WM8961 datasheet(40/116 Pages) WOLFSON

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WM8961

Pre-Production

PP, August 2009, Rev 3.1

DAC DIGITAL SIDETONE

A digital sidetone from the ADC is available at the DAC. 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 which may be present 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.

Note that when the ADC sidetone is used for the headphone output, and dynamic (Class W) power

saving is enabled (CP_DYN_PWR[1:0] = 0b11), the charge pump only monitors the DAC input level

rather than the ADC sidetone level. An ADC sidetone signal which is louder than the DAC input signal

could increase headphone output distortion because the charge pump settings are optimised for the

quieter DAC input signal. Hence dynamic (Class W) power saving is not recommended when the ADC

sidetone is louder than the DAC input. See also the ‘Charge pump Clocking’ section.

The digital sidetone is controlled as shown in Table 25.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R57 (39h)

DSP

Sidetone 0

7:4

ADCR_DAC_SVOL[3:0]

0000

Controls volume of ADC Right side tone,

3dB steps.

0000 : -36dB

0001 : -33dB

…

1111 : 0dB

(see Table 26 )

3:2

ADC_TO_DACR[1:0]

DAC Right Side-tone Control

11 = Unused

10 = Mix ADCR into DACR

01 = Mix ADCL into DACR

00 = No Side-tone mix into DACR

R58 (3Ah)

DSP

Sidetone 1

7:4

ADCL_DAC_SVOL[3:0]

0000

Controls volume of ADC Left side tone,

3dB steps.

0000 : -36dB

0001 : -33dB

…

1111 : 0dB

(see Table 26 )

3:2

ADC_TO_DACL[1:0]

DAC Left Side-tone Control

11 = Unused

10 = Mix ADCR into DACL

01 = Mix ADCL into DACL

00 = No Side-tone mix into DACL

Table 25 Digital Sidetone Control Registers

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