Editing Key signature (section)

== Overview ==
{{Image frame|content=<score>{
\omit Score.TimeSignature \relative c' {
  \time 2/1 b cis dis e fis gis ais b} }</score>|width=225|caption=[[B major]] scale using accidentals instead of a key signature}}
{{Image frame|content=<score>{
\omit Score.TimeSignature \relative c' {
  \key b \major \time 2/1 b cis dis e fis gis ais b} }</score>|width=260|caption=B major scale with the usual key signature}}

With any note as a starting point, a certain series of [[Interval (music)|intervals]] produces a [[major scale]]: whole step, whole, half, whole, whole, whole, half.

Starting on C, this yields C-D-E-F-G-A-B-C (a C-major scale). There are no sharps or flats in this scale, so the key signature for C has no sharps or flats in it. Starting on any other note requires that at least one of these notes be changed (raised or lowered) to preserve the major scale pattern. These raised or lowered notes form the key signature. Starting the pattern on D, for example, yields D-E-F{{music|sharp}}-G-A-B-C{{music|sharp}}-D, so the key signature for D major has two sharps—F{{music|sharp}} and C{{music|sharp}}.

Key signatures indicate that this applies to the section of music that follows, showing the reader which key the music is in, and making it unnecessary to apply accidentals to individual notes.

In standard [[Music notation#Modern notation|music notation]], the order in which sharps or flats appear in key signatures is uniform, following the [[circle of fifths]]: F{{music|sharp}}, C{{music|sharp}}, G{{music|sharp}}, D{{music|sharp}}, A{{music|sharp}}, E{{music|sharp}}, B{{music|sharp}}, and B{{music|flat}}, E{{music|flat}}, A{{music|flat}}, D{{music|flat}}, G{{music|flat}}, C{{music|flat}}, F{{music|flat}}. Musicians can identify the key by the number of sharps or flats shown, since they always appear in the same order. A key signature with one sharp must show [[F♯ (musical note)|F-sharp]],<ref name="orderofsharp">{{Cite web |url=https://www.dummies.com/art-center/music/guitar/how-to-read-key-signatures/ |title=How to Read Key Signatures}}</ref> which indicates [[G major]] or [[E minor]].

There can be exceptions to this, especially in 20th-century music, if a piece uses an unorthodox or synthetic scale and an invented key signature to reflect that. This may consist of sharps or flats that are not in the usual order, or of sharps combined with  flats (e.g., F{{music|sharp}} and B{{music|flat}}). Key signatures of this kind can be found in the music of [[Béla Bartók]], for example.

In a score, [[transposing instrument]]s will show a different key signature to reflect their transposition but their music is in the same concert key as the other instruments. Percussion instruments with indeterminate pitch will not show a key signature, and  [[timpani]] parts are sometimes written without a key signature (early timpani parts were sometimes notated with the high drum as "C" and the low drum a fourth lower as "G", with actual pitches indicated at the beginning of the music, e.g., "timpani in D–A"). In [[polytonal]] music, where different parts are actually in different keys sounding together, instruments may be notated in different keys.

[[File:Circle of fifths with musical keyboard.svg|thumb|right|400px|[[Circle of fifths]] showing [[major key|major]] and [[minor key]]s and their signatures]]