EDHS Vowels Pt.1

In speech supra-glottal cavities are shaped by the

articulators

Resonant frequencies are partly determined by

cavity size

resonances of the vocal tract are called

formants

Formants

peaks of resonance in the vocal tract

Are displayed in a wide band spectrogram as broad bands of energy

Forced Oscillation

an outside force imposes the oscillation frequency.

ex) a child on a swing being pushed at the same rhythm so that the child will fly higher and higher

When the imposed frequency of oscillation equals the natural frequency of oscillator

the result is resonance ( when both frequencies match up it leads to the maximum amplitude)

Cavities of the Vocal tract

-Oral cavity

-Nasal cavity

-Pharyngeal Cavity

-Laryngeal Cavity

In sound physics the length of the tube determines

which sound frequencies are accepted (reinforced/invigorated)

Tube representation of the vocal tract: Region between glottis and lips

can be modeled as a tube that is open at one end , closed at the other

Tube representation of vocal Tract: Glottis

(with adducted vocal folds) is the closed end

Tube representation of vocal tract: Lips

(separated for vowel production) form the open end

The vocal tract is a

tube of air

The vocal tract in neutral position

(the position for the schwa vowel [upside down e]) this tube has an almost constant diameter from bottom to top.

The fact that the vocal tract is not straight

does nit matter much acoustically.

The column of air is forces to vibrate when the glottal cycles start

-this is an example of forced oscillation

The open end of the tube (lips) will have a

velocity maximum(pressure minimum)

The closed end of the tube (glottis) will have a

velocity minimum (pressure maximum)

The sound produced by the larynx is a

complex (a fundamental and a series of harmonics)

Resonance Frequencies-

refer to the specific frequencies at which the vocal tract naturally vibrates or resonates.

When sound waves hit the end of the tube and transition into the open air, part of the sound is reflected back into the tube ,and part continues into the atmosphere

The reflected part of the sound undergoes a change:compression become rarefactions

Standing Wave effect

Standing waves occur when sound waves reflect back and forth in a confined space (like a tube). The reflections of the sound waves interact with the incoming sound waves ,creating specific patterns of high pressure (condensation) and low pressure (rarefaction) areas

Constructive Interference

where the reflected wave reinforces the original wave, making it stronger.(which leads to alternating points of high and low pressure ,called nodes and antinodes)

Destructive Interference

where the waves cancel each other out. (which leads to alternating points of high and low pressure ,called nodes and antinodes)

Frequency Formula

f= c/4L

Equation for Standing waves in a tube with one open end

f=( 2n+1) * c/4L

f=frequency

n=is an integer (starting from 0, and going up to positive whole numbers)

C= the speed of sound in air

L=is the length of the tube

1:3:5 Ratio

First harmonic (Fundamental Frequency)

• The lowest frequency (the fundamental frequency) that can resonate in the tube . f0=c/4L

Third Harmonic

• The second harmonic is skipped and we go to the third. f1=3 * c/4L

Fifth Harmonic

• The fifth harmonic is the next to resonate. Frequency is f2=5 *c/4L

Node

is the point in the standing wave where the air pressure remain constant, meaning there is no vibration of the particles at that point.

Antinode

It is the point in the standing wave where the air pressure variation is at its maximum, and the particles of the medium vibrate the most.

Closed end (glottis)

-Air pressure is at its maximum

-Air particle velocity must approach zero

Open end (lips)

-Air pressure is at a minimum

-Air particle velocity must be at maximum

Rule: For a tube closed at one end & open at the other, the tube will resonate best (the natural resonant frequency)

at a frequency that has a wavelength that is 4X the length of the tube

The first resonance (R1 or F1)

the first resonance frequency happens when the vocal tract acts like a tube closed at one end (glottis) and open at the other end (lips

L= 1/f(Wavelength)

wavelength = 4 x L

Higher resonance Formulas (R2,R3)

R2 occurs when L=3/4 (wavelength)

R3 occurs when L=5/4 (wavelength)

Even- numbers multiples yield opposing forces that interfere with the vibratory pattern; no resonance is produced

The larynx

produces a complex periodic sound (f0 and higher harmonics)(the source)

Vocal tract filters the sound source:

-Harmonics near formant frequencies resonate, and have high amplitudes

-Harmonics far from formant frequencies are filtered out

The frequency zones that become stronger by resonance in the vocal are

the Vowel formants

Formants

-Energy is rearranged over the spectrum by resonance effects

-Formants make up the identity of a vowel

In closed vowels , the tounge constriction above the throat created a

bottle shaped cavity.This cavity has a very low resonance frequency. It is known as the Helmholtz resonance effect.

Producing [u]

-Back vowel: tongue dorsum is raised and retracted toward velum

-Rounded vowel:lips are rounded and protruded

-Cavity shapes:large pharynx, large oral cavity, overall vocal tract lengthened by lip prorusion.

Producing [i]

• High vowel:tongue body is elevated into the oral cavity, leaving pharynx open;

• Front vowel: high point of the tongue is anterior, behind the alveolar ridge

• Cavity shapes: large pharynx, small oral cavity

Producing [a]

Low vowel: jaw and+tongue are lowered

Back Vowel: tongue is retracted into pharynx

Cavity shapes:small pharyngeal cavity, large oral cavity

The independence of source and filter means

that we produce sound (the source) and the way we shape that sound (the filter) are separate processes. This allows us to control them independently in speech.

The relative patterns of formants

Is stable across speakers (e.g., [i] always has a low F1, high F2

The absolute values of formants vary based

on vocal tract length, anatomical proportions, dialect, and individual speech style.

Vowel production is the result

of changing cavities through jaw opening and tongue positioning

-These changing cavities create different acoustic effects

Traditional classification based on impressions of articulation:

-Tongue shape

-Tongue Position

-Lip Posture

Acoustic description based on formants:

-F1(related to tongue height) and F2 (related to frontness/Backness) convey information on vowel quality

-Formant values correspond roughly to articulatory postures.

Congenitally deaf speakers often have deviant vowel spaces:

-Jaw and tongue placements are more constrained than in hearing speakers

-The range of formant values is not as great as in hearing speakers

Impaired vowel production may be evident in

apraxia of speech, dysarthria and cerebral palsy

Foreign accents

may involve errors in vowel production. (visual feedback may help speakers improve vowel production)