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Perception and Production in L2 Acquisition Week 1: A Brief Introduction to Acoustic Phonetics Tom Lentz (slides Ivana Brasileiro) Lab 1 12 november 2008.ppt.

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Presentation on theme: "Perception and Production in L2 Acquisition Week 1: A Brief Introduction to Acoustic Phonetics Tom Lentz (slides Ivana Brasileiro) Lab 1 12 november 2008.ppt."— Presentation transcript:

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2 Perception and Production in L2 Acquisition Week 1: A Brief Introduction to Acoustic Phonetics Tom Lentz (slides Ivana Brasileiro) Lab 1 12 november 2008.ppt

3 Acoustic Phonetics Physics of the speech signal Relationship between activity in the speaker's vocal tract and the resulting sounds Contrast: articulatory phonetics

4 What we will do… Key concepts: frequency, formants, and acoustic cues Measuring speech sound Vowels and formants (Acoustic cues: VOT) (Problems in Language Acquisition)

5 Frequency Cycles of vibration per second Measured in Hertz (Hz) E.g. 100 Hz = 100 repetition per second

6 Frequency Figure 1: Two periodic signals with frequencies of 200Hz and 400Hz

7 Sine Waves vs. Complex Sound Waves Sine waves: sounds formed by one frequency only Complex sound waves: all sounds which are not sine waves All complex sound waves can be described on the basis of the sine waves

8 Sine Waves vs. Complex Sound Waves Figure 2: three sine waves (left) and resulting complex sound wave (right) a b c d

9 Question If in figure 2, (a) has frequency A; (b) has frequency B and (c) has frequency C, what is the frequency of picture (d)? Answer: A

10 Speech Sounds Speech sounds are always complex waves Two sources of sounds –Vocal folds –Oral cavity Sounds produced with the vocal folds are periodic: usually perceived as voiced Sounds produced with the oral cavity are aperiodic: usually perceived as voiceless

11 Speech Sounds Periodic Aperiodic

12 Measuring Sounds Oscillogram Spectrum Spectrogram

13 Oscillogram Amplitude x time

14 Spectrum Shows all frequencies present in the signal at a given point in time

15 Spectrogram Combines properties of oscillogram and spectrum Measure three dimensions: time, frequency, and amplitude

16 PRAAT practice Task: find vocal fold vibration frequency Record your voice: which phonemes ? Analyse: how?

17 Formants (1) The shape of the vocal tract increases some frequencies and decreases others The increased frequencies can be seen in the spectrum as peaks; and in spectrograms as darker spots These frequency peaks are the formants

18 Formants (2) Formants are commonly used to describe vowels The first 3 formants (F1, F2 and F3) are important for the vowel quality Other formants (F4 and F5) are important for the naturalness of the speech sound

19 Vowels Acoustic Space Vowels are usually plotted in a F1 x F2 graph, since they play a prominent role in the quality of the vowel F1 in the y-axis and F2 in the x-axis This graphic represents the acoustic space of vowels, the so called vowel triangle (see handout monday)

20 Articulatory correlates F1 correlates with vowel height –higher F1, lower vowel F2 correlates with degree of frontness –higher F2, fronter vowel

21 Dutch Vowels

22 Acoustic Cues Refers to any piece of signal that has been found by experiment to have an effect on percept (Lieberman 1996) Examples of cues are: VOT, bursts, transitions, duration and formants

23 Voice Onset Time (VOT) Refers to the time of voicing in relation to the consonant articulation / release burst

24 Acoustic Cues No one-to-one relationship between cues and a single percept (see handout) Voicing contrast in Dutch has been shown to have about 6 acoustic correlates Cues differ in how important they are Cue reliance refers to how strongly listeners rely on a specific cue to identify a contrast Cue weighting refers to how much each cue counts

25 Problems in Language Acquisition Segmentation problem –Coarticulation –Cue ambiguity Mapping problem

26 Coarticulation Information about more than one sound is often encoded in the same portion of the acoustic signal

27 Cue ambiguity The interpretation of acoustic cues depends on their position in the signal (handout Kager) Example: VOT in English pin spin bin pin: aspirated, long lag VOT (30-35ms) spin: plain, voiceless unaspirated, short lag VOT bin: voiced, short lag VOT or prevoiced

28 Mapping problem How do phonetic categories relate to phonological categories? Allophonic variation Contextual variation Normalization


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