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<div class="refentry" title="vco2">
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<h2>
<span class="refentrytitle">vco2</span>
</h2>
<p>vco2 —
Implementation of a band-limited oscillator using pre-calculated tables.
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp50880928"></a>
<h2>Description</h2>
<p>
<span class="emphasis"><em>vco2</em></span> is similar to <a class="link" href="vco.html" title="vco"><em class="citetitle">vco</em></a>. But the implementation uses pre-calculated tables of band-limited waveforms (see also <a class="link" href="GEN30.html" title="GEN30"><em class="citetitle">GEN30</em></a>) rather than integrating impulses. This opcode can be faster than <span class="emphasis"><em>vco</em></span> (especially if a low control-rate is used) and also allows better sound quality. Additionally, there are more waveforms and oscillator phase can be modulated at k-rate. The disadvantage is increased memory usage. For more details about vco2 tables, see also <a class="link" href="vco2init.html" title="vco2init"><em class="citetitle">vco2init</em></a> and <a class="link" href="vco2ft.html" title="vco2ft"><em class="citetitle">vco2ft</em></a>.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp50886400"></a>
<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>vco2</strong></span> kamp, kcps [, imode] [, kpw] [, kphs] [, inyx]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="idp50940488"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>imode</em></span> (optional, default=0) -- a sum of values representing the waveform and its control values.
</p>
<p>
One may use any of the following values for <span class="emphasis"><em>imode</em></span>:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>16: enable k-rate phase control (if set, <span class="emphasis"><em>kphs</em></span> is a required k-rate parameter that allows phase modulation)</p>
</li>
<li class="listitem">
<p>1: skip initialization</p>
</li>
</ul>
</div>
<p>
</p>
<p>
One may use exactly one of these <span class="emphasis"><em>imode</em></span> values to select the waveform to be generated:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>14: user defined waveform -1 (requires using the <a class="link" href="vco2init.html" title="vco2init"><em class="citetitle">vco2init</em></a> opcode)</p>
</li>
<li class="listitem">
<p>12: triangle (no ramp, faster)</p>
</li>
<li class="listitem">
<p>10: square wave (no PWM, faster)</p>
</li>
<li class="listitem">
<p>8: 4 * x * (1 - x) (i.e. integrated sawtooth)</p>
</li>
<li class="listitem">
<p>6: pulse (not normalized)</p>
</li>
<li class="listitem">
<p>4: sawtooth / triangle / ramp</p>
</li>
<li class="listitem">
<p>2: square / PWM</p>
</li>
<li class="listitem">
<p>0: sawtooth</p>
</li>
</ul>
</div>
<p>
</p>
<p>
The default value for <span class="emphasis"><em>imode</em></span> is zero, which means a sawtooth wave with no k-rate phase control.
</p>
<p>
<span class="emphasis"><em>inyx</em></span> (optional, default=0.5) -- bandwidth of the generated waveform, as percentage (0 to 1) of the sample rate. The expected range is 0 to 0.5 (i.e. up to <a class="link" href="sr.html" title="sr"><em class="citetitle">sr</em></a>/2), other values are limited to the allowed range.
</p>
<p>
Setting <span class="emphasis"><em>inyx</em></span> to 0.25 (<span class="emphasis"><em>sr</em></span>/4), or 0.3333 (<span class="emphasis"><em>sr</em></span>/3) can produce a <span class="quote">“<span class="quote">fatter</span>”</span> sound in some cases, although it is more likely to reduce quality.
</p>
</div>
<div class="refsect1" title="Performance">
<a id="idp50949208"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>ares </em></span> -- the output audio signal.
</p>
<p>
<span class="emphasis"><em>kamp</em></span> -- amplitude scale. In the case of a <span class="emphasis"><em>imode</em></span> waveform value of 6 (a pulse waveform), the actual output level can be a lot higher than this value.
</p>
<p>
<span class="emphasis"><em>kcps</em></span> -- frequency in Hz (should be in the range -<span class="emphasis"><em>sr</em></span>/2 to <span class="emphasis"><em>sr</em></span>/2).
</p>
<p>
<span class="emphasis"><em>kpw</em></span> (optional) -- the pulse width of the square wave (<span class="emphasis"><em>imode</em></span> waveform=2) or the ramp characteristics of the triangle wave (<span class="emphasis"><em>imode</em></span> waveform=4). It is required only by these waveforms and ignored in all other cases. The expected range is 0 to 1, any other value is wrapped to the allowed range.
</p>
<div class="warning" title="Warning" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Warning: Warning">
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<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Warning]" src="images/warning.png" />
</td>
<th align="left">Warning</th>
</tr>
<tr>
<td align="left" valign="top">
<p>
<span class="emphasis"><em>kpw</em></span> must not be an exact integer value (e.g. 0 or 1) if a sawtooth / triangle / ramp (<span class="emphasis"><em>imode</em></span> waveform=4) is generated. In this case, the recommended range is about 0.01 to 0.99. There is no such limitation for a square/PWM waveform.
</p>
</td>
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</div>
<p>
<span class="emphasis"><em>kphs</em></span> (optional) -- oscillator phase (depending on <span class="emphasis"><em>imode</em></span>, this can be either an optional i-rate parameter that defaults to zero or required k-rate). Similarly to <span class="emphasis"><em>kpw</em></span>, the expected range is 0 to 1.
</p>
<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note: Note">
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<img alt="[Note]" src="images/note.png" />
</td>
<th align="left">Note</th>
</tr>
<tr>
<td align="left" valign="top">
<p>
When a low control-rate is used, pulse width (<span class="emphasis"><em>kpw</em></span>) and phase (<span class="emphasis"><em>kphs</em></span>) modulation is internally converted to frequency modulation. This allows for faster processing and reduced artifacts. But in the case of very long notes and continuous fast changes in <span class="emphasis"><em>kpw</em></span> or <span class="emphasis"><em>kphs</em></span>, the phase may drift away from the requested value. In most cases, the phase error is at most 0.037 per hour (assuming a sample rate of 44100 Hz).
</p>
<p>
This is a problem mainly in the case of pulse width (<span class="emphasis"><em>kpw</em></span>), where it may result in various artifacts. While future releases of <span class="emphasis"><em>vco2</em></span> may fix such errors, the following work-arounds may also be of some help:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>Use <span class="emphasis"><em>kpw</em></span> values only in the range 0.05 to 0.95. (There are more artifacts around integer values)</p>
</li>
<li class="listitem">
<p>Try to avoid modulating <span class="emphasis"><em>kpw</em></span> by asymmetrical waveforms like a sawtooth wave. Relatively slow (<= 20 Hz) symmetrical modulation (e.g. sine or triangle), random splines (also slow), or a fixed pulse width is a lot less likely to cause synchronization problems.
</p>
</li>
<li class="listitem">
<p>In some cases, adding random jitter (for example: random splines with an amplitude of about 0.01) to <span class="emphasis"><em>kpw</em></span> may also fix the problem.</p>
</li>
</ul>
</div>
<p>
</p>
</td>
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</div>
<div class="refsect1" title="Examples">
<a id="idp50960160"></a>
<h2>Examples</h2>
<p>
Here is an example of the vco2 opcode. It uses the file <a class="ulink" href="examples/vco2.csd" target="_top"><em class="citetitle">vco2.csd</em></a>.
</p>
<div class="example">
<a id="idp50961128"></a>
<p class="title">
<strong>Example 930. Example of the vco2 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 No messages</span>
-odac -iadc -d <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 vco2.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> 10
<span class="ohdr">nchnls</span> <span class="op">=</span> 1
<span class="comment">; user defined waveform -1: trapezoid wave with default parameters (can be</span>
<span class="comment">; accessed at ftables starting from 10000)</span>
itmp <span class="ohdr">ftgen</span> 1, 0, 16384, 7, 0, 2048, 1, 4096, 1, 4096, <span class="op">-</span>1, 4096, <span class="op">-</span>1, 2048, 0
ift <span class="opc">vco2init</span> <span class="op">-</span>1, 10000, 0, 0, 0, 1
<span class="comment">; user defined waveform -2: fixed table size (4096), number of partials</span>
<span class="comment">; multiplier is 1.02 (~238 tables)</span>
itmp <span class="ohdr">ftgen</span> 2, 0, 16384, 7, 1, 4095, 1, 1, <span class="op">-</span>1, 4095, <span class="op">-</span>1, 1, 0, 8192, 0
ift <span class="opc">vco2init</span> <span class="op">-</span>2, ift, 1.02, 4096, 4096, 2
<span class="oblock">instr</span> 1
kcps <span class="opc">expon</span> p4, p3, p5 <span class="comment">; instr 1: basic vco2 example</span>
a1 <span class="opc">vco2</span> 12000, kcps <span class="comment">; (sawtooth wave with default</span>
<span class="opc">out</span> a1 <span class="comment">; parameters)</span>
<span class="oblock">endin</span>
<span class="oblock">instr</span> 2
kcps <span class="opc">expon</span> p4, p3, p5 <span class="comment">; instr 2:</span>
kpw <span class="opc">linseg</span> 0.1, p3<span class="op">/</span>2, 0.9, p3<span class="op">/</span>2, 0.1 <span class="comment">; PWM example</span>
a1 <span class="opc">vco2</span> 10000, kcps, 2, kpw
<span class="opc">out</span> a1
<span class="oblock">endin</span>
<span class="oblock">instr</span> 3
kcps <span class="opc">expon</span> p4, p3, p5 <span class="comment">; instr 3: vco2 with user</span>
a1 <span class="opc">vco2</span> 14000, kcps, 14 <span class="comment">; defined waveform (-1)</span>
aenv <span class="opc">linseg</span> 1, p3 <span class="op">-</span> 0.1, 1, 0.1, 0 <span class="comment">; de-click envelope</span>
<span class="opc">out</span> a1 <span class="op">*</span> aenv
<span class="oblock">endin</span>
<span class="oblock">instr</span> 4
kcps <span class="opc">expon</span> p4, p3, p5 <span class="comment">; instr 4: vco2ft example,</span>
kfn <span class="opc">vco2ft</span> kcps, <span class="op">-</span>2, 0.25 <span class="comment">; with user defined waveform</span>
a1 <span class="opc">oscilikt</span> 12000, kcps, kfn <span class="comment">; (-2), and sr/4 bandwidth</span>
<span class="opc">out</span> a1
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="stamnt">i</span> 1 0 3 20 2000
<span class="stamnt">i</span> 2 4 2 200 400
<span class="stamnt">i</span> 3 7 3 400 20
<span class="stamnt">i</span> 4 11 2 100 200
<span class="stamnt">f</span> 0 14
<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="See Also">
<a id="idp50963392"></a>
<h2>See Also</h2>
<p>
<a class="link" href="vco.html" title="vco"><em class="citetitle">vco</em></a>,
<a class="link" href="vco2ft.html" title="vco2ft"><em class="citetitle">vco2ft</em></a>,
<a class="link" href="vco2ift.html" title="vco2ift"><em class="citetitle">vco2ift</em></a>, and
<a class="link" href="vco2init.html" title="vco2init"><em class="citetitle">vco2init</em></a>.
</p>
</div>
<div class="refsect1" title="Credits">
<a id="idp50965840"></a>
<h2>Credits</h2>
<p>Author: Istvan Varga</p>
<p>New in version 4.22</p>
</div>
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