "E" note. To play the extension notes, the player reaches back over the pegs 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 notes 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" and the low D.
The simplest type of mechanical aid is the use of wooden "fingers" that can be closed to press the string down and fret the C♯, D, Eb, 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 (e.g., a low D).
The most complicated mechanical aid for use with extensions are mechanical lever systems nicknamed machines. These lever systems, which superficially resemble the mechanisms of reed instruments such as the bassoon, include levers mounted 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.
A small number of bass players tune their strings in fifths, like a cello but an octave lower (C-G-D-A low to high). This tuning was used by the jazz player Red Mitchell and is increasingly used by classical players, notably the Canadian bassist Joel Quarrington. In classical solo playing the double bass is usually tuned a whole tone higher (F♯-B-E-A). This higher tuning is called solo tuning, whereas the regular tuning is known as "orchestral tuning." String tension differs so much between solo and orchestral tuning that a different set of strings is often employed that has a lighter gauge. Strings are always labelled for either solo or orchestral tuning, and published solo music is arranged for either solo or orchestral tuning. Some popular solos and concerti, such as the Koussevitsky Concerto are available in both solo and orchestral tuning arrangements.
Many contemporary composers specify highly specialized scordatura. Berio, for example, asks the player to tune his strings E-G♯-D-G in Sequenza XIVb and Scelsi asks for both F-A-D-E and F-A-F-E in Nuits.
A variant and much less-commonly used form of solo tuning used in some Eastern European countries is (A-D-G-C), which uses three of the strings from orchestral tuning (A-D-G) and then adds a high "C" string. Some bassists with five-string basses use a high "C" string as the fifth string, instead of a low "B" string. Adding the high "C" string facilitates the performance of solo repertoire with a high tessitura (range). Another option is to utilize both a low C (or B) extension and a high C string.
When choosing a bass with a fifth string, the player must decide between adding a higher or lower-tuned string. Six-stringed instruments are generally regarded as impractical. To accommodate the additional string, the fingerboard is usually slightly wider, and the top slightly thicker to handle the increased tension. Some five-stringed instruments are converted four-string instruments. Because these don't have wider fingerboards, some players find them more difficult to finger and bow. Converted four-string basses usually require either a new, thicker top, or lighter strings to compensate for the increased tension.
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