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204 lines
6.7 KiB
204 lines
6.7 KiB
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<H2><A ID="SECTION007106000000000000000">
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MIDI-style synthesizer</A>
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</H2>
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<P>
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Example C10.monophonic.synth.pd (Figure <A HREF="#fig03.16">3.16</A>) also implements a monophonic,
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note-oriented synthesizer, but in this case oriented toward MIDI
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controllability. Here the tasks of envelope generation and sequencing pitches
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are handled using control streams instead of audio signals. New
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control objects are needed for this example:
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<P>
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<DIV ALIGN="CENTER"><A ID="fig03.16"></A><A ID="3787"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 3.16:</STRONG>
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A MIDI-style monophonic synthesizer.</CAPTION>
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<TR><TD><IMG
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WIDTH="496" HEIGHT="459" BORDER="0"
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SRC="img351.png"
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ALT="\begin{figure}\psfig{file=figs/fig03.16.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{ $\mathrm{notein}$}$
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-->
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<IMG
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WIDTH="62" HEIGHT="40" ALIGN="MIDDLE" BORDER="0"
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SRC="img352.png"
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ALT="\fbox{ $\mathrm{notein}$}">:
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<A ID="3851"></A>MIDI note input. Three outlets give the pitch, velocity, and channel of
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incoming MIDI note-on and note-off events (with note-off events appearing as
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velocity-zero note-on events). The outputs appear in Pd's customary
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right-to-left order.
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<P>
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<BR><!-- MATH
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$\fbox{ $\mathrm{stripnote}$}$
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-->
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<IMG
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WIDTH="81" HEIGHT="40" ALIGN="MIDDLE" BORDER="0"
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SRC="img353.png"
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ALT="\fbox{ $\mathrm{stripnote}$}">:
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<A ID="3852"></A>filter out note-off messages. This passes
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(pitch, velocity) pairs through whenever the velocity is nonzero, dropping
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the others. Unlike <TT>notein</TT>, <TT>stripnote</TT> does not
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directly use hardware MIDI input or output.
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<P>
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<BR><!-- MATH
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$\fbox{ $\mathrm{trigger}$}$
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-->
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<IMG
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WIDTH="65" HEIGHT="40" ALIGN="MIDDLE" BORDER="0"
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SRC="img354.png"
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ALT="\fbox{ $\mathrm{trigger}$}">,
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<BR><!-- MATH
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$\fbox{ $\mathrm{t}$}$
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-->
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<IMG
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WIDTH="25" HEIGHT="39" ALIGN="MIDDLE" BORDER="0"
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SRC="img355.png"
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ALT="\fbox{ $\mathrm{t}$}">:
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<A ID="3853"></A>copy a message to outlets in right to left order, with type conversion. The
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creation arguments ("b" and "f" in this example) specify two outlets, one
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giving "bang" messages, the other "float" (i.e., numbers). One outlet
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is created for each creation argument. The outputs appear in Pd's standard
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right-to-left order.
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<P>
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The patch's control objects feed frequencies to the <TT>phasor~</TT> object
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whenever a MIDI note-on message is received. Controlling the amplitude (via
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the <TT>line~</TT> object) is more difficult. When a note-on message is
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received, the <TT>sel 0</TT> object outputs the velocity at right (because
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the input failed to match 0); this is divided by the maximum MIDI velocity of
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127 and packed into a message for <TT>line~</TT> with a time of 100 msec.
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<P>
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However, when a note-off is received, it is only appropriate to stop the sound
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if the note-off pitch actually matches the pitch the instrument is playing.
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For example, suppose the messages received are "60 127", "72 127",
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"60 0", and "72 0". When the note-on at pitch 72 arrives the pitch should
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change to 72, and then the "60 0" message should be ignored, with the note
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playing until the "72 0" message.
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<P>
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To accomplish this, first we store the velocity in the upper <TT>float</TT> object. Second, when the pitch arrives, it too is stored (the lower
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<TT>float</TT> object) and then the velocity is tested against zero (the
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"bang" outlet of <TT>t b f</TT> recalls the velocity which is sent to
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<TT>sel 0</TT>). If this is zero, the second step is to recall the pitch and
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test it (the <TT>select</TT> object) against the most recently received
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note-on pitch. Only if these are equal (so that "bang" appears at the
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left-hand-side outlet of <TT>select</TT>) does the message "0 1000" go to the
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<TT>line~</TT> object.
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<P>
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HREF="node50.html">Examples</A>
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HREF="node55.html">Analog-style sequencer</A>
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<ADDRESS>
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Miller Puckette
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2006-12-30
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