11 - Acoustics 1 Flashcards
Name one reason acoustics are important for speech
- can provide objective physical measure of speech disorders
- can i.d. specific parameters of disordered speech
- non-invasive, inexpensive, tech-friendly, readily available (e.g. Praat)
- can be used to make fairly reliable inferences about certain physiological events
- specific disordered acoustics parameters can be used for differential diagnosis, targets in treatment, biofeedback therapy, and treatment outcome measures
As sound moves through air, it stimulates air particles to experience compression and ______
Rarefaction
Is the velocity of particles greater at points of compression or rarefaction?
Rarefaction
Wavelength = ______ / frequency
velocity of sound
If a tone is presented at 200 Hz, what would the next 3 harmonics be?
400, 600, 800
What is the roll off rate for speech?
12 dB per octave
Output = source x radiation x ______
filter
The output is a combination of harmonics and ________
Formants
What two things do formants depend on?
Vocal tract length
Cross-sectional shape of vocal tract
What are formants?
Resonance frequencies of the vocal tract
Describe the “odd quarter wavelength relationship”
With a uniform tube closed at one end (like vocal tract being closed at vocal folds):
- “odd” refers to the formants being at odd multiples of the lowest resonance frequency
- “quarter wavelength” refers to the areas of maximum velocity (antinodes, best resonance)
In the formula to find a formant:
F=((2n-1) x c)/4L
what do n, c, and L refer to?
n = formant number (e.g. first formant is 1) c = speed of sound (34,400 cm/sec) L = tube length (17 cm vocal tract)
A node is a point of volume velocity ______ (minima/maxima)
Minima
Perturbation Theory stipulates that constricting a tube at volume velocity maximum causes a(n) _______ (reduction/increase) in frequency of the related formant
Reduction
What is the frequency of the most prominent nasal formant?
300 Hz (lower than 500 Hz for vocal tract because essentially lengthens vocal tract from 17 cm to 29 cm)
How do you get turbulent noise?
Generate high velocity air through constriction of vocal tract, causing eddies
__________ is the term for the critical flow velocity at which turbulence occurs (shift from laminar to turbulent flow)
Reynolds number
What is the critical Re value for turbulent speech noise?
Re = 1800
A ______ (smaller/larger) cross sectional area requires less flow velocity to achieve the critical Re
smaller
How are turbulent fricative noises shaped (filtered)?
By the resonating properties of the oral cavity in front of the occlusion
The Source Filter Model of speech acoustics includes what 3 sources?
- voicing
- turbulent noise
- transient bursts
Name 1 of the 3 considerations related to vocal tract length?
- lip protrusion
- laryngeal lowering
- children’s vocal tracts
How does nasal resonance influence the first formant?
Lower first formant (300 Hz) related to an increased length of the vocal tract
How do damping effects relate to nasal resonance?
Formants tend to have lower amplitudes (related to the nasal tissues acting as sound absorbers)
How does nasal resonance influence antiformants or zeros?
- nasals are produced with a bifurcation (splitting) of the vocal tract into 2 sections:
- open nasal cavity
- closed oral cavity - acts as sound absorber for specific frequencies (absorbed frequencies referred to as zeros/antiformants and appear as large valleys in amplitude/frequency spectra
The further back the place of articulation, the ____ (lower/higher) the frequency of the nasal zero
higher
Each of the 3 places of articulation for nasal resonance are associated with specific zero values. What are the 3 nasal sounds of articulation?
/m/: 750-1250 Hz
/n/: 1450-2200 Hz
‘ng’: >3000 Hz
Which types of phonemes are associated with turbulent noise?
Fricatives
Affricates
Stops
How is turbulent noise generated?
- noise generated by air passing through narrow constriction
- narrow constriction causes jet to form, which generates eddies (irregular rotations of air pressure and velocity)
- these eddies are referred to as turbulence, which generates random frequencies of sounds or noise
What is the formula for Re (value to determine turbulence)?
Re = (flow velocity/cross sectional area) / viscosity constant for air
How is fricative resonance related to turbulent noise?
The turbulent fricative noise is shaped (filtered) by the resonating properties of the oral cavity in front of the occlusion
e. g. for /s/ and ‘sh’ the resonator acts like a very short tube closed at one end
- this short tube results in a very high resonance (first formant) frequency, thus each fricative has specific resonance frequencies
How do resonance frequencies relate to posterior place of oral constriction (e.g. ‘s’ vs ‘sh’)?
Resonance frequencies decrease with posterior place of oral constriction
Fn = (2n-1) * c / 4L where L=2 cm (/s/) F(1) = (2(1)-1) * 34,400 / 4*2 F(1) = 34,400 / 8 F(1) = 4300 Hz
