WM8904
Pre-Production
DAC INTERFACE VOLUME BOOST
A digital gain function is available at the audio interface to boost the DAC volume when a small signal
is received on DACDAT. This is controlled using register bits DAC_BOOST [1:0]. To prevent clipping
at the DAC input, this function should not be used when the boosted DAC data is expected to be
greater than 0dBFS.
The digital interface volume is controlled as shown in Table 29.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R24 (18h)
DAC Input Volume Boost
00 = 0dB
10:9
DAC_BOOST
[1:0]
00
Audio
Interface 0
01 = +6dB (Input data must not
exceed -6dBFS)
10 = +12dB (Input data must not
exceed -12dBFS)
11 = +18dB (Input data must not
exceed -18dBFS)
Table 29 DAC Interface Volume Boost
DIGITAL SIDETONE
A digital sidetone is available when ADCs and DACs are operating at the same sample rate. Digital
data from either left or right ADC can be mixed with the audio interface data on the left and right DAC
channels. Sidetone data is taken from the ADC high pass filter output, to reduce low frequency noise
in the sidetone (e.g. wind noise or mechanical vibration).
When using the digital sidetone, it is recommended that the ADCs are enabled before un-muting the
DACs to prevent pop noise. The DAC volumes and sidetone volumes should be set to an appropriate
level to avoid clipping at the DAC input.
When digital sidetone is used, it is recommended that the Charge Pump operates in Register Control
mode only (CP_DYN_PWR = 0). See “Charge Pump” for details.
The digital sidetone is controlled as shown in Table 30.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R32 (20h)
Left Digital Sidetone Volume
(See Table 31 for volume range)
Right Digital Sidetone Volume
(See Table 31 for volume range)
Left DAC Digital Sidetone Source
00 = No sidetone
11:8
ADCL_DAC_SVOL
[3:0]
0000
DAC Digital
0
7:4
3:2
ADCR_DAC_SVOL
[3:0]
0000
00
ADC_TO_DACL
[1:0]
01 = Left ADC
10 = Right ADC
11 = Reserved
Right DAC Digital Sidetone Source
00 = No sidetone
1:0
ADC_TO_DACR
[1:0]
00
01 = Left ADC
10 = Right ADC
11 = Reserved
Table 30 Digital Sidetone Control
PP, Rev 3.3, September 2012
64
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
