This is a neologism for very common pattern in notating microtonal pitch systems. These are analogic extensions of basic Western music notation.
Nominal means that some pitches have specific names. In Western music notation, these names are the seven letters A B C D E F G (historically, H has also been used.) In a pentatonic notation, there would be only five names.
Accidental means that additional pitches arise as modifications (accidentals) of the named pitches. Unmodified pitches are natural notes. In Western music notation, the five "black keys" are named by adding "sharp" or "flat" to A-G.
The named pitches form a chain, with each one separated from the next by a specific interval. This interval can be said to generate the notation, or the notation can be said to be based on this interval. This interval traditionally has been a just or near-just 3/2. Other intervals are possible, and even desirable for certain edos like 13, 18 and 23.
Western musical notation uses 7 nominals in a chain of fifths, and is a heptatonic fifth-based notation.
Enharmonic equivalence may arise from this approach. This is when you have multiple names for the same pitch. C-sharp is enharmonically equivalent to D-flat, but only in 12-EDO, 24-EDO, 36-EDO, etc.
This page is incomplete, and will eventually contain or refer to
- How to use A-G circle-of-fifths notation to notate any tuning with a circle of fifths
- Non-A-G extensions, including Erv Wilson's greek letters, Bohlen-Pierce notation, Armodue number notation
- Mark Gould's connection of accidentals to bi-level MOS
- the term "albitonic"
- Connections to Sagittal notation proposal & Aaron Hunt's system