Just-noticeable difference

The just-noticeable difference, about 3.5 cents, is an estimation of the minimum difference in pitch that can be distinguished by the average listener. However, this number actually varies widely depending on listener as well as musical context, from up to 20 cents in some cases (certain casual listeners, for intervals and harmonies far from "landmarks" that boost recognizability) to a fraction of a cent in others (in contexts that depend on very fine aspects of harmony such as ringing induced by DR and high-complexity JI).

The conventional just-noticeable difference also defines an interval region of "unnoticeable commas" around the unison, which are the differences between intervals that are nearly identical in pitch. An example is the schisma. A temperament of an unnoticeable comma, or a temperament that is otherwise for the most part indistinguishable from just intonation, is called a microtemperament.

In some practices, this bound goes up to about 6 cents, which is the most precisely one is expected to intonate a pitch on certain instruments, and is a bit smaller than a kleisma (hence the kleisma's significance in the context of intonation).