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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
What is Soft & Hard Knee?
Controls whether the bend in the responsive curse is a sharp angle (hard knee) or has a rounded edge (soft knee)
26
What is Make-up Gain?
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
27
What is the Equal Loudness Curve?
Sound pressure, Frequency and Loudness perception
28
Why do we use RMS
Gives a better estimation to measure loudness compared with peak measurement
29
What is the phenomenon of the acoustic beats?
Amplitude modulation generated when summing 2 signals with a very similar frequency
30
What is Diotic & Dichotic?
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
31
What are the 3 Localisation cues?
Interaural Cues: ILD Interaural Level Differences ITD Interaural Time Differences Monoaural Cue: DDF Direction Dependent Filtering
32
What is the Cocktail Party Effect?
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
What is MAA?
The Minimum Audible Angle - the barely perceptible difference of localisation on the horizontal plane (azimuth) detectable by the hearing system
34
What is BMLD?
``` Binaural Masking Level Difference Sm-Nm 0dB Sb-N∅ 13dB Sb-Nb 0dB S∅-Nb 15dB Sm-Nb 9dB Sm-NT 3-10dB ```
35
What is BILD?
Binaural Intelligibility Level Difference | Difference in dB of the measured speech intelligibility between a dichotic condition & the Sm-Nm or Sb-Nb conditions
36
What is HRTF?
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
What is a Spectogram?
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
What is a Sonogram?
Ultrasound - > 20kHz Lower frequencies = deeper penetration and lower resolution Higher frequencies = shallower penetration but higher resolution
39
Name the 5 main features of a hearing aid
Microphone, Microchip, Amplifier, Battery and Receiver
40
How to work out the battery performance?
Capacity divided by Battery life (drain) eg: 130/0.75 = 173.333hours = 10.8 days Batteries don’t last forever!
41
What does Sampling Rate mean?
Means how often the digital circuit samples the original signal Represents frequency
42
What does Quantisation mean?
Means the number of levels/ steps which can be assigned Represents amplitude Expressed as bits (binary digits) 32 bit processors common now
43
What does Attack & Release mean?
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
What are the pros of a 2cc Coupler?
Pros • a cavity or test volume of predetermined shape & volume • allows for standardisation across across different tests & locations (enables fair comparison)
45
What are the cons of a 2cc Coupler?
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
What is the prescription formula for adult hearing aid fitting?
NAL (National Acoustic Laboratories) | NAL NL2 is the more up to date version
47
What is REMs?
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
What are the benefits of REMs?
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
What would stop you from being able to complete REMs?
Infections/ discharge/ otalgia Completely occluding wax Recruitment
50
What is REUR?
Real ear unaided response - response of the open ear canal | Typical resonant peak at 2.7kHz for adults
51
What is REOR?
Real ear occluded response - response with the ear canal blocked eg with a mould or ITE Resonant peak is lost
52
What is REAR?
Real ear aided response - response with the hearing aid inserted and turned on Also called REAG - Real ear aided gain
53
What is RECD?
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
What is REIG?
Real ear insertion gain - same as REAR but more advanced | Only displays the dB gain view of what the hearing aid is doing
55
What is the Occlusion Effect?
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
What is a sinusoidal vibration?
A vibration that contains a lot of harmonic overtones
57
What is Timbre?
The human hearing perception of frequency content (spectrum) and spectral envelope
58
What is CROS?
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
What is Bi-CROS?
Where both ears have a hearing loss same as CROS but the better ear also receives amplification
60
What is a DAI?
Allows BTE users to connect an external sound source directly to the aid bypassing the microphone
61
What is a Hearing Aid Test Box?
Used to measure hearing aid performance to the agreed parameters
62
What is Automatic Gain Control?
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
Why do we mask?
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
What is the Inter Aural Attenuation for AC?
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
What is the shadow? IAA
This is a result in when the non test ear is responding to the sound
66
Name the styles of ear moulds
``` 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
Why do we use venting for moulds?
Can modify the frequency response. Especially when pt has good low frequency hearing Improves occlusion effect Does increase risk of feedback
68
What is the fitting formulae objective for NAL-NL2?
Make speech intelligible & overall loudness comfortable | Provide more gain in low & high frequencies & less through mid frequency
69
What is the fitting formulae objective for DSL?
Widely recognised for paediatrics Avoidance of loudness discomfort Accommodates different listening environments
70
Why do we calibrate our equipment?
Compare to normal Safety & ensure all electric components work Avoid misdiagnosis
71
What is an audiological threshold?
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
Name types of feedback cancellation methods?
Adaptive gain reduction Adaptive notch filters Phase cancellation Adaptive feedback reduction algorithms
73
Why is it better to fit bilateral hearing aids?
Better sound quality Lowers risk of auditory deprivation Lowers the need for higher amplification Sound lateralisation
74
Why would you only fit one hearing aid?
May be easier or less over stimulating for those with dementia or cognitive delays If you have normal hearing in one ear
75
How to improve the SNR
Use digital multi channel compression Directional microphones Digital noise reduction
76
What are BAHA’s?
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
What are cochlear implants?
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
Name features of a test box
``` Chamber with tight fitting lid Loudspeaker Microphone Coupler Display screen ```

Audiology Phase One (2 decks)

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