1.5.5. The Spectrogram Viewer

The Spectrogram Viewer displays a spectrum of frequencies of an audio file (*.wav) or of the audio track of a video file. The horizontal axis represents time (though the viewer currently does not show a time ruler), the vertical axis frequency and color intensity represents the amplitude of a particular frequency range at a particular time.

For the creation of the spectrogram the data of the audio signal have to be transformed to a spectrum of frequencies. The transform applied in ELAN is a Fourier transform (a fast Fourier transform, FFT). The transform is applied successively to small segments of the audio signal ("sliding windows") and creates an array of frequency bins (each frequency bin representing a range of frequencies) for each segment. To reduce the effects of discontinuity resulting from this segmentation, a window function (see the window function options) can be applied to the segments before the transformation.

The viewer shows the usual red vertical bar, the crosshair, to indicate the current point in time. It also marks the boundaries of the selected time interval, currently by means of blue vertical lines (instead of a light blue overlay on the image).


Generation of the spectrogram image requires a considerable amount of processing, therefore it might be useful to switch off this viewer (see Section 1.5.21) if it doesn't serve your purposes (this is true for other viewers as well).

The spectrogram viewer

Figure 1.80. The spectrogram viewer

The viewer provides a few options to customize the appearance of the image. The context menu that is shown with a right click on the viewer contains the following items:

The spectrogram context menu

Figure 1.81. The spectrogram context menu


At the moment the settings are global (application wide) settings, but already open windows are not updated immediately when settings are changed.

The audio Spectrogram settings window contains two panels, one dedicated to visualization parameters and one to data transformation parameters.

Spectrogram display settings panel

Figure 1.82. Spectrogram display settings panel

The following parameters determine the visualization of the spectrogram:

Spectrogram transform settings panel

Figure 1.83. Spectrogram transform settings panel

The following parameters determine how the data of the audio signal are transformed to a spectrum of frequencies:

Apart from the Apply and Cancel buttons, there is Restore Defaults button which resets all settings to their default values (after clicking Apply).