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<H2><A NAME="SECTION0011109000000000000000">
Pitch shifter</A>
</H2>
<P>
Example G09.pitchshift.pd (Figure <A HREF="#fig07.33">7.33</A>) shows a realization of the pitch shifter
described in Section <A HREF="node115.html#sect7.pitchshift">7.9</A>. A delay line (defined and written
elsewhere in the patch) is read using two <TT>vd~</TT> objects. The delay
times vary between a minimum delay (provided as the ``delay" control) and the
minimum plus a window size (the ``window" control.)
<P>
<DIV ALIGN="CENTER"><A NAME="fig07.33"></A><A NAME="8317"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 7.33:</STRONG>
A pitch shifter using two variable taps into a delay
line.</CAPTION>
<TR><TD><IMG
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SRC="img849.png"
ALT="\begin{figure}\psfig{file=figs/fig07.33.ps}\end{figure}"></TD></TR>
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<P>
The desired pitch shift in half-tones (<IMG
WIDTH="12" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
SRC="img194.png"
ALT="$h$">) is first converted into a
transposition factor
<BR><P></P>
<DIV ALIGN="CENTER">
<!-- MATH
\begin{displaymath}
t = {2 ^ {h/12}} = {e ^ {\log(2)/12 \cdot h}} \approx {e ^ {0.05776 h}}
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t = {2 ^ {h/12}} = {e ^ {\log(2)/12 \cdot h}} \approx {e ^ {0.05776 h}}
\end{displaymath}">
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<P></P>
(called ``speed change" in the patch). The computation labeled ``tape
head rotation speed" is the same as the formula for <IMG
WIDTH="13" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
SRC="img112.png"
ALT="$f$"> given on Page
<A HREF="node115.html#sect7.psformula"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
SRC="file:/usr/local/share/lib/latex2html/icons/crossref.png"></A>. Here the positive interval (seven half-steps)
gives rise to a transposition factor greater than one, and therefore to a
negative value for <IMG
WIDTH="13" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
SRC="img112.png"
ALT="$f$">.
<P>
Once <IMG
WIDTH="13" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
SRC="img112.png"
ALT="$f$"> is calculated, the production of the two phased sawtooth signals and
the corresponding envelopes parallels exactly that of
the overlapping sample looper (example B10.sampler.overlap.pd, Page
<A HREF="node37.html#sect2.example.overlap"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
SRC="file:/usr/local/share/lib/latex2html/icons/crossref.png"></A>). The minimum delay
is added to each of the two sawtooth signals to make delay inputs for the
<TT>vd~</TT> objects, whose outputs are multiplied by the corresponding
envelopes and summed.
<P>
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<ADDRESS>
Miller Puckette
2006-12-30
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