1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<HTML> 3<HEAD> 4<META http-equiv="Content-Type" content="text/html; charset=windows-1252"> 5<META name="GENERATOR" content="IBM WebSphere Studio Homepage Builder Version 7.0.0.0 for Windows"> 6<META http-equiv="Content-Style-Type" content="text/css"> 7<TITLE>How to Use IIR_FilterBuilder</TITLE> 8<LINK rel="stylesheet" href="../../../css/nitro.css" type="text/css"> 9</HEAD> 10<BODY> 11<H1 align="left">How to Use IIR_FilterBuilder <IMG src="../../../image/TWL.gif"></H1> 12<P>One extended TWL feature is the ability to apply an IIR filter to microphone sampling data and speaker output data. See <A href="../SNDEX_SetIirFilter.html"><CODE>SNDEX_SetIirFilter[Async]</CODE></A> for information on setting IIR filters. This document explains how to use IIR_FilterBuilder, which is included with the TWL-SDK.</P> 13 <H2>Description</H2> 14 <P>The <CODE>$TwlSDK/docs/TechnicalNotes/IIR_FilterBuilder.xls</CODE> Excel spreadsheet is designed to calculate IIR filter parameters. The calculated parameters can be used as parameters for the <A href="../SNDEX_SetIirFilter.html"><CODE>SNDEX_SetIirFilter[Async]</CODE></A> functions.</P> 15 16 <P>To use this sheet, you need to enable the <B>Analysis ToolPak</B> from <B>Tools</B> > <B>Add-Ins</B> in the Excel main menu. (Excel 2003)</P> 17 18 <H2>Using the Tool</H2> 19 <P>Choose one of the following three sheets to use.</P> 20 <TABLE> 21 <TBODY> 22 <TR> 23 <TH width="20%">Sheet name</TH> 24 <TH width="80%">Filter types that can be calculated</TH> 25 </TR> 26 <TR> 27 <TD width="20%">Shelf Filters</TD> 28 <TD width="80%">Bass Shelf Filter, Treble Shelf Filter</TD> 29 </TR> 30 <TR> 31 <TD width="20%">EQ Filters</TD> 32 <TD width="80%">Band Pass Filter, Band Eliminate Filter</TD> 33 </TR> 34 <TR> 35 <TD width="20%">Butterworth Filters</TD> 36 <TD width="80%">High Pass Filter, Low Pass Filter</TD> 37 </TR> 38 </TBODY> 39 </TABLE> 40 41 <P>Usually, the light blue items in the following figure are the only items on the sheet for which entries are required. Each sheet has slightly different input items.</P> 42 <IMG src="img/TableForUserInput.gif"> 43 <P>The following tables shows the values that can be entered in each sheet.</P> 44 <DL> 45 <DT>Shelf Filters</DT> 46 <DD><TABLE> 47 <TR> 48 <TH width="25%">Input items</TH> 49 <TH width="75%">Description</TH> 50 </TR> 51 <TR> 52 <TD width="25%">Gain (dB)</TD> 53 <TD width="75%">Specify the amplitude gain.</TD> 54 </TR> 55 <TR> 56 <TD width="25%">fc (Hz)</TD> 57 <TD width="75%">Specify the cutoff frequency (frequency at which a 3 dB change occurs).</TD> 58 </TR> 59 <TR> 60 <TD width="25%">Fs (Hz)</TD> 61 <TD width="75%">Specify the sound sampling rate (47,610 or 32,730).</TD> 62 </TR> 63 <TR> 64 <TD width="25%">Bass/Treble</TD> 65 <TD width="75%">Specify "B" for a Bass Shelf Filter and "T" for a Treble Shelf Filter.</TD> 66 </TR> 67 </TABLE> 68 </DD> 69 70 <DT>EQ Filters</DT> 71 <DD><TABLE> 72 <TR> 73 <TH width="25%">Input items</TH> 74 <TH width="75%">Description</TH> 75 </TR> 76 <TR> 77 <TD width="25%">Gain (dB)</TD> 78 <TD width="75%">Specify the amplitude gain.</TD> 79 </TR> 80 <TR> 81 <TD width="25%">BW (Hz)</TD> 82 <TD width="75%">Specify the frequency bandwidth from the center frequency to the frequency at which a 3 dB change occurs.</TD> 83 </TR> 84 <TR> 85 <TD width="25%">fc (Hz)</TD> 86 <TD width="75%">Specify the center frequency for changing the amplitude.</TD> 87 </TR> 88 <TR> 89 <TD width="25%">Fs (Hz)</TD> 90 <TD width="75%">Specify the sound sampling rate (47,610 or 32,730).</TD> 91 </TR> 92 </TABLE> 93 </DD> 94 95 <DT>Butterworth Filters</DT> 96 <DD><TABLE> 97 <TR> 98 <TH width="25%">Input items</TH> 99 <TH width="75%">Description</TH> 100 </TR> 101 <TR> 102 <TD width="25%">High/Low</TD> 103 <TD width="75%">Specify "H" for a High Pass Filter and "L" for a Low Pass Filter.</TD> 104 </TR> 105 <TR> 106 <TD width="25%">fc (Hz)</TD> 107 <TD width="75%">Specify the cutoff frequency (frequency at which a 3dB change occurs).</TD> 108 </TR> 109 <TR> 110 <TD width="25%">Fs (Hz)</TD> 111 <TD width="75%">Specify the sound sampling rate (47,610 or 32,730).</TD> 112 </TR> 113 </TABLE> 114 </DD> 115 </DL> 116 117 <P>The following explanation uses the Shelf Filters sheet as an example.</P> 118 <IMG src="img/TableForUserInput.gif" align=left> 119 <P>If the values entered are as shown in the figure at the left, the frequency response graph, 1st biquad parameters, and 2nd biquad parameters will be updated in real time.<BR clear=left></P> 120 <IMG src="img/1stBiquadTable.gif" align=left> 121 <P>The figure to the left shows the calculated IIR filter parameters (the 1st biquad). The values for N0 through D2 correspond to the <A href="../SNDEXIirFilterParam.html"><CODE>SNDEXIirFilterParam</CODE></A> structure's members <CODE>no</CODE> through <CODE>d2</CODE>.</P> 122 <P>However, <B>Values</B>-type values must be type-cast to <CODE>u16</CODE> when they are inserted in the <A href="../SNDEXIirFilterParam.html"><CODE>SNDEXIirFilterParam</CODE></A> structure. Use <B>Hex</B>-type values because they can be passed unchanged.<BR clear=left></P> 123 <P>The <FONT color=blue>blue line</FONT> in the following figure shows the frequency response when this filter is applied. As you can see, its low frequencies are amplified by approximately 10 dB close to the 300-Hz boundary. </P> 124 <IMG src="img/frequencyResponseFig.gif"> 125 <P>By looking closely at the blue line, you can see that the high-frequency region drops to approximately -0.1 dB as a side effect of the filter. This can be corrected by using one more IIR filter stage.</P> 126 <IMG src="img/2ndBiquadTable.gif" align=left> 127 <P>The figure to the left shows the IIR filter parameters for the 2nd biquad. The values for N3 through D5 correspond to the <A href="../SNDEXIirFilterParam.html"><CODE>SNDEXIirFilterParam</CODE></A> structure's members <CODE>no</CODE> through <CODE>d2</CODE></P> 128<P>However, <B>Values</B>-type values must be cast to type <CODE>u16</CODE> when they are inserted in the <A href="../SNDEXIirFilterParam.html"><CODE>SNDEXIirFilterParam</CODE></A> structure. Use <B>Hex</B>-type values because they can be passed unchanged.<BR clear=left></P> 129 <P>The <FONT color=green>green line</FONT> shows the frequency response for the 2nd biquad only. The entire frequency band is amplified by approximately 0.1 dB. The <FONT color=red>red line</FONT> shows the results of applying both the 1st biquad and 2nd biquad. If there are no problems with the 1st biquad results, you do not necessarily need to apply a 2nd biquad.</P> 130 131<H2>Notes</H2> 132<P>You must take note of the following when setting the calculated parameters in the <A href="../SNDEXIirFilterParam.html"><CODE>SNDEXIirFilterParam</CODE></A> structure.</P> 133<UL> 134<LI><B>Values</B>-type values: These should be type-cast to <CODE>u16</CODE> when passed. 135<LI><B>Hex</B>-type values: These can be passed unchanged. 136</UL> 137<P> 138</P> 139 140<H2>Revision History</H2> 141<P> 142 2009/02/19 Added text about the Excel setting for enabling automatic calculation in this sheet.<BR> 2008/09/10 Added notes regarding the use of calculated parameters.<BR> 2008/09/06 Initial version.</P> 143<hr><p>CONFIDENTIAL</p></body> 144</HTML> 145 146 147<!-- <A href="../SNDEX_SetIirFilter.html">SNDEX_SetIirFilter[Async]()</A> --> 148 149
