Subject: Speech Processing

Topic: Speech Production, Acoustic Phonetics and Auditory Perception

Difficulty: Low

The physiology of speech:-

(i) Speech signal is generated when air expelled from the lungs acoustically excites the vocal cords producing a sequence sounds.

(ii) Lungs along with the diaphragm, are the main source of production for speech signals.

(iii) There are 3 main cavities of vocal tract:

(a) Pharynx (b) Oral cavity (c) Nasal cavity

(iv) While speaking the air gushes through the V-shaped opening called glottis and the larynx to the vocal tract.

(v) Its basic function is to manipulate the airflow by swiftly opening and closing the valves in the vocal cord, producing variety of sounds.

(vi) The vibration frequency is dependent on mass and tension. It varies from person to person.

(vii) From the nasal cavity to the pharynx, soft palate acts as a medium for connecting and isolating them from each other. The lower end of pharynx consists of Epiglottis and false vocal cord, to prevent the food from entering the larynx and are closed during swallowing, while opening during respiration.

(viii) Acoustics can vary with the help of moving our lips, tongue, palate, teeth and cheeks. It also depends on their size and shape. The walls and construction in the vocal tract also generates sound.

(ix) Organs responsible for speech are lungs, larynx and vocal tract, where the lungs provides the larynx with the airflow, while the larynx then modifies it to produce noisy wind-flow for vocal tract.

(x) Periodic, noisy and impulsive source are the basic categories of sound, where they generally are used in combinations. Example: the word 'shop' uses all three sources, where |sh| is noisy, |o| periodic and |p| impulsive.