Same vowel, different pitches

The following are computer-generated spectrum diagrams. Each shows the vowel [i] sung at successively higher pitches. Note how the distance between the harmonics increases as the pitch does, but the preferred resonating frequencies stay the same. The pitch has no effect on the preferred resonating frequencies of the vowel, though we can see that if the pitch gets high enough and the harmonics far enough apart, it can become very difficult to tell where the "bumps" are.