Monday, February 10, 2014

Chapter 3 Speech Science lecture notes --- hardest class this semester

Chapter 3. Articulatory system
– Spectrographic analysis of vowels and consonants (stops, fricatives, affricates)Lecture 8 – 02/10/14
·      Spectrographic analysis
o   Spectrography is a method of identifying frequency, amplitude, and duration of sounds.
o   Frequency is displayed on the vertical axis, time is represented on the horizontal axis, and intensity of acoustic energy is represented by the darkness of the trace on the screen.
·      Spectrographic analysis of vowels
o   Vowels are characterized by first three formants.
o   They appear as wide, dark horizontal stripes, reflecting the concentrations of intense acoustic energy at those harmonic frequencies that have been amplified by the vocal tract formants.
o   The first format (F1) in vowels is inversely related to vowel height
§  The higher the vowel, the lower the first format (and vice versa)
·      High /i/ and /u/ à F1 ~ 280-310
·      Mid-high /I/ and /ʊ/ à F1 ~ 400-450
·      Mid-low /ɛ/ and /ɔ/ à F1 ~ 550-590
·      Low /æ/ and /a/ à F1 ~ 690-710
o   The second format (F2) in vowels is somewhat related to degree of backness
§  The more front the vowel, the higher the second format (but affected by lip rounding).
Frequency Range
F2 ~ 2250 ~870
F2 ~ 1920 ~ 1030
F2 ~ 1770~880
F2 ~ 1660~1100
·      Spectrographic analysis of Diphthongs
o   A diphthong is a vowel that changes its resonance characteristics during its production.
o   Characterized by first three formant frequencies
o   Produced by uttering two vowels as one unit.
§  This results in formant transitions.
§  Steady-state formants at the beginning of the sound, followed by formant transition, and then another steady-state portion.
·      Spectrographic analysis of Stops
o   Four important acoustic features
§  Silent gap
·      Time during which the articulators are forming the blockage and oral pressure is building up. Seen as voice bar for voiced stops.
§  Release burst
·      Follows the silent gap. Seen as vertical line extending into high frequencies. Lasts for 10 – 30 ms.
·      Seen for stops in initial and medial position, but not for final position.
·      Bilabial stops – diffuse spectrum, with energy spread out over a wide range of frequencies and more energy in the lower frequencies than in the higher.
·      Alveolars – diffuse with increasing energy in the higher frequencies or spread out evenly.
·      Velars – Compact with energy concentrated in a relatively narrow region.
·      Voiceless stops have bursts that are longer in duration due to aspiration.
§  Format Transitions
·      Articulators move from constricted position to open position following the production of the sound.
·      Can occur either from a voiced sound occurring before the stop, or both, lasts around 50 ms.
·      The slope of transitions – depends on the place of articulation of the stop and vocal tract position following the sound
·      A very low F1 – complete constriction of the vocal tract.
·      The transition for F1 starts from nearly zero and increases to the appropriate frequency for the following vowel
§  Voice onset time (VOT)
·      VOT – time between the beginning of the stop burst and the onset of the vocal fold vibration for the following vowel.
·      This is measured in milliseconds and indicates the coordination between laryngeal and articulatory systems.
·      Four categories of VOT – depending on the timing between the release of the burst and the onset of the vocal fold vibration:
o   VOT lead – VOT is negative indicating that the vocal folds are vibrating before the articulatory release (occurs for voiced stops).
o   Simultaneous voicing – voice onset and articulatory release occur at the same time.
o   Short lag – onset of vocal vibration follows shortly after the release burst.
o   Long lag time – vocal fold vibration time is delayed relatively long time after the articulatory release
·      VOTs for Voiced stops –    - 20 ms to + 20 ms
·      VOTs for voiceless stops –     +25 ms to 100 ms
·      VOTs depend on the place of the stop articulation and increases as place of articulations moves backward.
·      Bilabials -  shortest VOTs.
·      Alveolars – intermediate VOTs
·      Velars – longest VOTs
·      Fricatives
o   On a spectrogram – wide band of energy distributed over a broad range of frequencies.
o   Energy in fricatives is much longer in duration than stops.
o   Specific range of frequencies and the intensity of aperiodic sounds depend on the place of articulation of the fricative.
o   Fricatives are characterized by white noise, which is aperiodic sound that has its energy distributed fairly evenly throughout the spectrum.
o   The spectrum for fricatives depends on place of articulation because fricative noise is resonated most strongly anterior to the articulatory constriction.
o   Fricatives that are produced anteriorly (e.g., /f/, /v/, /ϴ/) do not have much of a front resonating cavity, so they have very low-intensity spectrum spread out over a broad range of frequencies.
o   The alveolar and palatal fricatives have more intense acoustic energy at high frequencies because of the way that they are resonated.
§  Stridents (/s/, /z/, /ʃ/, /ᴣ/) have much more intense energy than the nonstridents (/f/, /v/, /ϴ/, /ᶞ/)
·      Affricates
o   They are produced quickly combining a stop with a fricative, so the acoustic characteristics of affricates have elements of both stops and fricatives.
o   Affricates have a silent gap associated with the stop part of the sound.
o   Frication noise related to the fricative portion of the affricate sound follows the silent gap.
o   Fricatives and affricates look very similar on a spectrogram, except that affricates are shorter in duration.
·      Relevant questions for exam(s)
o   Identifying the spectrograms of vowels (your clue would be mainly based on the first two formant frequencies)
o   Identifying the spectrograms of vowels (your clue would be the transition of formant frequencies)
o   Identification of spectrograms of stop consonants (clue would be voice bar (if any), release burst, VOT, and formant transitions)
o   Identification of fricatives (based on the spread of intense acoustic energy)

o   Learn the VOT for voiced and voiceless stops
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