C.9 Acoustic echo loss

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

C.9.1 Acoustic echo loss – Handset MS

The MS is mounted at the Loudness Rating Guardring Position (LRGP), (see annex 1 of ITU‑T recommendation P.76), with the earpiece sealed to the knife edge of the artificial ear, conforming to ITU‑T recommendation P.51.

A call is set up between the MS and the SS.

Where a user controlled volume control is provided it shall be set to maximum.

An implementation of the ITU‑T P.50 artificial speech shall be connected to the analogue or digital input of the reference speech encoder of the SS. This implementation could be a real time algorithm producing the artificial speech or a pre‑recorded tape of the artificial speech. Both "male" and "female" artificial speech is required.

A ten second segment of the "male" artificial speech is applied to the analogue or digital input of the reference speech encoder of the SS. The third octave power of the input signal shall be measured. The echo loss signal is not measured at his stage as the first ten second segment is used to allow any acoustic echo cancellation devices within the MS to adapt to the echo path.

Immediately afterwards a second ten second segment of the "male" artificial speech is applied to the analogue or digital input of the reference speech encoder of the SS. The third octave power of the echo signal is measured at the digital output of the reference speech decoder of the SS.

The difference between the third octave input power and the third octave output power is entered into the ITU‑T Recommendation G.122 TCL algorithm and the acoustic echo loss calculated.

The test shall be repeated with the "female" artificial speech and the results of both "male" and "female" averaged to give the final result.

C.9.2 Acoustic echo loss – Handsfree MS

– The handsfree MS is mounted as specified by the manufacturer and tested according to clauses B.4.2.1 or B.4.2.2, annex B.

– A speech call is set up between the MS and the SS.

– Where a user controlled volume control is provided it shall be set to nominal.

– Artificial speech conforming to ITU‑T Recommendation P.50, bandlimited to 200 Hz and 4 kHz shall be applied to the analogue or digital input of the reference speech encoder of the SS, at a level of –10 dBm0. This implementation could be a real time algorithm producing the artificial speech or a pre‑recorded tape of the artificial speech.

– The artificial speech shall comprise of a concatenation of three 10 s intervals of "male" and "female" voice. The first 10 s interval is not used for measurement purposes but allows any noise/echo cancelling devices in the MS to adapt. The second and third 10 s intervals consist of separately "male" and "female" artificial voice.

– The 1/3 octave filtered long‑term average spectrum of the signal power of the echo signal is measured at the digital output of the reference speech decoder of the SS and an average for the "male" and "female" voices obtained.

– The difference between the 1/3 octave input power and the 1/3 octave output power is entered into the ITU‑T G.122 TCL algorithm and the acoustic echo loss calculated.

– Steps b) to g) are repeated with the volume control set to the maximum user‑selectable position.