Which two formant frequencies are crucial for distinguishing one vowel from another?

Formant frequencies are resonant frequencies of the vocal tract and play a critical role in the perception of vowel sounds. The first two formant frequencies, F1 and F2, are particularly important for distinguishing between different vowel qualities. F1 is primarily associated with the height of the vowel (how open or closed the mouth is), while F2 is related to the frontness or backness of the vowel (where the highest point of the tongue is positioned in the mouth).

When the values of F1 and F2 change, they create different vowel sounds. For example, the vowel sound in "beat" has a different F1 and F2 than the vowel sound in "bit." Listeners are highly attuned to these two frequencies, which enables them to identify and differentiate vowel sounds in speech effectively.

The other formants, such as F3 and F4, do play roles in speech and can provide additional information about vowel quality or indicate dialectal variations, but they are not as crucial for vowel distinction as F1 and F2. This is why F1 and F2 are the correct answer to this question regarding the formant frequencies vital for vowel differentiation.