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Used to visualize the acoustic properties of speech.

Different filters (high-pass and low-pass) reveal components of speech. High-pass filtering highlights high-frequency components (e.g., fricatives), while low-pass filtering reveals low-frequency components (e.g., vowels and intonation).

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Speech production is described by the source/filter model.

Source: Sound originates from the vibration of vocal folds (for voiced sounds).

Filter: The vocal tract shapes the sound by amplifying or dampening certain frequencies.

This model is also used in musical instruments like brass instruments (e.g., trombone).

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are resonant frequencies that distinguish different vowel sounds.

F1: Lowest formant, determined by vowel openness.

F2: Second formant, related to tongue position (front/back).

F3: Third formant, contributes to vowel quality.

Formants are produced by the interaction between vocal fold vibrations and the vocal tract's shape and length.

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The resonant frequency of a vocal tract depends on its length and shape.

Example formula:

Fn = (2n-1) * (c / 4L), where n = formant number, c = speed of sound, L = vocal tract length.

Differences in vocal tract length between individuals produce distinct formant frequencies.

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Vowels use the entire vocal tract as a filter, whereas fricatives, such as [s], involve a shorter tract (alveolar ridge to lips), resulting in higher resonant frequencies.

Glottal fricative [h] uses the full vocal tract, like vowels.

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Classification of speech sounds in phonetics | Consonants and Vowels

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The vocal tract's shape isn't uniform (like a pipe), especially in nasal and lateral sounds, leading to complex resonance patterns.

For example, nasal consonants have additional resonance from the sinus cavities.

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Vowel acoustics can be modeled using tube models and perturbation theory. Both provide simplified explanations of how the shape and length of the vocal tract affect vowel sounds.

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Shapes determine vowel formants (frequencies).

Smaller cavities = higher pitch.

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Vocal folds create pulses, setting air into vibration.

Multiple frequencies (overtones) are produced.

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Three formants typically define vowel sounds.

Formants remain constant unless the vocal tract shape changes.

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Multiple Resonance Frequencies

Tubes have simultaneous resonance frequencies (pitches).

Frequencies change predictably when constricted at different locations in the vocal tract.

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Perturbation theory models vowel acoustics as perturbations in a uniform tube.

Example: Lip rounding constricts the diameter of the vocal tract, affecting formant frequencies.

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Constriction at Velocity Maxima (V): Decreases formant frequency.

Constriction at Pressure Maxima (P): Increases formant frequency.

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Constriction near the glottis (low vowels) raises F1 frequency.

Constriction near the lips (high, round vowels) lowers F1 frequency.

Same rules apply to F2 and F3.