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WM8775
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
LC attack (gain ramp-down) time
R18(12h)
0010010
ALC
3:0
ATK[3:0]
0010
ALC mode
Limiter Mode
0000: 250us
0000: 8.4ms
Control 3
0001: 16.8ms
0001: 500us… 0010:
1ms
0010: 33.6ms…
(time doubles with
every step)
(time doubles with
every step)
1010 or higher:
8.6s
1010 or higher: 256ms
7:4
DCY [3:0]
0011
LC decay (gain ramp-up) time
ALC mode
Limiter mode
0000: 33.5ms
0001: 67.2ms
0010: 134.4ms
0000: 1.2ms
0001: 2.4ms
0010: 4.8ms ….(time
….(time doubles for doubles for every
every step)
step)
1010 or higher:
34.3ms
1010 or higher:
1.2288s
TRANSIENT WINDOW (LIMITER ONLY)
To prevent the limiter responding to to short duration high ampitude signals (such as hand-claps in a
live performance), the limiter has a programmable transient window preventing it responding to
signals above the threshold until their duration exceeds the window period. The Transient window is
set in register TRANWIN.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R20(14h)
0010100
6:4
TRANWIN
[2:0]
010
Length of Transient Window
000: 0us (disabled)
001: 62.5us
Limiter Control
010: 125us
…..
111: 4ms
ZERO CROSS
The PGA has a zero cross detector to prevent gain changes introducing noise to the signal. In ALC
mode the register bit ALCZC allows this to be turned off if desired.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R17(11h)
0010001
7
ALCZC
0
PGA zero cross enable
0 : disabled
(disabled)
ALC Control 2
1: enabled
MAXIMUM GAIN (ALC ONLY) AND MAXIMUM ATTENUATION
To prevent low level signals being amplified too much by the ALC, the MAXGAIN register sets the
upper limit for the gain. This prevents low level noise being over-amplified. The MAXGAIN register
has no effect on the limiter operation.
The MAXATTEN register has different operation for the limiter and for the ALC. For the limiter it
defines the maximum attenuation below the static (user programmed) gain. For the ALC, it defines
the lower limit for the gain.
PP Rev 1.8, June 2004
25
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
