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165 lines
5.3 KiB
165 lines
5.3 KiB
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<H2><A ID="SECTION00661000000000000000">
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Wavetable oscillator</A>
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</H2>
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<P>
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Example B01.wavetables.pd, shown in Figure <A HREF="#fig02.12">2.12</A>, implements a wavetable
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oscillator, which plays back from a wavetable named "table10". Two new Pd
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primitives are shown here. First is the wavetable itself, which appears at
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right in the figure. You can "mouse" on the wavetable to change its shape and
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hear the sound change as a result. Not shown in the figure but demonstrated in
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the patch is Pd's facility for automatically calculating wavetables with
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specified partial amplitudes, which is often preferable to drawing waveforms by
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hand. You can also read and write tables to (text or sound) files for
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interchanging data with other programs. The other novelty is an object class:
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<P>
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<DIV ALIGN="CENTER"><A ID="fig02.12"></A><A ID="2400"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 2.12:</STRONG>
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A wavetable oscillator: B01.wavetables.pd.</CAPTION>
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<TR><TD><IMG
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WIDTH="554" HEIGHT="194" BORDER="0"
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SRC="img272.png"
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ALT="\begin{figure}\psfig{file=figs/fig02.12.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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<BR><!-- MATH
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$\fbox{ $ \mathrm{tabosc4}\sim $}$
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-->
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<IMG
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WIDTH="89" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img273.png"
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ALT="\fbox{ $ \mathrm{tabosc4}\sim $}">:
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<A ID="2554"></A>a wavetable oscillator. The "4" indicates that this class uses 4-point
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(cubic) interpolation. In the example, the table's name, "table10", is
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specified as a creation argument to the <TT>tabosc4~</TT> object.
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(You can also switch between wavetables dynamically by sending appropriate
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messages to the object.)
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<P>
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Wavetables used by <TT>tabosc4~</TT> must always have a period
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equal to a power of two; but as shown above, the wavetable must have three
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extra points wrapped around the ends. Allowable table lengths are thus
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of the form <IMG
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WIDTH="50" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
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SRC="img274.png"
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ALT="${2^m} + 3$">, such as 131, 259, 515, etc.
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<P>
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Wavetable oscillators are not limited to use as audio oscillators. Patch
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B02.wavetable.FM.pd (not pictured here) uses a pair of wavetable oscillators in series.
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The first one's output is used as the input of the second one, and thus
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controls its frequency which changes periodically in time.
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<ADDRESS>
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Miller Puckette
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2006-12-30
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