There are another set of sounds, known as the unvoiced and plosive sounds, which are not modified by the mouth in the same fashion. This basic sound is then filtered by the nose and throat (a complicated resonant piping system) to produce differences in harmonic content ( formants) in a controlled way, creating the wide variety of sounds used in speech. The human voice consists of sounds generated by the opening and closing of the glottis by the vocal cords, which produces a periodic waveform with many harmonics.
