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7<TITLE>Hardware Noise in Microphone Input: Overview</TITLE>
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11<H1 align="left">Hardware Noise in Microphone Input: Overview <IMG src="../../image/TWL.gif"></H1>
12<P>The explanation on this page relates to TWL hardware behavior.</P>
13<H2>Description</H2>
14<P>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 <A href="../../snd/sndex/SNDEX_SetIirFilter.html"><CODE>SNDEX_SetIirFilter[Async]</CODE></A> functions to implement an 8 kHz BEF filter. This type of filter will damp a specific frequency component.
15</P>
16
17<H2>Implementation</H2>
18<P>We recommend that you pass the following parameters (<A href="../../snd/sndex/SNDEXIirFilterParam.html"><CODE>SNDEXIirFilterParam</CODE></A> structure) to one of the <A href="../../snd/sndex/SNDEX_SetIirFilter.html"><CODE>SNDEX_SetIirFilter[Async]</CODE></A> functions.</P>
19<UL>
20	<LI>For a Sampling Frequency of 32.73 kHz</LI>
21	<UL>
22		<LI>n0: 6B36</LI>
23		<LI>n1: FC2D</LI>
24		<LI>n2: 6B36</LI>
25		<LI>d1: 03D3</LI>
26		<LI>d2: A994</LI>
27	</UL>
28	<LI>For a Sampling Frequency of 47.61 kHz</LI>
29	<UL>
30		<LI>n0: 7108</LI>
31		<LI>n1: C7D7</LI>
32		<LI>n2: 7108</LI>
33		<LI>d1: 3829</LI>
34		<LI>d2: 9DF0</LI>
35	</UL>
36</UL>
37
38<H2>Notes</H2>
39<P>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.</P>
40
41<H2>Revision History</H2>
42<P>2008/09/01 Initial version.</P>
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