Spectrograms

As we have seen on the previous page, waveforms can be fairly useful for identifying some interesting (high-level) features of speech. However, for an in-depth investigation of specific features of vowels, consonants and connected speech, the waveform view is certainly not the most useful view most phonetic analysis programs offer. A much more useful representation of the sound data is in form of a spectrogram. Unlike the waveform, which was a two-dimensional representation, the spectrogram actually provides us with a three-dimensional display of time (x-axis), frequency (y-axis) and intensity (z-axis), where the latter is represented by different degrees of ‘colour’ depth. Below, you can see two different variants of the same spectrogram, one in greyscale and one in colour.

greyscale spectrogram

colour spectrogram

When working with this type of audio data, it is always important to bear in mind that, when we change the display, we’re actually only changing ‘the view on the data’, but not the data itself! In order to view our data in form of a spectrogram, we’ll now have a look at two different options, one we can use in case we’re already displaying the data in a different from, such as a waveform, and one where we select the display ‘from scratch’, when opening a new file.

If you still have a file open in waveform view, use the right mouse button to click inside the waveform window. From the context menu that is displayed, choose ‘Apply Configuration...’ as depicted in the following screen shot:

Clicking on ‘Apply Configuration...’ will then bring up the same configurations option we’ve already seen when we opened our data file for display as a waveform, only that this time, we need to select ‘Spectrogram’ from the options. If you’re opening a new file, once you’ve passed the step where you’ve selected the file, you also need to select the same option.
Once you’ve selected the appropriate configuration, you should now see a spectrogram in the position where you might previously had a waveform display. However, this spectrogram is by default in greyscale, which is a little more difficult to interpret than a colour spectrogram, so we’ll now change it to a colour display. In order to do this, click with the right mouse button inside the spectrogram window and select ‘Properties...’ from the context menu.

You should now get the following properties dialogue displayed:

Switch the property for ‘Spectrogram color’ to ‘color’.
As before, create a selection, play it back and experiment with the different zoom options, so that you can see how the display changes and you get to see various levels of detail.