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Audiology Phase One > Audiological Techniques > Flashcards

Audiological Techniques Flashcards

1
Q

How do you calculate the frequency of a sound?

A

If the speed of sound is 320m/s you need to divide it by the wavelength
ie: 320m/s divided by 1.28m = 250Hz

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2
Q

What is an equalizer & what are the standard parameters?

A

A processor that modifies the frequency content (spectrum) of a sound
• Frequency - frequency of the band to process in Hz
• Gain - how much to enhance or diminish that band in dB
• Q - quality factor type of “bell” or curvature in units low Q means wider band high Q means narrow band

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3
Q

What does the Fourier Theorem say?

A

Every periodic complex tone is composed by a weighted sum of pure tones

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4
Q

What frequency does the phon & dB SPL scale coincide?

A

1000Hz

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5
Q

What does vibro tactile mean?

A

When low frequency sounds through the bone vibrator (B-C) are so loud they can be felt rather than heard

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6
Q

What is the absorption coefficient for a given material?

A

The Ratio between the sound absorbed and the sound reflected

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7
Q

What is an anechoic chamber?

A

A room with very acoustically absorbent materials on the walls

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8
Q

What is a Dynamic Range Compressor?

A

A processor that modifies the dynamic range of an audio signal

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9
Q

What are the standard parameters of a compressor?

A
  • Ratio
  • Threshold
  • Attack
  • Release
  • Make up Gain
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10
Q

What is the Duplex Theory?

A

The hearing system performs lateralization using mainly ITD for low frequencies BELOW 1000Hz & ILD for high frequencies ABOVE 1000Hz

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11
Q

Why is ILD a frequency dependant parameter?

A

Because the head absorbs different signals with different wavelengths & therefore different frequencies

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12
Q

Name the 3 rules of Masking

A

Rule 1: AC - diff of 40dB between both ears
Rule 2: BC - when there is a diff of 10dB of the BC above the AC
Rule 3: When Rule 1 doesn’t apply but the BC is more acute on one ear by 40dB than to AC in the other ear

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13
Q

What is a reverb?

A

An ensemble of echoes that are not anymore distinguishable one from another

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14
Q

What is an echo?

A

A single reflection of a sound signal on a surface

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15
Q

What does air-borne sounds mean?

A

Types of sound/noise transmitted by air & atmosphere such as the radio or traffic noise

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16
Q

Describe the Notch Equalisation Filter

A

Notch - Very high Q

Dips at 500dB

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17
Q

Describe Low-pass Equalisation Filter

A

Low-pass - Removes high frequencies

Dips from 1kHz

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18
Q

Describe High-pass Equalisation Filter

A

High-pass - removes low frequencies

Dips from 20-250Hz

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19
Q

Describe Band-pass Equalisation Filter

A

Band-pass - removes high & low frequencies

Dips at 20-250Hz then again at 2kHz

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20
Q

Describe Comb Equalisation Filter

A

Comb - more notches together

- Several dips close together

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21
Q

What is RMS?

A

Root Mean Square - an averaging function which allows a more accurate & realistic estimation of the loudness of a specific audio signal

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22
Q

What does Threshold mean?

A

The level above the signal which is reduced

Lower threshold means a larger portion of the signal is reduced

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23
Q

What does Ratio mean?

A

Determines the input/output ratio for signals ABOVE the threshold

1: 1 = no changes
2: 1 = if above threshold the signal is reduced by half

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24
Q

What is Attack & Release?

A

Controls how quickly the compressor acts
1ms = very fast
1sec = very slow

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25
Q

What is Soft & Hard Knee?

A

Controls whether the bend in the responsive curse is a sharp angle (hard knee) or has a rounded edge (soft knee)

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26
Q

What is Make-up Gain?

A

Because the compressor is reducing the amplitude of the signal a fixed amount of make-up gain can be added so that an optimum level can be used

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27
Q

What is the Equal Loudness Curve?

A

Sound pressure, Frequency and Loudness perception

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28
Q

Why do we use RMS

A

Gives a better estimation to measure loudness compared with peak measurement

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29
Q

What is the phenomenon of the acoustic beats?

A

Amplitude modulation generated when summing 2 signals with a very similar frequency

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30
Q

What is Diotic & Dichotic?

A

Diotic - relates to a sound stimulus presented to both ears in exactly the same way
Dichotic - related to a sound stimulus presented to one ear differently from the sound stimulus presented to the other ear

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31
Q

What are the 3 Localisation cues?

A

Interaural Cues:
ILD Interaural Level Differences
ITD Interaural Time Differences

Monoaural Cue:
DDF Direction Dependent Filtering

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32
Q

What is the Cocktail Party Effect?

A

The ability of segregating the speech on which the listener needs to focus from the other background signals using spatial attributes of the sound scene

33
Q

What is MAA?

A

The Minimum Audible Angle - the barely perceptible difference of localisation on the horizontal plane (azimuth) detectable by the hearing system

34
Q

What is BMLD?

A 
Binaural Masking Level Difference 
Sm-Nm 0dB
Sb-N∅ 13dB
Sb-Nb 0dB
S∅-Nb 15dB
Sm-Nb 9dB 
Sm-NT 3-10dB
35
Q

What is BILD?

A

Binaural Intelligibility Level Difference

Difference in dB of the measured speech intelligibility between a dichotic condition & the Sm-Nm or Sb-Nb conditions

36
Q

What is HRTF?

A

Head Related Transfer Function

- how a given sound wave input is filtered by the head, the pinna & the torso before the sound reaches the ear canal

37
Q

What is a Spectogram?

A

A plot of the sound’s frequency over time the X axis will present Time (sec) and the Y axis will present Frequency
The amount of energy present in each frequency is represented by the intensity of the colour - brighter the colour the more energy is present in the sound at that frequency

38
Q

What is a Sonogram?

A

Ultrasound - > 20kHz
Lower frequencies = deeper penetration and lower resolution
Higher frequencies = shallower penetration but higher resolution

39
Q

Name the 5 main features of a hearing aid

A

Microphone, Microchip, Amplifier, Battery and Receiver

40
Q

How to work out the battery performance?

A

Capacity divided by Battery life (drain)
eg: 130/0.75 = 173.333hours = 10.8 days
Batteries don’t last forever!

41
Q

What does Sampling Rate mean?

A

Means how often the digital circuit samples the original signal
Represents frequency

42
Q

What does Quantisation mean?

A

Means the number of levels/ steps which can be assigned
Represents amplitude
Expressed as bits (binary digits)
32 bit processors common now

43
Q

What does Attack & Release mean?

A

Attack time = Time taken for the compressor to react to an increased input signal
Release time = Time taken for the compressor to react to a decreased input signal

44
Q

What are the pros of a 2cc Coupler?

A

Pros
• a cavity or test volume of predetermined shape & volume
• allows for standardisation across across different tests & locations (enables fair comparison)

45
Q

What are the cons of a 2cc Coupler?

A

Cons -
• Not a good match across all frequencies
• The standard 2cc coupler is larger than many adult ears
• This means the aid generates lower SPL in the coupler than the ear
(smaller volume = higher intensity)

46
Q

What is the prescription formula for adult hearing aid fitting?

A

NAL (National Acoustic Laboratories)

NAL NL2 is the more up to date version

47
Q

What is REMs?

A

Real Ear Measurements - measurements in the ear made using a thin flexible tube attached to a probe microphone to verify you have reached the prescription target
This tube has to be inserted into the ear canal close to the TM

48
Q

What are the benefits of REMs?

A

Gives objective information about the sounds we are delivering to the patient - relative to their prescription target
Accounts the individuals ear shape
Quick to perform

49
Q

What would stop you from being able to complete REMs?

A

Infections/ discharge/ otalgia
Completely occluding wax
Recruitment

50
Q

What is REUR?

A

Real ear unaided response - response of the open ear canal

Typical resonant peak at 2.7kHz for adults

51
Q

What is REOR?

A

Real ear occluded response - response with the ear canal blocked eg with a mould or ITE
Resonant peak is lost

52
Q

What is REAR?

A

Real ear aided response - response with the hearing aid inserted and turned on
Also called REAG - Real ear aided gain

53
Q

What is RECD?

A

Real ear to coupler difference - involves using the 2cc coupler
Compare the SPL measured with the earmould to the SPL measured in the 2cc coupler

54
Q

What is REIG?

A

Real ear insertion gain - same as REAR but more advanced

Only displays the dB gain view of what the hearing aid is doing

55
Q

What is the Occlusion Effect?

A

It occurs when an object such as an ear mould fills the ear canal - it causes the person to perceive an echo-like “hollow” or “booming” sounds from their own voice (sensation of increased loudness) especially low frequency sounds eg chewing, talking or swallowing

56
Q

What is a sinusoidal vibration?

A

A vibration that contains a lot of harmonic overtones

57
Q

What is Timbre?

A

The human hearing perception of frequency content (spectrum) and spectral envelope

58
Q

What is CROS?

A

Contralateral Routing Of Signals

For unilateral hearing loss where worse ear is unaidable & the better ear is normal or near normal
Meaning better localisation of sounds in the better ear

59
Q

What is Bi-CROS?

A

Where both ears have a hearing loss same as CROS but the better ear also receives amplification

60
Q

What is a DAI?

A

Allows BTE users to connect an external sound source directly to the aid bypassing the microphone

61
Q

What is a Hearing Aid Test Box?

A

Used to measure hearing aid performance to the agreed parameters

62
Q

What is Automatic Gain Control?

A

Commonly known as compression, it limits the aid output by reducing its gain above a specific input level of sound (known as the knee point)

63
Q

Why do we mask?

A

Although headphones are designed to deliver sound to one ear at a time but there is a risk for cross-over so masking needs to be done to ensure accuracy

64
Q

What is the Inter Aural Attenuation for AC?

A

AC headphones is 40dB - so for example if you play sound at 50dB the opposite ear could hear the sound at 10dB (50-40)

65
Q

What is the shadow? IAA

A

This is a result in when the non test ear is responding to the sound

66
Q

Name the styles of ear moulds

A 
Solid - not commonly used 
Shell - occluding moulds - common
Skeleton - has large hole - common
Meatal tip - those who may struggle 
Half shell - bit fuller than meatal 
Skeleton- open 1 & open 2 even bigger holes more non occluding
67
Q

Why do we use venting for moulds?

A

Can modify the frequency response. Especially when pt has good low frequency hearing
Improves occlusion effect
Does increase risk of feedback

68
Q

What is the fitting formulae objective for NAL-NL2?

A

Make speech intelligible & overall loudness comfortable

Provide more gain in low & high frequencies & less through mid frequency

69
Q

What is the fitting formulae objective for DSL?

A

Widely recognised for paediatrics
Avoidance of loudness discomfort
Accommodates different listening environments

70
Q

Why do we calibrate our equipment?

A

Compare to normal
Safety & ensure all electric components work
Avoid misdiagnosis

71
Q

What is an audiological threshold?

A

Least amount of energy required to cause a firing rate in the hair cells that the subject will notice
Response to 2/3 tones to be accurate

72
Q

Name types of feedback cancellation methods?

A

Adaptive gain reduction
Adaptive notch filters
Phase cancellation
Adaptive feedback reduction algorithms

73
Q

Why is it better to fit bilateral hearing aids?

A

Better sound quality
Lowers risk of auditory deprivation
Lowers the need for higher amplification
Sound lateralisation

74
Q

Why would you only fit one hearing aid?

A

May be easier or less over stimulating for those with dementia or cognitive delays
If you have normal hearing in one ear

75
Q

How to improve the SNR

A

Use digital multi channel compression
Directional microphones
Digital noise reduction

76
Q

What are BAHA’s?

A

Bone anchored hearing aids - sends sounds through the skull bone to the inner ear
Used for those with middle or outer ear problems/ conductive HL

77
Q

What are cochlear implants?

A

Small electronic device that can help provide a sense of sound to those who are profoundly deaf or severely hard of hearing
Directly stimulate the auditory nerve
Better to fit at a younger age

78
Q

Name features of a test box

A 
Chamber with tight fitting lid 
Loudspeaker 
Microphone 
Coupler 
Display screen

Audiology Phase One (2 decks)

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