WM8706

Production Data

w

PD Rev 4.1 July 2005

14

Figure 9 shows the application and release of MUTE whilst a full amplitude sinusoid is being

played at 48kHz sampling rate. When MUTE (lower trace) is asserted, the output (upper trace)

begins to decay exponentially from the DC level of the last input sample. The output will decay

asserted, the output will restart almost immediately from the current input sample.

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

0

0.001

0.002

0.003

0.004

0.005

0.006

Time(s)

Figure 9 Application and Release of Soft Mute

The MUTEB pin is an input to select mute or not mute. MUTEB is active low; taking the pin low

causes the filters to soft mute, ramping down the audio signal over a few milliseconds. Taking

MUTEB high again allows data into the filter.

The automute function detects a series of zero value audio samples of 1024 samples long

being applied to both channels. After such an event, a latch is set whose output

(AUTOMUTED) is wire OR’ed through a 10kohm resistor to the MUTEB pin. Thus if the

MUTEB pin is not being driven, the automute function will assert mute.

If MUTEB is tied high, AUTOMUTE is overridden and will not mute unless the IZD register bit is

set. If MUTEB is driven from a bi-directional source, then both MUTE and automute functions

are available. If MUTEB is not driven, AUTOMUTED appears as a weak output (10k source

impedance) so can be used to drive external mute circuits. Automute will be removed as soon

as any channel receives a non-zero input.

A diagram showing how the various Mute modes interact is shown below in Figure 10.

IZD (Register Bit)

AUTOMUTED

(Internal Signal)

10k

Ω

Ω

Ω

Ω

MUT (Register Bit)

SOFTMUTE

(Internal

Signal)

MUTEB

PIN

Figure 10 Selection Logic for MUTE Modes