How is the quality of vowel sounds primarily influenced in speech?

The quality of vowel sounds is primarily influenced by the resonant frequencies of the vocal tract. When a person produces a vowel sound, the shape and configuration of the vocal tract play a crucial role in determining how the sound resonates as it travels from the vocal folds to the outside environment.

Each vowel sound has a unique set of formant frequencies—resonances of the vocal tract that are shaped by the positioning of the tongue, lips, and jaw. These formants are what give each vowel its distinct acoustic quality; for instance, the difference between the vowel sounds in "beat" and "boot" is primarily due to the differing configurations of the vocal tract when these sounds are produced.

In contrast, the speed of articulation, while affecting the overall fluency and clarity of speech, does not directly dictate vowel quality. Similarly, manner of airflow control contributes more to consonants and aspects of speech production rather than vowel quality itself. Pitch relates to the frequency of vibration of the vocal cords and is more about voice characteristics than the specific resonance qualities of vowel sounds.