4/3
| Interval information |
reduced,
reduced subharmonic
[sound info]
4/3 is the frequency ratio of the just perfect fourth. Its inversion is the perfect fifth, 3/2. In the florid organum of Medieval music, 4/3 was reliably considered a consonance, and indeed was frequently emphasized. Once major thirds with a tuning approximating 5/4 began to be treated as consonances, however, the perception of 4/3 was altered to where it was at times considered a dissonance.
In Aura's music theory, which is in some respects derived from both florid organum and the practices of later counterpoint, it should be noted that the traditional 1/1-4/3-3/2 suspension is considered a dissonance purely because of the presence of the 9/8 interval between the 4/3 and the 3/2, and likewise, a 1/1-4/3-16/9 quartal chord is also considered a dissonance because of the 16/9 interval between the notes on the outside of the chord.