Product Brief

WM2002

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Product Brief, September 2013, Rev 4.1

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WOLFSON AMBIENT NOISE CANCELLATION (ANC)

The Wolfson (ANC) engine within the WM2002 improves the intelligibility of a voice call by using

destructive interference to reduce the acoustic energy of the ambient sound.

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

programmed on integrated OTP memory. 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 WM2002 configuration parameters are determined during development and are

programmed in the OTP memory during production calibration. These 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 ANC engine employs digital circuits to process the ambient noise (microphone) signals; these

inputs are digitized by two Analogue to Digital Converters (ADCs), then filtered and processed in

accordance with the acoustic parameters programmed into the WM2002. The noise cancellation

signals are then output via two Digital to Analogue Converters (DACs) and mixed with the received

voice or audio playback (line) signals.

The ANC engine can support multiple noise cancellation filter coefficients, to enable best

performance under different ambient noise conditions and different audio playback conditions. Other

user-selectable options are also available, such as mute or talk-through modes.

A high pass filter provides rejection of wind noise and other low frequency signals .Noise cancellation

is applied selectively to different audio frequency bands. A configurable low frequency limiter protects

the loudspeaker from excessive signal levels, and ensures that the ANC algorithms deliver noise

reduction in the most sensitive frequency bands, without introducing distortion in other frequency

bands.

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

sound at the headphone audio output. The integrated noise gate automatically mutes the noise

cancelling input at low ambient noise levels; this ensures that the noise cancellation performance is

optimised across a wide range of input signal conditions. The noise gate threshold level, attack time

and decay time are all configurable.

The various functions of ANC engine, as described above, combine to form a comprehensive, stand-

alone noise-cancelling product.