184 lines
6.5 KiB
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184 lines
6.5 KiB
HTML
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original version by: Nikos Drakos, CBLU, University of Leeds
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<H2><A ID="SECTION007102000000000000000">
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Converting controls to signals</A>
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</H2>
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<P>
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Example C03.zipper.noise.pd (Figure <A HREF="node51.html#fig03.13">3.13</A>, part b) demonstrates the effect of
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converting a slowly-updated control stream to an audio signal. This introduces
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a new object:
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<P>
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<BR><!-- MATH
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$\fbox{ $\mathrm{line}$}$
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-->
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<IMG
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WIDTH="44" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img345.png"
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ALT="\fbox{ $\mathrm{line}$}">:
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<A ID="3847"></A>a ramp generator with control output. Like <TT>line~</TT>, <TT>line</TT> takes pairs of numbers as (target, time) pairs and ramps to the target in the
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given amount of time; however, unlike <TT>line~</TT>, the output is
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a numeric control stream, appearing, by default, at 20 msec time intervals.
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<P>
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In the example you can compare the sound of the rising and falling amplitude
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controlled by the <TT>line</TT> output with one controlled by the audio
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signal generated by <TT>line~</TT>.
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<P>
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The output of <TT>line</TT> is converted to an audio signal at the input of
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the <TT>*~</TT> object. The conversion is implied here by connecting a
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numeric control stream into a signal inlet. In Pd, implicit conversions from
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numeric control streams to audio streams is done in the fast-as-possible mode
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shown in Figure <A HREF="node43.html#fig03.04">3.4</A> (part a). The <TT>line</TT> output becomes a
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staircase signal with 50 steps per second. The result is commonly called
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"zipper noise".
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<P>
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Whereas the limitations of the <TT>line</TT> object for generating audio
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signals were clearly audible even over such long time periods as 300 msec, the
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signal variant, <TT>line~</TT>, does not yield audible problems until the time
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periods involved become much shorter. Example C04.control.to.signal.pd (Figure <A HREF="node51.html#fig03.13">3.13</A>,
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part c) demonstrates the effect of using <TT>line~</TT> to generate a 250 Hertz
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triangle wave. Here the effects shown in Figure <A HREF="node43.html#fig03.05">3.5</A> come into
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play. Since <TT>line~</TT> always aligns line segments to block boundaries, the
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exact durations of line segments vary, and in this example the variation (on
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the order of a millisecond) is a significant fraction of their
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length.
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<P>
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A more precise object (and a more expensive one, in terms of computation time)
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is provided for these situations:
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<P>
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<BR><!-- MATH
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$\fbox{ $\mathrm{vline}\sim$}$
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-->
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<IMG
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WIDTH="69" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img346.png"
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ALT="\fbox{ $\mathrm{vline}\sim$}">:
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<A ID="3848"></A>exact line segment generator. This third member of the "line" family
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outputs an audio signal (like <TT>line~</TT>), but aligns the endpoints of the signal to
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the desired time points, accurate to a fraction of a sample. (The accuracy
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is limited only by the floating-point numerical format used by Pd.) Further,
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many line segments may be specified withing a single audio block;
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<TT>vline~</TT> can generate waveforms at periods down to two samples
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(beyond which you will just get foldover instead).
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<P>
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The <TT>vline~</TT> object can also be used for converting numeric
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control streams to audio streams in the nearest-sample and two-point-interpolation
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modes as shown in Figure <A HREF="node43.html#fig03.04">3.4</A> (parts b and
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c). To get nearest-sample conversion, simply give <TT>vline~</TT> a
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ramp time of zero. For linear interpolation, give it a ramp time of
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one sample (0.0227 msec if the sample rate is 44100 Hertz).
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<ADDRESS>
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Miller Puckette
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2006-12-30
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