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162 lines
5.4 KiB
162 lines
5.4 KiB
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HREF="node34.html">Wavetable lookup in general</A>
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<H2><A ID="SECTION00663000000000000000">
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Using a wavetable as a sampler</A>
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</H2>
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<P>
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Example B04.sampler.pd (Figure <A HREF="#fig02.14">2.14</A>) shows how to use a wavetable as a
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sampler. In this example the index into the sample (the wavetable) is controlled
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by mousing on a number box at top. A convenient scaling for the number box is
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hundredths of a second; to convert to samples (as the input of
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<TT>tabread4~</TT> requires) we multiply by 44100 samples/sec times 0.01 sec to get 441 samples
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per unit, before applying <TT>pack</TT> and <TT>line~</TT> in much the same way
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as they were used in the previous example.
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The transposition you hear depends on how quickly you mouse up and down.
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This example has introduced one new object class:
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<P>
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<DIV ALIGN="CENTER"><A ID="fig02.14"></A><A ID="2430"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 2.14:</STRONG>
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A sampler with mouse-controlled index: B04.sampler.pd.</CAPTION>
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<TR><TD><IMG
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ALT="\begin{figure}\psfig{file=figs/fig02.14.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{ $\mathrm{hip}\sim$\ }$
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-->
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<IMG
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WIDTH="63" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img280.png"
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ALT="\fbox{ $\mathrm{hip}\sim$\ }">:
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<A ID="2558"></A>simple high-pass (low-cut) filter. The creation argument gives the roll-off
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frequency in cycles per second. We use it here to eliminate the constant
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(zero-frequency)
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output when the input sits in a single sample (whenever you aren't actively
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changing the wavetable reading location with the mouse). Filters are discussed
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in Chapter <A HREF="node127.html#chapter-filter">8</A>.
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<P>
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The <TT>pack</TT> and <TT>line~</TT> in this example are not included merely to
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make the sound more continuous, but are essential to making the sound
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intelligible at all. If the index into the wavetable lookup simply changed
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every time the mouse moved a pixel (say, twenty to fifty times a second) the
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overwhelming majority of samples would get the same index as the previous
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sample (the other 44000+ samples, not counting the ones where the mouse
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moved.) So the speed of precession would almost always be zero. Instead of
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changing transpositions, you would hear 20 to 50 cycles-per-second grit. (Try
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it to find out what that sounds like!)
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HREF="node34.html">Wavetable lookup in general</A>
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<ADDRESS>
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Miller Puckette
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2006-12-30
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