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<div class="refentry" title="noise">
<a id="noise"></a>
<div class="titlepage"></div>
<a id="IndexNoise" class="indexterm"></a>
<div class="refnamediv">
<h2>
<span class="refentrytitle">noise</span>
</h2>
<p>noise —
A white noise generator with an IIR lowpass filter.
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp32843856"></a>
<h2>Description</h2>
<p>
A white noise generator with an IIR lowpass filter.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp32844600"></a>
<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>noise</strong></span> xamp, kbeta</pre>
</div>
<div class="refsect1" title="Performance">
<a id="idp32855352"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>xamp</em></span> -- amplitude of final output
</p>
<p>
<span class="emphasis"><em>kbeta</em></span> -- beta of the lowpass filter. Should
be in the range of -1 to 1, exclusive of the end-points.
</p>
<p>
The filter equation is:
</p>
<div class="mediaobject">
<img src="images/noise-filter.png" alt="[Filter equation for filter in noise opcode.]" />
</div>
<p>
where <span class="emphasis"><em>x<sub>n</sub></em></span> is the original white noise and <span class="emphasis"><em>y<sub>n</sub></em></span> is lowpass filtered noise. The higher β is, the lower the filter's cut-off frequency. The cutoff frequency is roughly sr * ((1-kbeta)/2).
</p>
</div>
<div class="refsect1" title="Examples">
<a id="idp32894488"></a>
<h2>Examples</h2>
<p>
Here is an example of the noise opcode. It uses the file <a class="ulink" href="examples/noise.csd" target="_top"><em class="citetitle">noise.csd</em></a>.
</p>
<div class="example">
<a id="idp32895632"></a>
<p class="title">
<strong>Example 508. Example of the noise opcode.</strong>
</p>
<div class="example-contents">
<p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
<pre class="programlisting">
<span class="csdtag"><CsoundSynthesizer></span>
<span class="csdtag"><CsOptions></span>
<span class="comment">; Select audio/midi flags here according to platform</span>
-odac <span class="comment">;;;realtime audio out</span>
<span class="comment">;-iadc ;;;uncomment -iadc if realtime audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o noise.wav -W ;;; for file output any platform</span>
<span class="csdtag"></CsOptions></span>
<span class="csdtag"><CsInstruments></span>
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">ksmps</span> <span class="op">=</span> 32
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="ohdr">0dbfs</span> <span class="op">=</span> 1
<span class="oblock">instr</span> 1
kbeta <span class="opc">line</span> <span class="op">-</span>1, p3, 1 <span class="comment">;change beta value from -1 to 1</span>
asig <span class="opc">noise</span> .3, kbeta
asig <span class="opc">clip</span> asig, 2, .9 <span class="comment">;clip signal</span>
<span class="opc">outs</span> asig, asig
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="stamnt">i</span> 1 0 10
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
</div>
</div>
<p><br class="example-break" />
</p>
<p>
Here is an example of the noise opcode controlling the kbeta parameter with a GUI interface. It uses the file <a class="ulink" href="examples/noise-2.csd" target="_top"><em class="citetitle">noise-2.csd</em></a>.
</p>
<div class="example">
<a id="idp32898592"></a>
<p class="title">
<strong>Example 509. Example of the noise opcode controlled with a GUI.</strong>
</p>
<div class="example-contents">
<pre class="programlisting">
<span class="csdtag"><CsoundSynthesizer></span>
<span class="csdtag"><CsOptions></span>
<span class="comment">; Select audio/midi flags here according to platform</span>
<span class="comment">; Audio out Audio in No messages</span>
-odac <span class="comment">; -iadc -d ;;;RT audio I/O</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o noise.wav -W ;;; for file output any platform</span>
<span class="csdtag"></CsOptions></span>
<span class="csdtag"><CsInstruments></span>
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">kr</span> <span class="op">=</span> 4410
<span class="ohdr">ksmps</span> <span class="op">=</span> 10
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="opc">FLpanel</span> "noise", 200, 50, <span class="op">-</span>1 , <span class="op">-</span>1
gkbeta, gislider1 <span class="opc">FLslider</span> "kbeta", <span class="op">-</span>1, 1, 0, 5, <span class="op">-</span>1, 180, 20, 10, 10
<span class="opc">FLpanelEnd</span>
<span class="opc">FLrun</span>
<span class="oblock">instr</span> 1
iamp <span class="op">=</span> <span class="ohdr">0dbfs</span> <span class="op">/</span> 4 <span class="comment">; Peaks 12 dB below 0dbfs</span>
<span class="opc">print</span> iamp
a1 <span class="opc">noise</span> iamp, gkbeta
<span class="opc">printk2</span> gkbeta
<span class="opc">outs</span> a1,a1
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="comment">; Play Instrument #1 for one minute.</span>
<span class="stamnt">i</span> 1 0 60
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
</div>
</div>
<p><br class="example-break" />
</p>
</div>
<div class="refsect1" title="Credits">
<a id="idp32899584"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: John ffitch</td>
</tr>
<tr>
<td>University of Bath, Codemist. Ltd.</td>
</tr>
<tr>
<td>Bath, UK</td>
</tr>
<tr>
<td>December 2000</td>
</tr>
</table>
<p>
</p>
<p>New in Csound version 4.10</p>
</div>
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