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<B> Next:</B> <A NAME="tex2html1775"
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HREF="node83.html">Waveshaping and difference tones</A>
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<H2><A NAME="SECTION00952000000000000000">
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Octave divider and formant adder</A>
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</H2>
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<A NAME="sect5.octave"></A>
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<P>
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As suggested in Section <A HREF="node77.html#sect5.ringmod">5.2</A>, when considering the result of
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modulating a complex harmonic (i.e., periodic) signal by a sinusoid, an
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interesting special case is to set the carrier oscillator to <IMG
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WIDTH="27" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img98.png"
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ALT="$1/2$"> the
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fundamental frequency, which drops the resulting sound an octave with only
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a relatively small deformation of the spectral envelope. Another is to
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modulate by a sinusoid at several times the fundamental frequency, which
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in effect displaces the spectral envelope without changing the fundamental
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frequency of the result. This is demonstrated in Example E03.octave.divider.pd (Figure
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<A HREF="#fig05.10">5.10</A>). The signal we process here is a recorded, spoken voice.
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<P>
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<DIV ALIGN="CENTER"><A NAME="fig05.10"></A><A NAME="5803"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5.10:</STRONG>
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Lowering the pitch of a sound by an octave by determining its pitch
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and modulating at half the fundamental.</CAPTION>
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<TR><TD><IMG
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WIDTH="359" HEIGHT="371" BORDER="0"
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SRC="img487.png"
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ALT="\begin{figure}\psfig{file=figs/fig05.10.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 subpatches <TT>pd looper</TT> and <TT>pd delay</TT> hide details. The
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first is a looping sampler as introduced in Chapter <A HREF="node26.html#chapter-wavetable">2</A>.
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The second is a delay of 1024 samples, which uses objects that are introduced
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later in Chapter <A HREF="node104.html#chapter-delay">7</A>. We will introduce one object class here:
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<P>
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<BR><!-- MATH
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$\fbox{ \texttt{fiddle\~}}$
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-->
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<IMG
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WIDTH="78" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
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SRC="img488.png"
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ALT="\fbox{ \texttt{fiddle\~}}">:
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<A NAME="5955"></A>pitch tracker. The inlet takes a signal to analyze, and messages to
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change settings. Depending on its creation arguments <TT>fiddle~</TT>may have a
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variable number of outlets offering various information about the input
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signal. As shown here, with only one creation argument to specify window size,
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the third outlet attempts to report the pitch of the input, and the amplitude
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of that portion of the input which repeats (at least approximately) at the
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reported pitch. These are output as a list of two numbers. The pitch, which
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is in MIDI units, is reported as zero if none could be identified.
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<P>
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In this patch the third outlet is unpacked into its pitch and amplitude
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components, and the pitch component is filtered by the <TT>moses</TT> object so that
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only successful pitch estimates (nonzero ones) are used. These are
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converted to units of frequency by the <TT>mtof</TT> object. Finally, the frequency
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estimates are either reduced by <IMG
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WIDTH="27" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
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SRC="img98.png"
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ALT="$1/2$"> or else multiplied by 15, depending on
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the selected multiplier, to provide the modulation frequency. In the first
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case we get an octave divider, and in the second, additional high harmonics
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that deform the vowels.
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HREF="node81.html">Ring modulation and spectra</A>
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<B> <A NAME="tex2html1771"
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HREF="node4.html">Contents</A></B>
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HREF="node201.html">Index</A></B>
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<ADDRESS>
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Miller Puckette
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2006-12-30
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