WM8591GEDSSLASHV datasheet(35/50 Pages) WOLFSON

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WM8591

PP Rev 1.0 May 2005

ATTACK AND DECAY TIMES

The limiter and ALC have different attack and decay times which determine their operation. However,

the attack and decay times are defined slightly differently for the limiter and for the ALC. DCY and

ATK control the decay and attack times, respectively.

Decay time (Gain Ramp-Up). When in ALC mode, this is defined as the time that it takes for the

PGA gain to ramp up across 90% of its range (e.g. from –21dB up to +20 dB). When in limiter mode,

it is defined as the time it takes for the gain to ramp up by 6dB.

The decay time can be programmed in power-of-two (2

n) steps. For the ALC this gives times from

33.6ms, 67.2ms, 134.4ms etc. to 34.41s. For the limiter this gives times from 1.2ms, 2.4ms etc., up

to 1.2288s.

Attack time (Gain Ramp-Down) When in ALC mode, this is defined as the time that it takes for the

PGA gain to ramp down across 90% of its range (e.g. from +20dB down to -21dB gain). When in

limiter mode, it is defined as the time it takes for the gain to ramp down by 6dB.

The attack time can be programmed in power-of-two (2

n) steps, from 8.4ms, 16.8ms, 33.6ms etc. to

8.6s for the ALC and from 250us, 500us, etc. up to 256ms.

The time it takes for the recording level to return to its target value or static gain value therefore

depends on both the attack/decay time and on the gain adjustment required. If the gain adjustment is

small, it will be shorter than the attack/decay time.

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]

1001

ALC mode

0000: 33.5ms

0001: 67.2ms

0010: 134.4ms

….(time doubles for

every step)

1001: 17.15s

1010 or higher:

34.3s

Limiter mode

0000: 1.2ms

0001: 2.4ms

0010: 4.8ms ….(time

doubles for every

step)

1001: 614.4ms

1010 or higher:

1.2288s

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.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R17 (11h)

0010001

ALC Control 2

ALCZC

(enabled)

PGA Zero Cross Enable:

0 : disabled

1: enabled

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