Speech Science Week Three
Speech Science Week Three SLP5120
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This 6 page Class Notes was uploaded by Freya Kniaz on Sunday September 18, 2016. The Class Notes belongs to SLP5120 at Wayne State University taught by Li Hsieh in Fall 2016. Since its upload, it has received 8 views. For similar materials see Speech Science in Linguistics and Speech Pathology at Wayne State University.
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Date Created: 09/18/16
Speech Science Week Three Chapter One: The Nature of Sound I. Introduction A. Speaking requires multiple levels of perception, cognition, and neuromotor function. B. Acoustics: branch of physics that deals with the production, control, transmission, reception, and effects of sound. C. Bioacoustics: combination of biology and acoustics in the study of sound production and perception in animals (including humans) D. Speech is a p hysical phenomenon II. Basic Physics Concepts A. Mass (g or kg): amount of matter in an object B. Force (newton): any influence that causes an object to undergo a change in speed, direction, or shape; mass x force = acceleration C. Weight (newton): force of gravity on an object D. Volume (liter): quantity of threedimensional space occupied E. Density (g/cm3): mass per unit of volume F. Speed (m/s): distance traveled in a given unit of time G. Velocity (m/s): distance traveled in a given unit of time in a specific direction H. Momentum (kgm/s): mass times velocity of an object during motion I. Acceleration (a=F/m): change in velocity as a function of time J. Inertia (g or kg): resistance of an physical object to a change in its state of motion or rest K. Elasticity: property of a material that returns it to its original shape after it has been deformed by an external force (stress) L. Deformation: change in the shape or size of an object due to an applied force M. Strain: relative amount of deformation undergone by an object N. Stiffness: resistance of an elastic body to deformation by an applied force O. Work: force exerted over a distance (force x distance) P. Energy: ability to do work Q. Power: rate of work done or energy used in a period of time (work/time) R. Pressure: force acting on a specific surface area (force/area) III. Overview of Sound: sound occurs when a disturbance creates changes in pressure in a gas, liquid, or solid medium. IV. Air A. Brownian motion: due to their thermal energy air molecules constantly move around in random patterns and at extremely high speeds B. Pressure that is higher than atmospheric pressure is called positive pressure while pressure that is lower than atmospheric pressure is negative pressure. C. Air always moves from an area of high pressure to an area of lower pressure 1. It is the difference is pressure (pressure differential) which causes the air to flow and creates a driving pressure. D. Flow: movement of air through a particular area in a certain interval of time E. Volume velocity: rate of flow 1. Laminar flow: air that flows smoothly with molecules move in a parallel manner at the same speed 2. Turbulent flow: occurs when an obstacle in its way disturbs the flow 3. Vowels are produced with laminar flow while fricatives are produced with turbulent flow F. There is an inverse relationship between air volume and pressure; there is a direct relationship between air pressure and density G. Boyle’s Law: P V = P V 11 22 H. See Table 1.3 V. Sound: Changes in Air Pressure A. Air molecules undergo Brownian motion, creating a relatively steady pressure called ambient pressure B. Compression: an area of positive pressure in the wave C. Rarefaction: an area of negative pressure in the wave D. Hooke’s law: the restoring force is proportional to the distance of displacement and acts in the opposite direction E. Damping: each time the molecules move back and forth around their equilibrium positions, they do so with slightly less amplitude F. Sound wave motion is longitudinal G. Wave front: the outermost of a sphere area of compression around the vibrating source is followed by an area of rarefaction H. Inverse square law: the farther the changes in air pressure travel from the source, the more damped they become because the area of the wave front is directly proportional to the square of its distance from the source I. Simple harmonic motion: movement of vibration of the tuning fork and the movement of the mass/spring system J. Frequency: number of cycles that occur in one second; measure in Hertz K. Period: time it takes for one complete cycle to occur; measurement is in seconds L. Wavelength: distance covered by one complete cycle; measure in meter M. Amplitude: the maximum displacement from position to rest N. Periodic: a wave in which every cycle takes the same amount of time to occur as every other cycle O. Aperiodic: a wave in which individual cycles do not take the same amount of time, it cannot have a specific frequency, like noise VI. Pure Tones A. Pure tone: wave with only one frequency and is graphed as a sinusoidal wave B. Waveform: graph with time on the horizontal axis and amplitude on the vertical axis C. See Table 1.10, page 22 VII. Complex Sounds A. Complex sounds: characterized by waves that consist of two or more frequencies B. Periodic complex sounds consist of a series of frequencies that are systematically related to each other 1. Fundamental frequency: lowest frequency of the sound 2. Harmonic frequency: frequencies above the fundamental frequency, they are whole number multiples of the fundamental frequency C. All vowel sounds are complex and periodic D. Fourier analysis: process of identification of the harmonic in a comple periodic sound E. Aperiodic complex sounds also consist of two or more frequencies but the frequencies are not systematically related to each other; rather a broad range of frequencies make up the sound F. There are two kind of aperiodic complex sounds, differentiated on the basis of duration 1. Continuous: sounds that are able to be prolonged 2. Transient: extremely brief in duration 3. Voiceless fricatives are complex continuous aperiodic sounds, voiceless stops are complex aperiodic transient sounds G. Line spectrum: shows harmonics; the horizontal axis represent frequency and the vertical axis represents amplitude 1. Can show whether a sound is a pure tune (has one line) or a complex sound (more than one line) 2. No used to represent complex aperiodic sounds because these sounds are characterized by broad bands of frequencies H. Harmonic content: relationship between the frequencies in the sound and their respective amplitudes, shown on a line spectrum I. Continuous spectrum: Envelope of the wave is shown as a horizontal line that is understood to connect all the component frequencies in the sound 1. Not possible to tell if the sound is continuous or transient VIII. Sound Absorption, Reflection, Refraction, and Diffraction A. Incident wave: a sound wave generated by a vibrating source B. Absorption: damping of a wave, with diminishing changes in air pressure, boundaries differ in the amount of sound energy they absorb 1. Soft and/or porous surfaces are more absorbent while hard/smooth surfaces are less absorbent C. Reflection: some portion of the sound that is not transmitted or absorbed bounces back from the surface of the boundary and travels in the opposite direction of the incident wave D. Refraction: when a wave changes direction because of a local difference of temperature in the air 1. A temperature difference will cause the wave to refract toward the cooler air E. Diffraction: change in direction as a wave passes through an opening or travels around an obstacle, the longer a wavelength of the sound the more the wave diffracts. IX. Constructive and Destructive Interference A. Interference: incident and reflected waves combining with each other at any instant in time and space B. Constructive interference: combination produces greater deviations from normal Pamand therefore increased amplitude of the wave C. Destructive interference: an area of compression of one of the waves combines at exactly the same time with an area of rarefaction of the other wave, the amplitude of the resulting wave will be decreased D. Phase: relative timing of areas of high and low pressure in waves E. Reverberation: sound lasts slightly longer because of the interference; happens when a reflected sound wave arrives at one’s ear slightly delayed in time compared with the arrival of the incident wave at the same point 1. Can be desirable because it can increase the intensity of the sound reaching a listener 2. However, too much reverberation can interfere with communication by making the phonemes blend together and become garbled X. Attributes of Sounds A. The frequency of a vibrating object depends on its physical characteristics such as its length, thickness, density, and degree of stiffness or tension B. The range of frequencies that humans are capable of perceiving is around 20 to 20,000 Hz 1. Subsonic: frequency below range 2. Supersonic: frequency above range C. The decibel scale is designed to measure sounds in a way that takes into account their amplitudes and intensities in relation to how the sound is perceived in terms of loudness 1. It is a logarithmic scale: has the effect of compressing the trillions of intensities into a scale with far fewer levels 2. It is also a ration scale: it compares the relationship between the amplitudes and a standard reference sound a) The standard reference sound has a specific amplitude and a specific intensity → indicates the softest sound of a particular frequency that a pair of normal human ears can hear 50% of the time under ideal conditions b) The decibel unit is dimensionless unless it is anchored to a referent 3. Advantages: huge ranges of intensities are condensed, and the relationship between the decibel scale and absolute values of pressure/intensity is very similar to physiological function of the human auditory system D. Linear scale: scale in which unites are the same distance from each other, and units can be added or distracted E. Auditory area: graph that represent frequency along the horizontal axis and intensity along the vertical axis F. Threshold of pain: any frequency with an intensity around 130 DB will cause a sensation of pain G. Audiogram: way of representing an individual’s hearing by measuring his or her threshold at selected frequency levels 1. Plotted with frequency on horizontal access and dB on vertical axis 2. Normal hearing is typically better than or equal to 20dB Chapter Two: Resonance I. Introduction A. Resonance: tendency of a system to vibrate with greatest amplitude in response to a frequency that matches or comes close to its own natural frequency B. Natural frequency: frequency at which an object vibrates freely and is determined by the object’s length, density, tension, and stiffness C. Forced vibration is the basis of resonance D. Example: Figure 2.1, page 47 1. Tuning fork one supplies the applied or driving frequency 2. Tuning fork two is the resonator E. Resonant frequency: frequency at which the resonance occurs II. Acoustic Resonance A. Acoustic resonance occurs when an airfilled container or cavity is forced to vibrate by an applied frequency or frequencies B. Resonance within a tube occurs in such a way that some points along the wave vibrate with minimum amplitude (called nodes) and others vibrate with maximum amplitudes (called antinodes) C. Halfwave resonator: the areas of greatest pressure always occur somewhere within the tube but never at the ends D. Quarterwave resonator: tube that is open at one end and closed at the other (only one quarter of a wavelength can fit into the tube at any specific time E. Standing wave: the incident and reflected waves are identical and travel in opposite directions, so their areas of positive and negative pressure occur at the same time and location within the tube; wave therefore gives the appearance of being stationary F. Bandwidth: the range of frequencies that a resonator will respond to G. Narrowly tuned resonator: responds slowly to the driving frequencies H. Broadly tuned resonator: responds quickly to the applied frequencies, but the vibrations will also fade more quickly, it is heavily damped, common in hearing applications I. Cutoff frequency: defined as the point where the intensity transmission is reduced by one half, at which point the resonant system is considered to be unresponsive 1. 3 dB down point/halfpower points J. Resonance curve: graph that shows the way in which the resonator vibrates in response to any applied frequency 1. Center frequency: resonant frequency 2. Upper cutoff frequency: frequency above center frequency at which there is 3 dB less of response of the resonator 3. Passband: the frequencies between center frequency and upper cutoff frequency 4. Attenuation rate:the rate at which the resonator’s amplitude of response is attenuated K. Lowpass filter responds to acoustic energy below a specific upper cutoff frequency L. Highpass filter responds to acoustic energy above a designated lower cutoff frequency M. Bandpass filter passes energy in a particular range of frequencies between center frequency and upper cutoff frequency N. Bandstop filter attenuates frequencies within a particular range III. Vocal Tract Resonance A. The vocal tract is a tube filled with air and therefore an acoustic resonator B. The vocal tract can be thought of as a tube that is closed at one end (glottis) and open at the other (lips) → quarter wave resonator C. Each separate container of the vocal tract has its own resonating frequency therefore it is a variable resonator D. Formants: resonant frequencies of the vocal tract E. Like all complex periodic sounds, the glottal sound has a specific formant zero and harmonic that are whole number multiples of the fundamental 1. Human sounds always have the same formant zero F. Read SourceFilter Theory section on page 61 G. The vocal tract must change its shape in order to change resonance characteristics: length, location of construction, and degree of constriction H. The longer the resonator, the lower its RFs and vice versa I. The output spectrum of each vowel is different because different harmonic in the glottal source have been amplified or attenuated, depending on how to vocal tract resonances have changed J. There is an inverse relationship between formant one frequency and tongue height: the higher the tongue position, the lower the formant one frequency K. Formant two is related to the length of the oral cavity that is, the space in front of the tongue construction for the vowel L. Formant 1 and Formant 2 plots on page 67
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