1. Spectrogram & its reading
by Tae-Yeoub Jang

2. What is spectrogram? Begin to be used since 1940s
Another representation of frequency domain analysis
The most popular way of representing spectral information
3 dimensional representation
X-axis: Time
Y-axis: Frequency
Darkness (or color): Energy
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3. Spectrogram example (color resolution of word “compute”)
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4. Spectrogram example (grayscale of word “compute”)
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5. Wideband vs. Narrowband spectrograms of the question "Is Pat sad, or mad?" The 5th, 10th and 15th harmonics have been marked by white squares in two of the vowels
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6. Types of spectrogram Wideband spectrogram Narrowband spectrogram
better time resolution
eg) 15 msec window, 1 msec shift, 125 Hz bandwidth
Narrowband spectrogram
better frequency resolution
eg) 50 msec window, 1 msec shift, 40 Hz bandwidth
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7. Advantages & Disadvantages
Time alignment
Disadvantages
Less reliable than waveform
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8. Vowel Spectrogram
Formant frequencies are critical cues for vowel distinction
F1: Height
high vowels: low F1
F2: Backness
back vowels: low F2
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9. Example formant frequencies of English monophthongs         F3
2900
2550
2490
2640
2380
2300
2500
2390 F2
2250
1900
1770
1660
1100
1030
870
1500
1190 F1
280
400
550
690
710
450
310
900
640
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10. "heed, hid, head, had, hod, hawed, hood, who'd" (a male speaker, American English)
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11. Consonant Spectrogram
General
Acoustic structure more complicated than vowels
Adjacent sounds (especially vowels) convey important information  locus
High frequency characteristics
 especially for fricatives and affricates
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12. What is LOCUS
Information of formant transition from vowels into obstruents or from obstruents into vowels
The target frequency that each formant transition is heading toward as an obstruction is made, or the frequency the transition comes as the obstruction is released
The characteristic of the consonantal place and manner  roughly the same in different vowel contexts
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13. Stops General Fairly distinct locus for each place Burst
Silence during the closure (only at syllable onset position)
Virtually no difference during the closure
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14. Stops (cntd.) Voicing distinction
voiced: vertical striations for voiced sounds, less abrupt burst, frequently weakened to be like fricatives or approximants
voiceless: generally abrupt burst at higher frequency area
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15. Stops (cntd.) Place distinction bilabial alveolar velar
relatively low F2, F3 locus  rising into and falling out of vowel
weak and spread vertical lines
alveolar
F2 locus about 1800 Hz
Strong vertical lines
velar
Velar pinch: vowels F2, F3 merging
often double burst
long formant transitions
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16. Stops (cntd.) Manner distinction Silence duration, VOT, vowel F0
aspirated
short
long
high
tense
lax
med
low
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17. Examples -- “a bab, a dad, a gag”
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18. Place dependent loci
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19. Fricatives
General
Random noise pattern especially in high frequency regions
Place distinction
Labiodental [f, v]: rising locus into the following vowel
Dental [, ð]: major energy above 6000Hz
Alveolar [s, z]: major energy above 4000Hz
Alveopalatal [š, ž ]: major energy above 6000Hz
Glottal [h]: the trace of formant frequencies of neighbouring vowels
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20. Fricatives (cntd.) Weak vs. strong Strong [s, z, š, ž ]: darker bands
Weak [f, v, , ð ]: spread and fainter
Voiced [v, ð ]: often so weak and confused with nasals or approximants
Cues to tell [] from [f]: higher formants of [] fall into adjacent vowels
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21. Example – “fie, thigh, sigh, shy”
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22. Example – “ever, weather, fizzer, pleasure”
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23. Nasals General Place distinction
Formants similar to vowels but fainter
Very low F1 (about 250Hz), F2 (about 2500Hz), and F3 (about 3250Hz)
Place distinction
bilabial [m]: downward F2, F3 locus
alveolar [n]: less amount of F2 transition
velar [ŋ ]: velar pinch
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24. Examples -- “a Pam, a tan, a kang”
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25. Liquies & Approximants
General
Formants similar to vowels but fainter (especially at high frequency regions)
Approximately F1(250Hz), F2(1200Hz), F3(2400Hz)
Change in formant structure
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26. Liquids & Approximants (cntd.)
Phone specific properties
Labial glide [w]:
very low F1, F2 ( Hz|) and gets too close to each
relatively low F3
rapid falloff of spectral amplitude
Palatal glide [y]:
extremely low F1
extremely high F2, F3
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27. Liquids & Approximants (cntd.)
Phone specific properties (cntd.)
Flap [Ր]: soft burst, short duration
Retroflex [r]:
F3 dipping down close to F2
General lowering of F3, F4
Lateral [l]:
Low F1, F2 (approx. F1 250Hz, F2 1200Hz)
usually substantial energy in the high F region
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28. Example – “led, red, wed, yell”
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29. Final remarks
Spectrogram is not the only cue for acoustic distinction of speech sounds
Very often, the waveform is more reliable
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30. References & Links
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