Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 213)

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7.7.3. External Microphone/Speaker Calibration
The Si2494/39 speakerphone calibration is required for a new external speaker and microphone pair to work
properly with the speakerphone code. This section covers the following procedures:
 To calibrate the speaker and microphone module from a commercial reference platform to have the same
speaker loudness and microphone sensitivity relative to those of the active reference system.
 To calibrate the speakerphone gains so that the AEC/DTD input signal levels are ensured for optimal AEC/AES/
DTD performance.
The external analog gains on the Si24xx-VMB should be finalized before the performing the speakerphone
calibration.
7.7.3.1. Transmit Gain Calibration—Speakerphone Disabled
Figure 32 illustrates the reference setup where the commercial speakerphone is active with default settings. 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 speakerphone’s microphone. Play out white noise
as the near-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. Record the white noise level and disconnect the call.
Figure 32. Transmit Gain Reference Measurements
Figure 33 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 134. Place the same sound source at a distance of one foot from the speakerphone’s microphone. Play
out the same white noise as the near-end speech through the sound source, and adjust the transmit gain UB1 so
that the level at the Si24xx Tip/Ring is –15 dBm. Record the calibrated UB1 value.
Table 133. Simplex Speakerphone U Registers
Register Name Description Default Value
U1D5 SSPHLDTIM Extra time SSP stays in RX or TX mode to prevent frequent switching 0x0000
U1D6 SSPLTHRSH Local talker threshold 0x0000
U1D7 SSPRTHRSH Remote talker threshold 0x0000
U1D8 SSPBKTHRU Break-through threshold for speaker in auto-switch mode.
Disable feature by setting this to 7FFFh.
0x7FFF