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<div class="refentry" title="distort">
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<a id="IndexDistort" class="indexterm"></a>
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<h2>
<span class="refentrytitle">distort</span>
</h2>
<p>distort —
Distort an audio signal via waveshaping and optional clipping.
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp18464792"></a>
<h2>Description</h2>
<p>
Distort an audio signal via waveshaping and optional clipping.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp18465464"></a>
<h2>Syntax</h2>
<pre class="synopsis">ar <span class="command"><strong>distort</strong></span> asig, kdist, ifn[, ihp, istor]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="idp18475936"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>ifn</em></span> -- table number of a waveshaping
function with extended guard point. The function can be of any
shape, but it should pass through 0 with positive slope at the
table mid-point. The table size need not be large, since it is
read with interpolation.
</p>
<p>
<span class="emphasis"><em>ihp</em></span> -- (optional) half-power point (in cps)
of an internal low-pass filter. The default value is 10.
</p>
<p>
<span class="emphasis"><em>istor</em></span> -- (optional) initial disposition of
internal data space (see reson). The default value is 0.
</p>
</div>
<div class="refsect1" title="Performance">
<a id="idp18478024"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>asig</em></span> -- Audio signal to be processed
</p>
<p>
<span class="emphasis"><em>kdist</em></span> -- Amount of distortion (usually between 0 and
1)
</p>
<p>
This unit distorts an incoming signal using a waveshaping function
<span class="emphasis"><em>ifn</em></span> and a distortion index
<span class="emphasis"><em>kdist</em></span>. The input signal is first compressed using a
running rms, then passed through a waveshaping function which may modify
its shape and spectrum. Finally it is rescaled to approximately its
original power.
</p>
<p>
The amount of distortion depends on the nature of the shaping function
and on the value of <span class="emphasis"><em>kdist</em></span>, which generally ranges
from 0 to 1. For low values of <span class="emphasis"><em>kdist</em></span>, we should like
the shaping function to pass the signal almost unchanged. This will be
the case if, at the mid-point of the table, the shaping function is
near-linear and is passing through 0 with positive slope. A line function
from -1 to +1 will satisfy this requirement; so too will a sigmoid
(sinusoid from 270 to 90 degrees). As <span class="emphasis"><em>kdist</em></span> is
increased, the compressed signal is expanded to encounter more and more
of the shaping function, and if this becomes non-linear the signal is
increasingly <span class="emphasis"><em>bent</em></span> on read-through to cause
distortion.
</p>
<p>
When <span class="emphasis"><em>kdist</em></span> becomes large enough, the read-through process will
eventually hit the outer limits of the table. The table is not
read with wrap-around, but will <span class="quote">“<span class="quote">stick</span>”</span> at the end-points as the
incoming signal exceeds them; this introduces clipping, an
additional form of signal distortion. The point at which clipping
begins will depend on the complexity (rms-to-peak value) of the
input signal. For a pure sinusoid, clipping will begin only as
<span class="emphasis"><em>kdist</em></span> exceeds 0.7; for a more complex input, clipping might begin
at a <span class="emphasis"><em>kdist</em></span> of 0.5 or much less. <span class="emphasis"><em>kdist</em></span> can exceed
the clip point by any amount, and may be greater than 1.
</p>
<p>
The shaping function can be made arbitrarily complex for extra effect.
It should generally be continuous, though this is not a
requirement. It should also be well-behaved near the mid-point,
and roughly balanced positive-negative overall, else some
excessive DC offset may result. The user might experiment with
more aggressive functions to suit the purpose. A generally
positive slope allows the distorted signal to be mixed with the
source without phase cancellation.
</p>
<p>
<span class="emphasis"><em>distort</em></span> is useful as an effects process, and is usually combined with
reverb and chorusing on effects busses. However, it can
alternatively be used to good effect within a single instrument.
</p>
</div>
<div class="refsect1" title="Examples">
<a id="idp18516168"></a>
<h2>Examples</h2>
<p>
Here is an example of the distort opcode. It uses the file <a class="ulink" href="examples/distort.csd" target="_top"><em class="citetitle">distort.csd</em></a>.
</p>
<div class="example">
<a id="idp18517144"></a>
<p class="title">
<strong>Example 182. Example of the distort 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">;;;RT audio out</span>
<span class="comment">;-iadc ;;;uncomment -iadc if RT audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o distort.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
gifn <span class="ohdr">ftgen</span> 0,0, 257, 9, .5,1,270 <span class="comment">; define a sigmoid, or better </span>
<span class="comment">;gifn ftgen 0,0, 257, 9, .5,1,270,1.5,.33,90,2.5,.2,270,3.5,.143,90,4.5,.111,270</span>
<span class="oblock">instr</span> 1
kdist <span class="opc">line</span> 0, p3, 2 <span class="comment">; and over 10 seconds</span>
asig <span class="opc">poscil</span> 0.3, 440, 1
aout <span class="opc">distort</span> asig, kdist, gifn <span class="comment">; gradually increase the distortion</span>
<span class="opc">outs</span> aout, aout
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="stamnt">f</span> 1 0 16384 10 1
<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>
</div>
<div class="refsect1" title="Credits">
<a id="idp18519448"></a>
<h2>Credits</h2>
<p>Written by Barry L. Vercoe for Extended Csound and released in Csound5.</p>
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distrib
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Mageia
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5
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x86_64
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media
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core-release
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b707d9a4ee443103660a75ccb6e51334
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files
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541
