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171 lines
5.5 KiB
171 lines
5.5 KiB
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original version by: Nikos Drakos, CBLU, University of Leeds
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* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
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HREF="node21.html">Smoothed amplitude control with</A>
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HREF="node19.html">Constant amplitude scaler</A>
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<H2><A ID="SECTION00592000000000000000">
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Amplitude control in decibels</A>
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</H2>
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<P>
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Example A02.amplitude.pd shows how to make a crude amplitude control;
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the active elements
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are shown in Figure <A HREF="#fig01.12">1.12</A> (part a). There is one new object class:
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<P>
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<DIV ALIGN="CENTER"><A ID="fig01.12"></A><A ID="1273"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 1.12:</STRONG>
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The active ingredients to three patches: (a) A02.amplitude.pd; (b)
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A03.line.pd; (c) A05.output.subpatch.pd.</CAPTION>
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<TR><TD><IMG
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WIDTH="555" HEIGHT="350" BORDER="0"
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SRC="img149.png"
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ALT="\begin{figure}\psfig{file=figs/fig01.12.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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<BR><!-- MATH
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$\fbox{ $ \mathrm{dbtorms} $}$
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-->
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<IMG
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WIDTH="77" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img150.png"
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ALT="\fbox{ $ \mathrm{dbtorms} $}"> : Decibels to linear
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amplitude conversion. The "RMS" is a misnomer; it should have been named
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"dbtoamp",
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since it really converts from decibels to any linear amplitude unit, be it
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RMS, peak, or other. An input of 100 dB is normalized to an output of 1.
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Values greater than 100 are fine (120 will give 10), but values less than or
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equal to zero will output zero (a zero input would otherwise have output a
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small positive number). This is a control object, i.e., the numbers going in
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and out are messages, not signals. (A corresponding object,
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<!-- MATH
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$\fbox{ $ \mathrm{dbtorms}\sim $}$
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-->
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<IMG
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WIDTH="94" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
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SRC="img151.png"
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ALT="\fbox{ $ \mathrm{dbtorms}\sim $}">, is the signal correlate. However, as a
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signal object this is expensive in CPU time and most often we'll find
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one way or another to avoid using it.)
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<P>
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The two number boxes are connected to the input and output of the
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<TT>dbtorms</TT> object. The input functions as a control; "mouse" on it
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(click and drag upward or downward) to change the amplitude. It has been set to range from
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0 to 80; this is protection for your speakers and ears, and it's wise to build
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such guardrails into your own patches.
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<P>
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The other number box shows the output of the <TT>dbtorms</TT> object. It is
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useless
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to mouse on this number box, since its outlet is connected nowhere; it is here
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purely to display its input. Number boxes may be useful as controls, displays,
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or both, although if you're using it as both there may be some extra work to do.
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HREF="node21.html">Smoothed amplitude control with</A>
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<B> Up:</B> <A ID="tex2html834"
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HREF="node18.html">Examples</A>
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<B> Previous:</B> <A ID="tex2html828"
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HREF="node19.html">Constant amplitude scaler</A>
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<B> <A ID="tex2html836"
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HREF="node4.html">Contents</A></B>
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<B> <A ID="tex2html838"
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HREF="node201.html">Index</A></B>
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<ADDRESS>
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Miller Puckette
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2006-12-30
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