1. Acoustic Phonetics
3/14/00

2. Methods of Acoustic Analysis
Spectrograph: Produces visible patterns of acoustic energy called spectrograms
Spectrographic Analysis:
Acoustic signal changes rapidly & continuously
Need a dynamic analysis revealing spectral features
Short term running spectrum

3. Features of the Spectrogram
Spectrographic Analysis
Features of the Spectrogram
Time, Frequency & intensity
Time (horizontal axis): Phonetic elements will be from left to right
Frequency (Vertical axis): Increasing in upward direction
Intensity represented by a gray scale or as variations in darkness

4. Dimensions of Spectrograms
A. Burst of noise
B. Vowel with 4 formants
Time
C. Noise with high frequency energy

5. Wide Band Spectrogram Fricative noise: Above 3 or 4 kHz
Diphthong: Horizontal bands of energy

6. Wide Band vs. Narrow Band
Wide Band: analyzing filter wide, Hz
Good to show formants because they have a wide spread of acoustic energy
Narrow Band: analyzing filter is of higher resolution, 100 Hz
Good to show the harmonics of source spectrum

7. Vowel: Wide Band vs. Narrow Band

8. Digital Signal Processing
Basic objective of digital signal processing:
Convert the analog acoustic signal (Panel A) to a digital form (series of #’s)
How do we get a waveform into a digital computer?
Analog-Digital conversion (A-D): results in samples of time and amplitude
Correct sampling rate is important to reconstruct the wave form
Sampling rate must be 2x the bandwidth of analysis: Nyquist Frequency
Ex. Sample speech with a bandwidth of 5000 Hz, than the sampling rate should be 10,000 Hz

9. Analog-Digital Conversion
b. Time sampling intervals

10. Phonetic Quality: Vowels
Front Vowels:
Larger separation between F1 & F2
Small F2 & F3 separation
Frequency of F1= Tongue height
Back Vowels:
Small separation between F1 & F2
Large separation between F2 & F3
Central vowels:
Formant frequencies are evenly spaced
Moderate jaw opening causes mid-range F1

11. Two Formant Spectrograms: Front, Back & Central Vowels

12. Phonetic Quality: Consonants
Stop Consonants:
Acoustic Cues: Silent or low energy interval, burst, transition
Silent interval = oral constriction (i.e. closure of lips for /b/); also termed a stop gap
Voiced stops can be seen on the voice bar as noise energy
Burst = Articulatory constriction is released; energy released looks like noise on the spectogram
Transition= formant transition into following vowel

13. Voiceless Stop Consonants

14. Phonetic Quality: Consonants
Bilabial Stops (/p/, /b/):
F1 starts at zero & rises to F1 of next vowel
F2 starts at 800 Hz & rises to F2 of following vowel
F3 increases for following vowel
Alveolar Stops (/t/, /d/):
F1 same as for bilabial stops
F2 starts at 1800 Hz & rises to F2 of following vowel
Velar Stops (/k/, /g/):
F1 same as for bilabials
F2 has 2 starting points 1300 & 2300 Hz

15. Spectrogram with Transitions: /d a d/