Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 216)

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7.7.3.2. Receive Gain Calibration—Speakerphone Disabled
Figure 34 illustrates the reference setup where the commercial speakerphone is active with speaker set to
maximum volume. Using the reference commercial speakerphone, call the remote telephone and establish a voice
call. Place a sound source such as a PC speaker at a distance of one foot from the remote telephone microphone.
Play out white noise as the far-end speech through the sound source, and adjust the white noise level so that the
level at the speakerphone’s Tip/Ring is -15 dBm. Next, measure the speaker loudness by using a sound meter
(preferred) or a PC microphone to record the sound level at a distance of one foot from the speakerphone’s
speaker. Record the white noise level and speaker level loudness, and then disconnect the call.
Figure 34. Receive Gain Reference Measurements
Figure 35 illustrates the setup used to set the transmit gain. Here the modem has the AEC/AES disabled with
AT+VSP=0. Using the Si24xx-VMB, call the remote phone and establish a voice call. Use the command sequence
in Table 135. Send the same white noise as the far-end speech from the remote phone, and adjust the receive gain
UB5 so that the speaker loudness is the same as that of the reference speakerphone. Record the calibrated UB5
value.
Figure 35. Receive Gain Configuration