“Let it be unique for yourself and yet identifiable for others.” - Anna Wintour on style
Timbre is the unique sound that differentiates one voice from another and makes the speaker instantly recognisable. Because of this vocal phenomenon, I’ve always argued that timbre is the most defining characteristic of a voice. But what is its role in voice perception?
A study by Pernet and Belin looked at how these two characteristics of voice are used by listeners in identifying the gender of a speaker. The results indicated “pitch is used only when timbre information is ambiguous (i.e., for more androgynous voices)”. The authors explain that although, in general, voices tend to be lower for larger people (due to the corresponding larger size of the vocal apparatus), this generalisation is unreliable when discerning the gender of a speaker. This unreliability is due to the large overlap of voice sound frequencies shared between men and women (the gender neutral pitch range), and therefore, pitch alone is not enough to determine gender. In fact, listeners determine gender predominantly based on timbre.
So, what is timbre? Belin explains, “timbre is what allows differentiating two sounds that can have the same perceived pitch and loudness”. It is created by the combination of the fundamental frequency of the vocal fold vibrations and the way the vocal tract shape filters that vibration, boosting some overtones and muting others. According to Belin, timbre “reflects the mixture of harmonics and their relative height”.
Now, how can trans people manipulate their voices to create a pleasing timbre that is congruent with their gender? Enter the idea of resonators. The resonators of the vocal tract are spaces with air in them. These spaces have a frequency at which they easily vibrate.
To help understand this concept, think about making music with water bottles. When we blow across a bottle, the sound we hear is determined by the amount of air space in the bottle. If we change the amount of water, we change the amount of air space and we change the sound.
We have two such resonating spaces we can manipulate - the area behind the tongue and the oral cavity. Vibrations in these two areas produce formants, (F1 and F2, respectively) which are merely ‘boosting’ of the harmonics produced by the sound signal (vibrating vocal folds), or the fundamental frequency of the voice (F0). This is just the science-y way of saying that, just as with bottles of water, we can change the size and shape of our resonators to change the sound of our voices. These resonating spaces and how we change them give our voices their uniqueness.
I’ve taken these images from a website called voicescienceworks. An easy-to-understand explanation of the relationship between vocal harmonics and formants is found there. https://www.voicescienceworks.org/harmonics-vs-formants.html
For most people, manipulating the area behind the tongue is considerably more difficult than the mouth, although it can be done. Raising the larynx and the soft palate with the muscles of the throat will have an effect on this resonating space. Care needs to be taken with raising and holding the larynx, though, because there is increased potential in developing hyperfunction, (excessive muscle tension) which can result in discomfort and lead to other pathologies. In a review by Kim (2020), F1 is also responsive to changes in degree of mouth opening, such as by lowering the jaw and tongue position.
The second resonating space, the oral cavity, is much easier to manipulate and offers greater scope in the number of adjustments that can be made with the articulators: lips, teeth, cheeks, tongue, jaw. Fortunately, the formants produced here are also the most important in producing a perceptually feminine or masculine sound. A study by Kawitzky and McAllister focused on F2 analysis because, “The second formant (F2), which is influenced by the length of the oral cavity, has been shown to correlate most saliently with the perception of gender.” Kim concurs that changing the size and volume of the oral cavity alters F2. Altering tongue position and modifying articulation patterns can achieve narrowing of the oral cavity, thus reducing its volume or increasing the oral space and volume.
The bottom line: I work with resonating spaces. Whatever pitch range a client is targeting, I help them to learn to use the spaces to achieve the voice style they want. The result is the creation of a unique voice quality that is perceptually congruent with the desired gender identity.