the diversity of voice

With nearly eight billion people on the planet with nearly eight billion different voices, what makes a voice unique?

(Please note, the following features will vary cross-culturally.)

= how high or low your voice is. Pitch is measured in Hertz (Hz). When you speak, a "buzzy" sound is created in your voice box by the wave-like opening and closing of your vocal folds. Place two fingers near your Adam's apple to feel the buzz as you talk. Each complete open-close cycle is measured as 1 Hz. The more open-close cycles PER SECOND (!), the higher your pitch.

The physics behind your voice: As you prepare to speak your vocal folds (two delicate folds of mucous membrane) are drawn together as air flows up from the lungs. This column of air leads to a build-up of pressure below your vocal folds. Eventually the bottom of the vocal folds open, then the top as the air column travels upwards. This fast-moving column of air leaves a trail of low pressure behind it, which creates a kind of suction effect and draws the vocal folds together again. And the cycle repeats - as long as you're still talking. This is known as the Bernouilli effect.

Voice, age and gender: Our voices change over time. Children tend to have higher voices (more Hz per second) than adolescents and adults because their voices have not yet gone through puberty. When puberty begins, cis boys' vocal folds get thicker and heavier and they tend to vibrate more slowly, producing a lower pitch (less Hz per second). As they age, cis men's voices lose their bulk and this leads to an increase in pitch in later life. Cis women on the other hand, experience a lowering of pitch, thought to be the result of hormonal changes.

Tip: You can use an app such as Voice Analyst to see your pitch change as you go up and down with your voice. Make the video full screen to be able to see the Hz readings on the left.

= the way your vocal tract amplifies and modifies the sound created in your voice box. To keep things simple, think of your vocal tract as a tube, starting at your vocal folds and ending at your lips. This tube is usually longer in AMABs than AFABs. During puberty, gravity causes the voice box to drop in the neck, creating more distance between the vocal folds and lips. A longer vocal tract typically produces more chest resonance, and this is associated with the perception of a male voice. A shorter vocal tract tends to result in more head resonance. This tends to lead a listener to perceive the speaker as female. The overall shape of your vocal tract will also impact on your resonance. Take three kinds of acoustic guitar and play the exact same note (pitch). The quality of the sound will still differ as the sound reverberates around the different spaces inside the body of the guitar. The same happens with voice. The good news is that you can modify the length and shape of your vocal tract to introduce more head and chest resonance.

= how we vary our pitch over time to create meaning and emphasis. Some people have a wide pitch range (large gap between lowest and highest achievable note) and others have a more narrow range. People may change pitch often as they speak, others less so.

There are various different intonation patterns, for example rising, falling, rise-fall, fall-rise.
    - For some yes/no questions, we use a rising pattern: Are you thirsty?
    - For a statement, we use a falling pattern: I think we're lost.

While intonation is less important than pitch and resonance when it comes to gender perception, it is generally thought that feminine spectrum speakers use more "up-speak" (rise in pitch at end of sentences) and have a wider pitch range, while masculine spectrum speakers use a more definitive, falling intonation pattern. Feminine spectrum speakers are more likely to use intonation to signal changes in emphasis, whereas masculine spectrum speakers use loudness to achieve the same effect (see below).

= how loud or quiet our voices are. It's measured in decibels, or dB. Typically we speak at around 60-70 dB in conversation. If we need to shout, that's more like 70-80 dB. Masculine spectrum speakers tend to emphasise changes in meaning through changes in volume. Take the sentence "It's my tie." To emphasise "my", a masculine spectrum speaker will tend to increase volume on that word. 

                                                 65dB    75dB   65dB
                                                   "It's        MY       tie."

= the formation of speech sounds. When your voice travels from your vocal folds up your vocal tract, you make different consonant sounds by controlling the movement of different parts of your mouth and nose (the "articulators"). These include your

    - tongue
    - lips and teeth
    - alveolar ridge (bumpy ridge at the top of your mouth just behind
       your teeth)
    - hard palate
    - soft palate (velum)
    - nasal cavity

Consonants are vital to speech intelligibility. Take "pat" and "bat" in English. They mean different things yet they share a lot in common. They're produced in the same part of the mouth and control of the airflow is the same (stop/release). Only the voicing of the first sound is different (voiceless 'p' versus voiced 'b'). Well-controlled articulation allows you to clearly tell whether a speaker has said one or the other.

Vowels involve less articulators - the tongue and lips taking centre stage. Bring your tongue forward and high up in the mouth, spread your lips and the vowel will be a close front unrounded vowel. This [i] sound is heard in words like "cheese". Place the tongue further back and lower down in the mouth and round your lips and you'll hear an open back rounded vowel. This [ɒ] sound is the sound you hear in "not".

There is some evidence that more precise articulation contributes to perception of the speaker as female (Dacakis, Oates & Douglas, 2012). However, the level of evidence is not as great as for other aspects of voice such as pitch and resonance.








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