Subfifth

A subfifth, infrafifth or semidiminished fifth is an interval that spans four steps of the diatonic scale with a quality between diminished and perfect. It exists in neutralized diatonic scales as exactly one half of a minor ninth.

In just intonation, an interval may be classified as a subfifth if it is reasonably mapped to 4\7 and 13\24 (precisely four steps of the diatonic scale and six and a half steps of the chromatic scale).

As a concrete interval region, it is typically near 650 ¢ in size. It is too narrow to sound like a perfect fifth and too wide to sound like a tritone. Margo Schulter, in her article Regions of the Interval Spectrum, proposes an approximate range for a subfifth to be from 640 ¢ to 672 ¢. Of course, this categorization should not be taken for granted. Since music is subjective and culturally influenced, the borders of what is a superfourth are "fuzzy". Other descriptions are possible and legitimate.

Some of the simplest subfifths in just intonation are 16/11 (about 649 ¢) and 22/15 (about 663 ¢), both undecimal (11-based) subfifths; and 35/24 (about 653 ¢) and 72/49 (about 666 ¢), both septimal (7-based) subfifths.

Information about subfifths in the conventional interval region format may be found at Tritone.

The inversion of a subfifth is a superfourth.

See also

• Superfourth – the octave complement region