Post on 12-Feb-2016
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An important point…• When discussing source-filter theory, the sound
source was the glottal spectrum• When discussing stops (and fricatives and
affricates), we introduce a new sound source, noise produced within the oral cavity
• However, source-filter theory still holds even though the sound source is different…the vocal tract still filters the sound source, whether it is the complex periodic signal from vocal fold vibration, or a transient aperiodic signal produced during a stop release
Unit 4The Articulatory System II
I. The DiphthongsII. The GlidesIII. The LiquidsIV. The StopsV. The FricativesVI. The AffricatesVII. The Nasals
Fricatives
• Place– Labiodental /f/ /v/– Interdental // //– Alveolar /s/ /z/– Palatal // //– Glottal /h/
• Voicing– Voiced /v/ // /z/ // – Voiceless /f/ // /s/ // /h/
Fricatives
• Manner of production– severe vocal tract constriction– Air pressure behind constriction builds up– Air flow through the constricted path is very
high– At a critical point, the airflow becomes
turbulent– Turbulent flow is heard as noise – frication
Fricatives
• Aerodynamics• Airflow for vowels is laminar – molecules are
moving along in an orderly fashion (like the flow of water in a river or cars on the freeway)
• Airflow for fricatives is turbulent – molecules are moving is a disorderly way – (like the eddies of water when a large rock impedes the river’s flow)
Fricatives
• The physics of turbulence• For a given constriction/obstruction, there
is a critical flow velocity above which turbulence occurs -Reynolds number
Fricatives
Equation for turbulence
Re= V*h/– Re: Reynolds number– V: flow velocity : kinematic coefficient of viscosity (.15 cm/sec for air)– h: characteristic dimension (size of constriction)– Critical Re for speech ~1800
Fricatives
• In theory, the spectral characteristics of “white” noise, which has all frequencies in equal amplitude
• sound source characteristics should be the same regardless of place of articulation
Fricative source spectrum
Frequency
Am
plitu
de
Fricatives
• Question…• How do we distinguish different fricatives if
the sound source is the same?
Fricatives
• Answer…• The transfer function of the vocal tract will
shape the otherwise flat spectrum
Fricative: Vocal tract features
Fricative: Vocal tract features
• Vocal tract has – a back cavity (behind the constriction)– a front cavity (in front of the constriction)– Front cavity plays a more important role in
shaping the fricative spectrum– Longer the front cavity the lower the resonant
frequencies
Fricatives:
• Labiodental/interdental• very short front cavities = very high
resonant frequencies• Practically, there is little effect on shaping
the noise energy• Low energy diffuse spectrum
Labiodental /f/
Fricatives:
• Alveolar• front cavity length ~ 2.5 cm• F1=34000/4*2.5 = 3400 Hz• Intense energy at/above 3400 Hz
Alveolar /s/
Fricatives:
• Palatal• front cavity length longer than for /s/• Intense energy around 2000 Hz• Lip rounding increases front cavity length
and helps to reduce the frequency of the prominent energy
Palatal //
// vs. /s/
// /s/
Fricatives:
• Glottal• Spectrum shaped by whole vocal tract• Low energy diffuse noise with apparent
vowel-like formant values
Glottal /h/
Voiced/voiceless distinction
• Voiced fricative have two simultaneous sound sources
• Glottal sound source (voicing)• Frication (noise)• Both sound sources are shaped by the
vocal tract shape• Voiced fricatives will have low frequency
energy in the spectrograph (voice bar)
/z/ /s/
/z/
/s/
/s/ /z/ // // - The stridents
• These fricatives have much greater energy when compared to others
• Teeth serve as an obstacle to the airflow, which increases the turbulence and amplitude of the noise energy
Transitions
• Formant transitions also play a role in fricative identity
• More prominent cue for “weak” fricatives such as /f/ and // since energy for these is typically low and diffuse
Unit 4The Articulatory System II
I. The DiphthongsII. The GlidesIII. The LiquidsIV. The StopsV. The FricativesVI. The AffricatesVII. The Nasals
Affricates
• Place: – palatal (/t/, /d/)
• Voicing:– Voiceless (/t/)– Voiced (/d/)
Affricates
• Manner of production– Features of both stop and fricative– Vocal tract occlusion– Release from occlusion into a severe
constriction– Spectral features of //– “Rise-time” of burst differs for stop and
affricates
Affricate
Silent gap frication
/t/
Rise-time: stops vs. affricates
/t/
/t/
Nasal
• Place– Bilabial /m/– Alveolar /n/– Velar //
• Manner of production– Velopharyngeal port is open– Oral cavity is closed– Sound source: glottal spectrum
Nasals
• Distinct vocal tract configuration
Pharyngeal cavity
Oral cavity (closed)
Nasal cavity (open)
Nasal
• Acoustically, nasals are characterized by – Antiformants– Nasal formant
Nasal
• Closed oral cavity produces antiformants in the transfer function
• Antiformants are regions where energy is damped
• Location of antiformants is related to place of articulation
• As place of articulation moves back, the frequency of the anti-formant increases
Nasals
• /m/:antiformants 750-1200 Hz• /n/: antiformants 1450-2200 Hz• //: antiformants > 3000 Hz
Nasals
• Nasal formant• Strong low frequency band 250-500 Hz• Most prominent acoustic feature of nasals
Nasals
• Have formant transitions similar to oral stops
Initial position• Bilabial-rising F1 and F2• Alveolar-rising F1 and dropping F2• Velar-F2 and F3 “C” shaped
Nasals
bilabial alveolar velar
XI. THE NASALS
A. Define an antiformant and how their values change with place of articulation.
B. Draw the vocal tract configuration for a nasal.
C. What is a nasal formant?
Outline: ArticulationI. THE VOCAL TRACTII. SOURCE FILTER THEORY OF SPEECH
PRODUCTIONIII.CAPTURING SPEECH DYNAMICSIV. THE VOWELSV. THE DIPHTHONGSVI. THE GLIDESVII. THE LIQUIDSVIII. THE STOPSIX. THE FRICATIVESX. THE AFFRICATESXI. THE NASALSXII. PUTTING IT ALL TOGETHER: STUDYING
CONNECTED SPEECH PROCESSES
Name those acoustic events!
XII. PUTTING IT ALL TOGETHER: STUDYING CONNECTED SPEECH
PROCESSESA.Identify how coarticulatory processes may
be revealed in speech-related signals.B.Distinguish between the phonetic properties of
speech and suprasegmental features of speech.C.Identify and describe suprasegmental properties
of speech.D.Identify some key “problems” features that
speech production theories must address. E.Describe how speech disorders may be revealed
in articulatory processes.
What is coarticulation?
What is coarticulation?
• “An event in speech production in which adjustments of the speech production system are made simultaneously for two or more speech sounds” (Kent)
What is coarticulation?
• In other words, the features of speech elements will vary depending upon the context in which they are produced
Terms used that refer to this general concept
• Coarticulation• Coproduction• Contextual variation
Kinds of coarticulation
• A speech event can be influenced by a previous event
OR
• A speech event can be influenced by an upcoming event
Coarticulation
• Anticipatory (right-to-left) coarticulation– A segment’s features are influenced by
upcoming segment
S1 S2
Coarticulation
• Carryover (left-to-right) coarticulation– A segment’s features are influenced by a
previous segment
S1 S2
Examples of anticipatory coarticulation
• Lip protrusion has been observed three (or more) consonants in advance of a rounded vowel
• e.g. /stu/ (“stew”) will exhibit lip rounding through the /s/ and /t/
An (in)famous coarticulation study
Anticipatory coarticulation: Some implications from study of lip rounding
byFredericka Bell-Berti & Katherine Harris
Haskins LaboratoryNew Haven CT
Published in JASA Vol 65(3) 1979
Examples of anticipatory coarticulation
• Velopharyngeal opening can occur two vowels in advance of a nasal consonant
• e.g. /an/ will exhibit V-P opening during the /a/
Examples of anticipatory coarticulation
• Jaw opening for an open vowel may be observed two consonants in advance of the vowel
Examples of carryover coarticulation
• Velopharyngeal opening can continue into a vowel following a nasal consonant
• e.g. /nat/ will exhibit V-P opening during the /a/
Why is there coarticulation?
• Articulators cannot make quantum leaps from one static position to another
Carryover coarticulation
A possible reason?• Articulator are ‘sluggish’ and it takes time
to move on to the next sound
Anticipatory coarticulation
A possible reason?• Articulator are ‘sluggish’ and it takes time
to move on to the next sound
Suprasegmentals
• Intonation• Stress• Duration
Intonation
• Manner in which Fo is varied to mark linguistic aspects of speech
• Fo/pitch contour• Rise-fall pattern typical for declarative
sentences• Start-frequency - variable• End-frequency - stable
Sound pressure waveform
Fo contour
start Foend Fo
Intonation
• End-frequency may be related to the physiology of phonation
• Completing a speech breath – Psg is lower ~ lower Fo
But, this doesn’t have to be the case…
Intonation
• Questions are marked by a rising Fo contour
• Can override patterns for linguistic purposes
Stress
• Not the kind of stress you get around exam time
• Stress is applied to parts of speech• For example,
– Lexical stress– Emphatic stress
Stress
• Stress typically marked by– Higher Fo– Higher intensity– Longer duration– Vowels will be more clearly articulated than
unstressed– Perception of stress will result from some
combination of these acoustic features
Duration
• The length of speech sounds• Why are sounds as long as they are?
– Physical requirements of their production– Phonetic distinction (i.e. vowel length)– Context in which they are produced– Overall rate of speech