Acoustic aspect of speech sounds

AS ACOUSTIC, ARTICULATORY AND AUDITORY UNITS

SOUNDS OF SPEECH

Вопрос

Почему в случае выполнения потока легких проектов может быть обеспечена равномерная полная занятость при следующем соотношении численности групп: Аналитики : Программисты : Тестеры = 2 : 2 : 1 ? Почему это не выполняется для (сверх)тяжелых проектов?

 

Phonetics studies the speech system of the language, equal of importance with grammar and lexicology. Whatever the branch of phonetics might be: practical (normative), theoretical, suprasegmental they are all concerned with segmental phonemes, word stress, syllabic structure and intonation. Speech sounds can be analysed from the viewpoint of three aspects: (1) acoustic, (2) physiological / articulatory, (3) auditory / functional. That comes from the three branches of phonetics each corresponding to a different stage in the communication process. The aritculatory phonetics studies the way in which the air is set in motion, the movements of the speech organs and the coordination of these movements in the production of single sounds and trains of sounds. The acoustic phonetics studies the way in which the air vibrates between the speaker's mouth and the listener's ear. The auditory phonetics studies the hearing process.

 

 

Acoustically, speech sound is a physical phenomenon produced by the vibration of the vocal cords and perceived due to the vibrations of the layers of air which occur at the rate of 16 to 20 thousand times per second. This is the limit of human hearing.

Sounds may be periodical and non-periodical. The auditory impression of periodic waves is a musical tone or a speech tone. If the vibrations are not rhythmical, we hear noises.

Sound has a number of physical properties; the first of them is frequency, i.e. the number of vibrations per second. It is measured in cycles per second (cps). The greater the frequency, the higher the pitch, and vice versa. The frequency of sound depends on certain physical properties of the mechanism that causes vibration, such as mass, length and tension. A man's voice is lower than a woman's partly because his vocal cords are longer and thicker. With the increase of the vocal cords' tension the frequency increases and the pitch rises. The pitch of a sound is the perception of the frequency of repeated pressures on the ear-drum. A man's voice is lower in pitch than that of a woman's.

The second physical property of sound is intensity. Changes in intensity are perceived as variation in the loudness of a sound. The greater the amplitude of vibration, the greater the intensity of a sound; the greater the pressure on the ear-drums, the louder the sound. Intensity is measured in decibels (dbs).

Any sound has duration, it is its length or quantity of time during which the same vibratory motion, the same pattern, of vibration, are maintained. The duration of speech sounds is usually measured in milliseconds (msecs). The sound waves produced by the vibration of the whole body are called fundamental waves, they are perceived as fundamental tones. Waves, produced by parts of the body are called partial waves, they are perceived as partial tones, or overtones, or harmonics (обертони).

The analysis of a sound frequency and intensity at a definite period of time can be presented graphically with the help of a sound spectrograph. Acoustic characteristics of speech sounds are represented by spectrograms: linear or dynamic and intensity or instant. In instant spectrograms intensity is represented by vertical dimensions, frequency – by horizontal dimension. In linear representations of intensity spectrograms, the strength of harmonics is adequate to the blackness of spots: the stronger the harmonic, the blacker is the spot. Spectrographic analysis gives basis for acoustic definitions and classification of speech sounds [vowels]. One of such classifications was suggested by R. Jacobson, C. Fant and M. Halle. This classification is not only phonoacoustic but also phonemic.

Although acoustic descriptions, definitions and classifications of speech sounds are more precise than articulatory ones, they are practically inapplicable and useless in language teaching, because the acoustic features of speech sounds cannot be seen directly or felt by the language learner. Acoustic descriptions, however, can be applied in the fields of technical acoustics. They are of great theoretical value.

Both types of spectrograms have certain limitations: in linear spectrograms a succession of sounds can be measured but it is difficult to compare their exact quality. They reveal a lot of information about the sound changes in time.

The intensity representations of instant spectrograms can't be read off with any exactness, but their great merit is the possibility to record not only the exact quality, but also the changes of sounds of speech at a particular moment of time.

Spectrogram of vowels [i, u, ɑ]. [ɑ] is a low vowel, so its F1 value is higher than that of [i] and [u], which are high vowels. [i] is a front vowel, so its F2 is substantially higher than that of [u] and [ɑ], which are back vowels. The acoustics of vowels are fairly well understood. The different vowel qualities are realized in acoustic analyses of vowels by the relative values of the formants, acoustic resonances of the vocal tract which show up as dark bands on a spectrogram. The vocal tract acts as a resonant cavity, and the position of the jaw, lips, and tongue affect the parameters of the resonant cavity, resulting in different formant values. The acoustics of vowels can be visualized using spectrograms, which display the acoustic energy at each frequency, and how this changes with time. The first formant, abbreviated "F1", corresponds to vowel openness (vowel height). Open vowels have high F1 frequencies while close vowels have low F1 frequencies, as can be seen at right: The [i] and [u] have similar low first formants, whereas [ɑ] has a higher formant. The second formant, F2, corresponds to vowel frontness. Back vowels have low F2 frequencies while front vowels have high F2 frequencies. This is very clear at right, where the front vowel [i] has a much higher F2 frequency than the other two vowels. However, in open vowels the high F1 frequency forces a rise in the F2 frequency as well, so an alternative measure of frontness is the difference between the first and second formants. For this reason, some people prefer to plot as F1 vs. F2 – F1. (This dimension is usually called 'backness' rather than 'frontness', but the term 'backness' can be counterintuitive when discussing formants.)

R-colored vowels are characterized by lowered F3 values. Rounding is generally realized by a complex relationship between F2 and F3 that tends to reinforce vowel backness. One effect of this is that back vowels are most commonly rounded while front vowels are most commonly unrounded; another is that rounded vowels tend to plot to the right of unrounded vowels in vowel charts. That is, there is a reason for plotting vowel pairs the way they are.