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<div class="refentry">
<a id="zdf_1pole"></a>
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<a id="IndexZdf_1pole" class="indexterm"></a>
<div class="refnamediv">
<h2>
<span class="refentrytitle">zdf_1pole</span>
</h2>
<p>zdf_1pole —
Zero-delay feedback implementation of 1 pole filter.
</p>
</div>
<div class="refsect1">
<a id="idm281472867096296"></a>
<h2>Description</h2>
<p>
Zero-delay feedback implementation of a 1 pole (6 dB/oct) filter. Offers low-pass (default), high-pass, and allpass output modes.
</p>
</div>
<div class="refsect1">
<a id="idm281472867026440"></a>
<h2>Syntax</h2>
<pre class="synopsis">asig <span class="command"><strong>zdf_1pole</strong></span> ain, xcf [, kmode, istor]</pre>
</div>
<div class="refsect1">
<a id="idm281472867024344"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>istor</em></span> --initial disposition of internal data space.
Since filtering incorporates a feedback loop of previous output, the
initial status of the storage space used is significant. A zero value
will clear the space; a non-zero value will allow previous information to
remain. The default value is 0.
</p>
</div>
<div class="refsect1">
<a id="idm281472867022408"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>asig</em></span> -- high-pass output signal.
</p>
<p>
<span class="emphasis"><em>asig</em></span> -- input signal.
</p>
<p>
<span class="emphasis"><em>xcf</em></span> -- filter cutoff frequency (i-, k-, or a-rate).
</p>
<p>
<span class="emphasis"><em>kmode</em></span> -- filter output type. The default value is 0.
The output mode may be one of the following.
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>0 - low-pass</p>
</li>
<li class="listitem">
<p>1 - high-pass</p>
</li>
<li class="listitem">
<p>2 - allpass</p>
</li>
</ul>
</div>
<p>
</p>
</div>
<div class="refsect1">
<a id="idm281472867016152"></a>
<h2>Examples</h2>
<p>
Here is an example of the zdf_1pole opcode. It uses the file <a class="ulink" href="examples/zdf_1pole.csd" target="_top"><em class="citetitle">zdf_1pole.csd</em></a>.
</p>
<div class="example">
<a id="idm281472867014296"></a>
<p class="title">
<strong>Example 1152. Example of the zdf_1pole opcode.</strong>
</p>
<div class="example-contents">
<div class="refsect1">
<a id="idm281472685759320"></a>
<pre class="programlisting">
<span class="nt"><CsoundSynthesizer></span>
<span class="nt"><CsOptions></span>
-o dac
<span class="nt"></CsOptions></span>
<span class="nt"><CsInstruments></span>
<span class="vg">sr</span> <span class="o">=</span> <span class="mi">48000</span>
<span class="vg">ksmps</span> <span class="o">=</span> <span class="mi">1</span>
<span class="vg">nchnls</span> <span class="o">=</span> <span class="mi">2</span>
<span class="vg">0dbfs</span> <span class="o">=</span> <span class="mi">1</span>
<span class="kd">instr</span> <span class="nf">1</span>
a<span class="n">sig</span> <span class="o">=</span> <span class="nb">random</span><span class="p">:</span><span class="nb">a</span><span class="p">(</span><span class="o">-</span><span class="mf">1.0</span><span class="p">,</span> <span class="mf">1.0</span><span class="p">)</span>
a<span class="n">sig</span> <span class="o">=</span> <span class="n">zdf_1pole</span><span class="p">(</span>a<span class="n">sig</span><span class="p">,</span> <span class="nb">line</span><span class="p">(</span><span class="mi">220</span><span class="p">,</span> <span class="nb">p3</span><span class="p">,</span> <span class="mi">10000</span><span class="p">),</span> <span class="nb">p4</span><span class="p">)</span>
<span class="nb">outc</span><span class="p">(</span>a<span class="n">sig</span><span class="p">,</span> a<span class="n">sig</span><span class="p">)</span>
<span class="kd">endin</span>
<span class="kd">instr</span> <span class="nf">2</span>
a<span class="n">sig</span> <span class="o">=</span> <span class="nb">vco2</span><span class="p">(</span><span class="mf">0.5</span><span class="p">,</span> <span class="mi">220</span><span class="p">)</span>
a<span class="n">sig</span> <span class="o">=</span> <span class="n">zdf_1pole</span><span class="p">(</span>a<span class="n">sig</span><span class="p">,</span> <span class="nb">line</span><span class="p">(</span><span class="mi">220</span><span class="p">,</span> <span class="nb">p3</span><span class="p">,</span> <span class="mi">10000</span><span class="p">),</span> <span class="nb">p4</span><span class="p">)</span>
<span class="nb">outc</span><span class="p">(</span>a<span class="n">sig</span><span class="p">,</span> a<span class="n">sig</span><span class="p">)</span>
<span class="kd">endin</span>
<span class="nt"></CsInstruments></span>
<span class="nt"><CsScore></span>
<span class="nb">i</span><span class="mi">1</span> <span class="mi">0</span> <span class="mi">4</span> <span class="mi">0</span>
<span class="nb">i</span><span class="mi">1</span> <span class="mi">5</span> <span class="mi">4</span> <span class="mi">1</span>
<span class="nb">i</span><span class="mi">1</span> <span class="mi">10</span> <span class="mi">4</span> <span class="mi">2</span>
<span class="nb">i</span><span class="mi">2</span> <span class="mi">15</span> <span class="mi">4</span> <span class="mi">0</span>
<span class="nb">i</span><span class="mi">2</span> <span class="mi">20</span> <span class="mi">4</span> <span class="mi">1</span>
<span class="nb">i</span><span class="mi">2</span> <span class="mi">25</span> <span class="mi">4</span> <span class="mi">2</span>
<span class="nt"></CsScore></span>
<span class="nt"></CsoundSynthesizer></span>
</pre>
</div>
</div>
</div>
<p><br class="example-break" />
</p>
</div>
<div class="refsect1">
<a id="idm281472867012472"></a>
<h2>References</h2>
<p> This filter is based on the work of Will Pirkle that employs Vadim
Zavalishin's work with bilinear tranforms to create topology-preserving
transform (TPT) implementations of analog filters.</p>
<p>
</p>
<div class="orderedlist">
<ol class="orderedlist" type="1">
<li class="listitem">
<p>
Pirkle, Will. Designing Software Synthesizer Plug-ins in C++: For
RackAFX, VST3, and Audio Units. CRC Press, 2014.
</p>
</li>
<li class="listitem">
<p>
Pirkle, Will. AN-4: Virtual Analog (VA) Filter Implementation. 2013.
</p>
</li>
<li class="listitem">
<p>
Zavalishin, Vadim. "The Art of VA filter design." Native Instruments, 2012.
</p>
</li>
</ol>
</div>
<p>
</p>
</div>
<div class="refsect1">
<a id="idm281472867006984"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: Steven Yi</td>
</tr>
<tr>
<td>April 2017</td>
</tr>
</table>
<p>
</p>
<p>New in Csound 6.09.0</p>
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