audioiirfilter

audioiirfilter

Properties

GValueArray * a Read / Write
GValueArray * b Read / Write

Signals

void rate-changed Run Last

Types and Values

Object Hierarchy

    GObject
    ╰── GInitiallyUnowned
        ╰── GstObject
            ╰── GstElement
                ╰── GstBaseTransform
                    ╰── GstAudioFilter
                        ╰── GstAudioFXBaseIIRFilter
                            ╰── GstAudioIIRFilter

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

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/* 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

Functions

Types and Values

struct GstAudioIIRFilter

struct GstAudioIIRFilter;

Opaque data structure.

Property Details

The “a” property

  “a”                        GValueArray *

Filter coefficients (denominator of transfer function).

Flags: Read / Write


The “b” property

  “b”                        GValueArray *

Filter coefficients (numerator of transfer function).

Flags: Read / Write

Signal Details

The “rate-changed” signal

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

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.

Parameters

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.

 

Flags: Run Last