THE LINGUISTIC STUDY OF VOWELS: What is Sound? Sound is a disturbance of air molecules. A vibrating tuning fork is a good example. When it moves in one direction, it compresses the air molecules closest to it. When the tuning fork retracts, it pulls away from the molecules creating larger gaps between the molecules. The fork then moves back to the beginning point and then again in the first direction, and the whole cycle starts over. This picture below shows the molecules being bunched together as the tuning fork moves one way, then moving apart from one another as it goes in the opposite direction, but being bunched together again as the fork moves back in the first direction.

C A B A tuning fork produces a simple sound wave.

In the top picture the tuning fork produces a simple sound wave with lower frequency, which we would hear as a lower pitch. The bottom pictures show a higher frequency which we would hear as a higher pitch.

Human speech sounds are complex, not simple wave forms. Human speech sounds are filtered by the lips, tongue, teeth, palate, etc., to create highly complex wave forms. The top graph shows two simple wave forms that are added together to create the complex wave below

When producing a vowel the tongue can be High and forward, like in BEET High and back, like in BOOT Low, like in BAT or BOT BEE T BAT BOOT high low frontback BOT

Here are the complex waves on top and spectrograms below that identify the harmonic frequencies for the vowels in “bead,” “bid,” “bed,” and “bad.” The F1 band correlates with the height of the tongue and the F2 band correlates with how fronted or retracted the tongue is

The complex wave forms of different vowels appear quite different and offer linguists ways of tracking how the tongue moves during speech production These charts on the right are simplified versions of the information contained in the spectrograms above. The fist two peaks are the F1 and F2.

Where are the vowels of American English? Here is an F1-F2 plot of the vowels of American English from a study done in It excludes two-part vowels (diphthongs) of words like “time,” “house” and “toy.” heat hit bait bet hat food good toad caught cut cot

What else? Although linguists are interested in the study of the acoustic and physiological properties of vowels for their purely scientific value, one reason they are so interesting to US linguists is that the main differences in our various dialects are in the vowels. If you would like to see and hear about two major dialect areas emerging in the US today and how they differ in their vowels, please go to Computer Station 1.