WM8903LGEFK/RV Wolfson Microelectronics, WM8903LGEFK/RV Datasheet - Page 44

• Manufacturer Part Number: WM8903LGEFK/RV
• Description: Audio CODECs ULTRA LOW PWR HI FI CODEC
• Manufacturer: Wolfson Microelectronics

Specifications of WM8903LGEFK/RV

• Audio Codec Type: Stereo Codec
• No. Of Adcs: 2
• No. Of Dacs: 2
• No. Of Input Channels: 6
• No. Of Output Channels: 8
• Adc / Dac Resolution: 24bit
• Sampling Rate: 96kHz
• Operating Temperature Range: -40°C To +85°C
• Rohs Compliant: Yes
• Adcs / Dacs Signal To Noise Ratio: 96dB
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

WM8903
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ANTI-CLIP CONTROL
The DRC includes an Anti-Clip feature to avoid signal clipping when the input amplitude rises very
quickly. This feature uses a feed-forward technique for early detection of a rising signal level. Signal
clipping is avoided by dynamically increasing the gain attack rate when required. The Anti-Clip
feature is enabled using the DRC_ANTICLIP_ENA bit.
Note that the feed-forward processing increases the latency in the input signal path. For low-latency
applications (e.g. telephony), it may be desirable to reduce the delay, although this will also reduce
the effectiveness of the anti-clip feature. The latency is determined by the DRC_FF_DELAY bit. If
necessary, the latency can be minimised by disabling the anti-clip feature altogether.
The DRC Anti-Clip control bits are described in Table 18.
Table 18 DRC Anti-Clip Control
Note that the Anti-Clip feature operates entirely in the digital domain, i.e. after the ADC. It cannot be
used to prevent signal clipping in the analogue domain (e.g. in the input PGAs or ADCs), nor in the
source signal. Analogue clipping can only be prevented by reducing the analogue signal gain or by
adjusting the source signal.
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_DECAY_RATE.
The Quick-Release feature is enabled by setting the DRC_QR_ENA 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_THRESH_QR, then the normal decay rate (DRC_DECAY_RATE) is
ignored and a faster decay rate (DRC_RATE_QR) is used instead.
The DRC Quick-Release control bits are described in Table 19.
R40 (28h)
DRC 0
REGISTER
ADDRESS
BIT
5
1
DRC_FF_DELAY
DRC_ANTICLIP_
ENA
LABEL
DEFAULT
1
1
Feed-forward delay for anti-clip
feature
0 = 5 samples
1 = 9 samples
Time delay can be calculated as
5/f
rate.
Anti-clip enable
0 = disabled
1 = enabled
s
or 9/ f
PP, Rev 3.1, August 2009
s
DESCRIPTION
, where f
s
is the sample
Pre-Production
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