Amp 1 Final Exam Flashcards
1
Q
Define front end distortion and its cause?
A
it is distortion when the signal exceeds DR (usually a user’s own voice or loud music causes this)
2
Q
Describe why digital hearing aids have a lower microphone dynamic range:
A
the analog to digital converter only has a 16 bit, which means that (x6) the 96dB DR is smaller
3
Q
Describe how front-end distortion is managed in digital hearing aids:
A
dynamic range shift (cuts off soft sounds, so the mic is less sensitive to them), or increase the bit resolution (18 bit has a 108dB DR)
4
Q
Prepare to calculate Signal to Noise ratio and understand its meaning:
A
SNR = signal - noise
- positive number is signal is more than noise, negative number is noise is more than signal
- Meaning: tells us the strength of the desired signal arriving to the person, and if it is stronger or weaker than the background noise
5
Q
Bi-directional polar plot pattern and its directivty index
A
Bi-directional: nulls at 90 degrees on both sides
***** Directivity Index is the amount of attenuation, in SNR (low DI = low null)
6
Q
Cartoid polar plot pattern and its directivty index
A
null at 180 degrees (DI = 4.8 dB SNR)
7
Q
Hyper-cartoid polar plot pattern and its directivty index
A
nulls behind person on both sides, but has a small opening at 180 degrees (DI = 6dB SNR)
8
Q
Super-cartoid polar plot pattern and its directivty index
A
smaller nulls at 120 and 420 degree spots, but a larger opening at 180 degrees (DI = 5.7dB SNR)
9
Q
Be prepared to explain a polar plot in terms of sound collection and nulls:
A
A polar plot shows mic sensitivity as a 2 dimensional image above a person’s head. It also shows the null space, which are areas of attenuation.
10
Q
Explain raising or lowering a TK and what that does practically in the environment:
A
- Raising a TK = makes soft sounds more quiet (up TK, down soft sounds)
- Lowering a TK = makes soft sounds louder (down TK, up soft sounds)
Practical applications for this adjustment: we would want to lower the TK for a person that wants to hear those soft sounds if it helps enrich the environment. We would increase the TK for a person that wants to remove those “annoying” soft sounds if they perceive them as noise instead of a valuable signal.
11
Q
Explain expansion and its purpose:
A
Lower the intensity of very soft sounds and environmental noise (cuts out the sound of the rustling leaves, refrigerator, and the turning of a page)
CR: less than 1:1
12
Q
Describe the purpose of the test box, reference microphone, and coupler microphone:
A
The test box chamber eliminates reflections, keeps ambient noise low, and has a calibrated sound source and mic to keep everything standardized across all practices.
Reference mic: makes sure the intensity is standardized by calibrating the SPL output from the test box speaker
Coupler mic: listens to the sound coming from the HA
13
Q
What is an HA-1 coupler used for ?
A
CUSTOMS 2cc coupler simulates the ear canal with custom products (use fun-tac to attach it)
14
Q
What is a HA-2 coupler used for?
A
BTE also 2cc couples that has a tube that can attach an ear hook, and mimics the tubing that would go into the receiver
14
Q
What are 0.4cc wideband couplers used for?
A
RIC, CIC, IIC (smaller cavity)
15
Q
What is the Zwisklocki coupler used for?
A
research purposes only
15
Q
What is the purpose of a standardized coupler?
A
All couplers are used as a safeguard to be able to repeat the measurements over and over without variability, not meant to mimic a human ear!
15
Q
Why do we compare our device measurements against a spec sheet?
A
We compare a spec sheet to see if our in-office performance of the device is set to standards from the device’s manufacturer.
16
Q
Explain the process of converting:
A
An analog electrical signal to a digital signal: splicing the analog signal up into a bunch of pieces and them quantifying them onto either a 1 or a 0, then mathematically manipulating them to match the analog signal in numbers
17
Q
what is sampling rate?
A
moments in time of the analog signal, ex: the peak and trout of the sound wave
18
Q
what is Nyquist frequency?
A
The sampling rate is 2x higher than the frequency response. ex: 20k hz sampling rate becomes a 10k hz bandwidth (frequency response)
to accurately reconstruct a continuous signal from samples the sampling rate must be twice the highest freq present. The nyquist frequency is the highest frequency
19
Q
what is quantization?
A
mathmateically rounds each sample creating a digitized version of the signal. Results in a less idealized representation of the analog input. Characterized by Bit values. increase bit = increase resolution
20
Q
what is a quantization error?
A
the noise floor, it decreases when we increase the bit
21
Q
what is processing speed?
A
the time it takes for the acoustic signal to travel through ALL of the components and then into the ear canal, usually around 2-10 msec
22
how does a digital signal go back to electrical?
either straight to the receiver (best, cleanest, less noise) OR first through the AGC-O and then to the receiver if it’s a high output signal
23
Explain front end limitations associated with 16-bit processing :
How does this impact microphone sensitivities?
Mics can’t detect high sounds, causes distortion (peak clipping)
24
Explain front end limitations associated with 16-bit processing : How are these limitations resolved?
Shift the DR up to allow those higher sounds in without having to distort them, but this does cutoff lower input sounds
25
The function of auditory filters (critical bandwidths) in the cochlea?
we have 25 bands that allow us to pay attention to frequencies within each band and ignore other frequency signals
- low frequencies have more narrow bands (160Hz wide)
- high frequencies have more broad bands (2,500Hz wide)
26
The effect of low frequency masking on the damaged cochlea ?
upward spread of masking masks the low frequencies as well as the higher frequencies at that same intensity
27
what frequencies are impacted by noise?
below 1500Hz
28
Function/purpose of automatic microphone switching:
switch to directional when there is background noise + back to omnidirectional when it’s quiet
29
Function/purpose of adaptive directional mics:
automatically change the polar plot to put the null somewhere else if there is a speaker in that area (ex: null moves behind you in a car if the person next to you is speaking)
There are different nulls for different frequency bands
30
Practical programming decisions related to adaptive vs. fixed directional microphones
Adaptive are best for only a few noise sources in the null
Fixed is best for many noises in the null space, because the hearing aid will know to cut out all of it instead of changing the polar plot
31
Function/purpose of adaptive beamforming mics:
narrow the polar plot to focus more on one direction
Louder = narrower bandwidth
32
what is the only way to increase speech intelligibility?
THE ONLY WAY WE CAN INCREASE SPEECH INTELLIGIBILITY IN NOISE IS: DIRECTIONAL MICS (not digital noises reduction)
33
Differentiate modulation rate and depth for speech and noise.
Rate: the speed that a signal fluctuates (speech is slow, noise is fast)
Depth: amplitude changes in the signal (speech is varying, noise is steady)
34
How is poor SNR determined in a hearing aid?
The noise is louder than the speech, which drowns out the speech (has a slow modulation rate, high depth)
If there is noise in speech and the amplitudes are similar, then the SNR is low and that’s a difficult listening situation… however if the speech has more depth, then the SNR will be higher and we will get a good listening situation
35
Digital noise reduction: describe the attenuated signal
One with a low depth, and a fast rate (ex: fan/AC, vacuum, engine idle, hairdryer)
36
Describe the benefits and limitations of digital noise reduction
Benefits: listening comfort, directionality, lessens listening effort and cognitive load
Limitations: takes away some speech noises as well (if there are high frequencies in the speech and you are reducing noise, it can also cut off some of those high frequencies from speech)
37
The theory associated with low frequency output reduction:
“noise” is in the mid and low frequencies, so if we remove those low frequencies, we could hear the higher frequency speech sounds better…
38
Limitations of low frequency output reduction:
noise also exists in the high frequencies too, if your undesired signal is also speech, taking out those low frequencies will also take out the desired signal low frequencies too
39
Explain Weiner filter function and limitations:
a spectral subtraction method (subtracting the noise from the speech)
limitation: takes too many critical speech sound out of the signal
40
Describe 3 methods used to reduce external feedback:
1. Reduce external feedback/vent effect: increase snug fit or reduce vent size (limitation: causes occlusion)
2.Digital notch filter: reducing gain at 2-4kHz to reduce the feedback (limitation: takes out speech sounds in that frequency range too)
3.Digital feedback suppression: hearing aid creates an out of phase clone of the signal to cancel it out (limitation: has a beep to mimic tone and it can be annoying, can accidentally engage on things that aren’t feedback (ex: instrument), can distort the signal, and can drain battery life)
41
what is frequency lowering?
(shifting high frequency sounds to a lower frequency if they have a HL too far from being able to use amplification) the 3 types: linear frequency transposition, nonlinear frequency compression, and spectral envelope warping
We enable it immediately in ped, and later on for adults… there are no clear ways to see if it will benefit adults before we try it out
42
What is linear frequency transposition?
taking a high frequency band and moving it to a low frequency location (limitation: takes a while for a person’s brain to gather meaning for these new sounds, doesn’t work for some people)
43
What is nonlinear frequency compression?
takes inaudible high frequencies and compresses them into a lower frequency organization, maintains tonotopic order of frequencies (limitation: sounds more distorted)
44
What is Spectral envelope warping?
warping: keeping awareness in the high frequencies (maintains tonotopic organization) while also moving the signal to low frequency, so we will get both of the same signal at once but they are at different frequencies (limitation: it takes a while to get used too and it also sounds more distorted)
45
what are some digital wind noise reduction methods?
1. Low frequency filtering
2. Less affected HA sends signal into the the affected ear (head shadow, for example)
3. Directional mic switches to omnidirectional for the low frequencies
46
Describe the uses and benefits associated with wireless binaural processing technology
Uses: wind noise management, dual phone streaming, volume control, program matching, wdrc restoring ILD cues to the ear on the opposite ear
Benefits: improves spatial hearing (better ILD cues that get taken away by WDRC, this helps us improve localization and hearing in noise)
47
Understand how each factor impacts the final frequency response (bandwidth) and output of the device:
input stage variables: how sensitive the mic is to a broad frequency range
Processing stage variables: A/D converter sampling rate limits the highest frequency that can be produced (ex: nyquist theory says that the sampling frequency has to be 2x the the highest frequency)
A/D converter limits the intensity of the front-end input
Output stage variables:
Receiver size and design
Sound bore (ear hook, tube length, shape) standing waves can cancel the signals and the shape can change the output
48
Describe the purpose and function of a receiver:
transduce the electrical signal back into an acoustic (after the d—>a converter)
49
How are receivers designed differently to achieve the greatest high frequency output for severe hearing losses:
they use an armature that is moved by between two magnets, and the diaphragm follows the motion of the armature to replicate the signal, move the air, and transmit sound waves back out into the ear canal
- larger receiver for higher output (needed for severe losses)
- smaller device can accommodate higher frequencies better (because the diaphragm moves faster)
**** We need a dual receiver to do both low and high frequency outputs
50
Describe each receiver limitations:
saturation: peak clipping as a result of the output exceeding receiver capabilities (will drain the battery)
shock damage: receiver is dislodged and vibrations cause damage (signals are sent back to the mic and distorted)
Battery life: receiver is draining too much power from the battery
moisture + debris: they clog really easy, especially in the canal
51
Define soundbore path:
the column of air that the sound travels through from the receiver to the eardrum
52
What frequency range is impacted by changes to the sound bore:
thinner tube = low frequencies get decreased output AND shifts peak resonance down from 1kHz to 800Hz
Bigger output area of the tube (Libby horn): high frequencies increased output
53
Describe the impact of standing waves within the soundbore on the final output signal
same phase and frequency will combine and 180 out of phase will cancel
54
Describe the impact diameter change has on output and frequency response (i.e., thin tube effect; Libby horns):
smaller diameters (ex: thin tube) attenuates the high frequency outputs and moves the resonant peak down
Libby horn increases high frequency outputs (BTE boost at 3kHz, ITE boost at 6kHz)
55
Describe the purpose and limitation of a damper:
a damper is an acoustic resistor that
attenuates sound slightly as it passes through to smooth the output peaks
limitation: gets clogged easily (think of water on a thin screen)
56
What is a TMFS?
Telecoil Magnetic Field Simulator
Lie the device flat onto the T in the test box, and move it around to find the max output of the telecoil in that device (when I practiced, it was around 109 dB)
57
What is RSET?
Relative Simulated Equivalent Telephone Sensitivity
Difference between the SPLITS and the microphone output at reference test gain, ideally they should be equal!
+RSET means Tcoil is louder (lower HA volume when using Tcoil)
-RSET means acoustic mic is louder (raise HA volume when using Tcoil)
57
What is SPLITS?
Sound Pressure Level for an Inductive Simulator
The output measurement of the TMFS, I believe it is that same 109dB amount
58
What is SPLIV?
measuring SPL in a vertical magnetic field, to simulate a looped environment
RSLS - relative simulation for loop sensitivity
59
Degrees of pressure sore for medical documentation:
1. Red
2. Visible abrasion
3. Blister
4. Skin broken
60
Uses for stones of different grit and color:
Blue for silicone (has the lowest grit)
Low grit = removes large amount of material
White for acrylic or vinyl, its smaller and more grit
More grit = removes less material, smoother finish
ONLY polish acrylic!
61
A HA battery produces?
~1.25-1.5 volts
62
Disposable Zn-Air Battery:
contains zinc, is steady 1.25V over its life until it abruptly dies… it starts the reaction when the tab is removes and oxygen is combined with the battery, more stable than mercury, and remains stable for around 6 weeks
- size 675 is biggest, size 10 is smallest
- Have a 2-3 year shelf life
- Once tab is pulled off, the voltage rises for 24 hours
63
Rechargeable : Lithium ion :
most popular right now!
Pros: Very energy efficient, longer battery life, fast charging, lasts the life of the HA with no replacement
Cons: no replacement, replace every 3-4 years, mostly in high end devices
64
Rechargeable:
nickel-metal hydride:
Pros: 6 hour recharge time, same battery life as zinc
Cons: fades capacity over time, same cost as a lifetime of disposables
65
Rechargeable : silver-zinc:
discontinued in 2020
- 7 hour recharge and at least a day of battery life
- voltage runs high and drains capacity
- can damage the HA because it runs hot
- replaced annually for $150 (interchangable with zinc-air)
66
Review factors which may reduce battery life
environmental: moisture, high temperatures, dry climate, touching other metal
Patterns of use: keeping door closed when not using, streaming use
67
In office repairs :
disinfect, put in a fresh battery, mark L or R, and do ANSI check/listening check before repairing
Listening check: ling 6 sounds 12” from face, vary intensity, and check for directionality
- It is directional if you sound quieter when speaking to the back mic
- It is linear if the soft and loud intensities are both amplified
68
How to fix whistling in the HA?
check for wax, cracked tube or hook, vent placement, or shrinkage if vinyl, and then check digital feedback suppression (may have fallen out of calibration)
68
Common HA complaints?
whistling, distorted/noisy, volume low/device stopped working, and intermittency
69
How to fix distorted or noisy HA?
check for receiver output, battery contacts, mic port debris, wind screen debris, and dislodged receiver
70
How to fix volume low/device stopped working?
check mic port and wind screen for debris, sound bore for debris or crack, hard tubing, battery dead, charging issues, battery tab residue
When you remove the earhook and it gets louder, it’s a damper problem
71
How to fix intermittency in HA?
check the RIC wire, power usage, battery contacts, and battery power level
72
SOAP NOTE
Subjective / Objective / Assessment / Plan
Providers expect to see a comprehendible report in the A section (not audiology terms, just general results), and the P section to tell them what to do next
73
SBAR NOTE
Situation / Background / Assessment / Recommendation
They are gonna look at the recommendation section to see what they should do. Good for emails and phone calls because it gets the the point quickly
74
Define patient centered care:
Putting the patient’s needs above yours,, actively considering treatment options based on the patient and their family
75
Describe Medicare’s physician order requirements:
- Required for all audiology services except for diagnostic tests for a non-acute hearing condition
- Non-acute condition cannot involve balance concerns
- Final coverage is determined based on the reason that the tests are being ordered (outcome does not affect coverage, as long as there are no initial complaints, then medicare will cover 1 hearing eval a year!)
76
Define fiduciary as it relates to the PCC-based treatment plans that we recommend:
A person that can be trusted to provide their services for the patient’s best interest instead of their own
Not “selling” but recommending based on their needs and how it can benefit them
77
Differentiate those services Medicare will and will not reimburse:
WILL REIMBURSE: medical necessity…
diagnosis or treatment of a condition or injury
cure or relief of a condition or injury
not solely for the convenience of the insured
WILL NOT REIMBURSE:
When the condition is already known
When the reason for the test is related to hearing aids
78
Recognize the conditions under which medicare will not cover diagnostic assessments:
Anything related to hearing aids…
If another provider is billing for benefits that we perform (Incident to…)
79
CPT-4 Codes:
procedures
Ex: 92557 is a Comprehensive Audiogram
These are stronger than HCPCS, so choose CPT-4 when there is overlap
80
HCPCS Codes:
services and supplies
most services aren't covered by Medicare, but can be covered by 3rd party insurances
Ex: V5275 is for an earmold impression
81
ICD-10 Codes:
classification of disorder or symptoms
Must support the CPT-4 Codes used to diagnose the disorder
82
ANSI Pre-measurement setup:
all volumes on, compression at 1:1, all digital processing off, and if analog, potentiometer set to: SSPL 6 + LC )
83
ANSI OSPL90
outlet SPL at 90dB (identified loudest possible outcome that the device can deliver at a single frequency)
84
ANSI HFA OSPL90
calculates the average OSPL90 output for 1k, 1.6k, and 2.5k
Used to let you see how loud the device can get and if it reaches the needs without going to the MPO
85
ANSI HFA FOG
average gain for those frequencies at 50 dB SPL
used to estimate max possible gain when an average signal is inputted
86
ANSI Reference Test Gain:
17dB below the HFA FOG @50dB values
Not super useful in digital devices, but still part of the standard practice
87
ANSI Equivalent Input Noise (EIN):
measures internal noise of the HA
Should be less than 30dB
Used as a quality control check, but some research says that out of spec EIN is still fine
88
ANSI Total Harmonic Distortion:
determines if there are distortions/harmonics in the output that shouldn't be there
% Total Harmonic Distortion: should be below 10%
Used to see if device needs sent in for repair
89
ANSI Frequency Response
frequency limits of the bandwidth
calculation = HFA FOG - 20dB
90
How does a carbon microphone work?
The first electric HA that collected the acoustic signal and converted it from electric to analog signal and the receiver converts it back to acoustic. Sound waves hit the diaphram and compress the carbon balls which put off an electrical current.
91
How does a signal go from acoustic to electrical?
The diaphram in a microphone produces condensation and rarefaction movements that mimic the signal. The microphone uses this +/- movement to create an electrical current that mimics the acoustic wave.
92
Define temporal resolution and the auditory processes in which support it
Ability to detect small time-related changes like gap detection, phoneme duration, temporal ordering, and suprasegmentals.
Temporal envelope (overall changes in intensity, speech in quiet) contains temporal fine structure (rapid oscillations, speech in noise). CI's leave out fine structure and only use the temporal envelope.
93
Explain Binural Loudness Summation, its suprathreshold benefits? and how this supports hearing aid fitting strategies?
patients perceive louder sounds as louder with two ears listening (less gain needed). 3dB boost at threshold, 6dB boost suprathreshold, up to 9dB boost at high intensities. Less gain is needed to reach louder listening levels with two devices listening.
94
What does an IP rating Indicate?
Ingress protection rating
0-6 for solids (0 = no protection, 6= dust-tight)
0-8 for liquids (0 = no protection, 8=protected against long exposure to water/sweat)
95
High vs. Medium Vs. Low Viscosity
Low viscosity (runny + loose, for devices with deep insertion)
Medium viscosity (some stretch)
High viscosity (thick, stretches aperture)
96
High vs. Low Tensile Strength
The ability of the material to stay together during removal and not tear.
High - Does'nt tear as easy
Low - Low tears easier
97
Superior vs. Inferior Stress Relaxation
ability to be moved and return to original shape (silicast is best).
Superior - Does not distort on removal
Inferior - can distort
98
High vs. Low Contraction Ratio
shrinking over one week (silicone is best, methyl-methacrylate shrinks 3%)
High - will shrink
Low - little shrink
99
Describe the cause of the occlusion effect (OE) and associated patient complaints.
OE is the increased perception of your own voice when something is blocking your ear canals. The skull transuces low frequency energy generated by the voice because the signal becomes trapped in the ear canal. Common complains occur when LF theshold is better than 50 dB. Patients complain of their voice sounding booming, hollow, and in a barrel. The causes are the mold vent is too small, insufficient venting and/or canal length.
100
Describe two management techniques used to reduce the Occlusion Effect
1. stabilize a device in the bony part of the canal, so it can’t vibrate the bones.
2. use a vent to allow low frequencies to escape, and allow normal environmental sounds in.
101
What are the points of earmold retention?
Hook on the top and bottom of the concha for in the ear models.
Hook on the antitragus (canal lock) for in the canal models.
102
Describe the impact vent size has on high frequency output.
High frequencies can’t go through a vent because they don’t have the energy needed to overcome the inertia of the vent
