For the purposes of distinguishing vowels from each other, we are more interested in the frequency response curves (indicating the preferred resonating frequencies of the vocal tract) rather than in the raw spectrum of the wave.

Each of the preferred resonanting frequencies of the vocal tract (each bump in the frequency response curve) is known as a formant. They are usually referred to as F1, F2, F3, etc. For example, the formants for a typical adult male saying a schwa:

F1 first formant 500 Hz
F2 second formant 1500 Hz
F3 third formant 2500 Hz

By changing the vocal tract away from a perfect tube, you can change the frequencies that it prefers to vibrate at. That is, by moving around your tongue body and your lips, you can change the position of the formants.

Some vowel formants for Canadian English

Each of the following figures shows a computer-generated spectrum and response curve for a particular utterance of a Canadian English vowel by an adult male. The jagged lines show the harmonics. The curved line is the computer's guess, based on the harmonics in the spectrum, as to what the frequency response curve of the vocal tract must have been. The frequencies of the first two formants (as guessed by the computer) have been given for each vowel.











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