CDO 463 6 Vowels

  1. Vocal Tract Filter
    Source-Filter Theory
    • Acoustic theory of speech production
    • Speech results from a combination of sound source(s) and the filtering provided by the vocal tract.
    • An example of a forced vibration.
  2. Acoustic Properties of the Vocal Tract
    Uniform Tube Model 1
    • Length varies with age and gender:  males>females>children
    • as vocal tract length increases, resonant frequencies decrease.
    • Males:  L = 17 cm; F1 = c/4L = 34000/68 = 500 Hz, F2 = 1500 Hz
    • Females:  L = 14 cm; F1 = c/4L = 34000/56 = 607 Hz, F2 = 1821 Hz
  3. Damping:
    vocal tract is highly damped.  Low amplitude of force vibration, but broad range of frequencies resonated.
  4. Resonance Curve (frequency response)
    • Combination of the resonance curves for each natural frequency
    • Peaks:  regions of resonance
    • Valleys:  regions of damping
  5. Vocal Tract Damping Characteristics
    • Highly damped:
    • low amplitude of forced vibration
    • broad range of frequencies resonated.
  6. Formant: 
    • region of frequency resonated by the vocal tract due to its shape and corresponding frequency response
    • first two most important for vowel recognition
  7. Relationship between formants (filter) and harmonics (source)
    Formant:  Contains one or more harmonics from the voice (source)
  8. Monophthongs: 
    • vowel sounds produced with a relatively stable placement of the articulators.
    • Tongue Height:  high, mid, low
    • Tongue Advancement:  front, central, back
    • Lip Configuration:  rounded, unrounded, spread
    • Tension:  tense, lax
  9. Diphthongs: 
    vowel sounds produced with changing articulation
  10. Tongue Height: 
    • tongue moves from low to high (more constricted)
    • F1 decreases
    • F2 increases
    • compare /i/ and /æ/
  11. Tongue Advancement: 
    • tongue moves front-back
    • F1 increases
    • F2 decreases
    • compare /C/ and /æ/
  12. Lip Configuration: 
    • lip moves from rounded-unrounded (neutral)-spread
    • F1 increases
    • F2 increases
  13. Tension: 
    • tense-lax
    • duration:  tense vowels are longer than lax
    • f0:  higher for tense than lax vowels
    • formant frequencies:  small differences due to the tongue positioned slightly higher for tense vowels than lax vowels
  14. Measuring Formants
    Wide-band Spectrogram
    Place cursor into the middle of each band
  15. Measuring Formants
    Linear Predictive Coding (LPC) Spectrum
    • Special mathematical procedure for determining formants
    • Place cursor into the middle of each peak
  16. Measuring Formants
    Automatic analysis (LPC)
    • Use of software programs to automatically measure formant frequencies.
    • Generates a wide-band spectrogram and then automatically draws a tracing of the formants based on the LPC analysis
Card Set
CDO 463 6 Vowels
Speech acoustic vowels