Hardware Noise in Microphone Input: Overview

The explanation on this page relates to TWL hardware behavior.

Description

It has been confirmed that slight hardware noise at approximately 8 kHz will be mixed with microphone input on the TWL system. To remove this hardware noise and achieve clearer microphone input, use the SNDEX_SetIirFilter[Async] functions to implement an 8 kHz BEF filter. This type of filter will damp a specific frequency component.

Implementation

We recommend that you pass the following parameters (SNDEXIirFilterParam structure) to one of the SNDEX_SetIirFilter[Async] functions.

• For a Sampling Frequency of 32.73 kHz
• n0: 6B36
• n1: FC2D
• n2: 6B36
• d1: 03D3
• d2: A994
• For a Sampling Frequency of 47.61 kHz
• n0: 7108
• n1: C7D7
• n2: 7108
• d1: 3829
• d2: 9DF0

Notes

This filter can only be implemented in CODEC-TWL mode. Implementing the BEF filter will also damp normal 8 kHz components that are not noise.

Revision History

2008/09/01 Initial version.

CONFIDENTIAL