WM8281ECSSLASHR datasheet(71/392 Pages) CIRRUS

71 / 392 page

WM8281

Rev 4.0

MIC MUTE MIXER

The Mic Mute mixer function supports applications where two signal paths are multiplexed into a

single output. A typical use case is muting a microphone audio path and inserting a ‘comfort noise’

signal in place of the normal audio path.

The Mic Mute mixer function comprises two digital mixers (MICMIX and NOISEMIX), as illustrated in

Figure 28. A multiplexer selects one or other mixer as the Mic Mute output signal. Up to 4 input

sources can be selected for each mixer, and independent volume control is provided for each path.

MICMIX_VOL2

MICMIX_VOL3

MICMIX_VOL4

MICMIX_VOL1

MICMIX_SRC1

MICMIX_SRC3

MICMIX_SRC4

MICMIX_SRC2

Mic Mix

(Normal audio path)

NOISEMIX_VOL2

NOISEMIX_VOL3

NOISEMIX_VOL4

NOISEMIX_VOL1

NOISEMIX_SRC1

NOISEMIX_SRC3

NOISEMIX_SRC4

NOISEMIX_SRC2

Noise Mix

(Alternate signal path)

Mic Mute mixer (0Ch)

MICMUTE_MIX_ENA

MICMUTE_NOISE_ENA

Figure 28 Mic Mute Digital Mixers

The MICMIX and NOISEMIX control registers (see Figure 28) are located at register addresses

R1632 (0660h) through to R1647 (066Fh).

The full list of digital mixer control registers is provided in the “Register Map” section (Register R1600

through to R3000). Generic register definitions are provided in Table 8.

The Mic Mute mixer can be selected as input to any of the digital mixers or signal processing

functions within the WM8281 digital core. The bracketed number (0Ch) in Figure 28 indicates the

corresponding *_SRCn register setting for selection of the Mic Mute mixer as an input to another

digital core function.

The sample rate for the Mic Mute mixer and multiplexer is configured using the MICMUTE_RATE

to any signal chain that is asynchronous and/or configured for a different sample rate.

The control registers associated with the Mic Mute mixer function are described in Table 9.

The output of the Mic Mute mixer and multiplexer is enabled using MICMUTE_MIX_ENA.

The multiplexer is controlled using the MICMUTE_NOISE_ENA register bit, selecting MICMIX or

NOISEMIX as the output signal source.

Under recommended operating conditions, the MICMIX output is selected for normal (audio)

cond

itions, and the NOISEMIX output is selected for mute (or ‘comfort noise’) conditions.

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