WM8944BECSSLASHR datasheet(45/165 Pages) CIRRUS

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WM8944B

Rev 4.3

DYNAMIC CHARACTERISTICS

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

that the DRC responds to the peak signal amplitude over a period of time.

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

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

These register fields are described in Table 21. Note that the register defaults are suitable for general

purpose microphone use.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R31 (1Fh)

DRC Control 3

7:4

DRC_ATK [3:0]

0100

Attack rate relative to the input

signal (seconds/6dB)

0000 = Reserved

0001 = 181us

0010 = 363us

0011 = 726us

0100 = 1.45ms

0101 = 2.9ms

0110 = 5.8ms

0111 = 11.6ms

1000 = 23.2ms

1001 = 46.4ms

1010 = 92.8ms

1011 = 185.6ms

1100-1111 = Reserved

3:0

DRC_DCY [3:0]

0010

Decay rate relative to the input

signal (seconds/6dB)

0000 = 186ms

0001 = 372ms

0010 = 743ms

0011 = 1.49s

0100 = 2.97s

0101 = 5.94s

0110 = 11.89s

0111 = 23.78s

1000 = 47.56s

1001-1111 = Reserved

Table 21 DRC Time Constants

Under the following conditions, it is possible to predict the attack times with an input sine wave:

Decay rate is set at least 8 times the attack rate.

Attack time * input frequency > 1

To estimate the attack time for 10%-90%:

Attack Time = Register Value * 2.24

For example, if DRC_ATK = 1.45ms/6dB, then the attack time (10%-90%) = 1.45ms * 2.24 = 3.25ms.

The decay time for 10%-90% can be estimated using the graph in Figure 17.

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