B.4 Test arrangement

03.503GPPTransmission planning aspects of the speech service in the GSM Public Land Mobile Network (PLMN) systemTS

B.4.1 Electro‑acoustic equipment

Artificial mouth: unless specified otherwise, the artificial mouth shall conform to ITU‑T Recommendation P.51 [38].

Artificial ear: the ITU‑T Recommendation P.57 [46] Type 1 shall be used.

If requested by the terminal supplier, the ITU‑T Recommendation P.57 [46] Type 3.2 artificial ear shall be used for all tests. In this case the following apply:

– the low leakage option of Type 3.2 artificial ear shall be adopted;

– the force against the ear shall be as specified in ITU‑T Recommendation P.57 [46];

– sound pressure measurements shall be referred to the ERP as specified in ITU‑T Recommendation P.57 [46];

– no leakage correction shall be made in the calculation of RLR (i.e. LE=0).

If requested by the terminal supplier, the ITU‑T Recommendation P.57 [46] Type 3.4 artificial ear may be used. The positioning is defined in ITU-T Recommendation P.64.

The test report shall indicate the type of artificial ear used for the receive tests.

HATS: when a HATS is used, it shall conform to ITU‑T Recommendation P.58. In such a case, all the sending and receiving characteristics shall be tested with the HATS and it shall be indicated in the test report that the HATS was used.

B.4.2 Test arrangement for handsfree MS

B.4.2.1 Office type handsfree MS

The handsfree terminal is placed on a table according to ITU‑T Recommendation P.34 (clause 6.1: test table; clause 6.2: test arrangements and figure 3 of ITU‑T Recommendation P.34).

The artificial mouth axis and the microphone axis are coincident with the straight line drawn between point C and point B (see figure 9).

Figure 9: Measurement configuration

In case of two or more piece hands‑free MS, care shall be taken to ensure that the test arrangement does not modify the normal use of the hands‑free MS.

B.4.2.2 Car type handsfree MS

The hands‑free set is positioned in the car as specified by the manufacturer.

The HATS is placed inside the car as shown in figure 10. The lipring of the HATS is adjusted parallel to a plane defined by two parallel points defining a line 90 degrees. To the driving direction inside the car (e.g. A‑pillar) and perpendicular.

The manufacturer needs to define unambiguously the exact position of the Ear Canal Entrance point (EEP) relative to fixed positions inside the car, e.g. distance to the roof and distance to the upper edge of the windscreen.

Unless specified otherwise by the manufacturer, the distance between hands‑free MS‑microphone and lipring shall be as specified in figure 10.

Figure 10: Measurement configuration for car type applications

B.4.2.3 Use of HATS for testing the receive characteristics of the car type handsfree MS

B.4.2.3.1 Equalization of HATS

Due to the diffractions and reflections of torso, shoulder, head and pinna the HATS behaves differently from an ordinary measurement microphone. The transfer functions are directional and not flat. The typical head transfer function for different directions can be found in ITU‑T Recommendation. P.58 [1]. Since the characteristics of the artificial head are directional, a reference position must be found which gives comparable results to those obtained with an ordinary measurement microphone. For this reference position the HATS is equalized in such a way, that the measured frequency response is flat (like a standard measurement microphone). A suitable reference position is 0 degrees. In front of the HATS, anechoic condition. The equalization for this reference condition is known as "free field equalization".

For the measurement a HATS complying with the free‑field and diffuse field reception characteristic as described in ITU‑T Recommendation P.58 is used. This head is either a free‑field equalized HATS or the test set‑up as described in the following needs to be used.

The equalization is made for this reference position in an anechoic chamber (see figure 11). The minimum distance of the reference sound source is 1,5 m.

Figure 11: Set‑up for HATS free field calibration in an anechoic chamber

The measured free‑field response of the HATS is:

Hff(0,0,f)

From this the free‑field equalization is calculated:

HEQ(0,0,f) = 1/ Hff(0,0,f)

The equalization must be correct within  0,5 dB within the frequency range from 100 Hz to 8 kHz measured in 1/3rd octaves.

NOTE: The free‑field equalization of a HATS requires a very careful set‑up of the measurement. Due to the strong directivity of the HATS small deviations from the reference position (0,0) may cause wrong equalizer transfer functions.

The HATS set‑up for the measurements then is as follows.

Figure 12: Measurement set‑up for HATS (Heql(0,0,f) = free‑field equalizer left ear, Heqr(0,0,f) = free‑field equalizer right ear)

B.4.2.3.2 Combination of ear signals

The signals from the two ear microphones of HATS are combined as follows:

– the output signal of each channel is averaged in power for the complete time of the analysis;

– the power density spectra received by this averaging are added for each frequency;

– the sum of signals achieved by this procedure will be treated as the input signal for all further calculations such as frequency response measurements, loudness rating calculation etc. as defined in ITU‑T Recommendation P.34.

For receiving loudness rating calculations the hands‑free factor HFLE replaces the LE factor used in the algorithm P.79:

– HFLE = 6 dB.

NOTE 1: The summing of the two ear signals of the HATS as described above leads to a level increase of about 6 dB under ideal conditions. This reflects the difference of loudness perceived subjectively when listening monaural (one ear listening) compared to binaural listening.

NOTE 2: The additional correction of 6 dB takes into account the different preferred listening levels for hands‑free MS’s in comparison to handset listening. The diffraction effect of the HATS is produced by the HATS itself. So this effect, described in ITU‑T Recommendation P.34 is not taken into account for HATS measurements.

Annex C (normative):
Transmission requirements testing