1. Tom Lentz (slides Ivana Brasileiro)
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)

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