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<div class="refentry" title="rbjeq">
<a id="rbjeq"></a>
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<a id="IndexRbjeq" class="indexterm"></a>
<div class="refnamediv">
<h2>
<span class="refentrytitle">rbjeq</span>
</h2>
<p>rbjeq —
Parametric equalizer and filter opcode with 7 filter types, based
on algorithm by Robert Bristow-Johnson.
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp40011264"></a>
<h2>Description</h2>
<p>
Parametric equalizer and filter opcode with 7 filter types,
based on algorithm by Robert Bristow-Johnson.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp40063840"></a>
<h2>Syntax</h2>
<pre class="synopsis">ar <span class="command"><strong>rbjeq</strong></span> asig, kfco, klvl, kQ, kS[, imode]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="idp40064976"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>imode (</em></span>
optional, defaults to zero) - sum of:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>
1: skip initialization (should be used in tied, or
re-initialized notes only)
</p>
</li>
</ul>
</div>
<p>
and exactly one of the following values to select filter type:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>
0: resonant lowpass filter. kQ controls the resonance: at the
cutoff frequency (kfco), the amplitude gain is kQ (e.g. 20 dB for
kQ = 10), and higher kQ values result in a narrower resonance
peak. If kQ is set to sqrt(0.5) (about 0.7071), there is no
resonance, and the filter has a response that is very similar to
that of butterlp. If kQ is less than sqrt(0.5), there is no
resonance, and the filter has a -6 dB / octave response from about
kfco * kQ to kfco. Above kfco, there is always a -12 dB / octave
cutoff.
</p>
<div class="note" title="NOTE" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note: NOTE">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Note]" src="images/note.png" />
</td>
<th align="left">NOTE</th>
</tr>
<tr>
<td align="left" valign="top">
<p>
The rbjeq lowpass filter is basically the same as
ar pareq asig, kfco, 0, kQ, 2 but is faster to
calculate.
</p>
</td>
</tr>
</table>
</div>
<p>
</p>
</li>
<li class="listitem">
<p>
2: resonant highpass filter. The parameters are the
same as for the lowpass filter, but the equivalent
filter is butterhp if kQ is 0.7071, and "ar pareq
asig, kfco, 0, kQ, 1" in other cases.
</p>
</li>
<li class="listitem">
<p>
4: bandpass filter. kQ controls the bandwidth, which
is kfco / kQ, and must be always less than sr / 2. The
bandwidth is measured between -3 dB points (i.e.
amplitude gain = 0.7071), beyond which there is a +/-
6 dB / octave slope. This filter type is very similar
to ar butterbp asig, kfco, kfco / kQ.
</p>
</li>
<li class="listitem">
<p>
6: band-reject filter, with the same parameters as the
bandpass filter, and a response similar to that of
butterbr.
</p>
</li>
<li class="listitem">
<p>
8: peaking EQ. It has an amplitude gain of 1 (0 dB) at
0 Hz and sr / 2, and klvl at the center frequency
(kfco). Thus, klvl controls the amount of boost (if it
is greater than 1), or cut (if it is less than 1).
Setting klvl to 1 results in a flat response.
Similarly to the bandpass and band-reject filters, the
bandwidth is determined by kfco / kQ (which must be
less than sr / 2 again); however, this time it is
between sqrt(klvl) points (or, in other words, half
the boost or cut in decibels). NOTE: excessively low
or high values of klvl should be avoided (especially
with 32-bit floats), though the opcode was tested with
klvl = 0.01 and klvl = 100. klvl = 0 is always an
error, unlike in the case of pareq, which does allow a
zero level.
</p>
</li>
<li class="listitem">
<p>
10: low shelf EQ, controlled by klvl and kS (kQ is
ignored by this filter type). There is an amplitude
gain of klvl at zero frequency, while the level of
high frequencies (around sr / 2) is not changed. At
the corner frequency (kfco), the gain is sqrt(klvl)
(half the boost or cut in decibels). The kS parameter
controls the steepness of the slope of the frequency
response (see below).
</p>
</li>
<li class="listitem">
<p>
12: high shelf EQ. Very similar to the low shelf EQ,
but affects the high frequency range.
</p>
</li>
</ul>
</div>
<p>
The default value for imode is zero (lowpass filter,
initialization not skipped).
</p>
</div>
<div class="refsect1" title="Performance">
<a id="idp40074776"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>ar</em></span>
-- the output signal.
</p>
<p>
<span class="emphasis"><em>asig</em></span>
-- the input signal
</p>
<div class="note" title="NOTE" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note: NOTE">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Note]" src="images/note.png" />
</td>
<th align="left">NOTE</th>
</tr>
<tr>
<td align="left" valign="top">
<p>
If the input contains silent sections, on Intel CPUs a
significant slowdown can occur due to denormals. In such
cases, it is recommended to process the input signal with
"denorm" opcode before filtering it with rbjeq (and actually
many other filters).
</p>
</td>
</tr>
</table>
</div>
<p>
</p>
<p>
<span class="emphasis"><em>kfco</em></span>
-- cutoff, corner, or center frequency, depending on filter type,
in Hz. It must be greater than zero, and less than sr / 2 (the
range of about sr * 0.0002 to sr * 0.49 should be safe).
</p>
<p>
<span class="emphasis"><em>klvl</em></span>
-- level (amount of boost or cut), as amplitude gain (e.g. 1: flat
response, 4: 12 dB boost, 0.1: 20 dB cut); zero or negative values
are not allowed. It is recognized by the peaking and shelving EQ
types (8, 10, 12) only, and is ignored by other filters.
</p>
<p>
<span class="emphasis"><em>kQ</em></span>
-- resonance (also kfco / bandwidth in many filter types). Not
used by the shelving EQs (imode = 10 and 12). The exact meaning of
this parameter depends on the filter type (see above), but it
should be always greater than zero, and usually (kfco / kQ) less
than sr / 2.
</p>
<p>
<span class="emphasis"><em>kS</em></span>
-- shelf slope parameter for shelving filters. Must be greater
than zero; a higher value means a steeper slope, with resonance if
kS > 1 (however, a too high kS value may make the filter
unstable). If kS is set to exactly 1, the shelf slope is as steep
as possible without a resonance. Note that the effect of kS -
especially if it is greater than 1 - also depends on klvl, and it
does not have any well defined unit.
</p>
</div>
<div class="refsect1" title="Examples">
<a id="idp40081024"></a>
<h2>Examples</h2>
<p>
Here is an example of the <span class="emphasis"><em>rbjeq</em></span> opcode. It uses the file <a class="ulink" href="examples/rbjeq.csd" target="_top"><em class="citetitle">rbjeq.csd</em></a>.
</p>
<div class="example">
<a id="idp40082208"></a>
<p class="title">
<strong>Example 702. An example of the rbjeq 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 RT audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o rbjeq.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
imode <span class="op">=</span> p4
a1 <span class="opc">vco2</span> .3, 155.6 <span class="comment">; sawtooth wave</span>
kfco <span class="opc">expon</span> 8000, p3, 200 <span class="comment">; filter frequency</span>
asig <span class="opc">rbjeq</span> a1, kfco, 1, kfco <span class="op">*</span> 0.005, 1, imode
<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 5 0 <span class="comment">;lowpass</span>
<span class="stamnt">i</span> 1 6 5 2 <span class="comment">;highpass</span>
<span class="stamnt">i</span> 1 12 5 4 <span class="comment">;bandpass</span>
<span class="stamnt">i</span> 1 18 5 8 <span class="comment">;equalizer</span>
<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="idp40084512"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Original algorithm by Robert Bristow-Johnson</td>
</tr>
<tr>
<td>
Csound orchestra version by Josep M Comajuncosas, Aug 1999
</td>
</tr>
<tr>
<td>
Converted to C (with optimizations and bug fixes) by Istvan
Varga, Dec 2002
</td>
</tr>
</table>
<p>
</p>
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