Answer: High frequency= High harmonics= Different formants
Explanation:
We are given that sopranos can sing notes at very high frequencies.
Now, when they sing high notes it is difficult to understand their words.
According to the concept of harmonics, it is the integer multiple of the fundamental frequency. And formants are the different frequencies which in turn give us different vocalizations.
Now, the frequency is over 1000 Hz this implies that the harmonics will be greater and in turn formants will be different. So, this is the reason it is difficult to understand the words of sopranos when they are singing at very high frequencies.