WM8978
Production Data
w
PD, Rev 4.5, October 2011
54
3D STEREO ENHANCEMENT
The WM8978 has a digital 3D enhancement option to increase the perceived separation between the
left and right channels. Selection of 3D for record or playback is controlled by register bit
EQ3DMODE. Switching this bit from record to playback or from playback to record may only be done
when ADC and DAC are disabled. The WM8978 control interface will only allow EQ3DMODE to be
changed when ADC and DAC are disabled (ie ADCENL = 0, ADCENR = 0, DACENL = 0 and
DACENR = 0).
The DEPTH3D setting controls the degree of stereo expansion.
When 3D enhancement is used, it may be necessary to attenuate the signal by 6dB to avoid limiting.
REGISTER
ADDRESS
BIT LABEL DEFAULT
DESCRIPTION
R41 (29h)
3D
3:0
DEPTH3D[3:0]
0000
Stereo depth
0000: 0% (minimum 3D effect)
0001: 6.67%
....
1110: 93.3%
1111: 100% (maximum 3D effect)
Table 37 3D Stereo Enhancement Function
ANALOGUE OUTPUTS
The WM8978 has three sets of stereo analogue outputs. These are:
LOUT1 and ROUT1 which are normally used to drive a headphone load.
LOUT2 and ROUT2 – normally used to drive an 8
Ω
BTL speaker.
OUT3 and OUT4 – can be configured as a stereo line out (OUT3 is left output and
OUT4 is right output). OUT4 can also be used to provide a mono mix of left and right
channels.
LOUT2, ROUT2, OUT3 and OUT4 are supplied from SPKVDD and are capable of driving up to
1.5Vrms signals as shown in Figure 26. LOUT1 and ROUT1 are supplied from AVDD and can only
drive out a 1V rms signal (AVDD/3.3).
LOUT1, ROUT1, LOUT2 and ROUT2 have individual analogue volume PGAs with -57dB to +6dB
ranges.
There are four output mixers in the output signal path, the left and right channel mixers which control
the signals to speaker, headphone (and optionally the line outputs) and also dedicated OUT3 and
OUT4 mixers.
LEFT AND RIGHT OUTPUT CHANNEL MIXERS
The left and right output channel mixers are shown in Figure 26. These mixers allow the AUX inputs,
the ADC bypass and the DAC left and right channels to be combined as desired. This allows a
mono mix of the DAC channels to be done as well as mixing in external line-in from the AUX or
speech from the input bypass path.
The AUX and bypass inputs have individual volume control from -15dB to +6dB and the DAC volume
can be adjusted in the digital domain if required. The output of these mixers is connected to both the
headphone (LOUT1 and ROUT1) and speaker (LOUT2 and ROUT2) and can optionally be
connected to the OUT3 and OUT4 mixers.
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...