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HREF="node160.html">Using elementary filters directly:</A>
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<H2><A ID="SECTION001256000000000000000">
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Making and using all-pass filters</A>
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</H2>
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<P>
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<DIV ALIGN="CENTER"><A ID="fig08.33"></A><A ID="10672"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 8.33:</STRONG>
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All-pass filters: (a) making an all-pass filter from elementary
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filters; (b) using four all-pass filters to build a phaser.
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</CAPTION>
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<TR><TD><IMG
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WIDTH="484" HEIGHT="421" BORDER="0"
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ALT="\begin{figure}\psfig{file=figs/fig08.33.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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Example H14.all.pass.pd (Figure <A HREF="#fig08.33">8.33</A>, part a) shows how to make an all-pass
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filter out of a non-recirculating filter,
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second form (<TT>rzero_rev~</TT>) and a recirculating filter (<TT>rpole~</TT>).
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The coefficient, ranging from -1 to 1, is controlled in hundredths.
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<P>
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Example H15.phaser.pd (part b of the figure) shows how to use four all-pass filters to
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make a classic phaser. The phaser works by summing the input signal with a
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phase-altered version of it, making interference effects. The amount of phase
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change is varied in time by varying the (shared) coefficient of the all-pass
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filters. The overall effect is somewhat similar to a flanger (time-varying comb
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filter) but the phaser does not impose a pitch as the comb filter does.
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<P>
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<BR><HR>
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<ADDRESS>
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Miller Puckette
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2006-12-30
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</ADDRESS>
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