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Acoustics and psychoacoustics UQ > A&P exam 2018 > Flashcards

A&P exam 2018 Flashcards

1
Q

What is the physical definition of sound?

A

A form of mechanical energy produced when an object is set in vibration

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2
Q

What is the psychological definition of sound?

A

A sensation experienced by an individual

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3
Q

What is a simple sound?

A

A sound with only one frequency

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4
Q

What is simple harmonic motion?

A

A type of periodic or oscillation movement, where the particle or object moves back and forth from a point of equilibrium. In SHM, the restoring force is directly proportional to the displacement and acts in the direction opposite to that of the displacement.

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5
Q

Are sound waves transverse, longitudinal or trochoidal?

A

Longitudinal

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6
Q

What is sound pressure?

A

local pressure deviation from the ambient pressure caused by a sound wave

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7
Q

What is frequency and what are the associated equations?

A

Frequency is the number of times per second that a completed wave cycle passes an observer. It is measured in Hertz. The associated equations are f = 1/t and f=c(344)/wavelength

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8
Q

What is an octave?

A

The range contained in a doubling of frequency

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9
Q

What is the frequency range of human hearing?

A

20 - 20,000 Hz

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10
Q

What is a wavelength

A

The distance between two wave fronts, measured in meters

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11
Q

What is the period of a sound?

A

The time it takes to complete one cycle (seconds)

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12
Q

What are two factors that affect the speed of sound?

A

Temperature and stiffness/elastic modulus

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13
Q

What conditions are used when discussing the value of 344 m/s as speed of sound

A

In air at 1 atm pressure and 20 degrees C

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14
Q

How does temperature and elastic modulus affect sound?

A

Hotter and stiffer = faster, denser and colder = slower

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15
Q

What is the phase of a sound?

A

Describes the temporal relationship between two sounds, measured in degrees

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16
Q

What is the starting phase of a sound?

A

A measure of that sound waves position at the beginning of the sound recording

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17
Q

What phase is a sound at, at peak condensation?

A

90 degrees

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18
Q

What phase is a sound at, at peak rarefaction?

A

270 degrees

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19
Q

What measure was used to calculate the average amplitude of a simple sound?

A

RMS amplitude

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20
Q

Why was RMS amplitude used to calculate the average amplitude of a simple sound?

A

Because the amplitude falls and rises symmetrically above and below zero, so the average would equal zero

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21
Q

0 dB SPL equals how much pressure?

A

20 micropascal

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22
Q

0 dB IL equals how much intensity?

A

10 ^ -12 Watts/m2

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23
Q

What is the relationship between pressure and intensity?

A

if P is doubled, than I is quadrupled, because intensity is proportional to pressure

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24
Q

What is the dB equation for intensity?

A

dBIL = 10log (Im/10^-12) W/m2

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25
Q

What is the dB equation for pressure?

A

dB = 20log (Pm/20)

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26
Q

How many micropascal are in a pascal?

A

1000000

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27
Q

True or false, x dB IL = x dB SPL

A

True

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28
Q

Describe Minimum Audible Field

A

Minimum Audible Field is a method of measuring hearing sensitivity. It is the sound pressure level in dB of a tone at the threshold of audibility. It is measured by placing a subject in a free sound field, 1m from a speaker and asking the subject to listen binaurally for the quietest sound they can hear. The sound level is then measured by removing the subject and positioning a microphone at the place previously occupied by the subjects head.

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29
Q

What is the MAF threshold at 1000 Hz?

A

0 dB SPL

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30
Q

What is Minimum Audible Pressure?

A

A method of measuring hearing sensitivity. It is the sound pressure level (in dB) of a tone at the threshold of audibility. It is measured by placing a subject under headphones and asking the subject to listen monaurally for the quietest sound they can hear, played through a headphone placed over that ear. The sound level is then measured, or inferred by calculating the sound pressure level that had occurred at that subjects TM.

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31
Q

Why are the MAP thresholds worse than the MAF thresholds?

A

Because headphones give the listener a slight hearing loss- sound energy is reflected back into the ear

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32
Q

What is dBA?

A

dBA corrects dB SPL for the way that humans hear low intensity sounds, it heavily penalises low frequency sounds.

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33
Q

What is dB C?

A

Corrects for the way humans hear high intensity sounds. It mildly penalises low frequency sounds when calculating final dB value.

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34
Q

What is dB G?

A

A special weighting that corrects dB SPL to reflect the human response to infrasound

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35
Q

What is clinical zero?

A

0 dB HL

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36
Q

Where did clinical zero come from?

A

Based on measurements taken from large numbers of young, normal, healthy adults listening to pure tone frequencies under pre-defined conditions

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37
Q

What is the Leq value?

A

The amount of sound energy in the changing sound that would be present in a constant sound played at the Leq value for the same amount of time

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38
Q

What is 100% noise dose in Australia?

A

Leq 85 ( the sound energy in an 85 dB A sound played continuously for 8 hours)

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39
Q

How many dB is a double of intensity?

A

3dB

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40
Q

If Leq = 85, at how many hours would 88dB A be 100% noise dose

A

4 hours

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41
Q

What is dB HL

A

dB HL corrects dB SPL for the combined effects of a human wearing TDH 39/49/50 headphones with MX41/AR cushions. It can only be used in audiology for simple sounds at audiometric frequencies

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42
Q

What is dB SL

A

dB Sensation level, or not number of dB a sound is above an individual person’s threshold for that sound

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43
Q

What happens when two sounds meet 90 degrees in phase

A

Sound pressure increases, larger “push”

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44
Q

What happens when two sounds meet 180 degrees out of phase?

A

Sounds cancel each other out (result is minus infinity dB)

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45
Q

What is the dB increase when two sound pressures of the same value add together?

A

6dB

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46
Q

What is the dB increase when two sound intensities of the same value add together?

A

3dB

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47
Q

What happens when you double a sounds intensity?

A

Increases by 3dB

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48
Q

What happens when you halve a sounds intensity?

A

It loses 3 dB

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49
Q

What is the result when you subtract two sounds of the same intensity?

A

minus infinity dB

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50
Q

What happens when you change a sounds intensity by a known factor (e.g. 1000 times greater)

A

You place 1000/1 in the log formula

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51
Q

What is the formula for dB gain?

A

dB output - dB input

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52
Q

What is dB gain?

A

dB gain occurs when one sound enters a system and another sound exits that system.

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53
Q

What is the inverse square law?

A

The inverse square law states that for a spherical, free, progressive wave radiating out from a point source in all directions, the sound intensity on the surface of the wave front diminishes with distance at a rate of 6dB per doubling of distance

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54
Q

What is a complex sound?

A

A sound with two or more frequencies

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55
Q

True or false, the human ear is insensitive to phase differences

A

True

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56
Q

What is the fast Fourier transformation?

A

A way of breaking a complex signal into its component frequencies

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57
Q

What formulae do you use when calculating the dB for a complex sound?

A

same as for a simple sound (dB SPL = 20log Pm/20) and (dB IL = 10log Im/10^-12)

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58
Q

What is beating?

A

Beating occurs when two waves differ only slightly in frequency. The successive cycles of the two original waves move into and out of phase and so go through progressive cycles or reinforcement and cancellation

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59
Q

What is the range in difference between the sound frequencies that leads beating to occur?

A

Where sounds differ by <5-10 Hz

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60
Q

What is the beating frequency of the sounds 1000 Hz and 1003 Hz

A

3 Hz

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61
Q

What is the effect of mass on a sound wave?

A

Mass opposes the flow of energy because of inertia. Sound will lose energy and flow of energy will be delayed

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62
Q

What is the effect of stiffness on a sound wave?

A

Stiffness opposes the flow of energy because of compression. The flow of energy will be delayed

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63
Q

What is the effect of resistance on a sound wave?

A

Resistance opposes the flow of energy because of friction, but there is no delay in the flow of energy

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64
Q

What is impedance?

A

Opposition to the flow of energy

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65
Q

What is admittance?

A

How well energy flows through a system

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66
Q

What is the phase delay for mass?

A

90 degrees

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67
Q

What is the phase delay for stiffness?

A

270 degrees

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68
Q

What is the phase delay for resistance?

A

0 degrees

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69
Q

What type of frequency energy does mass oppose?

A

High frequency

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70
Q

What type of frequency energy does stiffness oppose?

A

Low frequency

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71
Q

What type of frequency energy does resistance oppose?

A

All frequencies

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72
Q

If mass = x, stiffness = x and resistance = y, what is the total impedance?

A

Y (mass and stiffness counteract)

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73
Q

If mass = 4 ohms, stiffness = 2 ohms and resistance = 1 ohm, what is the total impedance?

A

4(mass) - 2(stiffness) + 1(resistance) =3 ohms

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74
Q

What is resonant frequency?

A

A frequency at which the opposition offered by mass = the opposition offered by stiffness. This leaves only resistance to oppose the flow of energy and the most energy possible is flowing through a system

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75
Q

What is fundamental frequency?

A

The lowest frequency of a vibration/the frequency at which an object vibrates most simply.

76
Q

What is a harmonic

A

Linear multiples of the fundamental frequency (e.g. f0=1000, 2000, 3000, 4000)

77
Q

What is the first odd harmonic of a 1000Hz sound?

A

1000Hz

78
Q

What is free vibration?

A

Once force starts the object vibrating, the object continues to vibrate without requiring additional force

79
Q

What is a displacement node?

A

a point of no vibration, e.g. at the closed end of a tube

80
Q

What is a displacement antinode?

A

A point of maximum vibration/displacement of air particles e.g. at the open end of a tube

81
Q

What is the formula for resonant frequency of a tube?

A

fr = c /4L, (where L = the length of a tube in meters)

82
Q

If the length of a tube is 2.5 cm, what is it’s resonant frequency?

A 
fr = 331 / 4x0.025 m = 3310 Hz
fr  = 344 / 4x0.025 m = 3440 Hz

REMEMBER TO CONVERT INTO METERS

83
Q

What is the resonant frequency formula for a tube that is either open or closed at both ends?

A

fr = c/2L

84
Q

What is the. psychological definition of noise?

A

Any unwanted sound

85
Q

What is the acoustic definition of noise?

A

An aperiodic or random signal

86
Q

What is white noise?

A

A continuous spectrum composed of all frequencies in the human hearing spectrum

87
Q

What is pink noise?

A

A low pass filtered sound, resembling speech sound

88
Q

What is the signal to noise ration?

A

SNR represents how much more intense a signal is compared to a noise

89
Q

What is the formula for SNR when answer/question in dB?

A

SNR = dBs - dBn

90
Q

If S = 20dB and N= 10 dB, what is the SNR?

A

20 - 10 = 10

91
Q

What is distortion?

A

When the sound that comes out of a system is not equal to the sound that went into the system

92
Q

What is fidelity?

A

A system’s ability to reproduce the original sound signal

93
Q

What is frequency distortion?

A

When the frequency of the sound out, does not equal the frequency of the sound in.

94
Q

What is phase distortion?

A

When the phase of the sound out does not equal the phase of the sound in.

95
Q

What is amplitude distortion?

A

When the amplitude of the sound out does not equal the amplitude of the sound in

96
Q

What are the two types of distortion occurring as a result of amplitude distortion?

A

harmonic and intermodulation

97
Q

What is harmonic distortion?

A

When harmonics of the original signal are produced?

98
Q

What is intermodulation distortion?

A

Distortion that results from the interaction of two or more input signals

99
Q

What is the formula for total harmonic distortion

A

THD = distortion out/total out

100
Q

What is an acceptable level of THD for hearing aids?

A

below 0.05

101
Q

What is diffraction?

A

Happens when a wave encounters an obstacle of similar size to it’s wavelength and the waves bend and spread out through small openings, causing a sound shadow immediately behind the object

102
Q

What is sound reflection?

A

Happens when an object is larger than the wavelength of the sound and acts as a boundary to reflect the sound

103
Q

What is reverberation?

A

When a reflected sound arrives <0.1 seconds after a direct sound

104
Q

What is reverberation time?

A

The time taken for any sound to decay by 60dB SPL

105
Q

What are the five sound fields?

A

Combined, near, free, far and reverberant

106
Q

What is the free field?

A

The sound field the incident or direct sound is more intense than the reverberant sound, but the direct sound decreases less rapidly in intensity with distance from source

107
Q

What is the reverberant field?

A

Where the reverberant sound is more intense than the incident or direct sound

108
Q

In a sound treated room, where does the free field usually lie?

A

1-2 meters from the sound source

109
Q

What is the difference between discrimination and magnitude tasks

A

In discrimination tasks, the subject must indicate the presence of a sound, or when two sounds a different, but in magnitude tasks, the subject must indicate the how different the sounds are (the magnitude of difference)

110
Q

What is an absolute discrimination task?

A

Where the subject must discriminate between the absence or presence of a sound

111
Q

What is difference discrimination?

A

The ability to tell that one sound is different from another

112
Q

What is a magnitude estimation task?

A

Asking how different two sounds are from each other

113
Q

What is the difference between method of limits and method of adjustment?

A

In Method of limits, the experimenter controls the stimulus and the experimentee controls the response. In the Method of Adjustment, the experimentee controls both

114
Q

What is the formula for signal detection theory?

A

p(hit corrected) = {p(hit) - p(false alarms)} / p(correct rejections)

115
Q

What is the difference between the classic psychoacoustical techniques and the SDT?

A

The classic techniques used a quantal theory, which assumes that the subjects hearing threshold is fixed. The SDT use a continuum theory, which assumes that the subjects threshold is constantly varying along a continuum.

116
Q

What happens to a decision point if you instruct a subject to respond to even if they think they hear a sound but aren’t certain

A

Moves to the left

117
Q

What happens to a decision point if you instruct a subject to respond only when they are absolutely certain that they have heard a sound

A

Moves to the right

118
Q

What is the difference between pitch and frequency.

A

Pitch is the perceptual correlate of frequency

119
Q

What happens to difference threshold as frequency increases?

A

They become larger

120
Q

What happens to difference thresholds as intensity increases?

A

They become smaller

121
Q

What is Weber’s Law?

A

Webers law states that our ability to detect a change in a physical stimulus is constant when the absolute value of the stimulus and the size of the change are considered

122
Q

What is 1000 mels?

A

Reference value for pitch. The pitch of a 1000 Hz tone at 40 dB

123
Q

What is loudness?

A

The perceptual correlate of intensity

124
Q

What do x phons equal?

A

The loudness of a 1000Hz tone at x dB SPL

125
Q

What are phons?

A

Phons are a comparative value as they always refer to the loudness of a sound at 1000 Hz.

126
Q

What does 80 phons equal?

A

80 phons = the loudness of a 1000 Hz tone at 80 dB SPL

127
Q

What is a sone?

A

1 sone = the loudness of a 1000 Hz tone at 40 dB SL

128
Q

How many phons are there in one sone?

A

40 phons

129
Q

How many dB on average before sound loudness doubles?

A

10 dB

130
Q

How much louder than one sone is two sones

A

Twice as loud

131
Q

What is sound adaptation?

A

The response of a receptor cell to a steady stimulus declines as a function of time until it reaches a steady value at which the energy expended by the cell is just balanced by the metabolic energy available to sustain it

132
Q

What is sound fatigue?

A

Results from the application of a stimulus that is considerably in excess of that required to sustain the normal physiological response of the receptor cell. Fatigue is measured after stimulus has been removed

133
Q

Is Temporary threshold shift an example of sound adaptation or fatigue?

A

Adaptation

134
Q

How do you measure TTS?

A
  1. find subjects pre-exposure hearing threshold, 2. expose subject to fatiguing sound stimulus, 3. measure subjects post exposure threshold
    TTS = post exposure threshold - pre exposure threshold
135
Q

What are five factors influencing the TTS

A
  1. The duration of stimulus 2. Recovery time 3. Amplitude of stimulus 4. Frequency of stimulus 5. Frequency of the post exposure test signal
136
Q

What is the definition of masking?

A

The process by which the threshold of hearing of one sound is raised by the presence of another (masking) sound and the amount by which the threshold of hearing for one sound is raised by the presence of another (masking) sound, expressed in dB

137
Q

What are five types of maskers used in Audiology

A
  1. White noise, 2. pink noise 3. Broadband noise 4. Narrowband noise 5. Speech noise
138
Q

What is there percentage value associated with critical bandwidth?

A

6% of either side of the centre frequency

139
Q

What is azimuth?

A

Sound localisation on the horizontal plane

140
Q

What is elevation?

A

Sound localisation on the up/down plane

141
Q

If a sound originates from a point of zero degrees azimuth, what is the interaural time difference?

A

zero

142
Q

Which type of localisation techniques are used to locate high frequency sounds?

A

Interaural time difference and interaural intensity difference

143
Q

Which type of localisation techniques are used to locate low frequency sounds?

A

Interaural time difference and interaural phase difference

144
Q

Which type of localisation techniques are used to locate mid frequency sounds?

A

Interaural time difference

145
Q

What is the minimum audible angle?

A

By how much do I need to change a sounds physical location before a subject determines a different location

146
Q

What is the precedent effect?

A

Within a certain timeframe, an earlier arriving signal will dominate over a later arriving signal in determining the location of a sound

147
Q

What is the timeframe for the precedent effect?

A

Less than or equal to 50 ms

148
Q

What type of frequency sounds does the Pinna help localise?

A

High frequency

149
Q

What is another type of localisation cue?

A

Shoulder cue

150
Q

What is a masking level difference?

A

The masking level difference (MLD) is typically a threshold measure, and it allows easier detection of tone or speech in the presence of noise as a result of changing the phase of the signal or the masker.

151
Q

What is monotic sound presentation?

A

The S and/or N are presented to one ear only

152
Q

What is a diotic sound presentation?

A

The S is presented to both ears in exactly the same way and the N are presented to both ears in exactly the same way

153
Q

What is a dichotic sound presentation?

A

S and/or N are presented to both ears in different ways

154
Q

What happens if two sounds are presented from 45 degrees azimuth each

A

It will be perceived as zero azimuth

155
Q

What is the release from masking?

A

The effect of a dichotic stimulus on masking

156
Q

Name three parts of an Audiometer

A

The microphone, the Attenuator, headphones and oscillator

157
Q

Name three parts of a sound level meter

A

Microphone, Meter Scale, Range Switch

158
Q

What is a sound level meter?

A

Sound level meters measure sound pressure level and are commonly used in noise pollution studies for the quantification of almost any noise, but especially for industrial, environmental and aircraft noise.
Sound level meters are also used to calibrate sound producing equipment, such as audiometers.

159
Q

What is the missing fundamental?

A

The missing fundamental occurs when a listener perceives an underlying pitch in a complex sound when that complex sound does not contain the frequency matching that underlying pitch. The missing fundamental occurs because the auditory nerve fibres are firing at the peak of the complex wave envelope formed by the sum of the 3 tones. Only occurs in sounds that share a fundamental frequency (missing fundamental acts as the f0)

160
Q

If sounds that do not have a shared fundamental frequency come together to form a complex sound, will there be a missing fundamental?

A

No

161
Q

What is the critical bandwidth in relation to complex sounds and loudness perception?

A

The critical bandwidth is the range that, when exceeded leads to loudness summation of a complex sound. When sound frequencies fall within one critical band, a sound appears quieter than when sound frequencies fall in different critical bands. i.e. when simple sounds are very similar in frequency, our judgement of the loudness of the complex sound is based mostly on the intensity of the complex sound. When simple sounds are very different in frequency, the loudness of the complex sound is driven y the sum of the loudness of the complex sounds

162
Q

If complex sound 1 is make up of tone A at 40dB at 1000 Hz and tone B at 40dB at 1002 Hz. And complex sound 2 is made up of tone A at 40dB at 500 Hz and tone B at 40dB at 15000 Hz, which will appear louder and why?

A

Complex sound 2.
The simple sounds fall outside one critical band, and the total loudness approaches the sum of their individual loudness.

Complex sound 1 = 1.23 sones
Complex sound 2 = 2 sones

163
Q

How many critical bandwidths are thought to exist?

A

25-32

164
Q

How does the critical bandwidth phenomena influence speech?

A

Makes speech appear louder (spread across numerous critical bands)

165
Q

What is the equation for inverse square law, when the question is asked in w/m2?

A

Intensity is proportional to 1/d^2, where d = distance

166
Q

What is the formula for SNR when answer/question in pressure?

A

pressure of S/ pressure of noiseN

167
Q

What is twice as loud as 2 sones?

A

4 sones

168
Q

Do sones constantly double as loudness doubles?

A

yes

169
Q

What is the cone of confusion?

A

Set of locations (on a cone shape axis each side of the head) that have the same interaural time differences (ITD) and IID, where binaural cues are not enough to determine the location of the sound

170
Q

What is speech noise?

A

Speech noise is low-pass noise. It has energy distributed to approximate the long term speech spectrum.

171
Q

Why are binaural localisation cues of little use when trying to determine if a sound originated from directly in front versus directly behind?

A

Sound from the front arrives at the two ears at essentially the same time and is heard with no time delay difference between the ears. Pinna cues (monaural) will be useful

172
Q

Why might a person with no hearing above 4000 Hz have difficulty determining the elevation of a sound source?

A

Pinna cues rely on high frequency sounds (detect elevation plane)

173
Q

Rank the following from largest to smallest MLD: SmNo, SoNo, SπNo.

A

m(Monotic) o(Diotic) and π(Dichotic)
MLD (Masking level difference)
Largest to smallest = SπNo, SmNo, SoNo,

174
Q

Interaural time differences are at their greatest when the sound source is located at how many degrees azimuth?

A

90 or -90

175
Q

Monaural cues are better for localising sounds in the a)_____ plane, whilst binaural cues are better for localising sounds in the b)_____ plane.

A

a) elevation

b) Azimuth

176
Q

What is a sound level meter?

A

A sound level meter is an instrument used to measure sound pressure level, often to determine noise pollution levels or calibrate equipment. They can be analogue or Digital and include a microphone, range switch and meter scale.

177
Q

In which of the following signal and noise combinations will the signal be most easily heard by a normal hearing person?
a) SmNm b) SmNo c) SoNo

A

b)?

178
Q

Briefly describe one method for obtaining a psychophysical tuning curve.

A

A test stimulus remains fixed, while the masker is varied. Psychophysical tuning curve plots the dB of the masking intensity at different frequencies required to just mask a probe stimulus.

179
Q

What is a receiver operator characteristic curve?

A

plot the probability of a hit versus probability of a false alarm to determine the best ratio of these factors to minimise response bias.

180
Q

What is signal detection theory?

A

Subject must respond by declaring whether they heard or did not hear the sound. Experimenter determines the sound intensity and the number of times the stimulus will be presented. There will be a random presentation of signal and no noise (e.g. experimenter may choose 1000Hz at 5dB, and vary between 100 presentations of tone and 100 presentations of no tone.Subject is alerted that a presentation is coming. Subject is then alerted to say whether they heard or did not hear a tone. SDT formula is then used to calculate P(hit)Corrected

181
Q

What is the duplex theory of localisation?

A

Two interaural cues are usually used to locate sound, with the choice of cues dependent on the frequency of the sound

182
Q

How would you reduce reverberation in a classroom?

A

Place some rugs or carpet in the room.
Hang curtains or blinds in the windows.
Hang soft materials such as felt or corkboard on the walls.
Place tables at an angle around the room instead of in rows. This helps keep sounds from bouncing around the room.
Hang soft materials such as flags or student artwork around the room and from the ceiling.

183
Q

How do you find the cut off frequency of a sound filter?

A

Find maximum point of filter, go down 3dB and where that point meets (f), that is the cut off frequency

184
Q

What is the far field?

A

Sound field in the combined field, made up of free and reverberant field, where sound falls less rapidly

185
Q

If two sounds come together in phase and are measured in dB SPL, what will be the resulting increase?

A

6 dB increase (20log2/1)

186
Q

If two sounds come together in phase and are measured in dB IL,what will be the resulting increase?

A

6 dB (10log4/1)

Acoustics and psychoacoustics UQ (1 decks)

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