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WM8777
ANALOGUE TONE CONTROLS
Facilities are provided for implementation of analogue treble and bass tone controls on each of the
Front left, right and centre channels. External R and C values are used to set the corner frequencies
of these tone control functions, allowing the system builder to choose the required responses.
Adjustment of the amplitude of the required tone response is made electronically by writing the
required gain or attenuation value into the WM8777 over the serial control interface. Maximum boost
or attenuation of tone control values of +/-10dB in 1dB steps is provided.
A tone control bypass path is provided, plus input summing paths for Rear (i.e. Surround L/R),
Centre and LFE channels, to allow for creation of a stereo ‘mix-down’ signal when only two speakers
are supported. Each of these mix-down paths has independent gain adjust from 0dB to -6db in 1dB
steps.
An analogue input bypass path is also provided. This allows AIN6L and AIN6R to be output on the
FRONTL and FRONTR output channels making use of the volume controls if required.
In order to provide sufficient headroom for cases where significant amounts of analogue treble or
bass boost have been applied, a gain attenuation control is provided in the summing stage after the
tone adjust PGAs. This allows attenuation of -6dB, -12dB or -18dB to be applied. Re-adjustment of
the nominal 0dB signal level may then be made in the following volume control stage as required.
Stereo Mix-down inputs
AIN6L/R
RearL/R
Center
No-Sub Option LFE
Tone Control Bypass
0 to -6dB
Bass Managed Signal
pad
Bass
management filter
Main Volume Control
+20dB to -100dB
0, -6,
-12, -18dB
XIN3
DAC
Bass boost
Bass cut
Bass filter
XIN2
Bypass
pad
XSUMOP
pad
pad
FRONTL/R
Aux input
Treble boost
Treble cut
XIN1
pad
Treble filter
+/-10dB
Bass
Management
Figure 1 Tone Control Configuration - Front Left/Right (single channel shown)
To Front L/R
No-Sub Option LFE
0 to -6dB
Tone Control Bypass
Bass Managed Signal
pad
CIN3
Bass
management filter
Main Volume Control
+20dB to -100dB
0, -6,
-12, -18dB
DAC
Bass boost
Bass cut
Bass filter
CIN2
pad
Bypass
pad
CNTSUMOP
pad
Aux input
Treble boost
Treble cut
CNTR
CIN1
pad
Treble filter
+/-10dB
Bass
Management
Figure 2 Tone Control Configuration - Centre Channel
PP Rev 1.94 November 2004
13
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
