WM8961 datasheet(34/116 Pages) WOLFSON

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WM8961

Pre-Production

PP, August 2009, Rev 3.1

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).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R20 (14h)

Noise Gate

Control

7:3

NGTH

[4:0]

00000

Noise gate threshold

00000

-76.5dBfs

00001

-75dBfs

… 1.5 dB steps

11110

-31.5dBfs

11111

-30dBfs

NGG

Noise gate mode

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

WM8961 Datasheet(PDF) 34 Page - Wolfson Microelectronics plc

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