accidental

A symbol placed before a note-head in musical notation, or after a letter-name in a text description, which indicates some intonational change or adjustment relative to the tuning of the plain note or letter-name. The name "accidental" is derived from the fact that these notes are felt to lie outside the regular diatonic scale.

The standard musical accidentals are:

symbol   name           effect

  #   sharp         raise 1 semitone
  b   flat          lower 1 semitone
  x   double-sharp  raise 2 semitones (sometimes written ##)
  bb  double-flat   lower 2 semitones

There is also a "natural", which cancels the effect of a previously given accidental, whether that accidental occurs in a particular instance or in the key-signature.

In the standard 12-EDO scale, the double-sharps and double-flats have the effect of altering the pitch by a "whole-tone" and are often simply written as the equivalent natural with a change of letter-name (i.e., Cx = D, Bbb = A), but this is not necessarily the circumstance in other tunings. The exact amount of alteration by these standard accidentals depends on the size of the chromatic semitone in the given tuning.

In addition to these four standard accidentals, many others have been devised by microtonalists to specify various intonational adjustments. My own proposal is dubbed HEWM, which uses these additional symbols:

 - + < > v ^

and comes in two varieties, one based on extended just-intonation and the other (simpler) version based on 72-EDO. The latter eliminates the need for multiple instances of a particular symbol, because ++ equals > and >+ equals ^, etc, and bb and x are written as the equivalent natural with a change of letter-name, as with 12-EDO.


see also:

HEWM notation
Johnston notation


[from Joe Monzo, JustMusic: A New Harmony ]

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