Sound Structure I: Phonetics

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Sound Structure I Phonetics

• Acoustic phonetics
• Jan. 27

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Make vowel sounds from household materials
Buzzing sound Resonators
Vowels

a
i

From Mark Huckvale http//www.phon.ucl.ac.uk/hom
e/mark/vowels
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The source in speech production

• The production of speech consists of two kinds of
  operations (1) the generation of sound sources
  (the raw material), and (2) the
  processing/resonating of these sources by the
  vocal tract (the resonator).
• Vocal fold vibration generates buzzing sound,
  which is the raw material (source) for producing
  vowel sounds.

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The vibration of the vocal folds

• The aerodynamics of vocal fold vibration
• With the glottis (the space between the vocal
  folds) closed and an airstream issuing from the
  lungs, the excess pressure below the glottis
  (sub-glottal pressure) forces the vocal folds
  apart the air passing between the folds
  generates a Bernoulli force that quickly closes
  the glottis. The sub-glottal pressure builds up
  again, forcing the vocal folds apart again.
• The vibration of the vocal folds are periodic.
  The frequency of the vibration is determined by
  the air pressure in the lungs and by the vocal
  folds mechanical properties.

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Periodic and frequency

• Vocal fold vibration is a complex periodic
  motion, it can be decomposed into many Simple
  Harmonic Motions.
• Simple Harmonic Motion is the simplest periodic
  motion, in which a body oscillates about an
  equilibrium position (rest position) in a
  sinusoidal pattern. Tuning forks are such an
  example.

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Simple Harmonic Motion

• Properties of Simple Harmonic Motion
• displacement momentary distance from
• the rest point
• cycle one complete oscillation
• amplitude maximum displacement
• frequency number of cycles per second (Hz)
• period number of seconds per cycle
• What is the difference?

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Spectrum

• A complex periodic motion can be represented as a
  spectrum showing
• Frequency of each simple harmonic component on
  the x-axis
• Amplitude of each simple harmonic component on on
  the y-axis

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The source spectrum in speech production

• As the vocal folds open and close, puffs of air
  flow through the glottal opening. The frequency
  of these pulses determines the fundamental
  frequency (F0) and contributes to the perceived
  pitch of the produced sound.
• Besides F0, the glottal air flow also contains a
  large number of harmonics (overtones), whose
  frequencies are integer multiples of F0. The
  amplitude of the harmonics decreases gradually.

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Vocal tract is a resonator

• The vocal tract is a resonator. The resonance
  frequencies of the vocal tract, called formants,
  depend on its shape. The first resonance
  frequency is F1, the second resonance frequency
  is F2, and so on.
• The first two or three formants (their
  frequencies, not amplitudes) are most important
  in speech communication.

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Final product vowels

• The presence of the formats disrupts the
  uniformly sloping envelop of the source spectrum,
  imposing peaks at the formant frequencies.
  Formant frequencies determine vowel quality (/i/
  vs. /a/ vs. /u/ etc.)

Vowel spectrum
Vocal tract resonance
Source spectrum
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Acoustic vowel space
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Vowel formants

• Vowel height is closely related to the first
  formant frequency
• low vowels -gt higher F1
• Vowel frontness/backness is closely related to
  the second formant frequency
• front vowels -gt higher F2
• Formant frequencies of American English vowels
  (average)
• Male
  Female
• /i/ F1 270Hz F2 2290Hz F1
  310Hz F2 2790Hz
• /a/ F1 730Hz F2 1090Hz F1
  850Hz F2 1220Hz
• /u/ F1 300Hz F2 870Hz F1
  370Hz F2 950Hz

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Measuring vowel formants

• Formants can be displayed by computing a
  spectrogram, showing the energy in the signal at
  different frequencies.
• Spectrograms are a plot of the intensity of the
  frequency content of a signal as time progresses.
  The y-axis is frequency, the x-axis is time, and
  the intensity is shown on a grey-scale.
• Praat doing phonetics by computer.
  http//www.fon.hum.uva.nl/praat/

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The acoustics of consonants

• The sources of consonant sounds are either
  turbulent airflow (fricatives) or release of a
  compressed air behind a closure (stops). The
  sources are aperiodic, noises.
• Note White noise contains an equal
  distribution of energy spread over all
  frequencies, just as white light is composed of
  all of the colors of the spectrum of visible
  light.
• The resonator is the front cavity, i.e., the part
  of the oral cavity that is in front of the
  constriction place. The nasal cavity is used as a
  resonator in producing nasal sounds.

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Fricatives

• Fricatives have relatively long durations of
  noise, and it is this lengthy interval of
  aperiodic energy that distinguishes fricatives as
  a sound class. s, ? have more energy than f,
  ?.

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Stops

• Stops are dynamic, it has a series of
  articulatory postures
• Gap during closure, the only possible source
  is voicing (shown as a voice bar).
• Burst a transient noise produced when the
  oral closure is released
• Aspiration a diffuse noise generated at
  the larynx and possibly the lower pharynx. Its
  spectrum resembles that for the fricative h.
• tie, dye, style.

Gap
Aspiration
Burst
Voice bar
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VOT

• To further distinguish voiced/voiceless and
  aspirated/unaspirated, we can use Voice Onset
  Time (VOT).
• VOT is the duration of the period of time between
  the release of a plosive/stop and the beginning
  of vocal fold vibration. This period is usually
  measured in milliseconds (ms).
• It is useful to distinguish at least three types
  of VOT which are shown in the schematic diagram
  below

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Speech prosody

• Segments characterize speech sounds.
  Suprasegmental features (prosody) superimpose on
  segments or segmental sequences.
• Acoustic cues of prosody
• Pitch, determined by fundamental frequency
• Length, determined by duration
• Loudness, determined by amplitude
• Stress, tone, intonation, rhythm, etc.

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Tones

• Tone languages use pitch to make lexical
  contrasts (to distinguish words).
• contour tones (predominating in Chinese and the
  languages of southeast Asia) The tones are made
  up of dynamic pitch changes.
• Register tone (predominating in African
  languages). The tones are made up of a few pitch
  registers high, low, and maybe mid.

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Intonation in English

• A What types of foods are a good source of
  vitamins?
• B1 Legumes are a good source of vitamins.
• B2 Legumes are a good source of vitamins.
• A Id like to fly to Davenport, Iowa on TWA.
• B TWA doesnt fly there ...
• B1 They fly to Des Moines.
• B2 They fly to Des Moines.
• A1 I met Mary and Elenas mother at the mall
  yesterday.
• A2 I met Mary and Elenas mother at the mall
  yesterday.

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Intonation in English
legumes are a good source of VITAMINS
LEGUMES are a good source of vitamins
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Intonation in Mandarin Chinese

• Interaction between tone and intonation

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Rhythm

• Rhythm refers to the temporal organization of
  speech elements. It depends on many factors.
• At the segmental level, for example, vowels are
  longer before voiced stops than before voiceless
  ones. The effect is very large in English (bad
  vs. bat), but smaller in many other languages
  such as French.
• At the level of syllables, languages have
  different phonotactic constraints on syllable
  shape. For example, many dialects of Chinese
  allow only alveolar and velar nasals in the coda
  position.

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Rhythm

• In natural speech, over 70 of French and Spanish
  syllables were open (e . g ., CV and V) , while
  more than 50 of English syllables were closed (e
  . g ., CVC and VC).
• In Hawaiian there is never more than a single
  consonant between any two vowels, but in English
  there can be seven, as in texts spread. In Polish
  there are even more