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).

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).

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.

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.

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.

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.