WM8608 datasheet(38/54 Pages) WOLFSON

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WM8608

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PP Rev 1.5 March 2004

ATTACK AND DECAY TIMES

The attack time-constant ATK controls how fast the gain is reduced when the signal goes above the

threshold. It is defined as the time taken for the gain to reduce by 6dB. Normally a short attack time-

constant is used to prevent the signal clipping when a high-amplitude transient occurs.

The decay time-constant DCY controls how fast the gain is increased when the signal begins to fall

again. It is defined as the time taken for the gain to increase by 6dB. Normally, the decay time-

constant is much longer than the attack time-constant, to prevent the input signal from entering

repeated limiting cycles.

The frequency-dependent decay feature automatically detects the input frequency and sets the

decay time to decay slower for low frequency signals. This reduces low-frequency signal distortion by

preserving the waveform of each input cycle, whilst allowing the compressor to respond quickly to

high frequency transients. This feature is enabled via the FDEP control bit.

ZERO-CROSS

The Dynamic Peak Compressor has a zero cross detector to prevent gain changes introducing clicks

in the signal. The ZC is controlled by the same register R25 used in the volume control.

0dB

Output Level

(dB)

Peak Input Level [dB]

THRESH

[dB]

-6

-12

+12

-18

-24

-30

-36

-12

-18

-24

-30

-36

0dB

-6dB

-12dB

+6dB

+12dB

typical

Volume Control

Setting

Figure 22 Dynamic Peak Compressor Characteristics

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

PLENF

Front Channel Compressor Enable

0 = disable

1 = enable

PLENS

Surround Channel Compressor

Enable

0 = disable

1 = enable

R21 (15h)

Front,

Surround,

Front Centre

and Rear

Centre

Channel

Dynamic

Peak

Compressor

PLENC

Front Centre and Rear Centre

Channel Compressor Enable

0 = disable

1 = enable

Table 36 Front, Surround, Front Centre and Rear Centre Channel Dynamic Peak

Compressor (1)

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