26.1323GPPRelease 18Speech and video telephony terminal acoustic test specificationTS
The horizontal positioning of the HATS reference plane shall be guaranteed within 2° for testing hands-free equipment.
The HATS shall be equipped with a Type 3.3 Artificial Ear. For hands-free measurements the HATS shall be equipped with two artificial ears. The pinnae are specified in Recommendation P.57  for Type 3.3 artificial ears. The pinnae shall be positioned on HATS according to ITU-T Recommendation P.58 .
The exact calibration and equalization procedures as well as how to combine the two ear signals for the purpose of measurements can be found in ITU-T Recommendation P.581.
If not stated otherwise, the HATS shall be diffuse-field equalized using values from ITU-T Recommendation P.58 . For 1/3-octave band measurements, the inverse of the nominal diffuse field curve in P.58 table 3 shall be used. For 1/12-octave band measurements, the inverse of the nominal diffuse field curve in P.58 Annex A shall be used. For measurements requiring diffuse-field correction values for frequencies other than those used in the P.58 tables, linear interpolation on a log frequency scale from the P.58 Annex A values shall be used.
For hand-held hands-free UE, the setup corresponding to ‘portable hands-free’ in ITU-T Recommendation P.581 should be used.