This Recommendation specifies the electroacoustical characteristics of Head and Torso Simulators (HATS) to be used for telephonometric measurements. Both the sound generation and sound pick-up characteristics of these devices are specified. The proposed revision of Recommendation P.58 concerns new distortion and output linearity requirements for the Artificial Mouths of the HATS (as for Recommendation P.51) and describes the positioning on the HATS of the revised Type 3.2 and new Type 3.4 Artificial Ears.