audioiirfilter

audioiirfilter — Generic audio IIR filter with custom filter kernel

Synopsis

struct              GstAudioIIRFilter;

Object Hierarchy

  GObject
   +----GInitiallyUnowned
         +----GstObject
               +----GstElement
                     +----GstBaseTransform
                           +----GstAudioFilter
                                 +----GstAudioFXBaseIIRFilter
                                       +----GstAudioIIRFilter

Properties

  "a"                        GValueArray*          : Read / Write
  "b"                        GValueArray*          : Read / Write

Signals

  "rate-changed"                                   : Run Last

Description

audioiirfilter implements a generic audio IIR filter. Before usage the "a" and "b" properties have to be set to the filter coefficients that should be used.

The filter coefficients describe the numerator and denominator of the transfer function.

To change the filter coefficients whenever the sampling rate changes the "rate-changed" signal can be used. This should be done for most IIR filters as they're depending on the sampling rate.

Example application

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
/* 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., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

/* This small sample application creates a lowpass IIR filter
 * and applies it to white noise.
 * See http://www.dspguide.com/ch19/2.htm for a description
 * of the IIR filter that is used.
 */

/* FIXME 0.11: suppress warnings for deprecated API such as GValueArray
 * with newer GLib versions (>= 2.31.0) */
#define GLIB_DISABLE_DEPRECATION_WARNINGS

#include <string.h>
#include <math.h>

#include <gst/gst.h>

/* Cutoff of 4000 Hz */
#define CUTOFF (4000.0)

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, };
  gdouble x;

  if (rate / 2.0 > CUTOFF)
    x = exp (-2.0 * G_PI * (CUTOFF / rate));
  else
    x = 0.0;

  va = g_value_array_new (1);

  g_value_init (&v, G_TYPE_DOUBLE);
  g_value_set_double (&v, 1.0 - x);
  g_value_array_append (va, &v);
  g_value_reset (&v);
  g_object_set (G_OBJECT (element), "a", va, NULL);
  g_value_array_free (va);

  va = g_value_array_new (1);
  g_value_set_double (&v, x);
  g_value_array_append (va, &v);
  g_value_reset (&v);
  g_object_set (G_OBJECT (element), "b", va, 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 ("audioiirfilter", 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;
}

Synopsis

Element Information

plugin

audiofx

author

Sebastian Dröge <sebastian.droege@collabora.co.uk>

class

Filter/Effect/Audio

Element Pads

name

sink

direction

sink

presence

always

details

audio/x-raw, format=(string){ F32LE, F64LE }, rate=(int)[ 1, 2147483647 ], channels=(int)[ 1, 2147483647 ], layout=(string)interleaved

name

src

direction

source

presence

always

details

audio/x-raw, format=(string){ F32LE, F64LE }, rate=(int)[ 1, 2147483647 ], channels=(int)[ 1, 2147483647 ], layout=(string)interleaved

Details

struct GstAudioIIRFilter

struct GstAudioIIRFilter;

Opaque data structure.

Property Details

The "a" property

  "a"                        GValueArray*          : Read / Write

Filter coefficients (denominator of transfer function).


The "b" property

  "b"                        GValueArray*          : Read / Write

Filter coefficients (numerator of transfer function).

Signal Details

The "rate-changed" signal

void                user_function                      (GstAudioIIRFilter *filter,
                                                        gint               rate,
                                                        gpointer           user_data)      : Run Last

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.

filter :

the filter on which the signal is emitted

rate :

the new sampling rate

user_data :

user data set when the signal handler was connected.