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Spectrogram & its reading. 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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Spectrogram & its reading

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Spectrogram its reading l.jpg

Spectrogram & its reading


What is spectrogram l.jpg

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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Waveform spectrogram aligned l.jpg

Waveform & Spectrogram aligned

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Spectrogram example color resolution of word compute l.jpg

Spectrogram example (color resolution of word “compute”)

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Spectrogram example (grayscale of word “compute”)

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Wideband vs. Narrowbandspectrograms 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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Types of spectrogram

  • Wideband 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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Advantages & Disadvantages

  • Advantages

    • Time alignment

  • Disadvantages

    • Less reliable than waveform

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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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Examples of formant frequencies of English monophthongs

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Heed hid head had hod hawed hood who d a male speaker american english l.jpg

"heed, hid, head, had, hod, hawed, hood, who'd" (a male speaker, American English)

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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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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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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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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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Stops (cntd.)

  • Place distinction

    • bilabial

      • 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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Stops (cntd.)

  • Manner distinction

    • Silence duration, VOT, Following V F0

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Examples a bab a dad a gag l.jpg

Examples -- “a bab, a dad, a gag”

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Place dependent loci

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Fricatives

  • General

    • Random noise pattern especially in high frequency regions

    • Place distinction

      • Labiodental [f, v]: rising locus into the following vowel

      • Dental [T, D]: major energy above 6000Hz

      • Alveolar [s, z]: major energy above 4000Hz

      • Alveopalatal [s&, zà]: major energy above 6000Hz

      • Glottal [h]: the trace of formant frequencies of neighbouring vowels

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Fricatives (cntd.)

  • Weak vs. strong

    • Strong [s, z, s&, zà]: darker bands

    • Weak [f, v, T, D]: spread and fainter

      • Voiced [v, D]: often so weak and confused with nasals or approximants

      • Cues to tell [T] from [f]: higher formants of [T] fall into adjacent vowels

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Example fie thigh sigh shy l.jpg

Example –“fie, thigh, sigh, shy”

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Example ever weather fizzer pleasure l.jpg

Example –“ever, weather, fizzer, pleasure”

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Nasals

  • General

    • 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 [N]: velar pinch

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Examples a pam a tan a kang l.jpg

Examples -- “a Pam, a tan, a kang”

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Liquids & Approximants

  • General

    • Formants similar to vowels but fainter (especially at high frequency regions)

    • Approximately F1(250Hz), F2(1200Hz), F3(2400Hz)

    • Slow formant movements

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Liquids & Approximants(cntd.)

  • Phone specific properties

    • Labial glide [w]:

      • very low F1, F2 (600-1000Hz|) and gets too close to each

      • relatively low F3

      • rapid falloff of spectral amplitude (formant movements)

    • Palatal glide [y]:

      • extremely low F1

      • extremely high F2, F3

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Liquids & Approximants(cntd.)

  • Phone specific properties (cntd.)

    • Flap [R]: 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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Example led red wed yell l.jpg

Example –“led, red, wed, yell”

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Final remarks

  • Spectrogram is not the only cue for acoustic distinction of speech sounds.

  • When there is a mismatch between waveform & spectrogram, the waveform is more reliable in general.

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References & Links

  • http://cslu.cse.ogi.edu/tutordemos/SpectrogramReading/spectrogram_reading.html

  • http://hctv.humnet.ucla.edu/departments/linguistics/VowelsandConsonants/course

  • http://www.cs.indiana.edu/~port/teach/306/speech.acoustics.html

  • http://www.phon.ucl.ac.uk/courses/spsci/b203/week2-5.pdf

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