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<h2>
<span class="refentrytitle">foscil</span>
</h2>
<p>foscil —
A basic frequency modulated oscillator.
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp24020360"></a>
<h2>Description</h2>
<p>
A basic frequency modulated oscillator.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp24021080"></a>
<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>foscil</strong></span> xamp, kcps, xcar, xmod, kndx, ifn [, iphs]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="idp24029304"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>ifn</em></span> -- function table number. Requires a wrap-around guard point.
</p>
<p>
<span class="emphasis"><em>iphs</em></span> (optional, default=0) -- initial phase of waveform in table <span class="emphasis"><em>ifn</em></span>, expressed as a fraction of a cycle (0 to 1). A negative value will cause phase initialization to be skipped. The default value is 0.
</p>
</div>
<div class="refsect1" title="Performance">
<a id="idp24031224"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>xamp</em></span> -- the amplitude of the output signal.
</p>
<p>
<span class="emphasis"><em>kcps</em></span> -- a common denominator, in cycles per second, for the carrier and modulating frequencies.
</p>
<p>
<span class="emphasis"><em>xcar</em></span> -- a factor that, when multiplied by the <span class="emphasis"><em>kcps</em></span> parameter, gives the carrier frequency.
</p>
<p>
<span class="emphasis"><em>xmod</em></span> -- a factor that, when multiplied by the <span class="emphasis"><em>kcps</em></span> parameter, gives the modulating frequency.
</p>
<p>
<span class="emphasis"><em>kndx</em></span> -- the modulation index.
</p>
<p>
<span class="emphasis"><em>foscil</em></span> is a composite unit that effectively
banks two <span class="emphasis"><em>oscil</em></span> opcodes in the familiar
Chowning FM setup, wherein the audio-rate output of one
generator is used to modulate the frequency input of another
(the <span class="quote">“<span class="quote">carrier</span>”</span>). Effective carrier frequency =
<span class="emphasis"><em>kcps</em></span> * <span class="emphasis"><em>xcar</em></span>, and
modulating frequency = <span class="emphasis"><em>kcps</em></span> *
<span class="emphasis"><em>xmod</em></span>. For integral values of
<span class="emphasis"><em>xcar</em></span> and <span class="emphasis"><em>xmod</em></span>, the
perceived fundamental will be the minimum positive value of
<span class="emphasis"><em>kcps</em></span> * (<span class="emphasis"><em>xcar</em></span> - <span class="emphasis"><em>n</em></span> *
<span class="emphasis"><em>xmod</em></span>), <span class="emphasis"><em>n</em></span> = 0,1,2,... The input
<span class="emphasis"><em>kndx</em></span> is the index of modulation (usually
time-varying and ranging 0 to 4 or so) which determines the
spread of acoustic energy over the partial positions given by <span class="emphasis"><em>n</em></span>
= 0,1,2,.., etc. <span class="emphasis"><em>ifn</em></span> should point to a
stored sine wave. Previous to version 3.50,
<span class="emphasis"><em>xcar</em></span> and <span class="emphasis"><em>xmod</em></span> could be
k-rate only.
</p>
<p>
The actual formula used for this implementation of FM synthesis
is
<span class="emphasis"><em>xamp</em></span> * cos(2π * <span class="emphasis"><em>t</em></span> * <span class="emphasis"><em>kcps</em></span> *
<span class="emphasis"><em>xcar</em></span> +
<span class="emphasis"><em>kndx</em></span> * sin(2π * <span class="emphasis"><em>t </em></span>* <span class="emphasis"><em>kcps</em></span> *
<span class="emphasis"><em>xmod</em></span>) - π),
assuming that the table is a sine wave.
</p>
</div>
<div class="refsect1" title="Examples">
<a id="idp24128064"></a>
<h2>Examples</h2>
<p>
Here is an example of the foscil opcode. It uses the file <a class="ulink" href="examples/foscil.csd" target="_top"><em class="citetitle">foscil.csd</em></a>.
</p>
<div class="example">
<a id="idp24129040"></a>
<p class="title">
<strong>Example 288. Example of the foscil 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 foscil.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
kcps <span class="op">=</span> 440
kcar <span class="op">=</span> 1
kmod <span class="op">=</span> p4
kndx <span class="opc">line</span> 0, p3, 20 <span class="comment">;intensivy sidebands</span>
asig <span class="opc">foscil</span> .5, kcps, kcar, kmod, kndx, 1
<span class="opc">outs</span> asig, asig
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="comment">; sine</span>
<span class="stamnt">f</span> 1 0 16384 10 1
<span class="stamnt">i</span> 1 0 9 .01 <span class="comment">;vibrato</span>
<span class="stamnt">i</span> 1 10 . 1
<span class="stamnt">i</span> 1 20 . 1.414 <span class="comment">;gong-ish</span>
<span class="stamnt">i</span> 1 30 5 2.05 <span class="comment">;with "beat"</span>
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
</div>
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<p><br class="example-break" />
</p>
</div>
<div class="refsect1" title="See Also">
<a id="idp24131376"></a>
<h2>See Also</h2>
<p> More information about frequency modulation on Wikipedia: <a class="ulink" href="http://en.wikipedia.org/wiki/Frequency_modulation_synthesis" target="_top"><em class="citetitle">http://en.wikipedia.org/wiki/Frequency_modulation_synthesis</em></a></p>
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