WM8991 datasheet(59/174 Pages) WOLFSON

59 / 174 page

Pre-Production

WM8991

PP, May 2008, Rev 3.1

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.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R5 (05h)

11:10

DAC_BOOST

[1:0]

00b

DAC Input Volume Boost

00 = 0dB

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 21 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).

The digital sidetone will not function when ADCs and DACs are operating at different sample rates.

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.

The digital sidetone is controlled as shown in Table 22.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

12:9

ADCL_DAC_SVOL

[3:0]

0000b

Left Digital Sidetone Volume

(See Table 23 for volume range)

8:5

ADCR_DAC_SVOL

[3:0]

0000b

Right Digital Sidetone Volume

(See Table 23 for volume range)

3:2

ADC_TO_DACL

[1:0]

00b

Left DAC Digital Sidetone Source

00 = No sidetone

01 = Left ADC

10 = Right ADC

11 = Reserved

R13 (0Dh)

1:0

ADC_TO_DACR

[1:0]

00b

Right DAC Digital Sidetone Source

00 = No sidetone

01 = Left ADC

10 = Right ADC

11 = Reserved

Table 22 Digital Sidetone Control

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