WM8904
Pre-Production
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.
PP, Rev 3.3, September 2012
68
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
