3/1

3/1, the tritave or perfect twelfth, is the second most common equave after 2/1. In octave-equivalent systems, it is a fifth plus an octave, and can thus be seen as one of the two generators of Pythagorean tuning (see Perfect fifth for more info).

It can be seen as the most consonant interval after the octave, which is the reason for its usage as an equave in systems such as Bohlen-Pierce tuning. Tritave-equivalent systems tend to avoid prime 2, only involving ratios between odd numbers (such as 9/7 and 5/3). As such, timbres chosen for tritave-equivalent music tend to include mostly odd harmonics, such as the clarinet.