WM8904ECSSLASHR datasheet(55/188 Pages) WOLFSON

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Pre-Production

WM8904

PP, Rev 3.3, September 2012

GAIN LIMITS

The minimum and maximum gain applied by the DRC is set by register fields DRC_MINGAIN and

DRC_MAXGAIN. These limits can be used to alter the DRC response from that illustrated in Figure

29. If the range between maximum and minimum gain is reduced, then the extent of the dynamic

range control is reduced. The maximum gain prevents quiet signals (or silence) from being

excessively amplified.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R41 (29h)

DRC Control 1

3:2

DRC_MINGAIN [1:0]

Minimum gain the DRC can use

to attenuate audio signals

00 = 0dB (default)

01 = -6dB

10 = -12dB

11 = -18dB

1:0

DRC_MAXGAIN

[1:0]

Maximum gain the DRC can use

to boost audio signals

00 = 12dB

01 = 18dB (default)

10 = 24dB

11 = 36dB

Table 17 DRC Gain Limits

DYNAMIC CHARACTERISTICS

The dynamic behaviour determines how quickly the DRC responds to changing signal levels. Note

that the DRC responds to the average (RMS) signal amplitude over a period of time.

DRC_ATK determines how quickly the DRC gain decreases when the signal amplitude is high.

DRC_DCY determines how quickly the DRC gain increases when the signal amplitude is low.

These register fields are described in Table 18. Note that the register defaults are suitable for general

purpose microphone use.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R41 (29h)

DRC Control 1

15:12

DRC_ATK [3:0]

0011

Gain attack rate (seconds/6dB)

0000 = Reserved

0001 = 182µs

0010 = 363µs

0011 = 726µs (default)

0100 = 1.45ms

0101 = 2.9ms

0110 = 5.8ms

0111 = 11.6ms

1000 = 23.2ms

1001 = 46.4ms

1010 = 92.8ms

1011-1111 = Reserved

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