Silicon Laboratories SI2494/39, SI2493/57/34/15/04 manual Simplex Speakerphone U Registers

			AN93
		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.	0x7FFF
		Disable feature by setting this to 7FFFh.

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.

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