Articulation and Acoustics of Vowels

Vocal fold vibration model

Modeled using the spring mass system

This allows the mass to oscillate and create sound waves (puff of air) due to air pressure build up (Requires positive and negative forces)

Problem with the vocal fold model

1. Negative forces alone cannot account for continual energy from airstream to tissue

2. Oscillation will eventually die out from damping

3. Positive and negative forces are both needed

Glottal Signal

Periodic waveform that carries a whole frequency range that is rich in harmonics

Supplies acoustical energy needed for speech sounds

Energy must be modified to make different sounds

Source Filter Model

Source: Vocal folds produce a periodic signal with fundamental frequency and harmonics

Filter: Vocal tract shapes the sound, enhancing harmonics near formant frequencies and attenuating others

Holding a sound source constant while changing filters

1. Maintains constant pitch

2. Vary vowels

   • Change from [i] to [u]

Hold filter constant while changing source

1. Articulates a single vowel

2. Varies fundamental frequency

   • Low to high pitch

Excitation Frequency

Frequency used to calculate vibrations in a system

Since resonances are a product of the vocal tract shape, while excitation arises at the glottis

Low F1

Large pharynx and closed mouth

Ex: [i]

Low F2

Long oral cavity

Ex: [u]

High F1

Small pharynx and open mouth

Ex: [a]

High F2

Short Oral cavity

Ex: [i]

Producing [i]

High vowel: Tongue body elevated into oral cavity

Front vowel: High point of tongue is anterior, behind alveolar ridge

Low F1, High F2

Producing [a]

Low vowel: Jaw and tongue lowered

Back vowel: Tongue retracted into pharynx

High F1, Low F2

Producing [u]

High vowel: Tongue raised out of pharynx

Back vowel: Tongue dorsum raised and retracted toward velum

Rounded vowel: Lips rounded and protruded

Large pharynx, large oral cavity, vocal tract lengthened

Low F1 and F2

Formants and Vocal Tract Constrictions

Constriction at pressure: Raises formant frequency

Constriction at velocity: Lowers formant frequency