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133 Cards in this Set
- Front
- Back
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Any base raised to the zero power will equal ____.
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1
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Any base raised to the first power will equal _____.
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the base
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The log of 1 =___
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0
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When you divide logarithms you _______ components.
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subtract
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When you multiply logarithms you _______ components.
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add
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When you ________ logarithms you subtract components.
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divide
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When you ________ logarithms you add components
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multiply
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Log 2 = ___
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.3
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Log 4 = ___
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Log 2 + Log 2 = .3 + .3 = .6
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Why does sound fade away over time?
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Frictional resistance
Damping of vibration |
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What is the inverse square law?
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When sound is propagated in a free, unbounded medium, intensity decreases in a lawful way.
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Compressions form a "spherical shell", which is called _________.
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a wave front
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Compressions form a _________, which is called a wave front.
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"spherical shell"
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Wave front moves ________ and becomes progressively ________.
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outward
larger |
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At some distance from the source, the spherical shell becomes __________.
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a plane wave front
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If power remains constant but surface area increases, intensity __________.
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decreases
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Intensity varies __________ with the square of the distance.
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inversely
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Intensity varies inversely with the ________ of the distance.
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square
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If distance from the source is doubled, sound intensity ___________.
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decreases by a factor of 4
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If distance from the source is doubled, sound pressure ___________.
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decreases by a factor of 2
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If distance is doubled, by how much does the sound intensity level decrease?
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10 log 4 = 10 log2x2 = 10 (log 2 + log 2) = 10 (.3 + .3) = 6 dB
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Inverse square law only holds strictly in _____________.
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free, unbounded medium with no obstacles
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If a sound wave encounters obstacles, it will be ________, ________, ________ or ________
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reflected, refracted, diffracted or absorbed
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Reflection of Sound Waves
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Obstacle offers large acoustic impedance
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How much of a sound wave is reflected off water? How much is absorbed?
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99.9% reflected
0.1% absorbed |
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When sound waves are reflected off of an obstacle, how much does the speed change?
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It doesn't change.
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What happens with the inverse square law when sound energy is reflected?
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It does not hold.
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At what angle do reflected rays bounce off plane surfaces?
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At an angle equal to that which it hit the surface. (45 degrees on, 45 degrees off in the other direction from perpendicular)
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Sound wave reflection off plane, concave or convex surfaces.
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Angles of reflected waves to the perpendicular equal the angles of incident waves to the perpendicular
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Reflected waves are often called __________ or ___________.
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echoes
reverberating waves |
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Reverberant rooms
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Rooms with hard surfaces to maximize reflections (cafeterias)
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Anechoic rooms
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Rooms with soft surfaces to minimize reflections
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Reverberation time
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Time required for sound energy to decay by 60 dB relative to its original level
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What are the types of interference?
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Constructive - have constructive effects on the wave
Destructive - have destructive effects on the wave (cancel each other out) Standing Waves - When two progressive waves, incident and reflected, of same frequency & amplitude, travel in opposite directions in or along medium |
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Nodes
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Locations of zero displacement
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Antinodes
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Locations of maximum displacement
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What happens when a wave moves to another medium or encounters a change in the medium?
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Speed of propagation changes and rays are bent
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On a calm day on the water, during what time of day will sound travel further? Morning or Midday? Why?
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Early in the morning because warmer air is higher. Warmer air is less dense and causes sound to travel faster. Therefore, the wave bends, or refracts towards the water. It then reflects off of the water.
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Diffraction
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When a wave encounters a barrier, some energy is reflected back, wave fronts bend around the obstacle, reform and continue as plane wave fronts
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Absorption
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Opposition to sound transmission will exist at any boundary where impedances differ
Some sound energy will be absorbed by the new medium Intensity of absorbed wave will be less than intensity of incident wave |
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Absorption coefficient
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the proportion of energy in incident wave absorbed by material
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__________ have high absorption coefficient
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anechoic rooms
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What is the absorbing material in an anechoic chamber
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fiberglass wedges
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What are two types of sound treated rooms?
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anechoic rooms
sound isolated rooms |
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Sound isolated rooms
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Designed to reduce sound transmission through the walls
Resonably high absorption coefficient |
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Absorption is ________ ________ to reflection.
So, as ___________ increases, __________ decrease |
inversely proportional
absorption coefficient, reflection and reverberation time |
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What is absolute sensitivity?
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A measure of central tendency
How much sound intensity is required for the average person to just barely hear it |
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How are thresholds of audibility plotted?
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In dB SPL as a function of frequency
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A person with low sensitivity can be described as _________.
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very sensitive
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What influences the shape of the threshold audibility curve?
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Frequency response of the middle ear
Middle freq. are transmitted the most efficiently (least reflectance of sound) Low freq.- not as well due to stiffness of structures High freq.- not as well due to weight of structures |
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Minimum Audible Field Thresholds
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MAF
SPLs for pure tones at absolute threshold measured in a free field (over loudspeakers, facing source, both ears, 1 meter from source) |
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Minimum Audible Pressure Threshold
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MAP
Describe thresholds in terms of the sound pressure level at/near the listener's tympanic membrane Dependent on the earphones |
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Supra-aural headphones
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fit over the pinna
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Circum-aural headphones
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fit around the pinna
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Insert earphone headphones
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inserted into the ear canal
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Amplitude spectrum
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Graphic alternative to the waveform
Graphed as a straight vertical lines Shows amplitude (y-axis) as a function of frequency (x-axis) |
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How do you get the spectral envelope from an amplitude spectrum?
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By connecting the peaks of the vertical lines
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How do you find the next octave higher/lower?
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Doubling/Halving the frequency
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Line Spectra
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Energy only at frequencies identified by vertical lines
Height of vertical line reflects amplitude |
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Continuous Spectra
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Energy is present at all frequencies between certain frequency limits
Results in a horizontal line |
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Phase Spectrum
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Defines the starting phase as a function of frequency
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White noise
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equal energy in all wavelengths
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Dynamic range of the auditory system
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faintest audible sound (10 to the power of -12 intensity units) to loudest tolerable sound (10 to the power of 12 intensity units)
120 dB |
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Range of human hearing (in bels)
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12 bels
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Decibel
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Multiply the bel by 10
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Is it possible for a young, normally hearing individual to hear sounds at values of -5 or -10 dB?
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Yes
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If a sound is 4x the power of another sound:
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10 log 4/1 = 10(log4 - log1) = 10(log2 + log2 - log1) = 10(.3 + .3 - 0) = 10(.6) = 6 dB
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If a sound is 10 to the power of -14 watts/cm squared, how many dB IL is that?
re: 10 to the power of -16 watts/cm squared |
10 log 10^-14/10^-16 = 10 (-14 - -16) = 10 (2) = 20 dB IL
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Sound pressure
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force/unit area
dynes/cm^2 |
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Calculation for SPL
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20 log P1/PR
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Usual reference for SPL
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.0002 dynes/cm^2
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A decibel is ____ times the log of an intensity ratio and ____ times the log of a pressure level
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10
20 |
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A decibel is 20 times the log of a(n) _______ level and 10 times the log of a(n) _______ level
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pressure
intensity |
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What are the units for intensity level
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watts/meter^2 or watts/cm^2
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How do you figure out the range of human hearing? In bels? In dB?
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10^12 units = log10^12/log1 = 12/0 = 12 bels = 120 dB
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Pressure = _____/_____
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force/unit area
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If pressure increases by a factor of 10, intensity will increase by a factor of ____. Why?
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100, Because Intensity = Pressure^2
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Can you have sound in a vacuum? Why or why not?
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No, because there is no matter that can be moved
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What happens to the intensity of a reflected wave at point where it overlaps?
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It is increased
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If a sound takes longer to reverberate, is it softer/louder?
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louder
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What is an example of reflection, refraction and diffraction all occurring at the same time?
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The head shadow effect
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With the head shadow effect, which frequencies are harder to detect? Why?
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Low frequencies, because they have longer wavelengths
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Warmer air is _________ than cooler air so sound travels _________.
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less dense
faster |
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What is the natural frequency of the middle ear?
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1800 Hz
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What happens if the ossicles get heavier? What is this called?
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You may have high frequency hearing loss
"mass effect" |
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What happens when the ossicles are held very stiff? What is this called?
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You may have a low frequency hearing loss
"stiffness effect" |
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The best thresholds we can get are ____________.
About how many dB lower? |
Minimum audible field (MAF) thresholds
3 dB lower |
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Why is it hard to test hearing with dB SPL
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The level of "normal" is different for different frequencies
For example: at 1000 Hz-7 dB is normal; 2000-9 dB is normal |
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High threshold = ______ sensitivity
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low
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Sensation level
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Certain # of dB above a person's individual threshold
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If threshold is 10 dB HL and a tone is presented at 20 dB HL, what is the SL?
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10 dB SL
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Time intensity tradeoff
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The shorter the sound, the harder it is to detect
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Signal Duration
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The longer the signal, the easier it is to detect
The shorter the signal, the more power is needed for detection |
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Temporal Integration
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AKA "time-intensity trade-off"
The threshold can vary as a function of the duration of the signal Longer signals sound more intense |
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How long should a signal be for maximal performance of the auditory system?
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about 300 ms
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Once you _________ the time of a signal, you must _________ the power of that signal for maximal performance.
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decrease
increase |
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T/F Speech is a relatively uncomplex signal.
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True, music is a very complex signal
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What is differential sensitivity?
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Change in frequency in Hz that is required to hear a difference between two signals.
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Differential sensitivity is largely impacted by ________ to the ________ ________ ________.
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damage
outer hair cells |
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T/F Threshold of audibility is the most important thing the ear does.
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False, it is probably the least important thing the ear does.
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What did Weber find in the 1800s?
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That the difference that can just be detected is proportional to the value of the smaller weight
This is the "just noticeable difference" |
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Just Noticeable Difference
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AKA "difference limen"
Smallest difference a person can detect between 2 things Represents a proportion, not an absolute difference |
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What is the change in difference over the smaller of two values in differential sensitivity called?
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Weber Fraction
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Frequency Discrimination
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How far apart 2 freq. need to be for JND
1.6 Hz for sounds between 400 and 2000 Hz As intensity is raised, JND becomes smaller. |
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Intensity Discrimination
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The ear is very sensitive to differences of intensity
JND is about .5-1.0 dB (constant for a wide range of frequencies and intensities) |
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T/F For the most part, Weber fraction does not apply to hearing discrimination.
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True
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Why is it harder for a listener to tell the difference between a 50 ms and a 60 ms tone.
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There are additional cues
-50 ms tone would sound softer b/c of time-intensity trade-off -Spectra of very short tones is different -frequency info could "spread" to other regions of hearing |
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What is a gap detection task
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Listening for the gap of silence - are the 10 and 20 ms. gaps the same or different?
Similar to Weber's law, to detect a difference, second gap must be proportionally longer. |
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The source of a sound can be localized in which dimensions?
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horizontal
vertical near-far (range) |
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T/F Sound is composed of spatial dimensions
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False, sound itself has no spatial dimensions
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T/F You can never localize with one ear.
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True
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Azimuth
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How we tell which direction sound is coming from - measured in degrees
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How do we localize (i.e. what cues do we use)?
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Arrival of the sound at the ear
Intensity level of the sound at the ear How we use these cues depends on the frequency of the sound |
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What is interaural time difference?
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The difference in time of arrival at each ear.
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If 2 sounds arrive at different times, their ______ will be different in each ear.
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phase
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Interaural Intensity Difference
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Intensity will be greater on the side where the sound originates
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What is the difference in how we localize high and low frequencies?
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Low frequencies - time of arrival
High frequencies - intensity cues |
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Why will a sound reaching the right ear first sound louder in the right ear than the left ear?
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Because of the inverse square law (slight decrease in intensity with distance)
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Why will frequency differences cause differences in intensity?
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Higher frequencies will be blocked by the size and shape of a person's head
Low frequencies travel around corners, high frequencies don't |
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T/F It is easy for a listener to determine the location of mid and low frequency sounds.
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False, it is easy to tell the location of low and high frequency sounds (harder to tell for mid frequencies)
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Duplex Theory of Localization
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There are two cues we use for localization:
Interaural Intensity Difference Interaural Time Difference |
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What is the "cone of confusion"?
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When sounds come from directly in front or in back of you, they reach both ears at the same time and intensity
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Localization in the __________ plane is poorer than in the __________ plane.
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vertical
horizontal |
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What is the minimal audible angle?
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The smallest distance you can detect between 2 sounds
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What is the cocktail party effect?
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Diminished ability to discriminate sounds in background noise
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Lateralization
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Localization under headphones
You will hear the noise inside your head. The side you hear it from depends on intensity coming in through each side of the headphones Sometimes referred to as a "fused image" because it is heard as one sound even though the sound is presented in both ears. Example: Michael Jackson's Thriller |
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ITD greater than ______ will result in the perception of 2 different tones.
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2 ms
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T/F Sounds rarely occur in isolation
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True
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Masking
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Interaction of sounds
How much interference does one sound cause in the perception of another stimulus? Changes the softest sound you can easily hear |
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Tonal Masking
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Different tones mask differently
Maskers that are very near the frequency of a signal tone are more effective at masking than maskers that are far from the signal tone |
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Upward spread of masking
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Maskers of given frequencies mask out higher frequencies better than lower frequencies
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Noise Masking
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White noise contains a wide range of frequencies so we would expect it to be a very effective masker
For each dB increase in noise, we need to increase the signal the same amount to maintain detection |
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Signal to Noise Ratio
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Comparison of signal level to background noise
Subtract background noise from primary signal Signal - primary source (teacher's voice) Noise - any background noise (cars going by, fans, other kids) |
