Key signature
In musical notation,key signature isseriessharps or flats placed onstaff, designating notes thatto be played sharp or flat respectively unless otherwise notedan accidental. Key signaturesgenerally written immediately afterclef atbeginning oflinemusical notation, althoughcan appearother parts ofscore.
A key signaturenotsame askey,fact, key signaturesmerelyconveniencenotation. However, theyconvenient onlydiatonic or tonal music. Furthermore, some pieces which change key (modulate) insertnew key signature onstaff partway; while others use accidentals: natural signs"neutralize"key signatureother sharps or flats fornew key.
Image:b_maj.png
Fig 1. The B-Major scale
Forgiven modekey signature definesdiatonic scale whichpiecemusic uses. Most scales require that some notes be consistently sharpened or flattened.
For example, inkeyG major,leading-noteF sharp. The key signature indicates that each time an Fwritten instaff itin factbe played as F sharp.
Individual sharp, flat or natural signs that modify an individual note inpiececalled accidentals (for example, an F natural inpiece inkeyG). These overridekey signature forduration ofbaroccur in.
Figure 1 showskey signature ofscaleB-major. Any note whichonsame line or space as its five sharpsincreased from its natural pitch bysemitone. Although key signatures can technically consistany collectionsharps or flats, musical tradition dictates thatbe arranged infixed order according tokeymode ofpiece. As each major key has an equivalent relative minor key that may be represented withsame key signature. The same also appliesother modes such as LydianPhrygian.
The table below illustratesnumbersharps or flatseach key signature and relative major key signaturesminor scales. See: circlefifths.
| Key Sig. | Major Scale | Minor Scale |
|---|---|---|
| 0 | C major | A minor |
| 1# | G major | E minor |
| 2# | D major | B minor |
| 3# | A major | F# minor |
| 4# | E major | C# minor |
| 5# | B major | G# minor |
| 6# | F# major | D# minor |
| 7# | C# major | A# minor |
| 1b | F major | D minor |
| 2b | Bb major | G minor |
| 3b | Eb major | C minor |
| 4b | Ab major | F minor |
| 5b | Db major | Bb minor |
| 6b | Gb major | Eb minor |
| 7b | Cb major | Ab minor |
For key signaturessharps,first sharpplaced on F line (forkeyG major/E minor). Subsequent additional sharpsadded on C, G, D, A, EB. For key signaturesflats,first flatplaced onB line,subsequent flats on E, A, D, G, CF. There15 different key signatures, including"empty" signatureC major/A minor.
The key signaturesseven flatsseven sharpsvery rarely used, becausehave simpler enharmonic equivalents. For example,keyC# major (seven sharps)more simply represented as Db major (five flats) -modern practical purposes these keys aresame, because C#Db aresame note. Pieces are writtenthese seven sharp or flat keys, however. The third PreludeFugue from Book OneJohann Sebastian Bach's Well-Tempered Clavierin C# major,example.
In cryptography,key signature isresultapplyinghash function onkey, forpurposesimplifying operations on keys. For example, cryptographic keysoften quite largecumbersomecompare, souser who wantsverifypresence ofpublic key indatabase might usesmaller key signature rather than comparingwhole key.
