WM8281ECSSLASHR datasheet(140/392 Pages) CIRRUS

140 / 392 page

WM8281

140

Rev 4.0

AMBIENT NOISE CANCELLATION

The Cirrus Logic Ambient Noise Cancellation (ANC) processor within the WM8281 provides the

capability to improve the intelligibility of a voice call by using destructive interference to reduce the

acoustic energy of the ambient sound. The stereo ANC capability supports a wide variety of

headset/handset applications.

The ANC processor is configured using parameters that are determined during product development

and downloaded to the WM8281. The configuration settings are specific to the acoustic properties of

the target application. The primary acoustic elements in an application are typically the microphones

and the speaker, but other components such as the plastics and the PCBs also have significant

importance to the acoustic coefficient data.

Note that the ANC configuration parameters are application-specific, and must be recalculated

following any change in the design of the acoustic elements of that application. Any mismatch

between the acoustic coefficient data and the target application will give inferior ANC performance.

The signal path configuration settings are adjusted during product calibration to compensate for

component tolerances. Also, calibration allows DC offsets in the earpiece output path to be measured

and compensated, thus reducing power consumption and minimising any pops and clicks in the

output signal path.

The ANC processor employs stereo digital circuits to process the ambient noise (microphone) signals;

the noise input paths (analogue or digital) are selected as described in Table 6. The selected sources

are filtered and processed in accordance with the acoustic parameters programmed into the WM8281.

The resulting noise cancellation signals can be mixed with the output signal paths using the register

bits described in Table 63.

Noise cancellation is applied selectively to different audio frequency bands; a low frequency limiter

ensures that the ANC algorithms deliver noise reduction in the most sensitive frequency bands,

without introducing distortion in other frequency bands.

The ANC processor is adaptive to different ambient noise levels in order to provide the most natural

sound at the headphone audio output. The stereo ANC signal processing supports a very high level of

noise cancellation capability for a wide variety of headset/handset applications. It also incorporates a

noise gating function, which ensures that the noise cancellation performance is optimised across a

wide range of input signal conditions.

Note that the ANC configuration data is lost whenever the DCVDD power domain is removed; the

ANC configuration data must be downloaded to the WM8281 each time the device is powered up.

The procedure for configuring the WM8281

ANC functions is tailored to each customer’s application;

please contact your local Cirrus Logic representative for more details.

WM8281ECS/R Scheda tecnica(PDF) 140 Page - Cirrus Logic