Recommendation ITU-T P.57 specifies the electro-acoustical characteristics of artificial ears to be used for telephonometric measurements. Three devices are specified: a telephone band type for measurements on traditional telephone sets, an insert earphone type and a type faithfully reproducing the characteristics of the human ear.
The latter type (type 3) is specified in four configurations. The requirements of the third one (type 3.3 – Pinna simulator) have been slightly modified in this revision of Recommendation ITU‑T P.57 by specifying its construction by a softer elastomer.
Besides this, the description of the applicability of all couplers has been changed, now allowing for an overlap in their usability according to the receiver type under test.