The chord always carries an explicit bassPc on the lowered submediant,
which is what makes it an augmented sixth rather than the dominant seventh or
the altered supertonic seventh it shares pitch classes with, and an explicit
interval template naming exactly the tones that sound.
It also carries its spelling: the tones as toneSpellings, and the root and
bass as the usual hints. Those are what let the ordinary chord speller and
the symbol formatter name the chord — Ab C Eb F# and Ab7 for the German
sixth of C major — since a stack of thirds over that root would put a Gb
where the augmented sixth belongs. The spelling is the one the key is written
on, so a flat-side key takes the double flats it genuinely needs.
The lowered submediant is taken as eight semitones above the tonic in every
mode, since the chord is a chromatic alteration rather than a degree of the
prevailing scale.
Build an augmented-sixth chord in a key.
The chord always carries an explicit
bassPcon the lowered submediant, which is what makes it an augmented sixth rather than the dominant seventh or the altered supertonic seventh it shares pitch classes with, and an explicit interval template naming exactly the tones that sound.It also carries its spelling: the tones as
toneSpellings, and the root and bass as the usual hints. Those are what let the ordinary chord speller and the symbol formatter name the chord —Ab C Eb F#andAb7for the German sixth of C major — since a stack of thirds over that root would put a Gb where the augmented sixth belongs. The spelling is the one the key is written on, so a flat-side key takes the double flats it genuinely needs.The lowered submediant is taken as eight semitones above the tonic in every mode, since the chord is a chromatic alteration rather than a degree of the prevailing scale.