spectrum

## spectrum spectrum — Run an FFT on the audio signal, output spectrum data |

## Synopsis

    struct              GstSpectrum;

## Object Hierarchy

      GObject
       +----GInitiallyUnowned
             +----GstObject
                   +----GstElement
                         +----GstBaseTransform
                               +----GstAudioFilter
                                     +----GstSpectrum

## Properties

      "bands"                    guint                 : Read / Write
      "interval"                 guint64               : Read / Write
      "message"                  gboolean              : Read / Write
      "threshold"                gint                  : Read / Write
      "message-magnitude"        gboolean              : Read / Write
      "message-phase"            gboolean              : Read / Write
      "post-messages"            gboolean              : Read / Write
      "multi-channel"            gboolean              : Read / Write

## Description

The Spectrum element analyzes the frequency spectrum of an audio signal. If the "post-messages" property is TRUE, it sends analysis results as application messages named `"spectrum"` after each interval of time given by the "interval" property.

The message's structure contains some combination of these fields:

- GstClockTime `"timestamp"`: the timestamp of the buffer that triggered the message.

- GstClockTime `"stream-time"`: the stream time of the buffer.

- GstClockTime `"running-time"`: the running_time of the buffer.

- GstClockTime `"duration"`: the duration of the buffer.

- GstClockTime `"endtime"`: the end time of the buffer that triggered the message as stream time (this is deprecated, as it can be calculated from stream-time + duration)

- GstValueList of gfloat `"magnitude"`: the level for each frequency band in dB. All values below the value of the "threshold" property will be set to the threshold. Only present if the "message-magnitude" property is `TRUE`.

- GstValueList of gfloat `"phase"`: The phase for each frequency band. The value is between -pi and pi. Only present if the "message-phase" property is `TRUE`.

If "multi-channel" property is set to true. magnitude and phase fields will be each a nested GstValueArray. The first dimension are the channels and the second dimension are the values.

### Example application

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    /* GStreamer
     * Copyright (C) 2006 Stefan Kost <ensonic@users.sf.net>
     * Copyright (C) 2008 Jan Schmidt <jan.schmidt@sun.com>
     *
     * 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.
     */

    #include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    #include <gst/gst.h>

    static guint spect_bands = 20;

    #define AUDIOFREQ 32000

    /* receive spectral data from element message */
    static gboolean
    message_handler (GstBus * bus, GstMessage * message, gpointer data)
    {
      if (message->type == GST_MESSAGE_ELEMENT) {
        const GstStructure *s = gst_message_get_structure (message);
        const gchar *name = gst_structure_get_name (s);
        GstClockTime endtime;

        if (strcmp (name, "spectrum") == 0) {
          const GValue *magnitudes;
          const GValue *phases;
          const GValue *mag, *phase;
          gdouble freq;
          guint i;

          if (!gst_structure_get_clock_time (s, "endtime", &endtime))
            endtime = GST_CLOCK_TIME_NONE;

          g_print ("New spectrum message, endtime %" GST_TIME_FORMAT "\n",
              GST_TIME_ARGS (endtime));

          magnitudes = gst_structure_get_value (s, "magnitude");
          phases = gst_structure_get_value (s, "phase");

          for (i = 0; i < spect_bands; ++i) {
            freq = (gdouble) ((AUDIOFREQ / 2) * i + AUDIOFREQ / 4) / spect_bands;
            mag = gst_value_list_get_value (magnitudes, i);
            phase = gst_value_list_get_value (phases, i);

            if (mag != NULL && phase != NULL) {
              g_print ("band %d (freq %g): magnitude %f dB phase %f\n", i, freq,
                  g_value_get_float (mag), g_value_get_float (phase));
            }
          }
          g_print ("\n");
        }
      }
      return TRUE;
    }

    int
    main (int argc, char *argv[])
    {
      GstElement *bin;
      GstElement *src, *audioconvert, *spectrum, *sink;
      GstBus *bus;
      GstCaps *caps;
      GMainLoop *loop;

      gst_init (&argc, &argv);

      bin = gst_pipeline_new ("bin");

      src = gst_element_factory_make ("audiotestsrc", "src");
      g_object_set (G_OBJECT (src), "wave", 0, "freq", 6000.0, NULL);
      audioconvert = gst_element_factory_make ("audioconvert", NULL);
      g_assert (audioconvert);

      spectrum = gst_element_factory_make ("spectrum", "spectrum");
      g_object_set (G_OBJECT (spectrum), "bands", spect_bands, "threshold", -80,
          "message", TRUE, "message-phase", TRUE, NULL);

      sink = gst_element_factory_make ("fakesink", "sink");
      g_object_set (G_OBJECT (sink), "sync", TRUE, NULL);

      gst_bin_add_many (GST_BIN (bin), src, audioconvert, spectrum, sink, NULL);

      caps = gst_caps_new_simple ("audio/x-raw",
          "rate", G_TYPE_INT, AUDIOFREQ, NULL);

      if (!gst_element_link (src, audioconvert) ||
          !gst_element_link_filtered (audioconvert, spectrum, caps) ||
          !gst_element_link (spectrum, sink)) {
        fprintf (stderr, "can't link elements\n");
        exit (1);
      }
      gst_caps_unref (caps);

      bus = gst_element_get_bus (bin);
      gst_bus_add_watch (bus, message_handler, NULL);
      gst_object_unref (bus);

      gst_element_set_state (bin, GST_STATE_PLAYING);

      /* we need to run a GLib main loop to get the messages */
      loop = g_main_loop_new (NULL, FALSE);
      g_main_loop_run (loop);

      gst_element_set_state (bin, GST_STATE_NULL);

      gst_object_unref (bin);

      return 0;
    }

Last reviewed on 2011-03-10 (0.10.29)

## Synopsis

### Element Information

plugin | spectrum
author | Erik Walthinsen <omega@cse.ogi.edu>, Stefan Kost <ensonic@users.sf.net>, Sebastian Dröge <sebastian.droege@collabora.co.uk>
class | Filter/Analyzer/Audio

### Element Pads

name | sink
direction | sink
presence | always
details | audio/x-raw, format=(string){ S16LE, S24LE, S32LE, 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){ S16LE, S24LE, S32LE, F32LE, F64LE }, rate=(int)[ 1, 2147483647 ], channels=(int)[ 1, 2147483647 ], layout=(string)interleaved

## Details

### struct GstSpectrum

    struct GstSpectrum;

## Property Details

### The `"bands"` property

      "bands"                    guint                 : Read / Write

Number of frequency bands.

Default value: 128

### The `"interval"` property

      "interval"                 guint64               : Read / Write

Interval of time between message posts (in nanoseconds).

Allowed values: >= 1

Default value: 100000000

### The `"message"` property

      "message"                  gboolean              : Read / Write

Whether to post a 'spectrum' element message on the bus for each passed interval (deprecated, use post-messages).

Default value: TRUE

### The `"threshold"` property

      "threshold"                gint                  : Read / Write

dB threshold for result. All lower values will be set to this.

Allowed values: <= 0

Default value: -60

### The `"message-magnitude"` property

      "message-magnitude"        gboolean              : Read / Write

Whether to add a 'magnitude' field to the structure of any 'spectrum' element messages posted on the bus.

Default value: TRUE

### The `"message-phase"` property

      "message-phase"            gboolean              : Read / Write

Whether to add a 'phase' field to the structure of any 'spectrum' element messages posted on the bus.

Default value: FALSE

### The `"post-messages"` property

      "post-messages"            gboolean              : Read / Write

Post messages on the bus with spectrum information.

Default value: TRUE

Since 0.10.17

### The `"multi-channel"` property

      "multi-channel"            gboolean              : Read / Write

Send separate results for each channel

Default value: FALSE

Since 0.10.29