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207 lines
7.2 KiB
207 lines
7.2 KiB
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<H2><A ID="SECTION00881000000000000000">
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ADSR envelope generator</A>
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</H2>
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<P>
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Example D01.envelope.gen.pd (Figure <A HREF="#fig04.12">4.12</A>) shows how the <TT>line~</TT> object may
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be used to generate an ADSR envelope to control a synthesis patch (only the
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ADSR envelope is shown in the figure). The "attack" button, when pressed, has
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two effects. The first (leftmost in the figure) is to set the <TT>line~</TT> object on its attack segment, with a target of 10 (the peak amplitude) over 200
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msec (the attack time). Second, the attack button sets a <TT>delay 200</TT> object, so that after the attack segment is done, the decay segment can start.
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The decay segment falls to a target of 1 (the sustain level) after another 2500
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msec (the decay time).
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<P>
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<DIV ALIGN="CENTER"><A ID="fig04.12"></A><A ID="4744"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4.12:</STRONG>
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Using a <TT>line~</TT> object to generate an
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ADSR envelope.</CAPTION>
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<TR><TD><IMG
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WIDTH="222" HEIGHT="229" BORDER="0"
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SRC="img379.png"
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ALT="\begin{figure}\psfig{file=figs/fig04.12.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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The "release" button sends the same <TT>line~</TT> object back to zero over
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500 more milliseconds (the release time). Also, in case the
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<TT>delay 200</TT> object happens to be set at the moment the "release" button is pressed, a
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"stop" message is sent to it. This prevents the ADSR generator from
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launching its decay segment after launching its release segment.
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<P>
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In Example D02.adsr.pd (Figure <A HREF="#fig04.13">4.13</A>)
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we encapsulate the ADSR generator in a Pd abstraction
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(named <TT>adsr</TT>) so that it can easily be replicated. The design of the
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<TT>adsr</TT> abstraction makes it possible to control the five ADSR parameters
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either by supplying creation arguments or by connecting control streams to its
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inlets.
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<P>
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<DIV ALIGN="CENTER"><A ID="fig04.13"></A><A ID="4886"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4.13:</STRONG>
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Invoking the <TT>adsr</TT> abstraction.</CAPTION>
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<TR><TD><IMG
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WIDTH="217" HEIGHT="153" BORDER="0"
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SRC="img380.png"
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ALT="\begin{figure}\psfig{file=figs/fig04.13.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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In this example the five creation arguments (1, 100, 200, 50, and 300) specify
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the peak level, attack time, decay time, sustain level (as a percentage of peak
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level), and release time. There are six control inlets: the first to trigger
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the ADSR generator, and the others to update the values of the five parameters.
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The output of the abstraction is an audio signal.
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<P>
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This abstraction is realized as shown in Figure <A HREF="#fig04.14">4.14</A>. (You can open
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this subpatch by clicking on the <TT>adsr</TT> object in the patch.) The only
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signal objects are <TT>line~</TT> and <TT>outlet~</TT>. The three <TT>pack</TT> objects correspond to the three message objects from the earlier Figure
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<A HREF="#fig04.12">4.12</A>. From left to right, they take care of the attack, decay,
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and release segments.
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<P>
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<DIV ALIGN="CENTER"><A ID="fig04.14"></A><A ID="4887"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4.14:</STRONG>
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Inside the <TT>adsr</TT> abstraction.</CAPTION>
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<TR><TD><IMG
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WIDTH="583" HEIGHT="428" BORDER="0"
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SRC="img381.png"
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ALT="\begin{figure}\psfig{file=figs/fig04.14.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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The attack segment goes to a target specified as "$1" (the first
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creation argument of the abstraction) over "$2" milliseconds; these
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values may be overwritten by sending numbers to the "peak level" and "attack"
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inlets. The release segment is similar, but simpler, since the target is
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always zero. The hard part is the decay segment, which again must be set
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off after a delay equal to the attack time (the <TT>del $2</TT> object).
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The sustain level is calculated from the peak level and the sustain percentage
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(multiplying the two and dividing by 100).
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<P>
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The trigger inlet, if sent a number other than zero, triggers an
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onset (the attack
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and decay segments), and if sent zero, triggers the release segment.
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Furthermore, the ADSR generator may be reset to zero by sending a negative
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trigger (which also generates an onset).
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<ADDRESS>
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Miller Puckette
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2006-12-30
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