Vowels and formants
© Lloyd W. Hanson 1998
When discussing Vowels and Vowel Formants we are talking about three different things :
One is the phonated sound produced by the vocal folds which is comprised of a fundamental and many overtones, each a multiple of the fundamental. These are commonly referred to as H0, H1, H2, H3, etc. with H0 being the fundamental. These overtones tend to be sequentially weaker as you ascend in number. This overtone series will always keep its relation to the fundamental and will, therefore, rise and fall as the fundamental pitch of the phonated tone rises and falls.
Another is the resonance frequencies of the vocal tract which tends to emphasize a series of frequencies that relate to the vocal tract size and shape. However, the resonance frequencies of the vocal tract are not sequential in their strength as is the case with the overtones of the phonated sound. This is because the vocal tract is not a simple tube but rather a tube of varying sizes and shapes. For this reason it tends to emphasize some overtones of the phonated sound and de-emphasize others. And, of course, added to this complexity is the fact that the vocal tract is very adjustable. The resonance frequencies (formants) of the vocal tract are commonly referred to as F1, F2, F3, F4, and F5. Resonance frequencies (formants) above F5 are seldom given consideration in the research I have read.
The third consideration is the physical reality that each vowel has its own "fingerprint" which is defined by its unique frequencies at F1 and F2. F1 and F2 are usually referred as to as the vowel formants and if these formants are not produced by the vocal tract the vowel does not exist. Whenever you hear the formants for a particular vowel, that vowel is present. Wind blowing through a crack around a window sounds a bit like the [u] vowel because it produces the formants, or close to the formants, for the [u] sound. Small tinkling bells often seem to be saying the [i] vowel because they tend to produce the second formant for the [i] vowel sound.
These "fingerprint" frequencies (Formants 1 and 2) are not adjustable for each given vowel or variant of each vowel. That is, the formant frequencies for the [i] vowel for any given voice is more or less constant and remain within very specific limits in the frequency range. It is the reason you often hear these vowel formants called "fixed" formants.
You can experience these formants if you thump the side of your larynx with your finger while you mouth the [i, e, a, o, u] vowels. You will hear the lowest resonance of the vocal tract for the [i] and [u] vowels and the highest resonance for the [a] vowel. These are the F1 resonances for these vowels for your voice. If you modify these vowels you will hear other F1 resonances for the modified vowel. For example, if you mouth [i], [I], [e], [E] [ae] [a] you will hear a more gradual rising of the F1 resonance to the highest [a] resonance.
Although less obvious, you can sort of hear the F2 resonances if you again mouth the vowels as above but this time use a rather loud whisper. Here you will notice the highest resonance for the [i] vowel and the lowest resonance for the [u] vowel. These are the F2 resonances for these vowels for your voice.
The vocal tract resonances (formants) do not rise and fall with the phonated pitch produced by the vocal folds. These vocal tract resonances (formants) can only move up and down in pitch if the vocal tract itself is altered which, of course, changes the resonance frequencies of the vocal tract. For example, sopranos frequently find it necessary to raise the level of F1. To do this the vocal tract must be either shortened, or opened, or both. Female singers instinctively open their mouth as they sing above the staff and, at the highest notes, they tend to raise the larynx slightly. All of these adjustments help to raise the F1 formant.
Now we come to my statement above. The female voice has a built in problem. It is able to phonate a sound at the level of G5 and higher which is above the F1 formant for the [i] vowel. If the pitch of the phonated sound is above the F1 formant (the fingerprint) of the selected vowel, obviously, the F1 of the selected vowel will not be present and the vowel will not be easily identified. Opening the vocal tract will raise the F1 formant, but raising the F1 formant will place it in the pitch area of the F1 formant for another vowel, that is, the [a] vowel. Consequently, the most accessible solution is to use the F1 formant of the [a] vowel, which, as mentioned above, is the highest F1 formant for any of the vowels, and, in addition, attempt to raise that formant of that vowel by opening the mouth. Sopranos do this instinctively and correctly. But the vowel is no longer [i]. It has now become some form of the [a] vowel.
Of course, the soprano can open the mouth and still keep the back of the tongue high in a quasi [i] vowel position and this will give a bit of the [i] quality to the G5 and above pitch. She will be able, through this extreme position, to resonate the F2 formant of the [i] vowel but nothing she does will make it possible for her resonate the F1 formant of the [i] vowel. The F1 formant is lower than the pitch she is phonating. Because the F1 formant is the strongest and most decisive formant in defining any vowel, resonating only the F2 formant can create only a suggestion of a vowel.
None of the above is my idea. It is a common discussion that can be found in the writings of Coffin, Sundberg, Doscher, Delattre, Miller and in the new pedagogical text by a friend, Cliff Ware.
There are some basic principles of acoustics that need to be considered in any explanation of vocal technique if that technique is to be explained adequately. I have found that the Italians seem to have, traditionally, had the best grasp of vocal techniques that are a more natural expression of the use of the whole body. And all the research that has been done in the past 75 years tends to corroborate the accuracy of their techniques. However, there are many techniques that are based on erroneous physiological and acoustic information, yet work. The reason is that ultimately the voice teacher must rely on his/her ears to determine if the singer is singing in a healthy and functionally efficient manner. Voice science cannot replace these trained ears. I think our difficulty today is that we are not exposed to as much good singing as in days past and our ears are therefore not as well trained to know good singing.
Lloyd W. Hanson, DMA
Professor of Voice, Pedagogy
School of Performing Arts
Northern Arizona University
Flagstaff, Arizona 86011