8.5 Sidetone characteristics

26.1323GPPRelease 18Speech and video telephony terminal acoustic test specificationTS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

8.5.1 Connections with handset UE

The test signal to be used for the measurements shall be the British-English single talk sequence described in ITU-T Recommendation P.501 [22]. The spectrum of the acoustic signal shall be produced by the HATS. The test signal level shall be ‑4,7 dBPa measured at the MRP. The test signal level is calculated over the complete test signal sequence.

a) The handset UE is set up as described in clause 5. The application force shall be 13 N on the Type 3.3 artificial ear.

b) Where a user operated volume control is provided, the measurements shall be carried out at the nominal setting of the volume control. In addition the measurement is repeated at the maximum volume control setting. It is expected that for other positions of the volume control setting a consistent behaviour to that of the nominal and maximum settings should be observed. Additional measurements for these positions are not required,

c) Measurements shall be made at 1/12-octave intervals as given by the R.40 series of preferred numbers in ISO 3 [54] for frequencies from 100 Hz to 8 kHz inclusive. The averaged measured level at DRP in each frequency band is referred to the averaged test signal level measured in each frequency band.

d The sidetone path loss (LmeST), as expressed in dB, shall be calculated from each 1/3^rd-octave band (ITU-T Recommendation P.79 [16], table B.1, bands 1 to 20). The Sidetone Masking Rating (STMR), expressed in dB, shall be calculated from formula B-4 of ITU-T Recommendation P.79 [16], using m = 0.225 and the weighting factors in table B2 (unsealed condition) of ITU-T Recommendation P.79 [16]. No leakage correction (L_E) shall be applied. DRP-ERP correction is used.

e) In case the STMR is below the limit, the measurement shall be repeated with the electrical sidetone path disabled and both sets of results shall be reported. In case the STMR is below the limit also with the electrical sidetone path disabled, the result shall not be regarded as a failure. Disconnecting the call is normally disabling the electrical sidetone path; otherwise the UE can be switched off to enter the wanted state.

8.5.2 Headset UE

The test signal to be used for the measurements shall be the British-English single talk sequence described in ITU-T Recommendation P.501 [22]. The spectrum of the acoustic signal produced by the artificial mouth is calibrated under free-field conditions at the MRP. The test signal level shall be –4,7 dBPa measured at the MRP. The test signal level is calculated over the complete test signal sequence.

a) The headset UE is set up as described in clause 5.

d) The sidetone path loss (LmeST), as expressed in dB, shall be calculated from each 1/3^rd-octave band (ITU-T Recommendation P.79 [16], table B.1, bands 1 to 20). The STMR (in dB) shall be calculated from formula B-4 of ITU-T Recommendation P.79 [16], using m = 0.225 and the weighting factors in table B.2 (unsealed condition) of ITU-T Recommendation P.79 [16]. No leakage correction (L_E) shall be applied. DRP-ERP correction is used.

8.5.3 Hands-free UE (all categories)

No requirement other than echo control.

8.5.3a Electrical interface UE

a) The test signal to be used for the measurements shall be the British-English single talk sequence described in ITU-T Recommendation P.501 [22]. The active speech level of the signal shall be calibrated to -60 dBV for analogue and to -16 dBm0 for digital connections. The test signal level is calculated over the complete test signal sequence.b) The reference signal to be used for the calculation shall be the same as the test signal and is calibrated to ‑4.7 dBPa (independent of analogue or digital connection).

c) Where a user operated volume control is provided, the measurements shall be carried out at the nominal setting of the volume control. In addition, the measurement is repeated at the maximum volume control setting. It is expected that for other positions of the volume control setting a consistent behaviour to that of the nominal and maximum settings should be observed. Additional measurements for these positions are not required.

d) Measurements shall be made at 1/12-octave intervals as given by the R.40 series of preferred numbers in ISO 3 [54] for frequencies from 100 Hz to 8 kHz inclusive. The averaged measured level at the electrical receiving reference interface in each frequency band is referred to the averaged reference signal level measured in each frequency band.

e) The measured sidetone sensitivity is corrected by a default sensitivity of 21.7 dBPa/V for analogue and 0.9 dBPa/V for digital connections (corresponding both to a binaural wideband RLR of 8 dB). This correction transfers the measured electrical sensitivity via an ideal headset (assuming a flat transfer function regarding ERP) to the acoustical domain.

NOTE: The difference in dB between nominal receiving levels of analogue (-39 dBV) and digital (-16 dBm0 = -18.2 dBV) connection equals 20.8 dB. This offset is taken into account for the default sensitivity of the analogue connection (21.7 dBPa/V – 20.8 dB = 0.9 dBPa/V).

f) The sidetone path loss and the STMR (in dB) shall be calculated from formula 5-1 of ITU-T P.79 [16], using m=0.225 and the weighting factors in Table 3 of ITU-T P.79 [16]. Leakage correction shall not be applied.

8.5.4 Sidetone delay for handset, headset or electrical interface UE

a) The handset or headset terminal is setup as described in clause 5.

b) The test signal is a CS-signal complying with ITU-T Recommendation P.501 using a PN-sequence with a length, T, of 4 096 points (for a 48 kHz sample rate test system). The duration of the complete test signal is as specified in ITU-T Recommendation P.501. The level of the signal shall be ‑4,7 dBPa at the MRP for handset or headset UE. For electrical interface UE, the level of the signal shall be -60 dBV for analogue and to -16 dBm0 for digital connections.

c) The cross-correlation function Φxy(τ) between the input signal Sx(t) generated by the test system in send direction and the output signal Sy(t) measured at the artificial ear (for handset/headset UE) or at the electrical reference interface (for electrical interface UE) is calculated in the time domain:

(1)

d) The measurement window, T, shall be identical to the test signal period, T, with the measurement window synchronized to the PN-sequence of the test signal.

e) The sidetone delay is calculated from the envelope E(τ) of the cross-correlation function Φxy(τ). The envelope E(τ) is calculated by the Hilbert transformation H {xy(τ)} of the cross-correlation:

(2)

(3)

f) For handset/headset UE:
The first maximum of the envelope function occurs in correspondence with the direct sound produced by the artificial mouth; the second one occurs with a possible delayed sidetone signal. The difference between the two maxima corresponds to the sidetone delay.

For electrical interface UE:
Since there is no direct sound produced by the artifical mouth and captured by the artifical ear, the maximum of the envelope function directly corresponds to the sidetone delay. The send and receive delays of the analogue electrical reference interface shall be subtracted from the determined sidetone delay.

NOTE: It is assumed that the measured sidetone delay is less than T/2.