The standard display audio and phonetic analysis tools offer of sound file data ist that of a waveform. Below you can see an example of a waveform display in WaveSurfer:
A waveform is a display of the variations in pressure (y-axis; ordinate), plotted as a function of time (x-axis; abscissa). It can provide us with information about the relative intensity of individual sounds in a recording, as well as giving clues for pauses or the closure phases of plosives. The latter are indicated by the almost complete absence of a signal. Absolute silence, however, is fairly unlikely for most recordings because we almost always have some background noise. For a slightly more skilled reader, waveforms can also provide information about periodicity within the signal, which indicates voicing. The waveform view in most programs can also be ‘manipulated’ by zooming in on particular portions of the signal, which makes it easier to identify specific features.
Let’s practise using the waveform view a little:
- Start WaveSurfer. You should be presented with an initial screen like this:
If you haven’t done so before, download an appropriate audio file from one of the links provided on the page about sound files. Open this file in WaveSurfer by clicking on “File → Open...”, pressing CTRL+o or clicking on the open folder icon. You should then see the dialogue box below.
- Choose the appropriate folder, file name and file type from the dropdown lists and click on the button.
- Choose “Waveform” from the configurations options and click on
The result should look similar to my example from above.
- Select a portion of the waveform in the main waveform window by either dragging across it with the left mouse button pressed. Alternatively, you can click with the left mouse button at the position where you want your selection to start and set the right border of your selection by holding down the shift key and clicking again.
- Click on the black solid triangle pointing to the right in order to play back your selection.
- Adjust your selection by either repositioning the selection borders or dragging the borders with your mouse as illustrated in the graphic below.
- Try experimenting with the different zoom options:
from the left: ‘zoom in’, ‘zoom out’, ‘view whole file’ & ‘view selection’.
When you’ve finished going through all the steps above, just take a brief look at all the remaining menu options to familiarise yourself with some of the other capabilities of WaveSurfer, but don’t worry, you’re not expected to understand all of them.