How does a voice work, and why can it change as we grow?

Begin with air and tissue

Air from the lungs passes through the larynx, or voice box. With suitable tissue posture and driving pressure, airflow and deformable vocal folds can sustain vibration. Muscles adjust their posture and properties; they do not issue a separate command for every vibration cycle.

An opening is not a sound wave

The glottis is the opening between the folds. Its area, the flow passing through it, the movement of tissue and the sound pressure outside the mouth are related but different quantities. Our source trace prescribes normalized volume flow; it does not reconstruct the pictured tissue.

Count the repeating cycles

The fundamental frequency describes the repetition rate of these periodic sources. At 120 Hz, a cycle lasts about 8.33 milliseconds. At 240 Hz, it lasts about 4.17 milliseconds. For these regular sounds, this rate is a useful correlate of pitch.

Shape the sound above the folds

The connected spaces in the throat and mouth affect the source spectrum. Tongue, jaw and lip configuration changes those spaces. Different measured shapes can emphasize different existing harmonics while the source repeats at the same rate.

Open a real research object

The two halves come from an MRI-based research dataset. Their air passage is source-derived; their plastic shell and inlet adapter are manufactured research geometry. Teardown reveals the cavity while the sound experiment continues to use the assembled measurement.

Hear three distinct examples

Source alone plays the prescribed pulse. Through the model plays computed mouth flow shaped by a measured response. The original human recording is a separate dataset sample. Listening normalization makes comparison easier, but removes any claim to absolute sound-level differences.

Growth changes several things

Dimensions, tissue mass, structure, stiffness and control can change as a body grows. The resonating spaces also develop. A measured frequency change need not have a matching jump in fold length. One dimension cannot explain all voices or predict a person’s timetable.

Make a bounded conclusion

Save a starting case, change one condition and inspect both source spacing and the measured curve. A successful controlled software comparison teaches a relationship within this model. It does not establish complete biological independence of the two parts.

Rosenberg pulse C

The prescribed positive flow uses a cosine opening over 0.40 of a cycle, a cosine closing over 0.16, then zero. These parameters come from Rosenberg’s experimental pulse C, not a universal human waveform. Its cycle integral is 0.3018591636 in normalized units.

Complex harmonics retain phase

We compute Fourier coefficients with a 4096-point period and omit DC in audio. Each component at k times the source rate is multiplied by the complex measured transfer. Interpolating real and imaginary values avoids errors at wrapped phase boundaries.

What the transfer means

The dataset characterizes mouth volume flow divided by glottal volume flow for a rigid assembled model. Its experimental method uses pressure measurements and reciprocity. This ratio is not pressure gain at a listener’s ear, and a ratio above one is not a claim that the model creates energy.

A resonance is not a new oscillator

The ah model has a measured resonance near 517 Hz. A 120 Hz periodic source contains 120, 240, 360, 480 Hz and further multiples; filtering changes their complex weights. It does not insert a new 517 Hz sinusoid merely because the curve peaks there.

Formants and resonances

Formants are resonance-related features in a speech spectrum. We label independently measured response peaks as resonance frequencies. Every small local bump in data should not automatically be called a formant.

Only use measured frequency rows

The source files include padded values outside their valid 100–10,000 Hz band. Those values are not evidence of perfect transmission. Runtime data retain valid rows, while the harmonic calculation uses components up to 8,000 Hz.

Actual source files and geometry

The three selected configurations are /aː/, /iː/ and /uː/ from speaker 1. STL coordinates are millimeters. We reindex the original triangles and apply one common transform to each shape’s parts; different vowels are discrete meshes, not invented intermediate anatomy.

Why length alone is insufficient

Harries and colleagues observed gradually increasing vocal-fold length, while the marked frequency change did not coincide with a matching length jump. Zhang’s computational work varies stiffness, thickness, initial opening and pressure. Together they motivate a multi-factor explanation, not a fitted puberty equation.

Growing is not the same as actively stretching

Actively stretching existing tissue can change stiffness as well as dimensions. Tissue growth can also change mass and structure. A string formula with only length varied does not settle either process in layered, airflow-coupled vocal folds.

Source and filter can interact

Titze and colleagues investigated adult vocal exercises near source/formant crossovers and found evidence of interaction. Separate controls are a useful linear approximation here; living phonation can include feedback between tissue and the tract.

The source still repeats 120 times each second, but you switch from “ah” to “ee.” What changed in this experiment?

• The tract filter changed; the source repetition rate stayed fixed.
• The folds now repeat 240 times each second.
• Sound now travels through the ear in a different direction.

You double the source rate from 120 to 240 Hz while keeping the same tract. What happens to one source cycle?

• It takes twice as long.
• Its period halves from about 8.33 to 4.17 milliseconds.
• Its amplitude must double.

The “ah” model has a measured resonance near 517 Hz. Does that mean its source must vibrate at 517 Hz?

• Yes, a resonance is always the source fundamental.
• No. A 120 Hz source can be shaped by that resonance.
• No, because the filter deletes every harmonic.

Why is “growing folds get longer, so length explains every voice change” incomplete?

• Mass, structure, stiffness, and the tract can also change.
• Vocal folds are guitar strings, so only their length matters.
• Voices can never change during growth.

The three real MRI-derived models belong to one adult making different vowels. What can they show?

• Exactly how every child's throat will grow.
• Which gender a visitor is.
• How three static air-passage shapes can have different measured resonances.

You double all samples of one unnormalized waveform. Which statement follows?

• Its relative amplitude doubles while its component frequencies stay fixed.
• It becomes a vowel with twice the fundamental frequency.
• Everyone must perceive it as exactly twice as loud.

You pull apart the model's printed halves on screen. Why does the lesson still show the same measured curve?

• Real air passages sound exactly the same when cut open.
• Teardown is an inspection view; the curve was measured with the model assembled.
• The curve is a measurement from your phone's microphone.

Does controlling source and filter independently prove that they never influence each other in a living voice?

• Yes; separate controls prove complete biological independence.
• No; therefore the comparison teaches nothing.
• No. Real source–tract coupling can occur, while the linear separation is useful here.

MRI-derived geometry, measured transfer and reference audio

Scientific Data 7:255. Processed MRI, dental impressions, physical models, measurement method, valid band and Table 3. Article CC BY 4.0; the dataset has its own CC0 license.

Exact version and original files

CC0 1.0. Three matched speaker-1 configurations: inner surface, printable halves, measured transfer and reference sound. Local source/derivative hashes and geometry transforms are available in the asset record.

The prescribed source waveform

Figure 3 pulse C and experiment-1 opening/closing parameters. Our plotted computation is original; no licensed reuse of the published figure is claimed.

Length and voice change during puberty

Observed vocal-fold length and frequency. The marked change did not coincide with a matching jump in length. Abstract-level evidence; no fabricated participant trajectories or effect sizes.

Adolescent morphology and voice acoustics

MRI and acoustic measurements in 532 adolescents. Group associations do not supply individual identity, maturity or health predictions.

Interacting tissue and aerodynamic parameters

Computational manipulations of tissue stiffness, medial thickness, initial opening and subglottal pressure. Findings describe that model, not a personal fitted voice.

Living source–tract interaction

Eighteen adults performed vocal glides. Source/formant crossover findings bound our independent linear controls. The strenuous research exercises are not the home activity.

Real laryngeal image and temporal sampling

Figure 2 contains an actual larynx photo beside the setup illustration. CC BY 4.0; reproduced unmodified. The stacked graphic is not a cycle-frame sequence.

Optional comfortable-voice observation

Agency guidance supports avoiding strain and resting when tired or hoarse. The primary paper activity requires no voice production, throat contact or microphone.