WM8777
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MIXER CONTROL
Control of the front channel signal paths is via five software registers. The first three registers control
both the front left and right channels whilst the remaining two control the centre channel. When only
two speakers are available a stereo mix-down signal can be created by setting the REAR, CNTR and
LFE bits of the appropriate register.
Control of the tone characteristics for a channel is determined by writing to the XTRBL and XBASS
register bits (where X implies either Front L/R or Centre channel). The tone controls work by
adding/subtracting high/low-pass filtered signal content to the nominal 0dB bass-managed signal.
Thus when using the tone controls, the XBM bit should also be set. Note also that cut and boost
cannot be applied simultaneously. If both bits are set, the tone control signal path will be bypassed
but the amplifiers will remain enabled. To avoid pop-noises during dynamic tone control it is
recommending that this method is used to disable the tone control signal path. Setting both bits low
disables the path, however it will also cause the amplifiers to power down.
The mixer control registers (FTRBL, FBASS, CTRBL and CBASS) share the zero-cross detect circuit
used by the analogue volume control. Thus the ZCEN enable bit for a particular channel can be used
to determine whether or not the tone control signal path select signals are updated only on a zero-
cross condition.
The bypass path is selected by setting the FBYP bit for the front L/R channels and the CBYP bit for
the centre channel. The centre, rear and LFE channels can all be independently summed into the
front L/R channels by setting the CNTR, REAR and FLFE bits respectively. Each of these signal
paths has independent gain control from 0 to -6dB, adjustable in 1dB steps. These gains are
determined by writing to the attenuation registers CNTRGAIN, REARGAIN and FLFEGAIN
respectively.
The LFE channel can also be summed into the front centre channel by setting the CLFE bit. This
path also has independent gain control from 0 to -6dB, controlled by writing to the CLFEGAIN
register.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
(22h)
1:0
FTRBL[1:0]
00
Control treble boost and cut:-
00 = both off ( Amps disabled)
01 = Treble cut
FRONT Mixer
Control 1
10 = Treble boosted
11 = both off (Amps enabled)
Controls bass boost and cut:-
00 = both off (Amps disabled)
01 = Bass cut
3:2
FBASS[1:0]
00
10 = Bass boosted
11 = both off (Amps enabled)
4
5
FBM
0
0
Bass Managed Signal path
select
0 = Open
1 = Closed
FBYP
Tone Control Bypass signal
path select
0 = Open
1 = Closed
6
AIN6
0
0 = AIN6 not selected
1 = AIN6 applied to FRONT
channels
(23h)
2:0
FLFEGAIN[2:0]
000
Front LFE gain:
000 = 0dB
001 = 1dB
010 = 2dB
011 = 3dB
100 = 4dB
101 = 4.5dB
110 = 5dB
111 = 6dB
FRONT Mixer
Control 2
PP Rev 1.94 November 2004
14
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
