# spectrum

The Spectrum element analyzes the frequency spectrum of an audio signal. If the post-messages property is TRUE, it sends analysis results as element 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)
- A GST_TYPE_LIST value 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.
- A GST_TYPE_LIST 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 GST_TYPE_ARRAY value. The first dimension are the channels and the second dimension are the values.

## Example application

    /* 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., 51 Franklin St, Fifth Floor,
     * Boston, MA 02110-1301, 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,
          "post-messages", 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;
    }

## Hierarchy

    GObject
        ╰──GInitiallyUnowned
            ╰──GstObject
                ╰──GstElement
                    ╰──GstBaseTransform
                        ╰──GstAudioFilter
                            ╰──spectrum

## Factory details

Authors: – Erik Walthinsen , Stefan Kost , Sebastian Dröge

Classification: – `Filter/Analyzer/Audio`

Rank – none

Plugin – spectrum

Package – GStreamer Good Plug-ins

## Pad Templates

### `sink`

    audio/x-raw:
             format: { S16LE, S24LE, S32LE, F32LE, F64LE }
               rate: [ 1, 2147483647 ]
           channels: [ 1, 2147483647 ]
             layout: interleaved

Presence – always

Direction – sink

Object type – GstPad

### `src`

    audio/x-raw:
             format: { S16LE, S24LE, S32LE, F32LE, F64LE }
               rate: [ 1, 2147483647 ]
           channels: [ 1, 2147483647 ]
             layout: interleaved

Presence – always

Direction – src

Object type – GstPad

## Properties

### bands

    “bands” guint

Number of frequency bands

Flags : Read / Write

Default value : 128

### interval

    “interval” guint64

Interval of time between message posts (in nanoseconds)

Flags : Read / Write

Default value : 100000000

### message-magnitude

    “message-magnitude” gboolean

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

Flags : Read / Write

Default value : true

### message-phase

    “message-phase” gboolean

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

Flags : Read / Write

Default value : false

### multi-channel

    “multi-channel” gboolean

Send separate results for each channel

Flags : Read / Write

Default value : false

### post-messages

    “post-messages” gboolean

Whether to post a 'spectrum' element message on the bus for each passed interval

Flags : Read / Write

Default value : true

### threshold

    “threshold” gint

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

Flags : Read / Write

Default value : -60

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