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181 lines
5.5 KiB
181 lines
5.5 KiB
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<!--Converted with LaTeX2HTML 2002-2-1 (1.71)
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original version by: Nikos Drakos, CBLU, University of Leeds
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* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
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HREF="node124.html">Reverberator</A>
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<H2><A ID="SECTION0011109000000000000000">
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Pitch shifter</A>
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</H2>
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<P>
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Example G09.pitchshift.pd (Figure <A HREF="#fig07.33">7.33</A>) shows a realization of the pitch shifter
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described in Section <A HREF="node115.html#sect7.pitchshift">7.9</A>. A delay line (defined and written
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elsewhere in the patch) is read using two <TT>vd~</TT> objects. The delay
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times vary between a minimum delay (provided as the "delay" control) and the
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minimum plus a window size (the "window" control.)
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<P>
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<DIV ALIGN="CENTER"><A ID="fig07.33"></A><A ID="8317"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 7.33:</STRONG>
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A pitch shifter using two variable taps into a delay
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line.</CAPTION>
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<TR><TD><IMG
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WIDTH="443" HEIGHT="518" BORDER="0"
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SRC="img849.png"
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ALT="\begin{figure}\psfig{file=figs/fig07.33.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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The desired pitch shift in half-tones (<IMG
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WIDTH="12" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img194.png"
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ALT="$h$">) is first converted into a
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transposition factor
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<BR><P></P>
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<DIV ALIGN="CENTER">
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<!-- MATH
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\begin{displaymath}
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t = {2 ^ {h/12}} = {e ^ {\log(2)/12 \cdot h}} \approx {e ^ {0.05776 h}}
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\end{displaymath}
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-->
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<IMG
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WIDTH="232" HEIGHT="24" BORDER="0"
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SRC="img850.png"
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ALT="\begin{displaymath}
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t = {2 ^ {h/12}} = {e ^ {\log(2)/12 \cdot h}} \approx {e ^ {0.05776 h}}
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\end{displaymath}">
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</DIV>
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<BR CLEAR="ALL">
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<P></P>
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(called "speed change" in the patch). The computation labeled "tape
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head rotation speed" is the same as the formula for <IMG
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WIDTH="13" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img112.png"
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ALT="$f$"> given on Page
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<A HREF="node115.html#sect7.psformula"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
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SRC="crossref.png"></A>. Here the positive interval (seven half-steps)
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gives rise to a transposition factor greater than one, and therefore to a
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negative value for <IMG
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WIDTH="13" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img112.png"
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ALT="$f$">.
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<P>
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Once <IMG
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WIDTH="13" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
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SRC="img112.png"
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ALT="$f$"> is calculated, the production of the two phased sawtooth signals and
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the corresponding envelopes parallels exactly that of
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the overlapping sample looper (example B10.sampler.overlap.pd, Page
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<A HREF="node37.html#sect2.example.overlap"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
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SRC="crossref.png"></A>). The minimum delay
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is added to each of the two sawtooth signals to make delay inputs for the
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<TT>vd~</TT> objects, whose outputs are multiplied by the corresponding
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envelopes and summed.
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<B> Next:</B> <A ID="tex2html2416"
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HREF="node126.html">Exercises</A>
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HREF="node116.html">Examples</A>
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<B> Previous:</B> <A ID="tex2html2406"
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HREF="node124.html">Reverberator</A>
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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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