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WM8775

w

PP Rev 1.8, June 2004

25

REGISTER

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

LC attack (gain ramp-down) time

3:0

ATK[3:0]

0010

ALC mode

0000: 8.4ms

0001: 16.8ms

0010: 33.6ms…

(time doubles with

every step)

1010 or higher:

8.6s

Limiter Mode

0000: 250us

0001: 500us… 0010:

1ms

(time doubles with

every step)

1010 or higher: 256ms

LC decay (gain ramp-up) time

R18(12h)

0010010

ALC

Control 3

7:4

DCY [3:0]

0011

ALC mode

0000: 33.5ms

0001: 67.2ms

0010: 134.4ms

….(time doubles for

every step)

1010 or higher:

34.3ms

Limiter mode

0000: 1.2ms

0001: 2.4ms

0010: 4.8ms ….(time

doubles for every

step)

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

Limiter Control

6:4

TRANWIN

[2:0]

010

Length of Transient Window

000: 0us (disabled)

001: 62.5us

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

ALC Control 2

7

ALCZC

0

(disabled)

PGA zero cross enable

0 : disabled

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.