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<B> Next:</B> <A NAME="tex2html826"
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<H2><A NAME="SECTION00591000000000000000">
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Constant amplitude scaler</A>
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</H2>
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<P>
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Example A01.sinewave.pd, shown in Figure <A HREF="#fig01.11">1.11</A>, contains essentially the
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simplest possible patch that makes a sound,
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with only three object boxes. (There are also comments, and two message
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boxes to turn Pd's "DSP" (audio) processing on and off.) The three object boxes
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are:
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<P>
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<DIV ALIGN="CENTER"><A NAME="fig01.11"></A><A NAME="1256"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 1.11:</STRONG>
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The contents of the first Pd example patch: A01.sinewave.pd.</CAPTION>
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<TR><TD><IMG
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WIDTH="542" HEIGHT="608" BORDER="0"
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SRC="img145.png"
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ALT="\begin{figure}\psfig{file=figs/fig01.11.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{osc}\sim $}$
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-->
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<IMG
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WIDTH="57" HEIGHT="33" ALIGN="MIDDLE" BORDER="0"
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SRC="img146.png"
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ALT="\fbox{ $ \mathrm{osc}\sim $}">:
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<A NAME="1402"></A>sinusoidal oscillator. The
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left hand side input
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and the output are digital audio signals. The input is taken to be a
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(possibly time-varying) frequency in Hertz. The output is a sinusoid at
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the specified frequency. If nothing is connected to the frequency inlet,
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the creation argument (440 in this example) is used as the frequency.
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The output has peak amplitude one. You may set an initial phase by sending
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messages (not audio signals) to the right inlet. The left (frequency) inlet
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may also be sent messages to set the frequency, since any inlet that takes an
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audio signal may also be sent messages which are automatically converted to the
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desired audio signal.
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<P>
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<BR><!-- MATH
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$\fbox{ $*\sim$\ }$
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-->
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<IMG
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WIDTH="49" HEIGHT="34" ALIGN="MIDDLE" BORDER="0"
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SRC="img147.png"
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ALT="\fbox{ $*\sim$\ }">:
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<A NAME="1370"></A>multiplier. This exists in two
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forms. If a creation argument is specified (as in this example; it's 0.05),
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this box multiplies a digital audio signal (in the left inlet) by the number;
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messages to the right inlet can update the number as well. If no argument is
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given, this box multiplies two incoming digital audio signals together.
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<P>
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<BR><!-- MATH
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$\fbox{ $ \mathrm{dac}\sim $}$
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-->
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<IMG
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WIDTH="60" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img148.png"
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ALT="\fbox{ $ \mathrm{dac}\sim $}">:
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<A NAME="1403"></A>audio output device.
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Depending on your hardware, this might not actually be a Digital/Analog
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Converter as the name suggests; but in general, it allows you to send any
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audio signal to your computer's audio output(s). If there are no creation
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arguments, the default behavior is to output to channels one and two of
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the audio hardware; you may specify alternative channel numbers (one or many)
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using the creation arguments. Pd itself may be configured to use two or
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more output channels, or may not have the audio output device open at all;
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consult the Pd documentation for details.
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<P>
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The two message boxes show a peculiarity in the way messages are parsed in
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message boxes. Earlier in Figure <A HREF="node16.html#fig01.10">1.10</A> (part a), the message
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consisted only of the number 21. When clicked, that box sent the message "21"
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to its outlet and hence to any objects connected to it. In this current
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example, the text of the message boxes starts with a semicolon. This is a
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terminator between messages (so the first message is empty), after which the
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next word is taken as the name of the recipient of the following message. Thus
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the message here is "dsp 1" (or "dsp 0") and the message is to be sent, not
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to any connected objects--there aren't any anyway--but rather, to the object
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named "pd". This particular object is provided invisibly by the Pd program
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and you can send it various messages to control Pd's global state, in this case
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turning audio processing on ("1") and off ("0").
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<P>
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Many more details about the control aspects of Pd, such as the above, are
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explained in a different series of example patches (the "control examples") in
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the Pd release, but they will only be touched on here as necessary to
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demonstrate the audio signal processing techniques that are the subject of this
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book.
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