An international connection involving a 3G, LTE, NR or WLAN network and the PSTN should meet the overall loudness rating (OLR) limits in ITU-T Recommendation G.111 [4]. The national parts of the connection should therefore meet the send and receive loudness rating (SLR, RLR) limits in ITU-T Recommendation G.121 [5]. For the case where digital routings are used to connect the 3G, LTE, NR or WLAN network to the international chain of circuits, the SLR and RLR of the national extension will be largely determined by the SLR and RLR of the 3G, LTE, NR or WLAN network. The limits given below are consistent with the national extension limits and long term objectives in ITU-T Recommendation G.121 [5]. The SLR and RLR values for the 3G, LTE, NR or WLAN network apply up to the POI. However, the main determining factors are the characteristics of the UE, including the analogue to digital conversion (ADC) and digital to analogue conversion (DAC). In practice, it is convenient to specify loudness ratings to the Air Interface. For the normal case, where the 3G, LTE, NR or WLAN network introduces no additional loss between the Air Interface and the POI, the loudness ratings to the PSTN boundary (POI) will be the same as the loudness ratings measured at the Air Interface. However, in some cases loss adjustment may be needed for interworking situations in individual countries.

The nominal values of SLR/RLR to the POI shall be: Where a user-controlled receiving volume control is provided, the RLR shall meet the nominal value for at least one setting of the control. When the control is set to maximum, the RLR shall not be ≤ (equal or louder than) -13 dB and shall not be ≥ (equal or quieter than) -3 dB. With the volume control set to the minimum position the RLR shall not be ≥ (equal or quieter than) 24 dB and should not be ≥ (equal or quieter than) 18 dB. Compliance shall be checked by the relevant tests described in TS 26.132.

In the presence of background noise, the RLR at maximum volume control shall not be ≤ (equal or louder than) -13 dB. Compliance shall be checked by the relevant tests described in TS 26.132.

The nominal values of SLR/RLR to/from the POI shall be: Where a user-controlled volume control is provided, the RLR shall meet the nominal value for at least one setting of the control. It is recommended that a volume control giving at least 15 dB increase from the nominal RLR (louder) is provided for hands-free units. This is to allow for increased acoustic noise level in the usage environment. RLR at the maximum volume control setting should ≤ (equal or louder than) 1 dB. Compliance shall be checked by the relevant tests described in TS 26.132.

The nominal values of SLR/RLR to/from the POI shall be: Where a user-controlled volume control is provided, the RLR shall meet the nominal value for at least one setting of the control. The value of RLR at the maximum volume control shall be ≤ (equal or louder than) 12 dB. As a performance objective it is recommended that the RLR at the maximum volume control setting is ≤ (equal or louder than) 2 dB. Where a user-controlled volume control is provided, the RLR shall meet the nominal value for at least one setting of the control. It is recommended that a volume control range ≥ 15 dB be provided. Compliance shall be checked by the relevant tests described in TS 26.132.

The SLR and RLR should be measured and computed using methods given in ITU-T Recommendation P.380 [9]. This Recommendation currently gives a measuring technique for supra-aural earphone and insert type receivers. Study is continuing on other types of ear-pieces in ITU-T Study Group 12. The nominal values of SLR/RLR to/from the POI shall be: Where a user-controlled receiving volume control is provided, the RLR shall meet the nominal value for at least one setting of the control. When the control is set to maximum, the RLR shall not be ≤ (equal or louder than) -13 dB. With the volume control set to the minimum position the RLR shall not be ≥ (equal or quieter than) 18 dB and shall not be ≥ (equal or quieter than) 24 dB for a binaural headset. Compliance shall be checked by the relevant tests described in TS 26.132.

In the presence of background noise, the RLR at maximum volume control shall not be ≤ (equal or louder than) -13 dB. Compliance shall be checked by the relevant tests described in TS 26.132.

The maximum noise level produced by the apparatus at the output of the SS under silent conditions in the sending direction shall not exceed -64 dBm0(A). Compliance shall be checked by the relevant test described in TS 26.132.

The maximum (acoustic) noise level at the handset and headset UE when no signal is transmitted to the input of the SS shall be as follows:

• If no user-controlled receiving volume control is provided, or, if it is provided, at the setting of the user-controlled receiving volume control at which the RLR is equal to the nominal value, the noise measured at the DRP with diffuse-field correction contributed by the receiving equipment alone shall not exceed -57 dBPa(A).
• Where a volume control is provided, the measured noise shall be ≤ -54 dBPa(A) at the maximum setting of the volume control.

For the nominal volume control setting, the level of single frequency disturbances shall be ≤ -60 dBPa(A) in the frequency range from 100 Hz to 10 kHz. As a performance objective it is recommended that the level should be ≤ -64 dBPa(A). Compliance shall be checked by the relevant test described in TS 26.132.

The maximum noise level produced by the apparatus at the output of the SS under silent conditions in the sending direction shall be ≤ -64 dBm0(A). Compliance shall be checked by the relevant test described in TS 26.132.

The maximum A-weighted noise level when no signal is applied to the input of the SS shall be as follows: For the nominal volume control setting, the level of single frequency disturbances should be ≤ -90 dBV(A) for analogue and -67 dBm0(A) for digital connections in the frequency range from 100 Hz to 10 kHz. As a performance objective it is recommended that the level should be ≤ -94 dBV(A) for analogue and -71 dBm0(A) for digital connections. Compliance shall be checked by the relevant test described in TS 26.132.