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<title>Building Drums in PD</title>
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<div class="document" id="building-drums-in-pd">
<h1 class="title">Building Drums in PD</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr class="field"><th class="docinfo-name">Autor:</th><td class="field-body">Frank Barknecht</td>
</tr>
<tr><th class="docinfo-name">Contact:</th>
<td><a class="first last reference" href="mailto:fbar@footils.org">fbar@footils.org</a></td></tr>
</tbody>
</table>
<div class="abstract topic">
<p class="topic-title">Abstract</p>
<p>This quicktoot describes how PD can be used to build a simple drum
synthesizer with graphical controls and a step sequencer.</p>
</div>
<div class="contents topic" id="contents">
<p class="topic-title"><a name="contents">Contents</a></p>
<ul class="simple">
<li><a class="reference" href="#small-is-beautiful" id="id1" name="id1">Small is beautiful</a></li>
<li><a class="reference" href="#the-creator" id="id2" name="id2">The Creator</a></li>
<li><a class="reference" href="#bring-the-noise" id="id3" name="id3">Bring The Noise</a></li>
<li><a class="reference" href="#let-it-swing" id="id4" name="id4">Let It Swing</a></li>
<li><a class="reference" href="#going-faster" id="id5" name="id5">Going faster</a></li>
</ul>
</div>
<div class="section" id="small-is-beautiful">
<h1><a class="toc-backref" href="#id1" name="small-is-beautiful">Small is beautiful</a></h1>
<p>Pure Data - or short PD - is a multimedia software environment written
by Miller Puckette and others that can be used to make art in several
media like music, sound or graphics. In this quicktoot we will use the
sound generating capabilities of PD to build a module for drum sounds.
Our drum synthesizer will use a synthesis algorithm that's very
similar to the early analog or digital drumsynths of the eighties. We
will not use pre-recorded samples but instead employ simple sound
generators. You will be surprised, how effective this is and how much
variety is possible with just two or three sound sources. On the other
hand our design leaves room for improvment. By the end of this article
you will be able to add these on your own. Our drummer includes a
preset database: When you have found a sound, that you like, you can
save it and recall it again later.</p>
<p>I will not go into much detail on how to install or how to use PD: You
should read the documentation that comes with PD for that. I will of
course explain the more advanced features of PD used and everything
that is needed to follow this tutorial.</p>
</div>
<div class="section" id="the-creator">
<h1><a class="toc-backref" href="#id2" name="the-creator">The Creator</a></h1>
<p>Creating something in PD is very much like the genesis of a world as described
in, well, the Bible's first book "Genesis". In the beginning you have nothing,
just a large white area. You, the Creator, can create objects by a simple
button press "Ctrl-1", which actually means "Let there be an object". And there
was an object. But your first object is a small empty rectangle and it can do
nothing, it has no way of communicating, it isn't alive yet. To create a living
object you have to give it a name, you have to call it by typing the name onto
the object, for example "noise~". And there was noise. With time you can
populate the area with more objects, you can let them talk to each other, you
can create more worlds, and you will create by giving all of them names. We
maybe come to <tt class="literal"><span class="pre">[moses]</span></tt> later. Our drumsynth will have the name "angriff",
which is german for "attack". So our goal is, that someone can create a
drumsynth by typing the name "angriff" on a new object.</p>
<p>This is achieved in PD by a so called "abstraction". An abstraction is
simply a saved PD patch. So our very first and basically unusable
version of angriff is this: A nearly empty patch with a noise~ object
inside, saved under the name "angriff-01.pd".</p>
<div class="figure">
<p><img alt="angriff-01.png" src="angriff-01.png" /></p>
<p class="caption">angriff-01.pd, an unusable first version.</p>
</div>
<p>Even this can be used as an object. Just create a new, empty patch
(with "Ctrl-n"), put an object in it and call it "angriff-01", i.e. the
name of our first drum patch without the .pd-suffix.</p>
<p>Using the unusable angriff-01.pd in another patch.</p>
<p>PD searches for something that matches the object "angriff-01" in
several places: in the list of builtin objects like "noise~", in
external libraries or in its path for abstractions. If angriff-01.pd
is in the same directory as the using patch or in a path known to PD
through the startup option "-path /a/pd-path/", it gets found. If you
click on angriff-01, you can open it to see, what's inside.
Abstractions itself can use other abstractions so it's a good idea to
put often used functionality into abstractions. As our final drumsynth
should have a sound generating part and a GUI to control this, we will
seperate both parts from each other by use of abstractions. For the
synthesis of sound we will build and use an abstraction called "drumcenter"
inside of the main "angriff" patch. The main patch includes the control
elements for the parameters provided by "drumcenter". This way our
synthesis model and the view to the user are separated.</p>
</div>
<div class="section" id="bring-the-noise">
<h1><a class="toc-backref" href="#id3" name="bring-the-noise">Bring The Noise</a></h1>
<p>How do drums drum? Although human dummers can spend hours tuning their
drumset, drums are generally non-pitched, percussive sounds. So for
our first usable version of a drumsound we take some noise as a sound
source and put an amplitude envelope around the noise. A simple,
builtin envelope generator in PD is line~. drumcenter-01.pd show the
noise, the envelope and both multiplied together.</p>
<div class="figure">
<p><img alt="drumcenter-01.png" src="drumcenter-01.png" /></p>
<p class="caption">Enveloped noise, drumcenter-01.pd</p>
</div>
<p>If you listen to this patch, it already sounds a bit like a snare,
doesn't it? To make this sound a bit more variable we can use filtered
noise, for example with a lowpass or highpass filter. PD comes with
both, so lets use them. Her's the noise filtered with the lop~ filter
at a cutoff frequency of 400 Hertz:</p>
<div class="figure">
<p><img alt="drumcenter-02.png" src="drumcenter-02.png" /></p>
<p class="caption">Lowpass filtered and enveloped noise, drumcenter-02.pd</p>
</div>
<p>Now our patch is beginning to get a bit crammed and chaotic, so let's
replace some chords with "send" and "receive" pairs, abbreviated "s" and "r".
If we give those pairs names starting with $0, they get names starting
with unique numbers instead of the $0 while performing. This way, we
can later use several instances of our patches without conflicts
between their own send and receive variables. We can also hide stuff
we don't need to see in so called subpatches. Subpatches are areas
inside a patch that are hidden in an object box starting with <tt class="literal"><span class="pre">[pd]</span></tt>.
They are like curtains hiding things in a room, but the hidden objects
are a full part of the surrounding patch. The special objects <tt class="literal"><span class="pre">[inlet]</span></tt>,
<tt class="literal"><span class="pre">[outlet]</span></tt>, <tt class="literal"><span class="pre">[inlet~]</span></tt> and <tt class="literal"><span class="pre">[outlet~]</span></tt> create points of connections between
the surroundig patch and the subpatch. They work with abstractions as well.</p>
<div class="figure">
<p><img alt="drumcenter-03.png" src="drumcenter-03.png" /></p>
<p class="caption">Cleaning up in the house, drumcenter-03.pd</p>
</div>
</div>
<div class="section" id="let-it-swing">
<h1><a class="toc-backref" href="#id4" name="let-it-swing">Let It Swing</a></h1>
<p>I lied in the previous chapter: Drums are indeed pitched, although
just a little bit pitched. If a drummer kicks a bassdrum, the drum
begins to oscillate slightly at a low frequency. But this oscillation
is soon damped to an even lower frequency and then disapears. To
simulate this behaviour, we use PD's <tt class="literal"><span class="pre">[osc~]</span></tt> object with an added
frequency envelope as show in drumcenter-04.pd:</p>
<div class="figure">
<p><img alt="drumcenter-04.png" src="drumcenter-04.png" /></p>
<p class="caption">Percussive oscillator, drumcenter-04.pd</p>
</div>
<p>The right inlet of <tt class="literal"><span class="pre">[osc~]</span></tt> is used here to set the start phase of the
oscillator. If we wouldn't set it, it would be different everytime we
start the envelope, because an object like the <tt class="literal"><span class="pre">[osc~]</span></tt> is always on and
goes through its cycle even if we don't listen to it. The main inlet
sets the frequency, that's going from a starting value to a lower
frequency in a short time.</p>
</div>
<div class="section" id="going-faster">
<h1><a class="toc-backref" href="#id5" name="going-faster">Going faster</a></h1>
<p>So far we used <tt class="literal"><span class="pre">[line~]</span></tt> for all envelopes and a controlling message
like <tt class="literal"><span class="pre">[1,</span> <span class="pre">0</span> <span class="pre">50(</span></tt>. This tells <tt class="literal"><span class="pre">[line~]</span></tt> to first go immediatly to 1, then
start going to 0 for 50 milliseconds. For our oscillator frequency
this is fine, but instantly going to an amplitude of 1 produces
clicks, as you might have heard. So we need to specify an attack time,
in that the amplitude raises from 0. The first guess would be a
message like <tt class="literal"><span class="pre">[1</span> <span class="pre">10,</span> <span class="pre">0</span> <span class="pre">50(</span></tt>, but that simply doesn't work. So this has to
be solved with two messages to the <tt class="literal"><span class="pre">[line~]</span></tt> object, for example <tt class="literal"><span class="pre">[1</span> <span class="pre">10(</span></tt>
to go in 10 msecs to 1 and then the release: <tt class="literal"><span class="pre">[0</span> <span class="pre">50(</span></tt>. Between them a
<tt class="literal"><span class="pre">[del]</span></tt> is placed, that delays for as long as the first line segment's
duration is. But this also has a problem, as shown in the next figure:
a <tt class="literal"><span class="pre">[del]</span></tt> always delays in blocks of 64 samples, and that is a time of
around 1.45 msecs at a sampling rate of 44100 Hertz. A bit too long
for the short attack times used in drum synths.</p>
<div class="figure">
<p><img alt="fastline.png" src="fastline.png" /></p>
<p class="caption">Two line~ segments started with delay, fastline.pd</p>
</div>
<p>This problem isn't trivial at all and it appears everywhere, one wants
to contol messages in PD quicker than the signal blocksize allows, for
example in granular synthesis patches. A solution to this are "
Time-Tagged Triggers" (T3) as proposed by Gerhard Eckel and Manuel
Rocha Iturbide for Max/FTS. In PD T3-objects are made available as
externals in IEMLIB. Time-Tagged Triggers are a replacment for the
standard "bang" message that is normally used in PD or Max. Eckel
writes: "In Max/FTS, a T3 is nothing else than a message containing one
floating-point number which specifies the delay in ms after which,
counting from the current tick, the trigger should go off." We will now
use the T3 break point envelope generator <tt class="literal"><span class="pre">[t3_bpe]</span></tt> to generate faster
envelopes.</p>
</div>
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