Simple acoustics of plosives

The three phases of a typical plosive can be seen in a waveform and spectrogram as in Figure 7.2, which shows a voiced velar plosive between two vowels, in ‘a good (hobby)’.

During the closing phase, the formants move slightly. These movements are called transitions. They correspond to movements of the articulators into the closure. During the hold phase, the amplitude drops significantly because there is no airflow through the vocal tract. On release, there is a transient burst, seen as a sudden increase in energy, in the waveform and the spectrogram.

Although there is some voicing during the closure (notice the regular peaks in the waveform), it is quiet and its amplitude diminishes until eventually it stops. Voicing starts again very soon after the release of the closure.