WM8961
Pre-Production
NOISE GATE
When the signal is very quiet and consists mainly of noise, the ALC function may cause “noise
pumping”, i.e. loud hissing noise during silence periods. The WM8961 has a noise gate function that
prevents noise pumping by comparing the signal level at the input pins against a noise gate threshold,
NGTH. The noise gate cuts in when:
Signal level at ADC [dB] < NGTH [dB] + PGA gain [dB] + Mic Boost gain [dB]
This is equivalent to:
Signal level at input pin [dB] < NGTH [dB]
The PGA gain can then either be muted or held constant (preventing it from ramping up as it normally
would when the signal is quiet) using the NGG bit.
The table below summarises the noise gate control register. The NGTH control bits set the noise gate
threshold with respect to the ADC full-scale range. The threshold is adjusted in 1.5dB steps. Levels at
the extremes of the range may cause inappropriate operation, so care should be taken with set–up of
the function. Note that the noise gate only works in conjunction with the ALC function, and always
operates on the same channel(s) as the ALC (left, right, both, or none).
REGISTER
ADDRESS
BIT
LABEL
NGTH
DEFAULT
DESCRIPTION
Noise gate threshold
R20 (14h)
00000
7:3
Noise Gate
Control
[4:0]
00000 -76.5dBfs
00001 -75dBfs
… 1.5 dB steps
11110 -31.5dBfs
11111 -30dBfs
NGG
0
0
Noise gate mode
1
0
0 : Hold PGA gain static when noise
gate triggers (recommended)
1 : Mute ADC output when noise gate
triggers.
NGAT
Noise gate function enable
0 = disable
1 = enable
Table 16 Noise Gate Control
PP, August 2009, Rev 3.1
w
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
