Acoustics final ch. 4 and 5
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What is acoustic ouput for speech determined by?
- source characteristics
- the transfer function of the vocal tract
- the radiation characteristic as the sound moves from the enclosed vocal tract to the environment
What is a transfer function?
tells you what will happen to certain frequencies- how energy is transferred from input to output
How do you create a model of a vowel?
- start with a tube of:
- uniform cross-sectional diameter
- open at one end and closed at the other
- set length of tube to be appropriate for an adult male or female (male- 17 cm, female- 14.5 cm, child- 8.75 cm)
- the output will resemble the vowel "uh"
- this model is valid out to 5 kHz
- *long wavelengths act the same way in a straight line as they do in a curved tube
What are resonances in relation to a tube?
- a function of the length of the tube
- best excited at a frequency of 1/4wavelength (f = c/wavelength)
- odd multiples of this lowest resonant frequency
- changing with changes in the length (men vs women, adults vs children, Fn = (2n-1)c/4l)
- resonant frequency will occur at the odd quarter length formula
- /uh/ has least amount of constriction
What is lip radiation?
- the mouth opening is a boundary
- higher frequencies are resonated with greater amplitude than lower frequencies (atmosphere offers greater impedance to lower frequencies which results in larger particle displacement)
What happens since there is less impedance to higher frequencies?
- displacement is not affected as much
- newton's third law of motion (for every action, there is an equal and opposite reaction)
What is the effect of lip radiation?
- **trick! (talking about atmosphere?)
- -12 dB/octave leaving the larynx
- +6 dB/octave leaving the lips
- -12 + 6 = -6 dB/octave in the atmosphere
What is a standing wave?
- a wave that remains in constant position
- constructive interference
What is reflection?
change in direction of the wave
What is destructive interference?
positive and negative values are less positive or less negative than normal and lose amplitude
Where do reflections occur?
where the lips meet the atmosphere (a boundary)
Where will there be standing waves?
at particular frequencies determined by the volume velocity (U) or pressure (P)
Where is U at a minimum and what is P there?
- at the closed end of the tube
- P is at a maximum
Where is U at a maximum and what is P there?
- at the open end of the tube
- P is at a minimum
Where do air particles vibrate most effectively?
at the open end of the tube model
Where do air particles vibrate least effectively?
at the closed end of the tube model
Where do waves vibrate better?
as they come up and out of the mouth
What happens if wavelength matches the resonances of the tube?
- vibration will be reinforced
- frequencies at which the wavelengths have a maximum velocity (or minimum pressure) at the tube opening (lips) will be transmitted most effectively (with the greatest relative amplitude)
Where do the maxima of vibration occur?
- 1/4, 3/4, 5/4, etc times the length of the tube (quarter length multiples)- the resonances of the tube
- these are the only wavelengths with the appropriate max (min) pattern
Where is there a volume velocity maxima?
Where is there a minimum amplitude of vibration?
- max amp of vibration at antinodes
What are resonances a property of?
- the vocal tract
- they exist whether they are energized or not
What do resonances do to energy?
- they modify it
- they DO NOT add energy to the speech signal
- resonances do not make you louder
What can resonances tell us?
the transfer function- tell you what will happen to that frequency whether its there or not
What are the odds that there would be a formant frequency near a harmonic?
What are constrictions created by?
What will a constriction near a node or an antinode do?
- change the frequency of the formant
- is a perturbation of the standing wave in the vocal tract
What is the relationship between contriction and perturbation?
they are used interchangeably
What happens when there is a constriction near an antinode?
- volume velocity is maximum
- pressure is minimum
- formant frequency will be lowered
What happens when there is a constriction near a node?
- volume velocity is at a minimum
- pressure is maximum
- formant frequency is raised
How is F1 affected by nodes and antinodes?
- antinode- lowered by a constriction in the oral cavity near a volume velocity maximum (lips)
- node- raised by a constriction in the pharynx
How is F2 affected by nodes and antinodes?
- antinode- lowered by a constriction (at the lips or in the oropharynx)
- node- raised by a constriction (in the anterior oral cavity)
- *pg 31
How is F3 affected by nodes and antinodes?
- antinode- lowered by a constriction (at the lips or in the middle of the oral cavity)
- node- raised by a constriction (in the oropharynx or in the anterior oral cavity
What are all three formant frequencies lowered by?
What are all three formant frequencies raised by?
a constriction near the larynx
What is point vowel?
cover range of articulations needed to produce all vowels in English
What is included in the vowel quadrilateral?
- tongue height
- tongue advancement
- lip rounding
- corner and point vowels
Do articulators affect each other?
- they have a fair degree of independence, but articulator movements affect each other
- thus, formant frequencies are a product of the entire length and shape of the vocal tract
What can two different people say the vowel /i/ and it still sounds like the same vowel?
because it's not the absolute values of the frequency that help us to distinguish, but the relationship of the formant frequencies
What is the duration for tense and lax vowels?
- tense vowels are relatively long
- lax vowels are relatively short
What are tense and lax vowels?
- a phonetic description
- supposedly correlated with articulatory effort
- actually correlated with duration
What is a diphthong?
- two vowels forming a single nucleus
- on-glide and off-glide
- should see movement in formants
What is the relationship between high vowels and findamental frequency?
high vowels have a relatively higher fundamental frequency
/How is the tongue linked to the larynx?
- when you raise your tongue, your larynx raises too (makes pitch higher)
- hypoglossus pulls larynx up for high vowels, up to a 20 Hz difference
How are consonants usually described?
in groups according to their significant acoustic and articulatory properties
What are the groups consonants fall into?
How are stop consonants characterized?
by a complete closure somewhere in the vocal tract
What are the three phases of a stop consonant?
- reverse the steps for postvocalic stops
What is a stop gap?
- corresponds to the complete closure of the vocal tract (slience)
- minimum radiated acoustic energy (silence for voiceless stops, voice bar for voiced stops, 50-150 ms*)
What is a stop release (burst)?
- pressure has been rising behind the obstruction
- rapid release produces a transient (20-30 ms)
What follows the burst for voiceless stops?
- frication (air/noise)
- low freq. for /p/ (500-1500 Hz) (falling spectrum)
- high freq. for /t/ (above 4 kHz) (rising spectrum)
- mid-freq. for /k/ (1.5-4 kHz) (peaked spectrum)
What is a transient?
a short amount of noise
What are acoustic cues?
- stop gap
- release of pressure
How are /p t k/ distinguished from /b d g/?
What is voice onset time (VOT)?
- the interval between the release of the stop and the onset of vocal fold vibration
- for /b d g/ VOT from -20 to +20 ms with a mean of 10 ms
- for /p t k/ VOT from 25 to 80 ms with a mean of 45 ms
What are some cues for voicing?
- voice bar for intervocalic stops
- length of preceding vowel for final stops
Why can voiced stops have a negative onset time?
because you are measuring from where voicing starts which is actually before the burst (it can be up to 20 ms behind where the burst is)- you make a sound before actually saying the consonant /b/ (called voice bar)
When will vowels be longer in duration?
if they are followed by voiced consonants instead of voiceless
What are formant transitions?
- articulatory movement from stop to vowel entails a formant movement
- as the resonating chamber of the vocal tract changes, the formant frequencies change
- formant transitions are important for perception
- formant transitions are approximately 50 ms in duration
Why do formants move?
you are changing your vocal tract
Why do men have lower formant frequencies than women?
their vocal tracts are longer
How does F1 move for stop consonants?
How do F2 and F3 work for stop consonants?
- for /p b/ F2 and F3 rise slightly
- for /t d/ F2 falls and F3 rises slightly
- for /k g/ F2 and F3 separate steeply and rapidly
- however, a given stop is associated with a variety of transitions (there is no fixed pattern for perception)
What are the characteristics of articulation for fricatives?
- narrow constriction in the vocal tract (not a complete closure like stops)- no moment of silence in spectrum
- when are flow rate is high, turbulence results
- turbulence is complex, unpredictable air flow
- turbulent airflow is perceived as turbulent noise
- fricatives have a relatively long duration
What are fricatives divided into?
- sibilants (stridents)- greater noise energy (s, z, esh, yogh)
- nonsibilants (nonstridents)- f, v, theta, eth, h
What is laminar airflow?
airflow is neat and organized (predictable)
What is turbulent airflow?
airflow is messy and unorganized, noise (fricatives)
How are sibilants differentiated among themselves?
- voicing- pulses (glottal closures) for /z yogh/, no pulses for /s esh/
- noise spectrum- alveolar sibilants have higher frequency energy range from 4 kHz to 12 kHz, palatal sibilants have energy down to 3 kHz, spectral irregularities aren't important in perception
What are formant transition roles for sibilants?
formant transition locations depend on the articulation, but the transitions are not important perceptually for sibilants
Does /s/ have high frequency or low frequency energy?
- /esh/ has more low frequency energy
What are nonsibilants?
- /f v theta eth h/
- less noise energy than sibilants
- voiced nonsibilants will have quasi-periodic pulses (some periodicity)
- noise spectra are fairly flat and diffuse
What is the relationship between noise spectrum nonsibilant identification?
it is not known
What is the role of formant transitions for nonsibilants?
formant transitions are primary acoustical cue (noise spectrum may play secondary role)
What are affricates?
- described as a combination of stop and fricative
- /t-esh d-yogh/
What is the articulation for affricates?
- complete obstruction in the vocal tract
- intraoral pressure builds up
- release to generate fricative noise
What are acoustic features of affricates?
- rise time- time it takes amplitude measure/envelope to go from 0 to maximum level
- duration of frication
- relative amplitude in third formant region
- stop gap- complete obstruction in vocal tract and it shows up as silence
What is the articulation for nasals?
- complete closure in vocal tract
- sound radiated through nasal cavities
- sometimes called nasal stops
What is a nasal murmur?
sound of a nasal, acoustic waveform of nasal consonants
What are acoustics of nasals?
- nasal murmur
- associated strictly with nasal radiation of sound
- there are many spectral peaks, but most have low amplitude
- antiformants- loss of energy
- nasal formant (low frequency ~300 Hz, highest energy)
Why is consonant energy reduced for nasal formant?
because higher formants have reduced energy
What is the bandwidth for nasal formants?
narrower than for vowels
What are some acoustic features of nasals?
- highly damped formants (broad bandwidths compared to other consonants)
- formant transitions in connected speech
Why are nasal sounds dampened?
because of mucous in nose
What are glide consonants?
- also called approximants and semivowels
- /w j/
What is the articulation of glides?
- gradual articulatory motion
- narrow, but not closed, vocal tract
What are the acoustics of glides?
- formants for /w/ F1 and F2 are both low
- formants for /j/ low F1 and high F2
What distinguishes between glides?
F2 and F3
How are glides like vowels?
they have formants that we can see
What are liquid consonants?
- also included as semivowels
- /r l/
What are liquids characterized by?
- rapid movements
- formant structure
- F3 is the main difference
- antiformants for /l/
How do the 3rd and 4th formant frequencies act for /r/?
How do the 3rd and 4th formant frequencies act for /l/?
What do liquids, glides, and nasals depend on?
formant frequencies (ear looks for changes)
What do stops, fricatives, and affricates depend on?
their disruption (either the complete closure or the constriction)
What do nasals depend on?
their antiformants (more than formants)
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