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