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161 lines
5.2 KiB
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<H1><A ID="SECTION00840000000000000000"></A>
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<A ID="sect4.polyphony"></A>
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<BR>
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Polyphony
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</H1>
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<P>
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In music, the term
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<A ID="4665"></A><I>polyphony</I>
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is usually used to mean "more than one separate voices singing or playing at
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different pitches one from another". When speaking of electronic musical
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instruments we use the term to mean "maintaining several copies of some
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process in parallel." We usually call each copy a "voice" in keeping with the
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analogy, although the voices needn't be playing separately distinguishable
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sounds.
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<P>
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In this language, a piano is a polyphonic instrument, with 88 "voices". Each
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voice of the piano is normally capable of playing exactly one pitch. There
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is never a question of which voice to use to play a note of a given pitch,
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and no question, either, of playing several notes simultaneously at the
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same pitch.
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<P>
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Many polyphonic electronic musical instruments take a more flexible approach
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to voice management. Most software synthesis programs (like Csound) use
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a dynamic voice allocation scheme, so that, in effect, a new voice is
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created for every note in the score. In systems such as Max or Pd, which are
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oriented toward real-time interactive use, a
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<A ID="4667"></A><I>voice bank</I> is allocated in advance, and the work to be done (playing
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notes, or whatever) is distributed among the voices in the bank.
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<P>
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<DIV ALIGN="CENTER"><A ID="fig04.08"></A><A ID="4671"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4.8:</STRONG>
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A voice bank for polyphonic synthesis.</CAPTION>
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</DIV>
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<P>
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This is diagrammed in Figure <A HREF="#fig04.08">4.8</A>, where the several voices each
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produce one output signal, which are all added to make the total output of the
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voice bank. Frequently the individual voices will need several
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separate outputs; for instance, they might output several channels so that
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they may be panned individually; or they might have individual effect
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sends so that each may have its own send level.
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<ADDRESS>
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Miller Puckette
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2006-12-30
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