One minute speech in physics?
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Physics in Speech
An introduction to the physics of speech, with notes about helium speech
This short introduction to voice science, the vocal tract and the production of voiced speech also includes some notes about helium speech. We also have a multimedia introduction to the voice. A more detailed and scholarly introduction is given here.
The source-filter model of the vocal tract
Warnings
What helium does to speech
Some other phoneme classes
Gear for further investigations
Some explanatory notes
Related pages
The voice makes sounds in several different ways. You can make a wide range of hissing or wind noises by passing air through a small aperture between the lips, teeth, etc. When you make such a sound using a small aperture between your 'vocal cords', it's called whispering. These sounds are all caused by the turbulent flow of the air, and they contain a wide range of different frequenies.
A second way of making sound uses your 'vocal cords', which are technically called vocal folds, because they are more like folds of flesh than cords. These can vibrate at a frequency determined largely by the tension in the muscles that control them (high tension makes the frequency and therefore the pitch high), the mass of the tissue (post-pubescent males usually have larger folds and therefore deeper voices) and the pressure in your lungs. The vibration releases pulses of air into the vocal tract.
Informally, the vocal tract may be thought of as a peculiar megaphone that transmits sound from the 'voice box' into the air outside the speaker's or singer's mouth. The tract has several resonances – ie, the air at the lips vibrates more readily at some frequencies than others. You can vary these resonances by moving tongue and lips, and this variation has a lot to do with the different speech sounds produced, as we shall see below.