Production Data
WM8978
w
PD, Rev 4.5, October 2011
49
The DAC output phase defaults to non-inverted. Setting DACPOLL will invert the DAC output phase
on the left channel and DACPOLR inverts the phase on the right channel.
AUTO-MUTE
The DAC has an auto-mute function which applies an analogue mute when 1024 consecutive zeros
are detected. The mute is released as soon as a non-zero sample is detected. Automute can be
disabled using the AMUTE control bit.
DIGITAL HI-FI DAC VOLUME (GAIN) CONTROL
The signal volume from each hi-fi DAC can be controlled digitally. The gain and attenuation range is
–127dB to 0dB in 0.5dB steps. The level of attenuation for an eight-bit code X is given by:
0.5
(X-255) dB for 1
X
255;
MUTE for X = 0
REGISTER
ADDRESS
BIT LABEL DEFAULT
DESCRIPTION
R11
Left DAC
Digital Volume
7:0 DACVOLL
[7:0]
11111111
( 0dB )
Left DAC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
8 DACVU
Not
latched
DAC left and DAC right volume do
not update until a 1 is written to
DACVU (in reg 11 or 12)
R12
Right DAC
Digital Volume
7:0 DACVOLR
[7:0]
11111111
( 0dB )
Right DAC Digital Volume Control
0000 0000 = Digital Mute
0000 0001 = -127dB
0000 0010 = -126.5dB
... 0.5dB steps up to
1111 1111 = 0dB
8 DACVU
Not
latched
DAC left and DAC right volume do
not update until a 1 is written to
DACVU (in reg 11 or 12)
Table 28 DAC Digital Volume Control
Note:
An additional gain of up to +12dB can be added using the gain block embedded in the
digital peak limiter circuit (see DAC OUTPUT LIMITER section).
5-BAND EQUALISER
A 5-band graphic equaliser function which can be used to change the output frequency levels to suit
the environment. This can be applied to the ADC or DAC path and is described in the 5-BAND
EQUALISER section for further details on this feature.
3-D ENHANCEMENT
The WM8978 has an advanced digital 3-D enhancement feature which can be used to vary the
perceived stereo separation of the left and right channels. Like the 5-band equaliser this feature can
be applied to either the ADC record path or the DAC playback path but not both simultaneously. See
the 3-D STEREO ENHANCEMENT section for further details on this feature.
DAC DIGITAL OUTPUT LIMITER
The WM8978 has a digital output limiter function. The operation of this is shown in Figure 25. In this
diagram the upper graph shows the envelope of the input/output signals and the lower graph shows
the gain characteristic.
Summary of Contents for WM8978
Page 11: ...Production Data WM8978 w PD Rev 4 5 October 2011 11 SPEAKER OUTPUT THD VERSUS POWER...
Page 14: ...WM8978 Production Data w PD Rev 4 5 October 2011 14 AUDIO PATHS OVERVIEW...
Page 55: ...Production Data WM8978 w PD Rev 4 5 October 2011 55 Figure 26 Left Right Output Channel Mixers...
Page 60: ...WM8978 Production Data w PD Rev 4 5 October 2011 60 Figure 29 Speaker Outputs LOUT2 and ROUT2...