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Audiology3710
Acoustics and Psychoacoustics
| Question | Answer |
|---|---|
| What is acoustics? | the physical aspect of sound |
| What is sound? | in physical terms is an oscillation in particle displacement or pressure in a medium with internal forces |
| What is sound? | is created when some force sets an object into vibration to the extent that the molecular motion of the medium in which the object is situated occurs and a sound wave is propagate |
| What is Needed for Sound? | Source Force Medium |
| What is source? | a source of vibration a vibrator any object that can be set in motion (vibrate) can generate soun |
| What is force? | to set the source into vibration any external forc |
| What is medium? | for the transmission of motion originating at the source the medium must have mass and elasticit |
| What is mass? | the medium must have some degree of mass or density i.e., so many molecules or particles per unit are |
| What is elasticity? | the medium must be elastic i.e., must have the ability to regain its normal degree of density if its normal degree of density is disturbed or altere |
| How is sound transmitted? | it is the movement or motion of the molecules in the medium that transmits sound in air, the air particles/molecules movement of the air particles is the sound wav |
| Examples of vibratory motion | Examples of vibratory motion See-Saw Pendulu |
| What is a vibratory motion? | plotted moment to moment displacement from resting/starting position i.e., displacement from resting/starting position as a function of time |
| What is a vibratory motion? | movement will continue as long as the force is applied or sufficient energy (kinetic and potential ) is present to continue motion |
| What are the attributes of vibratory motion? | Cycle Period Frequency |
| What is a cycle? | one complete to and fro motion around the position of rest pendulum and see-saw went through one cycle of motion |
| What is frequency? | one complete to and fro motion around the position of rest pendulum and see-saw went through one cycle of motion |
| Examples of low and high frequency motion? | slow moving objects have a low frequency motion pattern fast moving objects have a high frequency motion pattern |
| What is period? | time required to complete one cycle of motion low frequency motion has a long period high frequency motion has a short perio |
| Realtionship b/w Period and frequency | there is an inverse relationship between frequency and period if you know the period, can calculate frequency since F=1/T if you know the frequency, can calculate period since T=1/ |
| To determine period: | T = 1/F where T= period in seconds F= frequency in cycles per second Example: if F = 1000 cycles per second, then T = 1/F T = 1/1000 cycles per second T = .001 seconds (one cycles lasts .001 seconds) |
| To determine frequency: | F = 1/T where F= frequency in cycles per second T= period in seconds Example: if T = .001 seconds, then F = 1/T F = 1/.001seconds F = 1000 cycles per second |
| Milliseconds | one thousand of a second 1000 msec in a second msec / 1000 = seconds seconds X 1000 = msec Remember: its is cycles per second Not, cycles per msec. |
| Hertz | Heinrich Rudolph Hertz (German physicist, 1857-1894) one cycle per second = one Hz 1000 cycles per second = 1000 Hz |
| Kilohertz | one thousand Hz 1 kHz = 1000 Hz .5 kHz = 500 H |
| Octaves | consist of six tones or 12 semitones doubling or halving of frequency e.g., 500 Hz and 2000 Hz would be octaves of 1000 Hz |
| what are the types of motion patterns | can be period can be aperiodic can be simple or complex |
| Periodic motion patterns | regularly repeats itself i.e., has a definable period can be simple or complex |
| Simple Period Motion Patterns | also referred to as: simple harmonic motion sinusoidal motion sine wave motion most elementary form of motion can be describe as plot of uniform circular motion |
| Complex Motion Patterns | Complex Periodic Motion periodic motion non-sinusoidal motion Complex Aperiodic Motion non-periodic motion non-sinusoidal motion Will talk about complex motion later |
| How sound waves are propagated? | it is the movement of the molecules/particles in the medium that is responsible for the propagation of sound |
| How are particles displaced? | particles next to the sound source are displaced or set into motion these particles in turn set the particle adjacent to them into motion particles move in the direction in which the force is applied |
| How are particles displaced? | if the medium is elastic, when the force is removed, the particles tend to return to their original (resting) position |
| What is the velocity of particle displacement? | the speed at which particle displacement occurs in air, approximately 1130 feet per second or 300 meters per second |
| What does the inverse square law state? | defines the rate at which the energy or amplitude of displacement decays energy decays at a rate determined by the inverse of the square of the distance traveled |
| Examples of the inverse law square law? | example Does a sound ever completely cease to exist? |
| What are the areas of displacement | compression rarefaction |
| What is compression? | part of the sound wave where the air particles are forced together air pressure is a function of particle density (particles per unit area) area of increased density and thus greater atmospheric pressure |
| What is rarefaction | when forced is removed, separation of air particles occur area of decreased density since there are fewer air particles per unit area area of less than atmospheric pressure |
| What is a sound wave? | a pressure wave alternating areas of compression and rarefaction compression: increased particle density, increased PATM rarefaction: decreased particle density, decreased PATM |
| Important points to remember: | alternating areas of compression and rarefaction air particles stay in a limited area degree of displacement from resting position - determined by force |
| Important points to remember: | degree of displacement decreases as distance from source increases – Inverse Square Law the velocity of particle displacement – determined by the speed of sound movement of air particles will be the same as source – simple or complex |
| What is a wavelength? | distance between the adjacent areas of compression and rarefaction inversely related to frequency Formula: = V/F = wavelength V = velocity F = frequencyExamples of Waveleng thus, as frequency increases, wavelength decrease |
| What is amplitude? | waveform – amplitude as a function of time up to this point, we have focused our attention on things along the X or time axis now we will focus our attention on things along the Y or amplitude axi |
| What is amplitude? | strength of signal level magnitude intensity |
| How to measure amplitude? | peak amplitude peak-to-peak-amplitude rms amplitude |
| How to measure RMS Amplitude? | a percentage of peak amplitude a more fruitful way to measure amplitude RMS – root mean square a SD measure also can be calculated by multiplying peak amplitude by .707 |
| What is intensity? | intensity is the strength of particle vibration the strength of particle vibration can be measured using: units of pressure - in dynes/cm2 or uPa units of power flow - in watts/cm2 |
| Human sensitivity? | range of pressures or powers that the human ear is sensitive to is quite large in power flow: 10 -16 watts/cm2 to 10 -2 watts /cm2 in pressure: .0002 dynes/cm2 to 2000 dynes/cm2 20 uPa to 200,000,000 uPA ratio of 1 to 10 milli |
| What is the Decibel? | dB named in the honor of A.G. Bell basic unit of intensity measurement represents the log of the ratio between a given sound power or pressure and a well defined power or pressure is a calculated value |
| What is dBIL? | dB Intensity Level uses units of power flow in watts/cm2 formula: dB IL = 10 x log I x / I r I x = measure sound power I r = reference sound power I r = 10 -16 watts/cm2 |
| What is dB spl? | dB Sound Pressure Level uses units of pressure in: dynes/cm2 uPa formula: dBSPL = 20 x log Px / Pr Px = measure sound pressure Pr = reference sound pressure Pr = .0002 dynes/cm2 or 20 uPA |
| What does dB=0? | 0 dB does not mean no sound 0 dB means: the ratio between the measured sound power or pressure is equal to the reference sound power or pressure log of 1 is 0 |
| What is a spectrum? | used to plot amplitude as a function of frequency |
| What are Simple Periodic Waveforms? | sound that results from simple periodic movement composed of energy at a single frequency |
| What are complex waveforms? | sound that results from complex movement/vibration composed of energy at a number of frequencies at various intensities two types: periodic and aperiodic |
| What are complex periodic waveforms? | non-sinusoidal but having a definable period resulting sounds consist of several frequency components with each component being a whole number multiple of the lowest frequency component |
| What is the Fundamental Frequency? | lowest frequency component is called the fundamental frequency or Fo |
| What is the use of the Fourier Analysis? | used to analyze a complex periodic wave find Fo and other frequency components |
| What is an aperiodic waveform? | complex movement with no definable period sounds that result from complex aperiodic vibration consists of several frequency components that are not related mathematically Can’t do Fournier Analysis |
| What is phase? | refers to the relative positioning in time of two or more stimuli |
| What is constructive interference? | when two sounds are in phase exactly the two sounds will interfere with each other in a manner that results in a single sound having an amplitude greater than either of the two individual sounds have an addition of amplitud |
| What is destructive interference? | two sounds are exactly out of phase i.e., 180 degrees out of phase, have destructive interference the result will be zero subtraction of amplitude since one wave will be in compression while the other is in rarefaction |
| How is a beat formed? | if two sounds are separated by half a cycle i.e., 90 degrees out of phase, will have both constructive and destructive interference |
| What are psychoacoustics? | the study of the relationship between an acoustic signal and subjective awareness answers the question “What can humans hear and what do they hear?” |
| Detection, discrimination and identification | Task 1. Did you hear it? 2. Describe the sound’s pitch and loudness 3. Can you name the sound? Ability 1. Detection 2. Discrimination 3. Identification |
| How is sound defined? | in psychological terms sound is the auditory sensation evoked by the propagation of “sound waves” |
| Human sensitivity to Frequency | 20 to 20,000 Hz Audible Range 500 to 8000 Hz Most Sensitive Range 500 to 2000 Hz Range Most Important for Speech Reception infrasonic Below 20 Hz ultrasonic Above 20,000 Hz e.g., bats |
| What are the differences between frequency and pitch? | physical vs. psychological (subjective awareness) as the frequency of sound increases, we perceive an increase in pitch |
| What are the differences between frequency and pitch? | as the frequency of sound decreases, we perceive a decrease in pitch not always a one-to-one ratio; frequency is absolute, pitch is relative |
| Human sensitivity to intensity | 0 dB to 140 dB 0 dB Threshold of Hearing 20 dB Threshold of Speech 120 dB Threshold of Discomfort 130 dB Threshold of Tickle 140 dB Threshold of Pain |
| What are the differences between intensity and loudness? | also, loudness can change even if intensity remain constant by changing another parameter of the sound e.g., frequency, duration, etc. will demonstrate in lab |
| Tangible Examples of Phase | beats standing wav |
| How is the Human Audibility Curve formed? | results from measuring the sensitivity of the human ear to different frequencies of sound plots the threshold of hearing (in dBSPL ) as a function of frequency |
| How is the Human Audibility Curve formed? | threshold – the lowest intensity level of a sound an individual can detect 50% of the time |
| What is the human audibility curve? | otologically normal hearing listeners between the ages of 19 and 26 years no history of ear disease no history of prolonged exposure to high intensity sound |
| What does the human audibility curve reveal? | reveals that the ear is not equally sensitive to all frequencies of sound i.e., need more intensity at some frequencies to detect the presence of the sound than at other frequencies differential sensitivity at hearing threshold |
| Three ways to measure human audibility | Minimal Audible Field (MAF) Minimal Audible Pressure (MAP) Coupler Pressure |
| What Minimal Audible Field (MAF) measures? | The intensity of sound needed to reach threshold with the individual listening in the sound field threshold is defined as the intensity of the sound measured at the listeners ear needed to reach threshold monaural condition binaural con |
| What Minimal Audible Pressure (MAP) measures? | the intensity of sound needed to reach threshold with individual listening with earphones threshold is defined as the intensity of the sound measured at the ear drum needed to reach threshold always monaural |
| What are the differences between MAF and MAP? | Sensitivity to Frequency MAF - human ear most sensitive at approximately 3800 Hz MAP - human ear most sensitive at approximately about 1000 Hz Sensitivity to Intensity MAF - binaural advantage of 3 dB MAF (monaural) vs. MAP - 6 dB adv |
| What coupler pressure measures? | the intensity of sound needed to reach threshold with individual listening with earphones threshold is defined as the intensity of the sound measured in an artificial ear needed to reach threshold |
| What is use to measure coupler pressure? | artificial ear is an NBS 6cc coupler used to establish Standards of Normal Hearing or Audiometric Zero or dBHL |
| Standards of Normal Hearing | ASA (1951) ISO (1964) ANSI (1969) |
| ANSI Standards of Normal Hearing (average hearing threshold for otologically normal hearing young adult) | at 125 Hz, 0dBHL = 45.5 dBSPL at 250 Hz, 0dBHL = 24.5 dBSPL at 500 Hz, 0dBHL = 11.5 dBSPL at 1000 Hz, 0dBHL = 7.0 dBSPL at 2000 Hz, 0dBHL = 8.5 dBSPL at 4000 Hz, 0dBHL = 9.0 dBSPL at 8000 Hz, 0dBHL = 13.0 dBSPL |
| What is the dB Hearing Level? | reference is normal hearing re: ANSI clinical decibel refers to the increase in the intensity of sound above normal hearing that is required to reach threshold used to measure hearing loss - deviation from normal hearing |
| What is the dB Hearing Level? | REMEMBER: dBHL means deviation from normal Problems: 20 dBHL equals how many dBSPL at 500 Hz? at 4000 Hz? 40 dBSPL equals how many dBHL at 1000Hz? at 250 Hz? |
| What is dB Sensation Level? | reference is an individual’s own hearing threshold used to describe the relationship between a stimulus and an individual’s hearing threshold |
| What is loudness level? | audibility curve reveals that the human ear is not equally sensitive to all frequencies of sound at threshold Does this remain true above threshold? to determine, use loudness level |
| What is loudness level? | Loudness Level of a frequency is equal to the level in dB of a 1000 Hz tone to which that frequency has been judged equally as loud measured in phons e.g., 10 phon means that a sound would be perceived as loud as a 1000 Hz, 10 dBSPL tone |
| How is loudness level determined? | experimental protocol and Equal Loudness Contours or Phon Lines |
| How Equal Loudness Contours or Phon Lines work? | link sounds that differ in frequency and intensity but would be perceived as being equal in loudness |
| What Equal Loudness Contours or Phon Lines reveal us? | sensitivity of the ear changes as intensity increases above threshold, i.e., above threshold the ear becomes more equally sensitive to frequency i.e., above threshold, equal intensity results in equal loudness |
| At 60 dBspl What Equal Loudness Contours reveal? | at 60 dBSPL , the ear is equally sensitive to the frequencies that compose the speech range 60 dBSPL corresponds to normal conversational leve |
| At 120 dBspl What Equal Loudness Contours reveal? | at 120 dBSPL , the ear becomes equally sensitive to all frequencies of sound |
| What is the difference between hearing and listening ? | Hearing – the ability to have access to acoustic information Listening – hearing with attention and intention |
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carolinazs
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