CDO 463 5 Acoustic Characteristics of Sound source

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CDO 463 5 Acoustic Characteristics of Sound source
2012-12-08 18:00:39
Acoustic Characteristics Sound source

Acoustic Characteristics of Sound source
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  1. Source Filter Theory
    • Acoustic theory of speech production
    • Speech is a result from a combination of sound sources and the filtering provided by the vocal tract.
    • an example of a forced vibration
  2. Sound sources
    • voice
    • turbulent vibration
    • transient vibration
  3. Sources of Energy for Sound Production
    Respiratory System
  4. Respiratory System
    provides the driving forces for both periodic and aperiodic sound production
  5. Breathing for life
    • approximately 12 times per minute
    • inspiration - active contraction of the diaphraigm and internal/external costal muscles
    • expiration - due primarily to passive forces as the elastic lung tissue gets smaller
  6. breathing for speech
    • controlled expiration
    • need for constant air pressure and flow
    • combination of muscular and elastic forces
    • timing of breaths influenced by linguitic factors
    • depth of breaths related to intensity, deeper for louder speech
    • valves in the upper vocal tract use air pressure and flow to create sound
  7. the larynx
    the first valve in the vocal tract. creates periodic and aperiodic sounds
  8. myoelastic-aerodynamic theory of voice production
    • vocal folds are adducted to midline, using the muscles of adduction
    • tracheal air pressure rises to a level sufficient to overcome laryngeal resistance and blow the folds apart.
    • the folds are pushed upwarndly and laterally, increasing the area of the glottis
    • vocal folds become maximally parted, resulting in a reduction in tracheal air pressure allowing the folds to return to midline
    • the process repeats itself
  9. medial compression
    • force with which vocal folds are held together
    • creates resistance to the flow of air through the glottis (space btw the vocal folds)
  10. resistance is determined by
    • medial compression
    • longitudinal compression - force with which the vocal folds are stretched (cricothyroid)
  11. glottis
    space btw the vocal folds
  12. Bernoulli forces
    suction perpendicular to air flow
  13. Elastic forces
    tissue properties of the vocal folds
  14. rest position of vocal folds
    vocal folds together
  15. rate at which vocal folds open and close
    • males 125
    • females 225
  16. glottis area function
    • shows a graph of the change in glottal area as a function of time during voice production.
    • fundamental frequency
    •   period of glottal wave
    • harmonic structure
    •   shape is saw tooth like
    • open quotient
    •   open time / (open time + close time)
  17. if the open quotient is lower, this means that
    the vocal folds are closed longer for louder sounds
  18. the glottal area function wave resembles
    • the saw tooth wave the most
    • use even and odd multiples
  19. As frequency increases the glottis
    spends more time open (less time in closed or rest position)
  20. on the glottal are range a 1 means
    that the vocal folds never quite come together
  21. the louder you talk..
    • the harder your vocal folds come together
    • which can cause swelling, polyps, etc.
  22. fundamental frequency
    • most common measure of voice
    •   relation to age
    •   relation to gender
    •   relation to musical scale
  23. phonational range and registers
    • pulse - lowest fundamental frequencies (aka glottal fry)
    • modal - range most common for speaking and singing.
    •    includes musical terms of chest and head voice
    • loft (falsetto) - highest fundamental frequencies
    • phonational range - the range that a person can produce - typically 2-3 octaves (12 semitones per octave)
  24. fundamental frequencies changes during spontaneous speech over the lifespan
    • start together
    • then both drop - males drop more significantly
    • toward end of life males increase some and females decrease some.
  25. fundamental frequency alone is..
    not necessarily a good indicator
  26. Determining range of vocal folds
    n = 39.86 x log(high f0 / low f0)

    n = # semitones
  27. measures
    • RAP = cut off .68
    • Shim = cut off 2.81
  28. fundamental frequency variability
    • long term
    •   standard deviation
    •   range (2-3 octaves)
    • short term
    •   perturbation - jitter and shimmer
  29. perturbation
    • cycle to cycle variability
    • changes from one cycle to another
  30. jitter looks at variability in terms of
  31. shimmer look at variability in terms of
  32. pulse range / vocal fry is
    the lowest fundamental frequency
  33. when someone has a voice disorder
    jitter and shimmer are expected to be higher
  34. voice quality
    • importance of harmonic structure
    • harmonics to noise ratio - quantitative measure
    • narrow-band spectograms - qualitative measure
  35. waveform
    • time between corresponding points = period (T)
    • f0 = 1/T
  36. wide band spectogram
    • same as waveform
    • vertical striations represent glottal pulses
  37. narrow-band spectogram
    • using harmonics to measure f0
    • since f0 * 10 = f10 / 10 = f0. measure f10 or the highest visible harmonic that you can accurately count and divide by 10 (or the number of the harmonic)
  38. narrow-band spectrum
    • same as narrow-band spectrogram.
    • using harmonics to measure f0
  39. automatic analysis
    use of software program to automtically measure f0