172 lines
6.0 KiB
HTML
172 lines
6.0 KiB
HTML
<!DOCTYPE html>
|
|
|
|
<!--Converted with LaTeX2HTML 2002-2-1 (1.71)
|
|
original version by: Nikos Drakos, CBLU, University of Leeds
|
|
* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
|
|
* with significant contributions from:
|
|
Jens Lippmann, Marek Rouchal, Martin Wilck and others -->
|
|
<HTML>
|
|
<HEAD>
|
|
|
|
<meta name="viewport" content="width=device-width, initial-scale=1.0">
|
|
|
|
|
|
<TITLE>Transfer functions for amplitude control</TITLE>
|
|
<META NAME="description" CONTENT="Transfer functions for amplitude control">
|
|
<META NAME="keywords" CONTENT="book">
|
|
<META NAME="resource-type" CONTENT="document">
|
|
<META NAME="distribution" CONTENT="global">
|
|
|
|
<META NAME="Generator" CONTENT="LaTeX2HTML v2002-2-1">
|
|
<META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css">
|
|
|
|
<LINK REL="STYLESHEET" HREF="book.css">
|
|
|
|
<LINK REL="next" HREF="node71.html">
|
|
<LINK REL="previous" HREF="node69.html">
|
|
<LINK REL="up" HREF="node68.html">
|
|
<LINK REL="next" HREF="node71.html">
|
|
</HEAD>
|
|
|
|
<BODY >
|
|
<!--Navigation Panel-->
|
|
<A NAME="tex2html1590"
|
|
HREF="node71.html">
|
|
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
|
|
SRC="next.png"></A>
|
|
<A NAME="tex2html1584"
|
|
HREF="node68.html">
|
|
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
|
|
SRC="up.png"></A>
|
|
<A NAME="tex2html1578"
|
|
HREF="node69.html">
|
|
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
|
|
SRC="prev.png"></A>
|
|
<A NAME="tex2html1586"
|
|
HREF="node4.html">
|
|
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents"
|
|
SRC="contents.png"></A>
|
|
<A NAME="tex2html1588"
|
|
HREF="node201.html">
|
|
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index"
|
|
SRC="index.png"></A>
|
|
<BR>
|
|
<B> Next:</B> <A NAME="tex2html1591"
|
|
HREF="node71.html">Additive synthesis: Risset's bell</A>
|
|
<B> Up:</B> <A NAME="tex2html1585"
|
|
HREF="node68.html">Examples</A>
|
|
<B> Previous:</B> <A NAME="tex2html1579"
|
|
HREF="node69.html">ADSR envelope generator</A>
|
|
<B> <A NAME="tex2html1587"
|
|
HREF="node4.html">Contents</A></B>
|
|
<B> <A NAME="tex2html1589"
|
|
HREF="node201.html">Index</A></B>
|
|
<BR>
|
|
<BR>
|
|
<!--End of Navigation Panel-->
|
|
|
|
<H2><A NAME="SECTION00882000000000000000">
|
|
Transfer functions for amplitude control</A>
|
|
</H2>
|
|
|
|
<P>
|
|
Section <A HREF="node60.html#sect4.curved">4.2</A> described using ADSR envelopes to control
|
|
amplitude, for which exponential or quartic-curve segments often give more
|
|
natural-sounding results than linear ones. Patches D03.envelope.dB.pd and D04.envelope.quartic.pd (the latter shown in Figure <A HREF="#fig04.15">4.15</A>)
|
|
demonstrate the use of decibel and quartic segments. In addition to amplitude,
|
|
in Example D04.envelope.quartic.pd the frequency of a sound is also controlled, using linear
|
|
and quartic shapes, for comparison.
|
|
|
|
<P>
|
|
|
|
<DIV ALIGN="CENTER"><A NAME="fig04.15"></A><A NAME="4770"></A>
|
|
<TABLE>
|
|
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4.15:</STRONG>
|
|
Linear and quartic transfer functions for changing amplitude and
|
|
pitch.</CAPTION>
|
|
<TR><TD><IMG
|
|
WIDTH="349" HEIGHT="369" BORDER="0"
|
|
SRC="img382.png"
|
|
ALT="\begin{figure}\psfig{file=figs/fig04.15.ps}\end{figure}"></TD></TR>
|
|
</TABLE>
|
|
</DIV>
|
|
|
|
<P>
|
|
Since converting decibels to linear amplitude units is a costly operation
|
|
(at least when compared to an oscillator or a ramp generator), Example D03.envelope.dB.pd uses table lookup to implement the necessary transfer function. This has the
|
|
advantage of efficiency, but the disadvantage that we must decide on the
|
|
range of admissible values in advance (here from 0 to 120 dB).
|
|
|
|
<P>
|
|
For a
|
|
quartic segment as in Example D04.envelope.quartic.pd no table lookup is required;
|
|
we simply square the <TT>line~</TT> object's output signal twice in succession.
|
|
To compensate for raising the output to the fourth power, the target values
|
|
sent to the <TT>line~</TT> object must be the fourth root of the desired
|
|
ones. Thus, messages to ramp the frequency or amplitude are first unpacked to
|
|
separate the target and time interval, the target's fourth root is taken
|
|
(via two square roots in succession), and the two are then sent to the
|
|
<TT>line~</TT> object. Here we have made use of one new Pd object:
|
|
|
|
<P>
|
|
<BR><!-- MATH
|
|
$\fbox{ $\mathrm{unpack}$}$
|
|
-->
|
|
<IMG
|
|
WIDTH="69" HEIGHT="41" ALIGN="MIDDLE" BORDER="0"
|
|
SRC="img383.png"
|
|
ALT="\fbox{ $\mathrm{unpack}$}">:
|
|
<A NAME="4907"></A>unpack a list of numbers (and/or symbols) and distribute them to separate
|
|
outlets. As usual the outputs appear in right-to-left order. The number of
|
|
outlets and their types are determined by the creation arguments. (See also
|
|
<TT>pack</TT>, Page <A HREF="node34.html#pdpack"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
|
|
SRC="crossref.png"></A>).
|
|
|
|
<P>
|
|
The next two patches, D05.envelope.pitch.pd and D06.envelope.portamento.pd, use an ADSR envelope generator
|
|
to make a pitch envelope and a simple <TT>line~</TT> object, also controlling
|
|
pitch, to make portamento. In both cases exponential segments are desirable,
|
|
and they are calculated using table lookup.
|
|
|
|
<P>
|
|
<HR>
|
|
<!--Navigation Panel-->
|
|
<A NAME="tex2html1590"
|
|
HREF="node71.html">
|
|
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
|
|
SRC="next.png"></A>
|
|
<A NAME="tex2html1584"
|
|
HREF="node68.html">
|
|
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
|
|
SRC="up.png"></A>
|
|
<A NAME="tex2html1578"
|
|
HREF="node69.html">
|
|
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
|
|
SRC="prev.png"></A>
|
|
<A NAME="tex2html1586"
|
|
HREF="node4.html">
|
|
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents"
|
|
SRC="contents.png"></A>
|
|
<A NAME="tex2html1588"
|
|
HREF="node201.html">
|
|
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index"
|
|
SRC="index.png"></A>
|
|
<BR>
|
|
<B> Next:</B> <A NAME="tex2html1591"
|
|
HREF="node71.html">Additive synthesis: Risset's bell</A>
|
|
<B> Up:</B> <A NAME="tex2html1585"
|
|
HREF="node68.html">Examples</A>
|
|
<B> Previous:</B> <A NAME="tex2html1579"
|
|
HREF="node69.html">ADSR envelope generator</A>
|
|
<B> <A NAME="tex2html1587"
|
|
HREF="node4.html">Contents</A></B>
|
|
<B> <A NAME="tex2html1589"
|
|
HREF="node201.html">Index</A></B>
|
|
<!--End of Navigation Panel-->
|
|
<ADDRESS>
|
|
Miller Puckette
|
|
2006-12-30
|
|
</ADDRESS>
|
|
</BODY>
|
|
</HTML>
|