Silicon Laboratories SI2493/57/34/15/04, SI2494/39 manual Receive Gain Reference Measurements

AN93

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

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