Plosives occur in several different acoustic forms. We will begin by looking at voiceless plosives such as p , t or k . The first important component of these sounds is silence. If you think of a word like ‘upper’ Ã p « , you can see that there must be a short silence in the middle of the word if a listener is to hear a p sound. When a voiceless plosive occurs at the beginning of a word (e.g. ‘pin’), the word begins with silence. This silence occurs during the time when no air is able to escape from the vocal tract because the plosive articulation closes the vocal tract completely. When the closure is released, things start happening very rapidly as far as acoustic events are concerned. The release of the air causes a small explosion, and this sound is aperiodic – it is like a very brief fricative. If the plosive is an aspirated one, as English p , t and k often are, this "release burst" is followed by a different sound – the sound of air rushing through the vocal tract. This is called aspiration, and is aperiodic (it is closely related to the h consonant).
Voiced plosives are periodic during the time that the vocal tract is closed; at this stage, instead of the silence that we find in voiceless plosives, we can hear (but only just) the vibration of the vocal folds coming from the larynx. Although we class English b , d and g as voiced plosives, they actually have very little voicing, so to hear a good example of a truly voiced plosive you should listen to some other languages: French, Spanish and Italian are good examples.