wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 45

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

Production Data
DYNAMIC RANGE CONTROL (DRC)
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The dynamic range controller (DRC) is a circuit which can be enabled in the digital data path of either
the Digital Microphone input or the DAC playback. The function of the DRC is to adjust the signal
gain in conditions where the input amplitude is unknown or varies over a wide range, e.g. when
recording from microphones built into a handheld system. The DRC can apply Compression and
Automatic Level Control to the signal path. It incorporates ‘anti-clip’ and ‘quick release’ features for
handling transients in order to improve intelligibility in the presence of loud impulsive noises.
The DRC is enabled by DRC_ENA, as shown in Table 13. It can be enabled in the Digital
Microphone path or in the DAC digital path, under the control of the DRC_DAC_PATH register bit.
Note that the DRC can be active in only one of these paths at any time.
Table 13 DRC Enable
COMPRESSION/LIMITING CAPABILITIES
The DRC supports two different compression regions, separated by a “knee” at input amplitude T.
For signals above the knee, the compression slope DRC_HI_COMP applies; for signals below the
knee, the compression slope DRC_LO_COMP applies.
The overall DRC compression characteristic in “steady state” (i.e. where the input amplitude is near-
constant) is illustrated in Figure 29.
Figure 29 DRC Compression Characteristic
The slope of the DRC response is determined by register fields DRC_HI_COMP and
DRC_LO_COMP respectively. 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.
R40 (28h)
DRC Control 0
DRC Output Amplitude (dB)
DRC_KNEE_OP
REGISTER
ADDRESS
(Y0)
BIT
15
14
DRC_ENA
DRC_DAC_PAT
H
LABEL
DRC_KNEE_IP
“knee”
DRC Input Amplitude (dB)
DEFAULT
0
0
0dB
DRC enable
0 = Disabled
1 = Enabled
DRC path select
0 = Digital Microphone path
1 = DAC path
PD, Rev 4.0, September 2010
DESCRIPTION
WM8918
45