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Analyze the harmonic structure of music

A good overview about the abc music notation standard can be found here:
The full documentation is available here:


The analysis line shows the resulting harmonies of the individual voices, all notes arranged in one octave.

Harmonic States:

A “Harmonic State” is an extension of the concept of the key which a listener of music perceives as the "current key". The difference between a key and a harmonic state is that a harmonic state can consist of different keys at the same time, when the key is not clear.

Sauterian Formula:

If we have a harmonic state with a single key, we can give the sauterian formula for a harmony in this key: We indicate which chord tones of the tonic, subdominant and dominant of the key are used to form the harmony, for example "T35D13S1". A "/" is used for a rest, "ind." if we have a harmonic state with more than one key. If there are tones in the harmony that are not part of tonic, subdominant or dominant, these tones are atonal tones and are appended after an "A". For tones which are part of two of the T,S and D chords, we write the formula which give the form with the lowest degree of dissonance (see below). For example: "T135" is used instead of "T135D1S5".

Degree of Dissonance:

There are definitions for consonance and dissonance in the theory used here:

If a harmony is atonal (there is no key that has all the notes of the harmony), we only indicate the number of atonal tones in the harmony (How many tones have to be removed to get a tonal harmony?). A "/" is used for a rest, "ind." if we have a harmonic state with more than one key (but single tones are always consonant). So, the possible values for the degree of dissonance are, sorted by increasing "dissonance":