In music, standard tuning refers to the typical tuning of a string instrument. This notion is contrary to that of scordatura, i.e. an alternate tuning designated to modify either the timbre or technical capabilities of the desired instrument.
A more recent family is the violin octet, which also features a standardized tuning system (see page).
Standard tunings in plucked string instruments cover many different instruments which are plucked either by the fingers or with a plectrum. Guitars and bass guitars have more standard tunings, depending on the number of strings an instrument has:
6-stringed guitar (most popular) – E2 A2 D3 G3 B3 E4 (ascending perfect fourths, with an exception between G and B, which is a major third. Low E falls a major third above the C on a standard tuned cello.
Guitar notation is an octave above the actual note, so Middle C (C4) in guitar notation is the third space on the treble clef, whereas the note written as one line below the treble clef is C3.
Drop-D – D2 A2 D3 G3 B3 E4 (commonly used by classical guitarists for certain pieces, and identical to standard guitar tuning, except for the low D, lowered one tone from the standard low E string, making a perfect fifth between 5th and 6th rather than a perfect fourth)
Renaissance lute – E2 A2 D3 F♯3 B3 E4 (commonly used by classical guitarists for certain pieces, and identical to standard guitar tuning, except for the F♯, lowered one semitone from the standard G string, making a perfect fourth between 2nd and 3rd rather than 3rd and 4th strings)
7-stringed guitar – B1 E2 A2 D3 G3 B3 E4 (identical, except for the low B, which is a perfect fourth below the low E on a 6-stringed guitar)
7-stringed guitar (George Van Eps) – A1 E2 A2 D3 G3 B3 E4 (more commonly used by jazz players, with a low A below the low E)
7-stringed guitar (Lenny Breau) – E2 A2 D3 G3 B3 E4 A4 (used rarely but famously, with a high A a fourth above the high E)
8-stringed guitar – F♯1 B1 E2 A2 D3 G3 B3 E4 (identical to the 7-stringed guitar, with the addition of a low F♯ string a perfect fourth below the low B)
4-stringed bass guitar (most popular) – E1 A1 D2 G2 (its standard tuning coincides with that of a 4-stringed double bass)
5-stringed bass – B0 E1 A1 D2 G2 (identical to 4-stringed bass with the addition of a low B string a perfect fourth below the E).
6-stringed bass – B0 E1 A1 D2 G2 C3 (identical to 5-stringed bass with the addition of a high C string a perfect fourth above the G).
Baritone (older use) / 6 string bass (older use) such as the Fender Bass VI – E1 A1 D2 G2 B2 E3 (like a standard guitar but an octave lower, and often played like a standard guitar rather than a bass guitar.
Baritone guitar (contemporary versions) – B1 E2 A2 D3 F♯3 B3 a fourth below standard tuning, although A1 to A3; a fifth lower is also used.
12-string guitar E3 E2 A3 A2 D4 D3 G4 G3 B3 B3 E4 E4 in six two-string courses.
Guitars are thus normally tuned in fourths, with the exception of a major third between the 2nd and 3rd strings. This is done to simplify fingering. A few guitarists, mostly those using tapping, play without this interval, instead tuning in all fourths; thus on a six-string guitar the top two strings become C and F instead of B and E. Other unusual tunings include all major thirds, all minor thirds, and various other choices.
In standard notation, the guitar sounds one octave lower than it is written. This is to avoid switching between treble and bass clef, or using ledger lines or 8vb, since it is very common to play past the 12th fret on the E string (E5) and drop down to lower open string notes. This is also more practical for the whole playing range of E2–C♯6 (on a 21-fret guitar), as it can fit easily into the treble clef when written as E3–C♯7. Transposing by an octave may be explicitly indicated by a suboctave clef, where a treble clef has an '8' placed below it, or a normal treble clef may be used for simplicity.
Other plucked string instruments and their respective standard tunings include:
Banjo (Five-stringed): G4 D3 G3 B3 D4 for bluegrass; old time and folk banjoists use this and a wide variety of other tunings
Mandola: C3 G3 D4 A4 (same as standard viola tuning)
Mandolin: G3 D4 A4 E5 (same as standard violin tuning)
Pipa: A2 D3 E3 A3 (most common and used in Chinese orchestra; several other tunings exist)
Balalaika (Prima): E4 E4 A5 (the two identical Es are on strings of different gauges)