196 lines
7.8 KiB
HTML
196 lines
7.8 KiB
HTML
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
|
||
|
|
|
||
|
|
<!--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>
|
||
|
|
<TITLE>Envelope Generators</TITLE>
|
||
|
|
<META NAME="description" CONTENT="Envelope Generators">
|
||
|
|
<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="node60.html">
|
||
|
|
<LINK REL="previous" HREF="node58.html">
|
||
|
|
<LINK REL="up" HREF="node58.html">
|
||
|
|
<LINK REL="next" HREF="node60.html">
|
||
|
|
</HEAD>
|
||
|
|
|
||
|
|
<BODY >
|
||
|
|
<!--Navigation Panel-->
|
||
|
|
<A NAME="tex2html1431"
|
||
|
|
HREF="node60.html">
|
||
|
|
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/next.png"></A>
|
||
|
|
<A NAME="tex2html1425"
|
||
|
|
HREF="node58.html">
|
||
|
|
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/up.png"></A>
|
||
|
|
<A NAME="tex2html1419"
|
||
|
|
HREF="node58.html">
|
||
|
|
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/prev.png"></A>
|
||
|
|
<A NAME="tex2html1427"
|
||
|
|
HREF="node4.html">
|
||
|
|
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/contents.png"></A>
|
||
|
|
<A NAME="tex2html1429"
|
||
|
|
HREF="node201.html">
|
||
|
|
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/index.png"></A>
|
||
|
|
<BR>
|
||
|
|
<B> Next:</B> <A NAME="tex2html1432"
|
||
|
|
HREF="node60.html">Linear and Curved Amplitude</A>
|
||
|
|
<B> Up:</B> <A NAME="tex2html1426"
|
||
|
|
HREF="node58.html">Automation and voice management</A>
|
||
|
|
<B> Previous:</B> <A NAME="tex2html1420"
|
||
|
|
HREF="node58.html">Automation and voice management</A>
|
||
|
|
<B> <A NAME="tex2html1428"
|
||
|
|
HREF="node4.html">Contents</A></B>
|
||
|
|
<B> <A NAME="tex2html1430"
|
||
|
|
HREF="node201.html">Index</A></B>
|
||
|
|
<BR>
|
||
|
|
<BR>
|
||
|
|
<!--End of Navigation Panel-->
|
||
|
|
|
||
|
|
<H1><A NAME="SECTION00810000000000000000"></A>
|
||
|
|
<A NAME="sect4.adsr"></A>
|
||
|
|
<BR>
|
||
|
|
Envelope Generators
|
||
|
|
</H1>
|
||
|
|
|
||
|
|
<P>
|
||
|
|
An
|
||
|
|
<A NAME="4571"></A><I>envelope generator</I> (sometimes, and more justly, called a
|
||
|
|
<A NAME="4573"></A><I>transient generator</I>) makes an audio signal that smoothly rises and
|
||
|
|
falls as if to control the loudness of a musical note.
|
||
|
|
Envelope generators were touched on earlier in Section <A HREF="node12.html#sect1.synth">1.5</A>.
|
||
|
|
Amplitude control by multiplication (Figure <A HREF="node10.html#fig01.04">1.4</A>) is the most direct,
|
||
|
|
ordinary way to use one, but there are many other possible uses.
|
||
|
|
|
||
|
|
<P>
|
||
|
|
Envelope generators have come in many forms over the years, but the simplest
|
||
|
|
and the perennial favorite is the
|
||
|
|
<A NAME="4577"></A><A NAME="4578"></A><I>ADSR</I> envelope generator. ``ADSR" is an acronym for
|
||
|
|
``Attack, Decay, Sustain, Release", the four segments of the
|
||
|
|
ADSR generator's output. The ADSR generator is turned on and off by a control
|
||
|
|
stream called a ``trigger". Triggering the ADSR generator ``on" sets off its
|
||
|
|
attack, decay, and sustain segments. Triggering it ``off" starts the
|
||
|
|
release segment. Figure <A HREF="#fig04.01">4.1</A> shows the block
|
||
|
|
diagram representation of an ADSR envelope generator.
|
||
|
|
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DIV ALIGN="CENTER"><A NAME="fig04.01"></A><A NAME="4583"></A>
|
||
|
|
<TABLE>
|
||
|
|
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4.1:</STRONG>
|
||
|
|
ADSR envelope as a block diagram, showing the trigger input (a
|
||
|
|
control stream) and the audio output.</CAPTION>
|
||
|
|
<TR><TD><IMG
|
||
|
|
WIDTH="83" HEIGHT="174" BORDER="0"
|
||
|
|
SRC="img356.png"
|
||
|
|
ALT="\begin{figure}\psfig{file=figs/fig04.01.ps}\end{figure}"></TD></TR>
|
||
|
|
</TABLE>
|
||
|
|
</DIV>
|
||
|
|
|
||
|
|
<P>
|
||
|
|
There are five parameters controlling the ADSR generator. First, a
|
||
|
|
<I>level</I> parameter sets the output value at the end of the attack segment
|
||
|
|
(normally the highest value output by the ADSR generator). Second and third,
|
||
|
|
the <I>attack</I> and <I>decay</I> parameters give the time duration of the
|
||
|
|
attack and decay segments. Fourth, a <I>sustain</I> parameter gives the level
|
||
|
|
of the sustain segment, as a fraction of the level parameter. Finally, the
|
||
|
|
<I>release</I> parameter gives the duration of the release segment. These five
|
||
|
|
values, together with the timing of the ``on" and ``off" triggers, fully
|
||
|
|
determines the output of the ADSR generator. For example, the duration of the
|
||
|
|
sustain portion is equal to the time between ``on" and ``off" triggers, minus
|
||
|
|
the durations of the attack and decay segments.
|
||
|
|
|
||
|
|
<P>
|
||
|
|
|
||
|
|
<DIV ALIGN="CENTER"><A NAME="fig04.02"></A><A NAME="4593"></A>
|
||
|
|
<TABLE>
|
||
|
|
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 4.2:</STRONG>
|
||
|
|
ADSR envelope output: (a) with ``on" and ``off" triggers separated;
|
||
|
|
(b), (c) with early ``off" trigger; (d), (e) re-attacked.</CAPTION>
|
||
|
|
<TR><TD><IMG
|
||
|
|
WIDTH="332" HEIGHT="530" BORDER="0"
|
||
|
|
SRC="img357.png"
|
||
|
|
ALT="\begin{figure}\psfig{file=figs/fig04.02.ps}\end{figure}"></TD></TR>
|
||
|
|
</TABLE>
|
||
|
|
</DIV>
|
||
|
|
|
||
|
|
<P>
|
||
|
|
Figure <A HREF="#fig04.02">4.2</A> graphs some possible outputs of an ADSR
|
||
|
|
envelope generator. In
|
||
|
|
part (a) we assume that the ``on" and ``off" triggers are widely enough
|
||
|
|
separated that the sustain segment is reached before the ``off" trigger is
|
||
|
|
received.
|
||
|
|
Parts (b) and (c) of Figure <A HREF="#fig04.02">4.2</A> show the result of following an
|
||
|
|
``on" trigger quickly by an ``off" one: (b) during the decay segment, and (c)
|
||
|
|
even earlier, during the attack. The ADSR generator reacts to these situations
|
||
|
|
by canceling whatever remains of the attack and decay segments and continuing
|
||
|
|
straight to the release segment. Also, an ADSR generator may be retriggered
|
||
|
|
``on" before the release segment is finished or even during the attack, decay,
|
||
|
|
or sustain segments. Part (d) of the figure shows a reattack during the
|
||
|
|
sustain segment, and part (e), during the decay segment.
|
||
|
|
|
||
|
|
<P>
|
||
|
|
The classic application of an ADSR envelope is using a voltage-control keyboard
|
||
|
|
or sequencer to make musical notes on a synthesizer. Depressing and releasing
|
||
|
|
a key (for example) would generate ``on" and ``off" triggers. The ADSR
|
||
|
|
generator could then control the amplitude of synthesis so that ``notes" would
|
||
|
|
start and stop with the keys. In addition to amplitude, the ADSR generator
|
||
|
|
can (and often is) used to control timbre, which can then be made to evolve
|
||
|
|
naturally over the course of each note.
|
||
|
|
|
||
|
|
<P>
|
||
|
|
<HR>
|
||
|
|
<!--Navigation Panel-->
|
||
|
|
<A NAME="tex2html1431"
|
||
|
|
HREF="node60.html">
|
||
|
|
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/next.png"></A>
|
||
|
|
<A NAME="tex2html1425"
|
||
|
|
HREF="node58.html">
|
||
|
|
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/up.png"></A>
|
||
|
|
<A NAME="tex2html1419"
|
||
|
|
HREF="node58.html">
|
||
|
|
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/prev.png"></A>
|
||
|
|
<A NAME="tex2html1427"
|
||
|
|
HREF="node4.html">
|
||
|
|
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/contents.png"></A>
|
||
|
|
<A NAME="tex2html1429"
|
||
|
|
HREF="node201.html">
|
||
|
|
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index"
|
||
|
|
SRC="file:/usr/local/share/lib/latex2html/icons/index.png"></A>
|
||
|
|
<BR>
|
||
|
|
<B> Next:</B> <A NAME="tex2html1432"
|
||
|
|
HREF="node60.html">Linear and Curved Amplitude</A>
|
||
|
|
<B> Up:</B> <A NAME="tex2html1426"
|
||
|
|
HREF="node58.html">Automation and voice management</A>
|
||
|
|
<B> Previous:</B> <A NAME="tex2html1420"
|
||
|
|
HREF="node58.html">Automation and voice management</A>
|
||
|
|
<B> <A NAME="tex2html1428"
|
||
|
|
HREF="node4.html">Contents</A></B>
|
||
|
|
<B> <A NAME="tex2html1430"
|
||
|
|
HREF="node201.html">Index</A></B>
|
||
|
|
<!--End of Navigation Panel-->
|
||
|
|
<ADDRESS>
|
||
|
|
Miller Puckette
|
||
|
|
2006-12-30
|
||
|
|
</ADDRESS>
|
||
|
|
</BODY>
|
||
|
|
</HTML>
|