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<H1><A ID="SECTION00830000000000000000"></A>
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<A ID="sect4.declick"></A>
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<BR>
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Continuous and discontinuous control changes
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</H1>
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<P>
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Synthesis algorithms vary widely in their ability to deal with discontinuously
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changing controls. Until now in this chapter we have assumed that controls
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must change continuously, and the ADSR envelope generator turns out
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to be ideally suited for such controls. It may even happen that
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the maximum amplitude of a note is less than the current value of the amplitude
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of its predecessor (using the same generator) and the ADSR envelope will simply
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ramp down (instead of up) to the new value for an attack.
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<P>
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This isn't necessarily desirable, however, in situations where an envelope
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generator is in charge of some aspect of timbre: perhaps, for example, we don't
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want the sharpness of a note to decrease during the attack to a milder one, but
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rather to jump to a much lower value so as always to be able to rise during the
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attack.
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<P>
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This situation also can arise with pitch envelopes: it may be desirable to
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slide pitch from one note to the next, or it may be desirable that the pitch
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trajectory of each note start anew at a point independent of the previous
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sound.
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<P>
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Two situations arise when we wish to make discontinuous changes to synthesis
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parameters: either we can simply make them without disruption (for instance,
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making a discontinuous change in pitch); or else we can't, such as a change in
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a wavetable index (which makes a discontinuous change in the output). There
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are even parameters that can't <I>possibly</I> be changed continuously; for
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example, a selection among a collection of wavetables. In general,
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discontinuously changing the phase of an oscillator or the amplitude of a
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signal will cause an audible artifact, but phase increments (such as pitches)
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may jump without bad results.
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<P>
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In those cases where a parameter change can't be made continuously for one
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reason or another, there are at least two strategies for making the change
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cleanly:
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<I>muting</I> and <I>switch-and-ramp</I>.
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<P>
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<BR><HR>
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<A ID="CHILD_LINKS"><STRONG>Subsections</STRONG></A>
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<LI><A ID="tex2html1461"
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HREF="node62.html">Muting</A>
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<LI><A ID="tex2html1462"
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HREF="node63.html">Switch-and-ramp</A>
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HREF="node62.html">Muting</A>
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HREF="node58.html">Automation and voice management</A>
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<B> Previous:</B> <A ID="tex2html1448"
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HREF="node60.html">Linear and Curved Amplitude</A>
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HREF="node4.html">Contents</A></B>
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<ADDRESS>
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Miller Puckette
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2006-12-30
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