WM8281ECSSLASHR datasheet(79/392 Pages) CIRRUS

79 / 392 page

WM8281

Rev 4.0

The slope of the DRC response is determined by register fields DRCn_HI_COMP and

DRCn_LO_COMP. A slope of 1 indicates constant gain in this region. A slope less than 1 represents

compression (i.e. a change in input amplitude produces only a smaller change in output amplitude). A

slope of 0 indicates that the target output amplitude is the same across a range of input amplitudes;

this is infinite compression.

When the noise gate is enabled, the DRC response in this region is determined by the

DRCn_NG_EXP register. A slope of 1 indicates constant gain in this region. A slope greater than 1

represents expansion (ie. a change in input amplitude produces a larger change in output amplitude).

When the DRCn

_KNEE2_OP knee is enabled (“Knee2” in Figure 31), this introduces the vertical line

in the response pattern illustrated, resulting in infinitely steep attenuation at this point in the response.

The DRC parameters are listed in Table 14.

REF

PARAMETER

DESCRIPTION

DRCn_KNEE_IP

Input level at Knee1 (dB)

DRCn_KNEE_OP

Output level at Knee2 (dB)

DRCn_HI_COMP

Compression ratio above Knee1

DRCn_LO_COMP

Compression ratio below Knee1

DRCn_KNEE2_IP

Input level at Knee2 (dB)

DRCn_NG_EXP

Expansion ratio below Knee2

DRCn_KNEE2_OP

Output level at Knee2 (dB)

Table 14 DRC Response Parameters

The noise gate is enabled when the DRCn_NG_ENA register is set. When the noise gate is not

enabled, parameters 5, 6, 7 above are ignored, and the DRCn_LO_COMP slope applies to all input

signal levels below Knee1.

The DRCn_KNEE2_OP knee is enabled when the DRCn_KNEE2_OP_ENA register is set. When this

bit is not set, then parameter 7 above is ignored, and the Knee2 position always coincides with the

low end of the DRCn_LO_COMP region.

The “Knee1” point in Figure 31 is determined by register fields DRCn_KNEE_IP and

DRCn_KNEE_OP.

Parameter Y0, the output level for a 0dB input, is not specified directly, but can be calculated from the

other parameters, using the equation:

Y0 = DRCn_KNEE_OP - (DRCn_KNEE_IP x DRCn_HI_COMP)

Gain Limits

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

DRCn_MAXGAIN and DRCn_NG_MINGAIN. These limits can be used to alter the DRC response

from that illustrated in Figure 31. If the range between maximum and minimum gain is reduced, then

the extent of the dynamic range control is reduced.

The minimum gain in the Compression regions of the DRC response is set by DRCn_MINGAIN. The

mimimum gain in the Noise Gate region is set by DRCn_NG_MINGAIN. The minimum gain limit

prevents excessive attenuation of the signal path.

The maximum gain limit set by DRCn_MAXGAIN prevents quiet signals (or silence) from being

excessively amplified.

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