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Perception and Production in L2 Acquisition Week 1: A Brief Introduction to Acoustic Phonetics

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

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Perception and Production in L2 Acquisition Week 1: A Brief Introduction to Acoustic Phonetics

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

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

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

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

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

  6. 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

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

  8. 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

  9. 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

  10. Speech Sounds Periodic Aperiodic

  11. Measuring Sounds • Oscillogram • Spectrum • Spectrogram

  12. Oscillogram • Amplitude x time

  13. Spectrum • Shows all frequencies present in the signal at a given point in time

  14. Spectrogram • Combines properties of oscillogram and spectrum • Measure three dimensions: time, frequency, and amplitude

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

  16. 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

  17. 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

  18. 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)

  19. Articulatory correlates • F1 correlates with vowel height • higher F1, lower vowel • F2 correlates with degree of frontness • higher F2, ‘fronter’ vowel

  20. Dutch Vowels

  21. 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

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

  23. 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

  24. Problems in Language Acquisition • Segmentation problem • Coarticulation • Cue ambiguity • Mapping problem

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

  26. 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

  27. Mapping problem • How do phonetic categories relate to phonological categories? • Allophonic variation • Contextual variation • Normalization

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