WM8904ECSSLASHR datasheet(68/188 Pages) WOLFSON

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WM8904

Pre-Production

PP, Rev 3.3, September 2012

DAC SOFT MUTE AND SOFT UN-MUTE

The WM8904 has a soft mute function. When enabled, this gradually attenuates the volume of the

DAC output. When soft mute is disabled, the gain will either gradually ramp back up to the digital gain

setting, or return instantly to the digital gain setting, depending on the DAC_UNMUTE_RAMP register

bit.

To mute the DAC, this function must be enabled by setting DAC_MUTE to 1.

Soft Mute Mode would typically be enabled (DAC_UNMUTE_RAMP = 1) when using DAC_MUTE

during playback of audio data so that when DAC_MUTE is subsequently disabled, the sudden volume

increase will not create pop noise by jumping immediately to the previous volume level (e.g. resuming

playback after pausing during a track).

Soft Mute Mode would typically be disabled (DAC_UNMUTE_RAMP = 0) when un-muting at the start

of a music file, in order that the first part of the track is not attenuated (e.g. when starting playback of

a new track, or resuming playback after pausing between tracks).

DAC muting and un-muting using volume control bits

DACL_VOL and DACR_VOL.

DAC muting and un-muting using the DAC_MUTE bit.

If soft Mute Mode is not enabled (DAC_UNMUTE_RAMP = 0):

Setting the DAC_MUTE bit causes the volume to ramp down

at a rate controlled by DAC_MUTERATE.

Clearing the DAC_MUTE bit causes the volume to return to

the un-muted level immediately.

DAC muting and un-muting using the DAC_MUTE bit.

If soft Mute Mode is enabled (DAC_UNMUTE_RAMP = 1):

Setting the DAC_MUTE bit causes the volume to ramp down.

Clearing the DAC_MUTE bit causes the volume to ramp up to

the un-muted level at a rate controlled by DAC_MUTERATE.

Figure 36 DAC Mute Control

The volume ramp rate during soft mute and un-mute is controlled by the DAC_MUTERATE bit. Ramp

rates of fs/32 and fs/2 can be selected, as shown in Table 35. The ramp rate determines the rate at

which the volume is increased or decreased. The actual ramp time depends on the extent of the

difference between the muted and un-muted volume settings.

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