WM8945
Production Data
Note that the Anti-Clip feature operates entirely in the digital domain. It cannot be used to prevent
signal clipping in the analogue domain nor in the source signal. Analogue clipping can only be
prevented by reducing the analogue signal gain or by adjusting the source signal.
The Anti-Clip and Quick Release features should not be used at the same time.
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 22.
REGISTER
ADDRESS
BIT
LABEL
DRC_QR
DEFAULT
DESCRIPTION
R29 (1Dh)
DRC Quick-release Enable
0 = Disabled
2
1
DRC Control 1
1 = Enabled
R34 (22h)
DRC_QR_THR
[1:0]
DRC Quick-release threshold (crest
factor in dB)
3:2
1:0
00
00
DRC Control 6
00 = 12dB
01 = 18dB
10 = 24dB
11 = 30dB
DRC_QR_DCY
[1:0]
DRC Quick-release decay rate
(seconds/6dB)
00 = 0.725ms
01 = 1.45ms
10 = 5.8ms
11 = reserved
Table 22 DRC Quick-Release Control
The Anti-Clip and Quick Release features should not be used at the same time.
DRC INITIAL VALUE
The DRC can be set up to a defined initial condition based on the expected signal level when the
DRC is enabled. This can be set using the DRC_INIT bits in register R35 (23h) bits 4 to 0.
Note: This does NOT set the initial gain of the DRC. It sets the expected signal level of the DRC input
signal when the DRC is enabled.
REGISTER
ADDRESS
BIT
LABEL
DRC_INIT
DEFAULT
DESCRIPTION
R35 (23h)
Initial value at DRC startup
00000 = 0dB
4:0
00000
DRC Control 7
00001 = -3.75dB
… (-3.75dB steps)
11111 = -116.25dB
PD, May 2011, Rev 4.1
44
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
