CE 40763 Digital Signal Processing Fall 1992 Speech Production

CE 40763Digital Signal Processing

Fall 1992

Speech ProductionHossein Sameti

Department of Computer Engineering Sharif University of Technology

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Speech Generation and Perception :

The study of the anatomy of the organs of speech is required as a background for articulatory and acoustic phonetics.

An understanding of hearing and perception is needed in the field of both speech synthesis and speech enhancement and is useful in the field of automatic speech recognition.

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Schematic diagram of the human speech production :

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Organs of Speech : Lungs and trachea :◦ source of air during speech.

◦ The vocal organs work by using compressed air; this is supplied by the lungs and delivered to the system by way of the trachea.

◦ These organs also control the loudness of the resulting speech.

◦ The trachea and lungs together constitute the pulmonary tract.

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Organs of Speech : The Larynx :◦ This is a complicated system of cartilages and muscle

containing and controlling the vocal cords. Principle parts are : Cricoid cartilage Thyroid cartilage Arytenoid cartilage Vocal cords

◦ The place where the vocal folds come together is called the glottis.

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Glottal closure during voicing

folds

folds

Vocal folds

During breathing

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Organs of Speech : The Vocal Tract :◦ Laryngeal pharynx

beneath epiglottis◦Oral pharynx

behind tongue, between epiglottis and velum◦Nasal pharynx

Above velum, rear end of nasal cavity◦Oral cavity

Forward of the velum and bounded by lips, tongue and palate◦Nasal cavity

Above the palate and extending from the pharynx to the nostrils

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Vocal Tract

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Vocal Tract Model

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A General Discrete-Time Model For Speech Production

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Time Waveform Of Volume Velocity Of The Glottal Source Excitation

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Magnitude Spectrum Of One Pulse Of The Volume Velocity At The Glottis

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Position Of The Vocal Cords And Cartilages (a) For Phonation (b) For Whispering

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Speech Production : The operation of the system is divided into two

functions :◦ Excitation◦Modulation

Excitation(glottis)

Modulation(vocal tract)

Radiate

speech

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Vocal VowelsAH EE

EH OH OO

Duck Call

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Speech Production : Excitation :is done in several ways◦ Phonation (making of a voiced sound)

This is the oscillation of the vocal cords

The arytenoid cartilages close and stretch the vocal cords

When air forced through the vocal, they vibrate

The opening and closing of the cords breaks the airstream up into pulses

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Speech Production : The repetition rate of the pulses is termed pitch.

At low levels of air pressure oscillation may become irregular, this irregularities are known as “vocal fry”.

Speech sounds accompanied by phonation are called voiced; others, unvoiced or mute.

◦ Whispering (speak softly) The vocal cord are drown together, but with small triangular

opening between arytenoid cartilages

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Speech Production :◦ Frication

Frication can occur with or without phonation

◦ Compression If the release is abrupt and clean, the sound is a stop or plosive

If gradual and turbulent, the sound can pass into the related fricative and is termed an affricative

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Speech Production :◦Vibration

If air is forced through a closure other than the vocal cords, vibrations may be set up

Modulation◦ This is what we do to impose information on the glottal

output Articulatory phonetics: how the organs of speech are positioned to

produce any given speech sound

Acoustic phonetics: what the measurable acoustical correlates of any given speech sound are and how acoustical features in general correspond to phonetic and articulatory ones

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Hearing and perception : Hearing is a process which sound is received and

convert into nerve impulse

Perception is the post-processing within the brain by which the sounds heard are interpreted and given meaning

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The structure of peripheral auditory system :

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Sectional View Of The Human Ear

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Hearing : The ear is divided into three parts:◦ The outer ear:

Consist of the pinna (visible, convolved cartilage) Its convolved shape is provide some directional cues

The external canal (external auditory meatus) Uniform tube, 2.7 cm long by 0.7 cm across through It has a number of resonant frequencies at 3 kHz

The eardrum (tympanic membrane) Is a stiff, conical structure at the end of the meatus It vibrate in response to the sound

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Hearing :◦ The middle ear

Is an air-filled cavity

Separated from the outer ear by the tympanic membrane

Connected to the inner ear by the oval and round window

Connected to the outside world by way of the eustachian tube

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Hearing : eustachian tube permit equalization of air pressure between the

middle air and the surrounding atmosphere

the middle ear contain three tiny bone (ossicles) Malleus (hammer)

Incus (anvil)

Stapes (stirrup)

The function of the ossicles Impedance transformation

Amplitude limiting

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Hearing :◦ The inner ear

vestibular apparatus Used for balance and sensing orientation

The round and oval window

Cochlea Is a snail-shape passage communication with the middle ear via the round and oval window It consist the transducers which convert acoustical vibration to verve

impulses

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The Cochlea as It Would Appear If Unwound

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Cross Section Of One Turn Of The Cochlea

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Position Of Maximum Amplitude Along Basilar Membrance As A Function Of Applied Frequency

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Frequency Response Of a Point On The Basilar Membrance