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<a href="#gst-plugins-good-plugins-audiofirfilter.synopsis" class="shortcut">Top</a>
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<a href="#gst-plugins-good-plugins-audiofirfilter.description" class="shortcut">Description</a>
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<a href="#gst-plugins-good-plugins-audiofirfilter.object-hierarchy" class="shortcut">Object Hierarchy</a>
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<a href="#gst-plugins-good-plugins-audiofirfilter.properties" class="shortcut">Properties</a>
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<a href="#gst-plugins-good-plugins-audiofirfilter.signals" class="shortcut">Signals</a>
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<div class="refentry">
<a name="gst-plugins-good-plugins-audiofirfilter"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle"><a name="gst-plugins-good-plugins-audiofirfilter.top_of_page"></a>audiofirfilter</span></h2>
<p>audiofirfilter — Generic audio FIR filter with custom filter kernel</p>
</td>
<td valign="top" align="right"></td>
</tr></table></div>
<div class="refsynopsisdiv">
<a name="gst-plugins-good-plugins-audiofirfilter.synopsis"></a><h2>Synopsis</h2>
<a name="GstAudioFIRFilter"></a><pre class="synopsis">struct <a class="link" href="gst-plugins-good-plugins-audiofirfilter.html#GstAudioFIRFilter-struct" title="struct GstAudioFIRFilter">GstAudioFIRFilter</a>;
</pre>
</div>
<div class="refsect1">
<a name="gst-plugins-good-plugins-audiofirfilter.object-hierarchy"></a><h2>Object Hierarchy</h2>
<pre class="synopsis">
<a href="/usr/share/gtk-doc/html/gobject/gobject-The-Base-Object-Type.html#GObject">GObject</a>
+----<a href="/usr/share/gtk-doc/html/gstreamer-0.10/GstObject.html">GstObject</a>
+----<a href="/usr/share/gtk-doc/html/gstreamer-0.10/GstElement.html">GstElement</a>
+----<a href="/usr/share/gtk-doc/html/gstreamer-libs-0.10/GstBaseTransform.html">GstBaseTransform</a>
+----<a href="/usr/share/gtk-doc/html/gst-plugins-base-libs-0.10/gst-plugins-base-libs-gstaudiofilter.html#GstAudioFilter">GstAudioFilter</a>
+----GstAudioFXBaseFIRFilter
+----GstAudioFIRFilter
</pre>
</div>
<div class="refsect1">
<a name="gst-plugins-good-plugins-audiofirfilter.properties"></a><h2>Properties</h2>
<pre class="synopsis">
"<a class="link" href="gst-plugins-good-plugins-audiofirfilter.html#GstAudioFIRFilter--kernel" title='The "kernel" property'>kernel</a>" <a href="/usr/share/gtk-doc/html/gobject/gobject-Value-arrays.html#GValueArray"><span class="type">GValueArray</span></a>* : Read / Write
"<a class="link" href="gst-plugins-good-plugins-audiofirfilter.html#GstAudioFIRFilter--latency" title='The "latency" property'>latency</a>" <span class="type">guint64</span> : Read / Write
</pre>
</div>
<div class="refsect1">
<a name="gst-plugins-good-plugins-audiofirfilter.signals"></a><h2>Signals</h2>
<pre class="synopsis">
"<a class="link" href="gst-plugins-good-plugins-audiofirfilter.html#GstAudioFIRFilter-rate-changed" title='The "rate-changed" signal'>rate-changed</a>" : <a href="/usr/share/gtk-doc/html/gobject/gobject-Signals.html#G-SIGNAL-RUN-LAST:CAPS"><code class="literal">Run Last</code></a>
</pre>
</div>
<div class="refsect1">
<a name="gst-plugins-good-plugins-audiofirfilter.description"></a><h2>Description</h2>
<p>
audiofirfilter implements a generic audio <a class="ulink" href="http://en.wikipedia.org/wiki/Finite_impulse_response" target="_top">FIR filter</a>. Before usage the
"kernel" property has to be set to the filter kernel that should be
used and the "latency" property has to be set to the latency (in samples)
that is introduced by the filter kernel. Setting a latency of n samples
will lead to the first n samples being dropped from the output and
n samples added to the end.
</p>
<p>
The filter kernel describes the impulse response of the filter. To
calculate the frequency response of the filter you have to calculate
the Fourier Transform of the impulse response.
</p>
<p>
To change the filter kernel whenever the sampling rate changes the
"rate-changed" signal can be used. This should be done for most
FIR filters as they're depending on the sampling rate.
</p>
<p>
</p>
<div class="refsect2">
<a name="idp4594584"></a><h3>Example application</h3>
<div class="informalexample"><pre class="programlisting">
/* GStreamer
* Copyright (C) 2009 Sebastian Droege <sebastian.droege@collabora.co.uk>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/* This small sample application creates a bandpass FIR filter
* by transforming the frequency response to the filter kernel.
*/
#include <string.h>
#include <math.h>
#include <gst/gst.h>
#include <gst/fft/gstfftf64.h>
static gboolean
on_message (GstBus * bus, GstMessage * message, gpointer user_data)
{
GMainLoop *loop = (GMainLoop *) user_data;
switch (GST_MESSAGE_TYPE (message)) {
case GST_MESSAGE_ERROR:
g_error ("Got ERROR");
g_main_loop_quit (loop);
break;
case GST_MESSAGE_WARNING:
g_warning ("Got WARNING");
g_main_loop_quit (loop);
break;
case GST_MESSAGE_EOS:
g_main_loop_quit (loop);
break;
default:
break;
}
return TRUE;
}
static void
on_rate_changed (GstElement * element, gint rate, gpointer user_data)
{
GValueArray *va;
GValue v = { 0, };
GstFFTF64 *fft;
GstFFTF64Complex frequency_response[17];
gdouble tmp[32];
gdouble filter_kernel[32];
guint i;
/* Create the frequency response: zero outside
* a small frequency band */
for (i = 0; i < 17; i++) {
if (i < 5 || i > 11)
frequency_response[i].r = 0.0;
else
frequency_response[i].r = 1.0;
frequency_response[i].i = 0.0;
}
/* Calculate the inverse FT of the frequency response */
fft = gst_fft_f64_new (32, TRUE);
gst_fft_f64_inverse_fft (fft, frequency_response, tmp);
gst_fft_f64_free (fft);
/* Shift the inverse FT of the frequency response by 16,
* i.e. the half of the kernel length to get the
* impulse response. See http://www.dspguide.com/ch17/1.htm
* for more information.
*/
for (i = 0; i < 32; i++)
filter_kernel[i] = tmp[(i + 16) % 32];
/* Apply the hamming window to the impulse response to get
* a better result than given from the rectangular window
*/
for (i = 0; i < 32; i++)
filter_kernel[i] *= (0.54 - 0.46 * cos (2 * G_PI * i / 32));
va = g_value_array_new (1);
g_value_init (&v, G_TYPE_DOUBLE);
for (i = 0; i < 32; i++) {
g_value_set_double (&v, filter_kernel[i]);
g_value_array_append (va, &v);
g_value_reset (&v);
}
g_object_set (G_OBJECT (element), "kernel", va, NULL);
/* Latency is 1/2 of the kernel length for this method of
* calculating a filter kernel from the frequency response
*/
g_object_set (G_OBJECT (element), "latency", (gint64) (32 / 2), NULL);
g_value_array_free (va);
}
gint
main (gint argc, gchar * argv[])
{
GstElement *pipeline, *src, *filter, *conv, *sink;
GstBus *bus;
GMainLoop *loop;
gst_init (NULL, NULL);
pipeline = gst_element_factory_make ("pipeline", NULL);
src = gst_element_factory_make ("audiotestsrc", NULL);
g_object_set (G_OBJECT (src), "wave", 5, NULL);
filter = gst_element_factory_make ("audiofirfilter", NULL);
g_signal_connect (G_OBJECT (filter), "rate-changed",
G_CALLBACK (on_rate_changed), NULL);
conv = gst_element_factory_make ("audioconvert", NULL);
sink = gst_element_factory_make ("autoaudiosink", NULL);
g_return_val_if_fail (sink != NULL, -1);
gst_bin_add_many (GST_BIN (pipeline), src, filter, conv, sink, NULL);
if (!gst_element_link_many (src, filter, conv, sink, NULL)) {
g_error ("Failed to link elements");
return -2;
}
loop = g_main_loop_new (NULL, FALSE);
bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
gst_bus_add_signal_watch (bus);
g_signal_connect (G_OBJECT (bus), "message", G_CALLBACK (on_message), loop);
gst_object_unref (GST_OBJECT (bus));
if (gst_element_set_state (pipeline,
GST_STATE_PLAYING) == GST_STATE_CHANGE_FAILURE) {
g_error ("Failed to go into PLAYING state");
return -3;
}
g_main_loop_run (loop);
gst_element_set_state (pipeline, GST_STATE_NULL);
g_main_loop_unref (loop);
gst_object_unref (pipeline);
return 0;
}
</pre></div>
</div>
<p>
</p>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="refsect2">
<a name="idp4974264"></a><h3>Element Information</h3>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">plugin</span></p></td>
<td>
<a class="link" href="gst-plugins-good-plugins-plugin-audiofx.html#plugin-audiofx">audiofx</a>
</td>
</tr>
<tr>
<td><p><span class="term">author</span></p></td>
<td>Sebastian Dröge <sebastian.droege@collabora.co.uk></td>
</tr>
<tr>
<td><p><span class="term">class</span></p></td>
<td>Filter/Effect/Audio</td>
</tr>
</tbody>
</table></div>
</div>
<hr>
<div class="refsect2">
<a name="idp3536304"></a><h3>Element Pads</h3>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">name</span></p></td>
<td>sink</td>
</tr>
<tr>
<td><p><span class="term">direction</span></p></td>
<td>sink</td>
</tr>
<tr>
<td><p><span class="term">presence</span></p></td>
<td>always</td>
</tr>
<tr>
<td><p><span class="term">details</span></p></td>
<td>audio/x-raw-float, width=(int){ 32, 64 }, endianness=(int)1234, rate=(int)[ 1, 2147483647 ], channels=(int)[ 1, 2147483647 ]</td>
</tr>
</tbody>
</table></div>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term">name</span></p></td>
<td>src</td>
</tr>
<tr>
<td><p><span class="term">direction</span></p></td>
<td>source</td>
</tr>
<tr>
<td><p><span class="term">presence</span></p></td>
<td>always</td>
</tr>
<tr>
<td><p><span class="term">details</span></p></td>
<td>audio/x-raw-float, width=(int){ 32, 64 }, endianness=(int)1234, rate=(int)[ 1, 2147483647 ], channels=(int)[ 1, 2147483647 ]</td>
</tr>
</tbody>
</table></div>
</div>
</div>
<p>
</p>
</div>
<div class="refsect1">
<a name="gst-plugins-good-plugins-audiofirfilter.details"></a><h2>Details</h2>
<div class="refsect2">
<a name="GstAudioFIRFilter-struct"></a><h3>struct GstAudioFIRFilter</h3>
<pre class="programlisting">struct GstAudioFIRFilter;</pre>
<p>
Opaque data structure.
</p>
</div>
</div>
<div class="refsect1">
<a name="gst-plugins-good-plugins-audiofirfilter.property-details"></a><h2>Property Details</h2>
<div class="refsect2">
<a name="GstAudioFIRFilter--kernel"></a><h3>The <code class="literal">"kernel"</code> property</h3>
<pre class="programlisting"> "kernel" <a href="/usr/share/gtk-doc/html/gobject/gobject-Value-arrays.html#GValueArray"><span class="type">GValueArray</span></a>* : Read / Write</pre>
<p>Filter kernel for the FIR filter.</p>
</div>
<hr>
<div class="refsect2">
<a name="GstAudioFIRFilter--latency"></a><h3>The <code class="literal">"latency"</code> property</h3>
<pre class="programlisting"> "latency" <span class="type">guint64</span> : Read / Write</pre>
<p>Filter latency in samples.</p>
<p>Default value: 0</p>
</div>
</div>
<div class="refsect1">
<a name="gst-plugins-good-plugins-audiofirfilter.signal-details"></a><h2>Signal Details</h2>
<div class="refsect2">
<a name="GstAudioFIRFilter-rate-changed"></a><h3>The <code class="literal">"rate-changed"</code> signal</h3>
<pre class="programlisting"><span class="returnvalue">void</span> user_function (<a class="link" href="gst-plugins-good-plugins-audiofirfilter.html#GstAudioFIRFilter"><span class="type">GstAudioFIRFilter</span></a> *filter,
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gint"><span class="type">gint</span></a> rate,
<a href="/usr/share/gtk-doc/html/glib/glib-Basic-Types.html#gpointer"><span class="type">gpointer</span></a> user_data) : <a href="/usr/share/gtk-doc/html/gobject/gobject-Signals.html#G-SIGNAL-RUN-LAST:CAPS"><code class="literal">Run Last</code></a></pre>
<p>
Will be emitted when the sampling rate changes. The callbacks
will be called from the streaming thread and processing will
stop until the event is handled.
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody>
<tr>
<td><p><span class="term"><em class="parameter"><code>filter</code></em> :</span></p></td>
<td>the filter on which the signal is emitted</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>rate</code></em> :</span></p></td>
<td>the new sampling rate</td>
</tr>
<tr>
<td><p><span class="term"><em class="parameter"><code>user_data</code></em> :</span></p></td>
<td>user data set when the signal handler was connected.</td>
</tr>
</tbody>
</table></div>
</div>
</div>
</div>
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