4.3.5 Human voice and its properties

Many animals are capable of producing sounds, predominantly to express their sexual instincts, but also to raise awareness about a possible danger or to scare an attacker.

Some animals make use of sounds to navigate in space – ecolocation -.

Sound manipulation in man is closest to perfection. Articulated human speech is used for both communication and signalling.

The human voice can be generated as air is expired from the lungs. It passes through the larynx and over the vocal chords – making them vibrate. The pinch of the voice is given by the length of the vocal chords 1. The air column now travels up into the pharynx, and nasal and oral cavities where they resonate with the different structures within. What makes every voice unique is its timbre – different overtones are created as air travels through the previously mentioned structures which differ in most individuals.

adh_sense_1_0The basic acoustic elements of human speech are phonemes. The are divided into two types, according to origin and function.

  • vowels
  • consonats

Vowels: Are primarily produced in the larynx.

According to the Helmholtz resonance theory, the basic tones are created by the vocal chords, and do not require a build up of pressure in upper cavities. These are then amplified through resonance in the cavities above the glottis.

Vowels have a period nature. It has been identified that vowels occupy different formats in their acoustic spectrum. A format is a harmonic of a note augmented by a resonance (I think the best way to think of these formats is just thinking about fundamental frequencies. The first format is the lowest frequency a vowel has).


Consonants require the build-up of pressure in the cavities above the glottis. They are produce either by the whirling air in the narrowed-down part of the articulation space – fricatives – or as an “explosion” after a quick release of the built-up pressure.

They are non-periodic.

According to the aural impression they are classified as:

  • vibrant
  • sibilant
  • soft consonants

Vowels contribute to the intensity of the voice, while consonants contribute to its comprehensibility.

  1. Males and females have different vocal fold sizes. Adult male voices are usually lower pitched due to longer and thicker folds. The male vocal folds are between 1.75 cm and 2.5 cm (approx 0.75″ to 1.0″) in length,while female vocal folds are between 1.25 cm and 1.75 cm (approx 0.5″ to 0.75″) in length. The vocal cords of children are much shorter than those of adult males and females. The difference in vocal fold length and thickness between males and females causes a difference in vocal pitch.