Acoustic Phonetics. Chapter 8

Transcription

1 Acoustic Phonetics Chapter 8 1

2 1. Sound waves Vocal folds/cords: Frequency: 300 Hz

3 1.1 Sound waves: The parts of waves We will be considering the parts of a wave with the wave represented as a transverse wave as in the following diagram: In the above diagram the white line represents the position of the medium when no wave is present. This medium could be imagined as a rope fixed at one end a few feet above the ground and held by you at the other end. The yellow line represents the position of the medium as a wave travels through it. We simply say that the yellow line is the wave. If we consider the rope mentioned before, this wave could be created by vertically shaking the end of the rope. Often, when several waves are traveling along a medium as shown above, the continuous group of waves is called a wave train. 3

4 1.2 Sound waves: What is crest and trough? The section of the wave that rises above the undisturbed position is called the crest. That section which lies below the undisturbed position is called the trough. These sections are labeled in the following diagram: 4

5 1.3 Sound waves: What is amplitude? The term amplitude can have slightly different meanings depending upon the context of the situation. Its most general definition is that the amplitude is the maximum positive displacement from the undisturbed position of the medium to the top of a crest. This is shown in the following diagram: 5

6 1.4 What is positive & negative amplitude? The displacements of positive and negative amplitudes are shown in the following diagram: Sometimes it is necessary to discuss an amplitude at a certain point along the wave. Several of these amplitudes are shown in the following diagram: 6

7 1.5 Sound waves: What is wavelength? The wavelength of a wave is the distance between any two adjacent corresponding locations on the wave train. This distance is usually measured in one of three ways: crest to next crest, trough to next trough, or from the start of a wave cycle to the next starting point. Actually, the a wavelength exists between any point on a wave and the corresponding point on the next wave in the wave train. A few of such distances are shown below: 7

8 2.1 What is frequency? 1. Frequency refers to how many waves are made per time interval. This is usually described as how many waves are made per second, or as cycles per second. 2. If ten waves are made per second, then the frequency is said to be ten cycles per second, written as 10 cps. 3. Usually, we use the unit Hertz to state frequency. A frequency of 10 cps is noted as a frequency of 10 Hertz. So, one cycle per second is one Hertz, as in: 1 cps = 1 Hertz or it is abbreviated this way: 1 cps = 1 Hz 120 cps = 120 Hz 350 cps = 350 Hz 8

9 2.2. Sound waves and the frequency Frequency: The number of complete repetitions (cycles) of variations in air pressure occurring in a second. The unit of frequency measurement is the hertz (Hz)

10 2.3 Sound waves with different frequencies? 100 Hz 200 Hz second 10

11 2.4. Frequencies and sound waves Frequency: 300 Hz Frequency: 500 Hz

12 2.5 High & low frequencies and sound waves Frequency: 100 Hz Hz Try to listen to the following sounds: 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 100, 20, 10, 8, 6, 5 12

13 2.6 More varieties of frequencies 16 Hz 4000 Hz 32 Hz 5000 Hz 64 Hz 8000 Hz 100 Hz Hz 160 Hz Hz 200 Hz Hz 250 Hz 320 Hz 900 Hz Hz 400 Hz 300 Hz Hz 450 Hz 1000 Hz 1600 Hz 2000 Hz 13

14 3. Formants Formants 1-4: leaves (Amanda) Time (s) Time (s) 14

15 3.1 Formants with lines Formants 1-4: leaves (Amanda) Time (s) Time (s) 15

16 3.2 Formants of different vowels See CBCAP (The vowel acoustics) 16

17 3.2 The relationship between F1 and F2 Formant 1: reflecting the high or low of the vowel in the oral tract Formant 2: reflecting the backness of the vowel in the oral tract Try to use praat to figure out the relationship described above. See also CBCAP 17

18 3.3 The Assignment Try to examine the articulation positions and sounds. 1. Draw the matrix to represent space of oral tract Make sure that the X and Y axes (with X axis = 3000 Hz and Y axis = 1500 Hz) 2. Try to produce different vowels by yourself 3. Try to collect the acoustic info of the first and second formants by means of any speech analyzer (e.g., PRAAT) 4. Try to locate each vowel according to the sets of formant values from speech analyzers 18

19 4 Formants of consonants See CBCAP 1. Aerodynamic effects 2. Degree of constriction 3. Place of articulation 4. Voicing 5. Nasalization 19

20 4.1 Aerodynamic effects See CBCAP 20

21 4.2.1 Degree of constriction See CBCAP 21

22 4.2.2 Degree of constriction See CBCAP 22

23 4.2.3 Degree of constriction See CBCAP 23

24 4.3 Place of articulation See CBCAP 24

25 4.4.1 Voicing See CBCAP 25

26 4.4.2 Voicing See CBCAP 26

27 4.4.3 Voicing See CBCAP 27

28 4.4.4 Voicing See CBCAP 28

29 4.4.5 Voicing See CBCAP 29

30 4.5.1 Nasalization See CBCAP 30

31 4.5.2 Nasalization See CBCAP 31

32 4.5 Nasalization See CBCAP 32

33 4.6 Summary and conclusion See CBCAP 33

34 4.7 Summary and conclusion See CBCAP 34

35 4.8 Summary and conclusion See CBCAP 35

36 4.9 Summary and conclusion See CBCAP 36

37 4.10 Summary and conclusion See CBCAP 37

38 4.11 Summary and conclusion See CBCAP 38

39 4.11 Summary and conclusion See CBCAP 39

40 4.12 An expression with only the first formants Time (s) 40

41 4.13 An expression with only the second formants Time (s) 41

42 4.14 An expression with only the third formants Time (s) 42

43 4.15 An expression with only the first three formants Time (s) 43

44 4.16 An expression with only the consonants Time (s) 44

45 4.17 An expression with everything but F Time (s) 45

46 4.18 An expression with everything Time (s) 46

47 4.19 Try to read the following pairs in PRAAT 1. A bab, a dad, a gag Compare the changing of the formants (voice bar?) 2. A Pam, a tan, a kang 3. fie, thigh, sign, shy 4. ever, weather, fizzer, pleasure 5. led, red, wed, yell See p. 197 for general conclusions and show your work to your neighbors and discuss with them. 47

48 5. Loudness and intensity 1. In general, the loudness of a sound depends on the size of the variations in air pressure that occur. Just as frequency is the acoustic measurement most directly corresponding to the pitch of a sound, so acoustic intensity is the appropriate measure corresponding to loudness. The intensity is proportional to the average size, or amplitude, of the variations in air pressure. It is usually measured in decibels (abbreviated as db) relative to the amplitude of some other sounds. 2. The human ear can hear (perhaps tolerate would be a better word) a range of about 120 db, although if you persist in listening to sounds 110 to 120 db above the quietest sound you can hear you will soon go deaf, as many rock musicians have found out. When one sound has an intensity 5 db greater than another, then it is approximately twice as loud. A change in intensity of 1 db is a little more than the just noticeable difference in loudness. (use Soundforge to demonstrate) 48

49 5.1 Intensity and fundamental frequencies Use PRAAT to test the intensity. 49

50 6. Pitch and frequency The pitch of a sound is that auditory property that enables a listener to place it on a scale going from low to high, without considering its acoustic properties. In practice, when a speech sound goes up in frequency, it also goes up in pitch. For the most part, at an introductory level of the subject, the pitch of a sound may be equated with its fundamental frequency, and, indeed, some books do not distinguish between the two terms, using pitch for both the auditory property and the physical attribute. 50

51 6.1 No voice, no pitch marked 1. The sentences used as illustrations of different intonations contained almost no voiceless sounds and hardly any voiced stops or fricatives. This is because voiceless sounds have no vocal fold pulses and therefore no pitch. Voiced stops and fricatives also perturb the smooth pitch curve. 2. Voiced sounds have a regular waveform of the kind that you hear as having a recognizable pitch. In voiceless sounds, the variations in air pressure are caused by the smooth flow of the airstream being interrupted by being forced through a narrow channel or directed over irregular surfaces. In the sound waves that are produced, there are usually more rapid (and therefore higher frequency) variations in air pressure than occur during voiced sounds. For a male voice, the frequency of the vocal fold vibrations in speech may be between 80 and 200 Hz. A woman's voice may go up to about 400 Hz. The predominant frequencies in voiceless sounds are usually above 2,000 Hz. 51

52 6.2 Examples 52

53 7. Spectrograms of an expression 1. Read the expression: She came back and started again. 2. He left here three days ago. (Use PRAAT and discuss with your neighbors.) 53

54 7.1 Spectrograms with broad/narrow bands Figure 8.16 (p. 203) (Use KAY for demonstration.) 54