IEEE 1652-2008 pdf download IEEE Standard for the Application of Free Field Acoustic Reference to Telephony Measurements
2. Normative references
The following referenced documents are indispensable for the application of this document For datedreferences, only the edition cited applies. For undated references, the latest edition of the referenceddocument (including any amendments or corrigenda) applies.
ITU-T Recommendation P.57 (2005)Artificial Ears.
ITU-T Recommendation P.58 (1996) Head and Torso Simulator for Telephonometry.
ITU-T Recommendation P.581 (2000), Use of head and torso simulator (HATS) for hands-free terminaltesting.
3 Definitions
For the purposes of this standard, the following terms and definitions apply. The Authoritative DictionaryofIEEE Standards Terms should be referenced for terms not defined in this clause.
3,1 diffuse field: Sound field in which the time average of the mean-square sound pressure is everywherethe same and the flow of acoustic energy in all directions is equally probable.
3.2 drum reference point (DRP): A point located at the end of the ear canal, corresponding to the eardrumposition. Syn: eardrum reference point.
3.3 eardrum reference point (DRP): See: drum reference point.
3.4 ear reference point (ERP): A virtual point for acoustic and geometric reference located outside theentrance to the ear canal. The exact location is specified for each type of ear simulator.
3.5 free field: (simple definition) Sound field free of reflections.
3.6 free field: (complete definition) Sound field in a homogenous, isotropic medium free from boundaries.
In practice, the effects of boundaries on a free field are negligible over the region of interest.
3.7 head and torso simulator (HATS) for telephonometry: Manikin extending downward from the topof the head to the waist, designed to simulate the sound pick-up characteristics and the acoustic difractionproduced by a median human adult and to reproduce the acoustic field generated by the human mouth.
3.8 orthotelephonic: The acoustical relationship between two people of equal height facing one another ata distance of 1 m in a quiet non-reverberant room.
4. The listening experience
4.1 Acoustical reference points
A measurement may be made at one point, but translated to another point, This may be necessary due toinaccessibility of the desired acoustical point.
An acoustic reference point is somewhat like an electrical test point. The traditional reference point fortelephony measurements is the ERP. Measurements of a telephone receiver may actually be collected at theERP, or at the (simulated) eardrum (DRP), or possibly some other place. If the measurement is collected atsome point other than the ER, it is then translated to the ERP. In other words, the measurement isprocessed so that the result is the same as if it had been collected at the ERP in the first place. When usingHATS, the measurement is collected at the DRP, where the microphone is located. The measurement isthen translated to the ERP. But as the rest of this document demonstrates, the ERP is not the optimumacoustical reference point
4.2 Orthotelephonic Reference
The orthotelephonic reference is a face-to-face conversation in a free field, at a distance of I m.
The distance can be measured with respect to the mouth reference point (MRP) and the ERP, the center ofthe head, or some combination, but the basic idea is the same. (See Figure 1.)
A telephone conversation using a handset is intended to approximate the acoustical experience of a face-to.face (free field) conversation, at least at one ear. The orthotelephonic reference is therefore fundamental incvaluating telephone performance. Even though a handset is placed on the ear, and partly closes it, theacoustical performance should nonetheless be evaluated using the free field as the reference condition.