wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 49

• Manufacturer Part Number: wm8918
• Description: Ultra Low Power Dac For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

Production Data
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QUICK RELEASE CONTROL
The DRC includes a Quick-Release feature to handle short transient peaks that are not related to the
intended source signal. For example, in handheld microphone recording, transient signal peaks
sometimes occur due to user handling, key presses or accidental tapping against the microphone.
The Quick Release feature ensures that these transients do not cause the intended signal to be
masked by the longer time constants of DRC_DCY.
The Quick-Release feature is enabled by setting the DRC_QR bit. When this bit is enabled, the DRC
measures the crest factor (peak to RMS ratio) of the input signal. A high crest factor is indicative of a
transient peak that may not be related to the intended source signal. If the crest factor exceeds the
level set by DRC_QR_THR, then the normal decay rate (DRC_DCY) is ignored and a faster decay
rate (DRC _QR_DCY) is used instead.
The DRC Quick-Release control bits are described in Table 18.
Table 18 DRC Quick-Release Control
GAIN SMOOTHING
The DRC includes a gain smoothing filter in order to prevent gain ripples. A programmable level of
hysteresis is also used to control the DRC gain. This improves the handling of very low frequency
input signals whose period is close to the DRC attack/decay time. DRC Gain Smoothing is enabled
by default and it is recommended to use the default register settings.
The extent of the gain smoothing filter may be adjusted or disabled using the control fields described
in Table 19.
Table 19 DRC Gain Smoothing
R40 (28h)
DRC Control 0
R41 (29h)
DRC Control 1
R40 (28h)
DRC Control 0
REGISTER
REGISTER
ADDRESS
ADDRESS
12:11
BIT
BIT
7:6
5:4
2
3
0
DRC_GS_HYST
DRC_GS_HYST
DRC_QR_THR
DRC_QR_DCY
DRC_GS_ENA
_LVL [1:0]
DRC_QR
LABEL
LABEL
[1:0]
[1:0]
DEFAULT
DEFAULT
01
00
00
1
1
1
Quick release enable
0 = disabled
1 = enabled
Quick release crest factor threshold
00 = 12dB
01 = 18dB (default)
10 = 24dB
11 = 30dB
Quick release decay rate
(seconds/6dB)
00 = 0.725ms (default)
01 = 1.45ms
10 = 5.8ms
11 = Reserved
Gain smoothing hysteresis
threshold
00 = Low
01 = Medium (recommended)
10 = High
11 = Reserved
Gain smoothing enable
0 = disabled
1 = enabled
Gain smoothing hysteresis enable
0 = disabled
1 = enabled
PD, Rev 4.0, September 2010
DESCRIPTION
DESCRIPTION
WM8918
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