Vowel Modification Fundamentals

Vowel modification is a voice technique in which the vocal tract posture of one vowel is changed slightly to achieve a desired difference in the voice’s timbre, often with the idea that the vocal tract posture of the starting vowel is made more similar to the vocal tract posture of another vowel. Vowel modification is a useful tool for exploring how changing the shape of our vocal tracts can affect the timbre of our voices. 

Vowel Qualities

There are three primary aspects of vocal tract posture for vowel production. These are vowel height, backness, and rounding. Vowel height is a spectrum of close (high) to open (low). In a close vowel, the tongue is high and close to the roof of the mouth. In an open vowel, the tongue is low and is not close to the roof of the mouth. Vowel backness is a spectrum of front to back. In a front vowel, the tongue is articulating the vowel near the front of the mouth. In a back vowel, the tongue is articulating the vowel further from the front of the mouth. Vowel rounding is a spectrum of rounded to unrounded, though most vowels are simply referred to as one or the other. In a rounded vowel, the lips are narrowed or pursed. In an unrounded vowel, the lips are spread or relaxed. A rhotacized vowel is a vowel that features an r-sound. A retroflex or bunched tongue shape is normally seen in rhotacized sounds. It should be noted that tongue positions are not an entirely accurate way of describing vowels as our perception of vowels is determined by acoustic aspects of the voice known as formants. An IPA (International Phonetic Alphabet) vowel chart may be used to interpret the qualities of different vowels.

Formants

In the voice, a formant is a concentration of acoustic energy resulting from the preservation of that energy around one of the vocal tract’s resonance frequencies. The acoustic energy that is preserved is typically provided by one or more harmonics in voiced sounds. Readers may observe the presence of formants in their own voices by experimenting with programs designed to produce narrowband or broadband spectrograms or otherwise designed to directly analyze formants. Acoustic phenomena such as formants, resonances, and harmonics will not be explained at length here. Further reading on the topic is recommended, although not necessary for the understanding of this piece.

Formants’ Effects on Timbre

Timbre is the perception of qualities of a sound apart from its loudness and pitch, and can be thought of as the color or character of the sound.  The frequency values of formants in the voice determine several important timbral qualities of its sound, which in turn affect its pleasantness, stylistic appropriateness, and even the perceived gender and emotion the voice may carry. The voice has many audible formants, but only the first three will be discussed here.

The first formant is responsible for the perception of vowels, along with the second and (to a much lesser degree) third formants. It is also responsible for determining perception of whether the voice’s timbre is open (sometimes phrased as hooty, whoopy, or floaty) or closed (sometimes phrased as called, yelled, or belted). Care should be taken not to confuse an open or closed timbre with an open or close vowel quality, as the description timbre and vowel quality tend to be inverted in this regard. A higher first formant, specifically one at or above the frequency value of the second harmonic, is likely to result in a seemingly more closed timbre. A lower first formant, specifically one below the second harmonic, is likely to result in a seemingly more open timbre. A higher first formant will likely result in the voice being registered as more feminine, while a lower first formant is likely to result in the voice being registered as more masculine. 

The second formant, apart from its role in creating vowel sounds, plays a large role in determining how brightly or darkly the voice is perceived. A higher second formant is likely to cause a sound to be perceived as more shrill, while a lower one is likely to cause it to seem more dull.

The third formant contributes to perception of brightness and darkness in the voice in a similar fashion to the second formant, but to a lesser extent. More notable, though, is that the third formant is primarily responsible for our perception of rhoticity or r-colored sounds in the voice when lowered.

In general it can be observed that higher formants will typically result in brighter, more buzzy sounds, while lower formants will typically result in darker, more rounded sounds.

Vowel Qualities’ Effects on Formants

As mentioned earlier, the frequency values of formants are reliant on the resonance frequencies of the vocal tract. The resonance frequencies of the vocal tract, and therefore the frequency values of formants in the voice, are reliant on the shape of the vocal tract. The first formant’s frequency value is primarily reliant on the spatial volume of the throat, or pharynx. The second formant’s frequency value is primarily reliant on the spatial volume of the mouth, or oral cavity. The third formant’s frequency value is primarily reliant on the shape of the tongue, specifically in the middle of the mouth, as well as the position of the lips. Below is a table describing the general (not exhaustive) relationships of vowel qualities to the voice’s formants.

Vowel QualityPhysical ChangeFormantFrequency Value
CloseHigher Tongue1Lowered
OpenLower Tongue1Raised
BackMore Backward Tongue2Lowered
FrontMore Forward Tongue2Raised
RoundedNarrowed Lips2 + 3Lowered
UnroundedSpread Lips2 + 3Raised
RhotacizedRetroflex Tongue or Back of Tongue Bunched3Lowered

Exploratory Exercises

Voice users may transition between vowels and other sounds as a method to explore the modulation of formants in the voice. For these exercises, it is recommended that the voice user is equipped with an IPA vowel chart and a formant analysis program. Links to these can be found in the External Links section below.

Exercise 1 – Close and Open

1.) While maintaining a steady pitch, practice sliding slowly between the ⟨ɯ⟩ vowel and the ⟨ɑ⟩ vowel. 

2.) Pay attention to the sound of transitioning between the vowels. 

  • What do you hear?
  • How does your voice change as you approach either vowel?
  • Does either vowel sound higher or lower, even though you didn’t change your pitch?

3.) Pay attention to the physical sensation of transitioning between the vowels. 

  • What do you feel?
  • Can you recognize the sensation of your tongue rising to form the close ⟨ɯ⟩ vowel?
  • Can you recognize the sensation of your tongue lowering to form the open ⟨ɑ⟩ vowel?

4.) On your formant analysis program, observe how the first formant changes drastically between these vowels while the other formants remain relatively stable.

Exercise 2 – Back and Front

1.) While maintaining a steady pitch, practice sliding slowly between the ⟨ɯ⟩ vowel and the ⟨i⟩ vowel. 

2.) Pay attention to the sound of transitioning between the vowels. 

  • What do you hear?
  • How does your voice change as you approach either vowel?
  • Does either vowel sound higher or lower, even though you didn’t change your pitch?

3.) Pay attention to the physical sensation of transitioning between the vowels. 

  • What do you feel?
  • Can you recognize the sensation of your tongue going backward to form the back ⟨ɯ⟩ vowel?
  • Can you recognize the sensation of your tongue going forward to form the front ⟨i⟩ vowel?

4.) On your formant analysis program, observe how the second formant changes drastically between these vowels while the other formants remain relatively stable.

Exercise 3 – Rounded and Unrounded

1.) While maintaining a steady pitch, practice sustaining an ⟨i⟩ vowel. While you sustain that vowel, slowly shape your lips into an o-shape while keeping everything else in your mouth stable. This should result in the ⟨y⟩ vowel.

2.) While maintaining a steady pitch, practice sliding slowly between the ⟨i⟩ vowel and the ⟨y⟩ vowel.

3.) Pay attention to the sound of transitioning between the vowels. 

  • What do you hear?
  • How does your voice change as you approach either vowel?
  • Does either vowel sound higher or lower, even though you didn’t change your pitch?

4.) Pay attention to the physical sensation of transitioning between the vowels. 

  • What do you feel?
  • Can you recognize the sensation of your lips narrowing to form the rounded ⟨y⟩ vowel?
  • Can you recognize the sensation of your lips spreading to form the unrounded ⟨i⟩ vowel?

5.) On your formant analysis program, observe how the second and third formants change drastically between these vowels while the other formants remain relatively stable.

Exercise 4 – Combination

1.) While maintaining a steady pitch, practice sustaining an ⟨u⟩ vowel, then slide to an ⟨ə⟩ vowel, and then slide to an ⟨æ⟩ vowel. Then, practice the same in reverse.

2.) Pay attention to the sound of transitioning between the vowels. 

  • What do you hear?
  • How does your voice change as you approach the ⟨æ⟩ vowel? 
  • How does your voice change as you approach the ⟨u⟩ vowel?
  • Does either vowel sound higher or lower, even though you didn’t change your pitch?

3.) Pay attention to the physical sensation of transitioning between the vowels. 

  • What do you feel?
  • Can you recognize the sensation of your tongue becoming open and front while your lips spread to form the ⟨æ⟩ vowel?
  • Can you recognize the sensation of your tongue and lips relaxing to form the ⟨ə⟩ vowel?
  • Can you recognize the sensation of your tongue becoming close and back while your lips narrow to form the ⟨u⟩ vowel.

4.) On your formant analysis program, observe how the first three formants change while shifting between these vowels.

Exercise 5 – Rhoticity

1.) While maintaining a steady pitch, practice sustaining an ⟨i⟩ vowel. Then, starting with the ⟨i⟩ vowel, slowly pronounce the word “ear” in a generally American accent. This should result in an r-sound being formed.

2.) While maintaining a steady pitch, practice slowly sliding back and forth between the ⟨i⟩ vowel and the r-sound.

3.) Pay attention to the sound of transitioning between ⟨i⟩ vowel and the r-sound. 

  • What do you hear?
  • How does your voice change as you approach either sound?
  • Does either point of the word sound higher or lower, even though you didn’t change your pitch?

4.) Pay attention to the physical sensation of transitioning between the ⟨i⟩ vowel and the r-sound. 

  • What do you feel?
  • Can you recognize the sensation of your tongue toward the middle of the roof of your mouth to form the r-sound?
  • Can you recognize the sensation of your tongue returning to its original position to form the ⟨i⟩ vowel?

5.) On your formant analysis program, observe how the third formant changes drastically between these sounds while the other formants remain relatively stable.

Practical Applications

Voice users can make practical choices based on what they’ve discovered in their reading and while performing the exploratory exercises in the previous section. Exercise 4 – Combination is a great starting point for playing around with broad changes. If you want a brighter, more brilliant sound, try experimenting with changing the physical sensation of your articulation to be more similar to that of the ⟨æ⟩ vowel. If you want a darker, more robust sound, try experimenting with changing the physical sensation of your articulation to be more similar to that of the ⟨u⟩ vowel. 

 Taking note of the timbral qualities that are common in singing styles you enjoy is a great place to start when deciding what modifications you might want to make to your own timbre. Contemporary styles such as pop and modern musical theatre tend to favor a brighter timbre, while classical styling tends to favor a darker one. A notable amount of indie-style singers favor the character a consistent rhoticity in their voice can bring.

As you become more comfortable with the practice of changing the resonances of your voice using vowel mods, you may notice even more interesting possible strategies, such as how a more open vowel may help you to belt as it raises the voice’s first formant, or how a more close vowel may help you to use a falsetto or head voice as it lowers the voice’s first formant.

Closing Statement

While vowel modification is a wonderful and substantial technique for modifying the timbre of one’s voice, it is by no means the only way of doing so! There are many different techniques and aspects of our voices that we can modify, and you are very much encouraged to learn about and explore them. Remember to always practice good vocal hygiene habits and to always remain curious!

External Links

1. Interactive IPA Charts

2. Formant Analysis Program

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