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Lucas Cordiviola
2022-04-12 23:17:03 -03:00
parent 1ca5c25706
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@@ -83,11 +83,11 @@ 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
<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
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.
@@ -113,9 +113,9 @@ 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
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
sustain portion is equal to the time between "on" and "off" triggers, minus
the durations of the attack and decay segments.
<P>
@@ -123,8 +123,8 @@ the durations of the attack and decay segments.
<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>
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"
@@ -135,23 +135,23 @@ ADSR envelope output: (a) with ``on" and ``off" triggers separated;
<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
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)
"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,
"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
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.