How the voice works: the larynx, the vocal folds, and what sets your pitch

Three systems, not one

People talk about the voice as though it lives in one place. It does not. Voicing requires three systems working together, and almost every question about changing a voice becomes clearer once you know which of the three you are asking about.

This is the source–filter model, and it is the single most useful idea in the whole subject. The source sets your pitch. The filter sets much of what people actually hear as identity. They are almost independent of one another, which is why two people can speak at exactly the same pitch and sound nothing alike, and why voice training can change how a voice is read without changing its pitch at all.

It is also why surgery has a narrower effect than people expect. Pitch surgery operates on the source. It does not touch the filter.

The larynx

The larynx sits at the top of your windpipe, in the front of the neck. You can feel it: rest your fingers gently on the front of your throat and swallow, and the whole structure rides up and then settles. It is a small cage of cartilage, ligaments and muscle, and it has three jobs, in order of evolutionary priority.

1. Keeping food out of your lungs

   This is what it is fundamentally for. When you swallow, the larynx lifts and the epiglottis folds over the airway. Voice is a secondary use of a valve that exists to stop you drowning in your own dinner.

2. Sealing the chest for effort

   Closing the folds tightly traps air in the chest and gives your torso rigidity — which is what you do involuntarily when lifting something heavy, pushing, or coughing.

3. Making sound

   The most recent and least essential job, and the one this entire site is about.

The main structures worth knowing by name, because they come up in any surgical conversation:

• Thyroid cartilage. The largest piece, shaped like a shield folded down the middle. Its front angle is what protrudes as the laryngeal prominence, or Adam’s apple. Reducing that prominence is what chondrolaryngoplasty does.
• Cricoid cartilage. A complete ring below the thyroid cartilage — the only complete ring of cartilage in the entire airway.
• Arytenoid cartilages. A pair of small pyramids sitting on the back of the cricoid. The vocal folds attach to them, and their movement opens and closes the folds. Almost all fine control of voicing happens here.
• Vocal folds. Two bands running front to back inside the thyroid cartilage, meeting at the front at the anterior commissure. Together with the gap between them they form the glottis.

The vocal folds are layered, and the layers matter

Calling them cords is misleading. They are not strings. Each fold is a layered structure, and the layering is what makes human voice possible.

The innermost layer is muscle — the thyroarytenoid, or vocalis. Over that sits the vocal ligament. Over that sits the lamina propria, and over everything sits a thin, wet mucosal surface. The critical feature is that the surface layer is loosely attached to what lies beneath, so it can slide over it. This loose layer is Reinke’s space, and it lets the mucosa travel across the body of the fold in a wave with each cycle of vibration.

That mucosal wave is what gives a healthy voice its richness. Anything that stiffens the surface layer or fills that space degrades it, which is why conditions affecting the mucosa cause such disproportionate changes in voice quality. Reinke’s edema is precisely this: fluid accumulating in that space, making the folds heavy and floppy, and dropping the voice.

How sound is actually produced

Here is the part that surprises people: your vocal folds are not powered. No muscle is contracting rhythmically at 200 times a second. Nothing in the body moves that fast on command.

What happens instead is a self-sustaining oscillation, described by the myoelastic–aerodynamic theory of voice production, and the cycle runs like this:

1. The folds close

   Muscles bring them together across the airway. This is the only part you consciously initiate.

2. Pressure builds beneath them

   You breathe out. Air cannot get through the closed folds, so pressure rises below.

3. Pressure forces them apart

   When it exceeds what the folds can hold, they blow open from the bottom upward, and a puff of air escapes.

4. They snap shut again

   Two forces close them: the tissue’s own elasticity pulling it back, and the Bernoulli effect — fast-moving air through the narrow gap drops the pressure between the folds and sucks them together.

5. Repeat

   Pressure rebuilds instantly and the cycle restarts, hundreds of times a second, with no further instruction from you.

Each opening releases one puff of air. A rapid train of puffs is a buzz, and the rate of the puffs is the fundamental frequency, written f0 and measured in hertz. Two hundred puffs per second is 200 Hz. That is your pitch, and it is the number the pitch range explorer measures.

What determines your pitch

The folds behave like any vibrating object: longer and heavier means slower, shorter and lighter means faster. Three properties set the rate.

Tension is how you sing a scale. The cricothyroid muscle tilts the thyroid cartilage forward against the cricoid, stretching the folds and raising pitch. Relaxing it lowers pitch. This is the ordinary, voluntary mechanism, and it is limited: you can only stretch so far before the voice becomes effortful and eventually flips into falsetto.

Length and mass are the fixed baseline — the floor and ceiling that tension operates between. They are set by anatomy, and they are what surgery changes. Adult male vocal folds are typically around 17 to 25 mm long; adult female folds around 12 to 17 mm. That difference, together with the thickness that comes with it, is most of the reason male voices average roughly 85–155 Hz and female voices roughly 165–255 Hz.

Why testosterone changes voices and oestrogen does not

This asymmetry is the single most consequential fact in voice transition, and it is a direct consequence of the anatomy above.

During a testosterone puberty, the larynx grows. The thyroid cartilage enlarges and its front angle sharpens — producing the visible laryngeal prominence — and the vocal folds lengthen and thicken substantially. Longer, heavier folds vibrate more slowly, and the voice drops. It is a structural change to the instrument.

Structural changes of this kind are not reversible by hormones. Oestrogen does not shrink a larynx or shorten vocal folds, so for trans women it does not raise pitch at all. This is why voice is the one area of transition where oestrogen does essentially nothing, and why the options are therapy and, for a minority, surgery.

Testosterone works in the other direction because it is doing new growth rather than undoing old growth. It thickens and lengthens the folds of an adult larynx, and the voice deepens permanently — commonly by three to ten semitones over about a year. That is far more than any exercise or technique can achieve, and it does not reverse if testosterone is later stopped. The full picture is in our testosterone voice timeline.

The power supply, and why it is underrated

The lungs get treated as background, but a large share of voice problems are breath problems wearing a disguise. The relevant quantity is subglottic pressure — the air pressure beneath the closed vocal folds. Too little and the folds cannot be driven into vibration at all, which is why a voice trails off into creak at the end of a long sentence. Too much, sustained over hours, and the folds collide harder than they should, which is the mechanism behind nodules in teachers and singers.

Loudness is largely a function of this pressure rather than of effort at the larynx, which is the single most useful thing to know about projecting a voice. People who need to be heard usually squeeze the throat, which raises effort and fatigue without adding much volume. Driving the same voice with better breath support is louder and less tiring at once. This is why vocal hygiene for professional voice users is mostly about breath and amplification rather than throat remedies.

What puberty does, and why it is one-way

Before puberty, boys’ and girls’ larynges are near enough identical in size, and children’s speaking pitch sits somewhere around 250 to 300 Hz regardless of sex. Everything that separates adult male and female voices happens in a window of a few years.

Under testosterone, the thyroid cartilage enlarges and its front angle narrows from roughly 120 degrees toward 90, which is what makes the laryngeal prominence visible. The vocal folds lengthen substantially and thicken. Because the two changes compound — longer and heavier — the pitch drop is large, typically around an octave. The instability of the adolescent voice comes from the folds growing faster than the nervous system’s calibration for them, which is the same reason trans men on testosterone go through a cracking phase described in the testosterone timeline.

Under oestrogen, none of this happens. The larynx stays close to its pre-pubertal size, the folds lengthen only modestly, and the pitch drop is small. The asymmetry is not a quirk of hormone therapy; it is a fact about growth. Growth can be caused later, which is why testosterone still works on an adult larynx. It cannot be reversed later, which is why oestrogen does not.

The filter: why pitch is only part of the story

The buzz leaving your vocal folds sounds nothing like a voice. It is a raw, harsh sound containing a fundamental frequency plus a long series of harmonics above it. Everything recognisable happens after that, in the vocal tract.

The tube above the larynx — throat, mouth, nose — resonates. Frequencies matching its natural resonances are amplified; others are damped. These amplified bands are called formants, and they do most of the work of identity. Moving your tongue and lips changes formants and produces vowels. The overall size of the tube changes formants too, and a larger tube pushes them lower.

A testosterone puberty lengthens the vocal tract as well as the folds, which is why male voices sound darker and fuller quite apart from being lower. It is also why raising pitch alone tends not to work: a high-pitched voice with low formants reads as a man speaking high, not as a woman. Changing formants means changing the effective size and shape of the tube — raising the larynx slightly, brightening the oral space — and that is trainable. It is the core of what voice feminisation training teaches, and it explains why pitch accounts for only roughly half of perceived vocal femininity.

What each operation actually changes

With the anatomy in place, the operations stop being mysterious. Each one alters one of the three pitch determinants.

Two things follow from this table, and they are the reason it is worth understanding the anatomy at all.

First, none of these procedures touches the filter. Every one of them operates on the source. Surgery moves your pitch; it does not change your resonance, your intonation or your speech pattern. That is why surgeons ask for voice therapy before and after, and why surgery alone reliably disappoints people who expected it to deliver a complete voice.

Second, the anterior commissure is precious. Several procedures work at the front of the folds, where they meet. Scarring there degrades the mucosal wave and costs voice quality permanently. It is the reason experienced surgeons are conservative in that area, the reason both folds are rarely operated on at once in some conditions, and a reasonable thing to ask a surgeon about directly.

What to take from this

Pitch is a number produced by the length, mass and tension of two small bands of tissue. It is real, it is measurable, and it can be changed surgically within limits. But it is one input into a system, and the system that turns a buzz into a recognisable voice sits above the larynx, where no scalpel goes.

If you are weighing up surgery, the useful question is not “how many hertz will this move me.” It is “is pitch the thing that is actually limiting me, or is it resonance and speech pattern.” For a majority of people it turns out to be the latter, which is why therapy comes first. For the minority where pitch genuinely is the constraint, surgery moves a floor that nothing else can, and the pitch range explorer is a reasonable place to see where you sit.

Keep reading

• Falsetto vs head voice
• Testosterone voice timeline
• Vocal fry explained
• Type 3 thyroplasty

Sources

Frequently asked

How does the human voice actually work?

Three systems: the lungs supply air, the larynx converts that airflow into a buzz with a fundamental frequency, and the throat and mouth shape that buzz into a recognisable voice. This is the source-filter model. The source sets your pitch; the filter sets much of what people hear as identity. They are largely independent, which is why two people at the same pitch can sound completely different.

What determines the pitch of your voice?

Three properties of the vocal folds: length, mass and tension. Longer and heavier folds vibrate more slowly, giving a lower pitch; tighter folds vibrate faster, giving a higher one. Tension is the part you control moment to moment when you sing a scale. Length and mass are set by anatomy and are what surgery changes.

Do the vocal folds move by muscle contraction?

No. No muscle contracts hundreds of times a second. The folds are brought together by muscle, then air pressure below forces them apart and their own elasticity plus the Bernoulli effect snaps them shut. That cycle then sustains itself without further instruction. Each opening releases one puff of air, and the rate of those puffs is your fundamental frequency.

Why does oestrogen not raise vocal pitch?

Because a testosterone puberty makes a structural change: the larynx grows and the vocal folds lengthen and thicken permanently. Oestrogen does not shrink a larynx or shorten vocal folds, so it cannot undo that. Testosterone works in the other direction because it is causing new growth rather than reversing old growth, which is why it lowers voices by three to ten semitones.

What does voice surgery actually change?

Each procedure alters one pitch determinant. Glottoplasty shortens the vibrating length of the folds to raise pitch. Cricothyroid approximation permanently increases tension to raise pitch. Type 3 thyroplasty shortens the larynx so the folds slacken, lowering pitch. Chondrolaryngoplasty changes appearance only. None of them touches resonance or speech pattern.