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<h2 class="title" style="clear: both"><a id="OrchUDO"></a>User Defined Opcodes (UDO)</h2>
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<p>
Csound allows the definition of opcodes inside the orchestra header using the opcodes <a class="link" href="opcode.html" title="opcode"><em class="citetitle">opcode</em></a> and <a class="link" href="endop.html" title="endop"><em class="citetitle">endop</em></a>. The defined opcode may run with a different number of control samples (<a class="link" href="ksmps.html" title="ksmps"><em class="citetitle">ksmps</em></a>) using <a class="link" href="setksmps.html" title="setksmps"><em class="citetitle">setksmps</em></a>.
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<p>
To connect inputs and outputs for the UDO, use <a class="link" href="xin.html" title="xin"><em class="citetitle">xin</em></a> and <a class="link" href="xout.html" title="xout"><em class="citetitle">xout</em></a>.
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<p>
An UDO looks like this:
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<pre class="programlisting">
<span class="oblock">opcode</span> Lowpass, a, akk
<span class="opc">setksmps</span> 1 <span class="comment">; need sr=kr</span>
ain, ka1, ka2 <span class="opc">xin</span> <span class="comment">; read input parameters</span>
aout <span class="opc">init</span> 0 <span class="comment">; initialize output</span>
aout <span class="op">=</span> ain<span class="op">*</span>ka1 <span class="op">+</span> aout<span class="op">*</span>ka2 <span class="comment">; simple tone-like filter</span>
<span class="opc">xout</span> aout <span class="comment">; write output</span>
<span class="oblock">endop</span></pre>
<p>
This UDO called <span class="emphasis"><em>Lowpass</em></span> takes 3 inputs (the first is a-rate, and the next two are k-rate), and delivers 1 a-rate output. Notice the use of <a class="link" href="xin.html" title="xin"><em class="citetitle">xin</em></a> to receive inputs and <a class="link" href="xout.html" title="xout"><em class="citetitle">xout</em></a> to deliver outputs. Also note the use of <a class="link" href="setksmps.html" title="setksmps"><em class="citetitle">setksmps</em></a>, which is needed for the filter to work properly.
</p>
<p>To use this UDO within an instrument, you would do something like:</p>
<pre class="programlisting">
afiltered Lowpass asource, kvalue1, kvalue2</pre>
<p>See the entry for <a class="link" href="opcode.html" title="opcode"><em class="citetitle">opcode</em></a> for detailed information on UDO definition.
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<p>
You can find many ready made UDO's (or contribute your own) at <a class="ulink" href="http://www.csounds.com/" target="_top"><em class="citetitle">Csounds.com</em></a>'s <a class="ulink" href="http://www.csounds.com/udo/" target="_top"><em class="citetitle">User Defined Opcode Database</em></a>.
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