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<h2>
<span class="refentrytitle">logbtwo</span>
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<p>logbtwo —
Performs a logarithmic base two calculation.
</p>
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<div class="refsect1" title="Description">
<a id="idp28779424"></a>
<h2>Description</h2>
<p>
Performs a logarithmic base two calculation.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp28780152"></a>
<h2>Syntax</h2>
<pre class="synopsis"><span class="command"><strong>logbtwo</strong></span>(x) (init-rate or control-rate args only)</pre>
</div>
<div class="refsect1" title="Performance">
<a id="idp28790448"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>logbtwo</em></span>() returns the logarithm base two of <span class="emphasis"><em>x</em></span>. The range of values admitted as argument is .25 to 4 (i.e. from -2 octave to +2 octave response). This function is the inverse of <span class="emphasis"><em>powoftwo</em></span>().
</p>
<p>
These functions are fast, because they read values stored in tables. Also they are very useful when working with tuning ratios. They work at i- and k-rate.
</p>
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<div class="refsect1" title="Examples">
<a id="idp28792432"></a>
<h2>Examples</h2>
<p>
Here is an example of the logbtwo opcode. It uses the file <a class="ulink" href="examples/logbtwo.csd" target="_top"><em class="citetitle">logbtwo.csd</em></a>.
</p>
<div class="example">
<a id="idp28793384"></a>
<p class="title">
<strong>Example 401. Example of the logbtwo 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>
<span class="comment">; Audio out Audio in</span>
-odac -iadc <span class="comment">;;;RT audio I/O</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o logbtwo.wav -W ;;; for file output any platform</span>
<span class="csdtag"></CsOptions></span>
<span class="csdtag"><CsInstruments></span>
<span class="comment">; Initialize the global variables.</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> 1
<span class="comment">; Instrument #1.</span>
<span class="oblock">instr</span> 1
i1 <span class="op">=</span> <span class="opc">logbtwo</span>(3)
<span class="opc">print</span> i1
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="comment">; Play Instrument #1 for one second.</span>
<span class="stamnt">i</span> 1 0 1
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
</div>
</div>
<p><br class="example-break" />
Its output should include a line like this:
</p>
<pre class="screen">instr 1: i1 = 1.585</pre>
<p>
</p>
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<div class="refsect1" title="See Also">
<a id="idp28826440"></a>
<h2>See Also</h2>
<p>
<a class="link" href="powoftwo.html" title="powoftwo"><em class="citetitle">powoftwo</em></a>
</p>
</div>
<div class="refsect1" title="Credits">
<a id="idp28827512"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: Gabriel Maldonado</td>
</tr>
<tr>
<td>Italy</td>
</tr>
<tr>
<td>June 1998</td>
</tr>
</table>
<p>
</p>
<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>July 1999</td>
</tr>
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<p>
</p>
<p>Example written by Kevin Conder.</p>
<p>New in Csound version 3.57</p>
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