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<H2><A ID="SECTION00663000000000000000">
Using a wavetable as a sampler</A>
</H2>
<P>
Example B04.sampler.pd (Figure <A HREF="#fig02.14">2.14</A>) shows how to use a wavetable as a
sampler. In this example the index into the sample (the wavetable) is controlled
by mousing on a number box at top. A convenient scaling for the number box is
hundredths of a second; to convert to samples (as the input of
<TT>tabread4~</TT> requires) we multiply by 44100 samples/sec times 0.01 sec to get 441 samples
per unit, before applying <TT>pack</TT> and <TT>line~</TT> in much the same way
as they were used in the previous example.
The transposition you hear depends on how quickly you mouse up and down.
This example has introduced one new object class:
<P>
<DIV ALIGN="CENTER"><A ID="fig02.14"></A><A ID="2430"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 2.14:</STRONG>
A sampler with mouse-controlled index: B04.sampler.pd.</CAPTION>
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SRC="img279.png"
ALT="\begin{figure}\psfig{file=figs/fig02.14.ps}\end{figure}"></TD></TR>
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<BR><!-- MATH
$\fbox{ $\mathrm{hip}\sim$\ }$
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<IMG
WIDTH="63" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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ALT="\fbox{ $\mathrm{hip}\sim$\ }">:
<A ID="2558"></A>simple high-pass (low-cut) filter. The creation argument gives the roll-off
frequency in cycles per second. We use it here to eliminate the constant
(zero-frequency)
output when the input sits in a single sample (whenever you aren't actively
changing the wavetable reading location with the mouse). Filters are discussed
in Chapter <A HREF="node127.html#chapter-filter">8</A>.
<P>
The <TT>pack</TT> and <TT>line~</TT> in this example are not included merely to
make the sound more continuous, but are essential to making the sound
intelligible at all. If the index into the wavetable lookup simply changed
every time the mouse moved a pixel (say, twenty to fifty times a second) the
overwhelming majority of samples would get the same index as the previous
sample (the other 44000+ samples, not counting the ones where the mouse
moved.) So the speed of precession would almost always be zero. Instead of
changing transpositions, you would hear 20 to 50 cycles-per-second grit. (Try
it to find out what that sounds like!)
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<ADDRESS>
Miller Puckette
2006-12-30
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