Final Written Study Guide Flashcards
Explain the process of converting An analog electrical signal to a digital signal
Then sound goes to the analog to digital converter to go from an analog electric signal to a digital signal
ADC - when converting an analog signal to a digital signal the signal is sampled at discrete intervals (sampling rate)
Takes snapshots of the analog audio - must have 2 snapshots per wave cycle in order to accurately represent the frequency (one at the peak and one at the trough) - the higher the sample rate the more precise the recreation of the original audio is
The quality of the captured audio sample is determined by
sample rate - how many samples of the original signal are taken in periods of time
bit depth - determines the amount of possible amplitude values that can be recorded for each sample amplitude; The smaller the bit, the more noise you get; The greater the bit depth, the greater the detail in the audio
Quantization - each sampled value is rounded to the nearest value within a set of discrete levels and these levels are defined by the resolution of the ADC
Quantization error = noise floor
results in front-end distortion we see because for every bit is only 6 dB DR
16-bit digital word = DR of 96 dB
Digital signal now has numbers associated w/ it and moves to DSP
Explain the process of converting
A digital signal back to electrical
converts amplified electric signal back to an acoustic signal
armature (flexible strip of metal balanced between two magnets like a diving board) is magnetized as the electrical current flows through the coil and it moves up in the positive direction towards that magnetic and down to the negative magnetic mimicking the electrical sine wave which is attached to the diaphragm above it and as the armature moves so does the diaphragm and this diaphragm movement causes the push and pull of the air creating an acoustic signal
what is sampling rate
number of times per second an analog signal is sampled to create a digital signal - how we capture frequency information
Sampling rate takes regular snapshots of the continuous analog electric signal wave at evenly spaced moments in time & DSP only uses those snapshots (sampled points) and ignores everything else
In order to capture the wave correctly how many shots for each cycle is needed
2
one at the highest point and one at the lowest point
If you do not get enough snapshots, the wave’s frequency will not be able to be accurately recognized
what sampling rate do you want
high rate
more snapshots taken- the more accurate the original continuous wave is represented due to more sampling points
what is the nyquist theorem
Nyquist rate is 2x the given frequency to be measured accurately
minimum sample rate for the highest frequency wanting to be measured
what is bit depth
Measures the amplitude of the signal - horizontal measurement
Higher bit depth = more possible vertical amplitude values & more precisely the exact amplitude of a given sample can be recorded
It also means a wider dynamic range
what is Quantization (Bit Resolution)
Depending on the bit depth, the exact amplitude value is rounded up or down to the nearest value using quantization
Higher quantization = more fluid sample
Lower = more choppy sample
what is quantization error
The difference between the original acoustic signal and the transduced digital signal
Creates noise = noise floor
Every bit only has —-dB of dynamic range
6
16-bit digital word = DR of
96 dB
Noise floor in the hearing aid is noise created in the circuit due to quantization error
TRUE
waht is an algorith
Analytical calculations applied to the digital signal
They add, subtract or multiply strings of digital words
It creates a step by step set of decisions to achieve the desired result
explain how algorithm works
ha is listening to environment and to the acoustic scene and deciding when combo of characteristics happen (spectral, temporal, amplitude) will automatically change programs and improvise the digitized signal processing to match any given listening environment
Explain front end limitations associated with 16-bit processing, and how this impacts microphone sensitivities. How are these limitations resolved?
The smaller the bit, the more noise you get
The greater the bit depth, the greater the detail in the audio
16-bit processing has a dynamic range of 96 dB - it can collect sounds up to this but past this the sound becomes distorted
We get this dynamic range because each digital bit increase the front end dynamic range by 6dB
Solution: the dynamic range shifts by lifting the 96 dB higher to collect more sound sounds but it does this by sacrificing soft sounds
what is an auditory filter, its function, effect of LF masking on a damaged cochlea and frequencies impacted by noise
Cochlea is a series of overlapping band pass filters (frequencies that are grouped together because they are close together on the cochela) that allow certain regions on it to stimulate to a specific frequency region while ignoring frequencies outside of the band
The filters have a lot of overlap with each other so HF bands pick up LF signals from adjacent critical bands and as a result, noise can mask signals from adjacent critical bands
In normal hearing, sharp tuning curves allow for precise frequency discrimination & perception of sounds
w/ HL, the curve is broader and noise can easily affect perception of the desired signal
Broadening of the filters is mainly on the LF side, leading to the increasing of LF masking. So the LF noise masks the region it normally would but also spills over to the overlapping HF bands around it making it more difficult for the PT to use the cues to understand the speech over the noise
how many bands are in the as
25 bands
LF bandwidths are narrow - only 160 Hz wide
HF bandwidths are wide- up to 2500 hz
what is upward spread of masking
Intense 250 hz LF noise will mask that frequency region but the masking will also spill over to the overlapping HF critical bands
Noise energy peaks around 250 Hz but upward spread of masking impacts audibility up to about 1500 Hz
Types of Noise that Impact Intelligibility
Steady state signals
Random noise with an intensity frequency spectrum like speech (speech like sounds)
10-talker babble
4 talker babble
2 talker babble
Which is harder to hear in?
Room reverberation
what are the methods of sound cleaning technology
spatial domain
temporal domain
spectral
Differentiate modulation rate and depth for speech and noise.
Speech & noise signals have time differences
Modulation rates
Speed of the signal
Speech = slow rate
Noise = fast rate
Modulation depth
Amplitude variations bw loudest and softest portions of the signal
Intensity of the variations
Speech = highly variable
Noise = steady over time
How is poor SNR determined in a hearing aid?
it looks at the mod rate and depth
for noise, mod rate is slow and mod depth is steady over time so it takes this and eliminates it from the signal
how does digital noise reduction work
Steady state noise
Idling engine, hair dryer, vacuum etc.
Only acts on fast mod rates & low mod depths
Varying degrees can be applied to each frequency range
doesn’t improve speech intelligibility
Can improve listening comfort, reduce listening effort, reduce cognitive load
does DNR improve speech intelligibility
no
doesn’t improve speech intelligibility
Can improve listening comfort, reduce listening effort, reduce cognitive load
Methods of sound cleaning technology used in the spectral domain
HA here looks at a signal’s frequency to control the signal
Theory is that If noise is below 1.5 and then understanding speech comes from mid and high frequencies reducing the output in low frequencies will improve speech intelligibility in noise
if we attenuate and reduce lf amp and leave in hf, then we will probably improve speech intelligibility
issue: there is noise still in HF not just all in the LF
Methods of sound cleaning technology used in the spatial domain
noise here is managed by directional mic technology
by turning in the direction of the signal the ha provides spacial separation from the speech and noise
adaptive vs fixed
beamforming
superior when only a few noise sources are present
adaptive
superior in the presence of multiple noise sources
fixed
what is automatic mic switching
ha automatically listen to seen and when they think there is enough noise in the room, switch from omnidirectional to directional
Will switch to a fixed direction (one polar plot) or an adaptive directional mic (multiple polar plots)
purpose of automatic mic switching
Switching occurs automatically and continuously
Microphones revert to omni-directional mode in quiet
Feature has an override switch
Polar plots allow reverse directionality to supply a side or backwards zoom
sometimes you want to hear what is behind you and not what is in front
driving in the car
sitting with group in class or in movie theatre and friends are behind you
what is adaptive directional mic
turns directional mics on and off when needed
Directionality of a mic sensitivity is determined by external and internal time delay
Here time delay is digitally manipulated to shift the azimuth of a null based on sounds location
Automatically changes the null as locations of undesired signals moves behind the listener - null steering
Can steer across a BB frequency range or in narrower frequency ranges
what are broadband and multiband mics
Broadband and multiband mics varies null point for different frequency ranges (bunch of polar plots stacked on top of each other
what is beamforming
Has a very narrow beamwidth (only azimuths of + 25°, + 35°, + 50°
Monitors overall intensity of environment
When signal is <55 SPL widest beamwidth activates
As environmental intensity increases (>75 SPL) smallest beamwidth is activated
ONLY thing we can do in digital ha tech to improve speech intelligibility is to
enable directional mics
Explain Weiner filter function and limitations
Spectral subtraction approach, measures short term noise spectrum during gaps in speech
Improves acceptance of background noise but doesn’t improve intelligibility
Worlds good on steady noise but not fluctuating so it is not effective in real time noisy situations
Reads between the lines in desired signal and takes out background noise found in the modulations of speech
what are 3 methods to reduce external feedback
Reduce external feedback loop
Digital notch filtering
Digital feedback cancellation
explain Reduce external feedback loop
Increase snugness of mold to reduce size of slit leaks
Or decrease vent size to stop feedback path
Limitation: both increases OE
explain digital notch filtering
Removes frequencies around the noise - reduces gain around 2-4 kHz where feedback occurs
HA between this range with notch creates a notch in frequency response so we don’t amplify sound in those regions -
reduction in gain from 2-4 kHz and if you don’t turn the volume up it won’t cause feedback
Limitation 35% of intelligibility comes from this range alone so you stop feedback but stopped audibility of important speech sounds so reduced speech intelligibility
explain digital feedback cancellation
When HA detects feedback (identified due to steady state noise bw 2-4 kHz) an algorithm creates an out of phase clone of the signal (duplicate of the feedback) and this causes the clone to be subtracted from the amp path and in turn attenuates the feedback
Describe the limitations of each feedback reduction method (DFS)
Algorithms can cause brief feedback until the out of phase tone can activate
Any sustained tone can start an algorithm (whistle, violin, etc.)
Audible beep when an external signal is mistaken for feedback - entrainment
Feedback cancellation can distort or attenuate parts of speech
Faster battery drainage and life
what are the 3 types of frequency lower
linear frequency transposition
nonlinear frequency compression
spectral envelope warping
what is frequency lowering
Only works from high to low
Best for steeply sloping HF HL
tries to improve HF audibility by shifting it down to LF
do we turn FL on for adults initially
measure signal audibility, turn feature on later
use auditory closure skills so it is less imperative we turn it on
do we turn frequency lowering on for children initially
they are learning language and audibility of s and z is important for them, as soon as it is identified it is turned on
explain linear frequency transpostion
CUT AND PASTE into LF, takes the highs and shoves it into the lows
Improves HF audibility by moving HF band one octave down to LF region
explain nonlinear frequency compression
piano keys
HF range is compressed into a LF range; squishes it down into the audible region
maintain tonotopic order more, lowered all the frequencies, squished into lower frequency space, close to each frequencies close to their original spot
explain spectral envelope warping
Leave the HF where it is but also COPY and PASTE into LF
Keeping a portion in HF but also transposing portion down to LF range
*oticon colors
how does digital wind noise reduction work
Wind turbulence only affects one diaphragm so the HA talk to each ither and take the signal on the opposite side and transmit it and overlay it so it seems like the noise went away and improves snr in that environment
LF filtering can be applied - energy of wind is around 300 hz
Describe the uses and benefits associated with wireless binaural processing technology
HA’s talk to each other
Wind noise management - how does this work
Dual phone - ha streams call into opposite ear to get binaural herring
Volume control
Program
how does binaural help with ILD
How does it support improved awareness of ILD in HA’s
As it arrives to second ear it is lower and wdr adds more gain on that same side so the ILD are gone so you cannot hear well in noise so binaural wireless the one ha tells that ha to not add as much wdrc
One ear will tell the other ear to not add as much wdrc so it doesn’t lose ILD
what is digital data logging
Helps with counseling topics & ways to customize them to meet their lifestyle needs
Which is better for high noise environments? fixed or adaptive? why?
Fixed is better for more noises because it attenuates all the signals
Adaptive is better for a few noise sources because it is not smart enough to determine which ones to attenuate; it doesn’t know how to function
The more BB the noise the greater the effect on speech
works on steady state noise, improves listening effort, working memory, reduces cognitive load but doesn’t improve speech intelligibility
Can improve listening comfort, reduce listening effort, reduce cognitive load
digital noise reduction (temp domain)
Most noise is <1500 Hz, if we reduce output here it will reduce background noise but it assumes all competing signals are in the LFs and this is not true
Background noise is in HF too
spectral domain
what is the test box for
Acoustic chamber
Reduces reflections
Low ambient room noise
Calibrated sound sourccw
what are the speakers for
Emit measurement signal
what is the refrence mic
Calibrates SPL output from speakers
waht is the coupler mic
Measurement mic collecting output from the HA
Simulates size of the canal
Custom products - ITE & ITC
Uses fun tak to attach HA to it
ha 1
Traditional BTE w/ earhook
Attach directly to hook
ha 2
Only for verifit 2
Used for CIC, IIC, RIC
Smaller cavity volume mimics the deeper placement of the device
Realistic picture of frequency response in >HFs
.4cc
what is the zwislocki coupler
Better simulates characteristics of the ear canal
Avg canal has HF SPL that is higher than the LF SPL
OSPL 90- Output SPL @ 90 dB
This shows output for a 90dB SPL input signal (MPO)
Loudest possible output point device can produce for a 90 dB input signal & represents a single frequency
HFA OSPL 90- HF Avg output SPL @ 90dB
Calculates the average OSPL 90 output for 1, 1.6 and 2.5 kHz
*3 triangles at the bottom
HFA FOG - HF avg full-on gain
Shows avg gain for 1, 1.6, 2.5 for a 50 dB signal
Estimates the max gain available at different frequencies when an avg input signal is amplified
Equivalent Input Noise (EIN)
Measures the internal noise of the HA
Typically 25- 30 dB SPL is acceptable
Should be below 5-10%
High DL are indicators the device is close to failing (most likely the receiver) & needs sent in for a repair
% THD
Compares output of an input signal coming from 0-deg azimuth to the input signal coming from 180-deg azimuth
directional mic front to back ratio
Larger differences (FBRs) suggests a greater directivity index is achieved to improve SNR & speech understanding in noise
yes
Degree of attenuation is dependent on amount of modulation in the signal and intensity of the signal
digital noise reduction
what signal is emitted form TMTF T in box
electromagnetic
SPLITS
output response of telecoil (horizontal = phone)
telecoil output it louder than the mic output
+ RSETS
vtelecoil ouput is softer than the mic output
- RSETS
SPLIV
SPL in a vertical magnetic field
Looped environment
SPLIV - output of telecoil
RTLS - difference bw mic and telecoil
true
first limitation to frequency response of HA
sampling rate
how does input stage impacts the final frequency response (bandwidth) and output of the device
mic can collect wide frequency response from environment but as signal transduces through HA the range and output changes so that final output and frequency response are dependent on
how does processing stage variables impacts the final frequency response (bandwidth) and output of the device
dynamic range of mic is impacted by bit rate of adc converter
how does output stage variables impacts the final frequency response (bandwidth) and output of the device
Receiver size & design
Acoustic parameters - sound bore (earhook, tube length & shape
Signal changes as it travels through the sound bore
Standing waves can cancel the signal & the shape of the sound bore can increase or decrease HF output
purpose of a receiver
converts amplified electric signal back to an acoustic signal
how does a receiver work
armature (flexible strip of metal balanced between two magnets like a diving board) is magnetized as the electrical current flows through the coil and it moves up in the positive direction towards that magnetic and down to the negative magnetic mimicking the electrical sine wave which is attached to the diaphragm above it and as the armature moves so does the diaphragm and this diaphragm movement causes the push and pull of the air creating an acoustic signal
Receiver sizes determine the final HF output
\
true
HF signals need _____ diaphragm movements
rapid
Smaller contemporary receivers are capable of _____ frequency responses
highr
what is the problem with large receivers for severe losses
limit output bandwidth (frequency response)
HF are lost due to increase armature flexibility
what is the solution tothe loss of hf with larger receivers
two receiver system (dual receivers?)
Output from both receivers added together when it reaches the ™
One is for LF
One is for HF
what is the benefit of two receiver system for severe losses
reduces battery drain, gives a good EHF output w/out compromising a lot in LF and minimizes saturation distortion potential
what is receiver saturaton
This happens when the receiver output is reached resulting in peak clipping or the receiver having a higher voltage and battery drain
HA output range has been exceeded leading to distortion due to peak clipping
what is shock damage
Caused by a dislodged receiver where the vibration goes back into the mic adding extra frequencies to the input signal leading to distortion
how does cerumen/moisture debris affect receivers
break because of moisture, debris, oil, gets into it and clogs it up
Can block the receiver diaphragm and cause reduced output of the receiver
what is the soundbore path
A column of air that sound waves pass through leaving a receiver that arrives to the ™
Final output & bandwidth (frequency response) of device changes based on a sound bore paths acoustic parameters/physical properties
Do ric devices have a sound bore?
no
what happens in sound bore flaring
HF output is changed based on the side of the flare
Increases HF depending on length and size of the flare
what happens to frequency range with thin tube
Making the tube thinner decrease the HF output & shifts the peak resonance down to lower frequencies (1000 hz down to 800)
Describe the impact of standing waves within the soundbore on the final output signal
This happens when reflection in the sound bore causes the wave to overlap with itself
This causes two waves of the same frequency to either be in phase creating a single sound that is louder or two identical waves 180 deg out of phase and cancel each other out
Thin tube in standing waves changes HF response. How
Smaller internal diameters of a thin tube cause reduction in HA HFO & shifts tube resonance down to around 800 Hz
how does libby horn change output and frequency response
nternal horn shape increases HFO
what needs to happen for libby horn to increase HFO
internal diameter over a specific length needs to be increased gradually
issue: benefit depends on maintaining length of flare canal
cannot just be a flare has to have a certain length
cannot always get diameter or length to fit into individual horn
Depth of soundbore in canal
Increased length = Increased SPL for ALL frequencies
what is the purpose of a damper
Acoustic resistor
Physical barrier to reduce sound
Smooths the resonances in the final frequency response
Does so by attenuating sounds slightly to smooth the peaks
what is a limitation of dampers
Sound waves lose energy as they travel through the damped material
Amount of acoustic resistance applied to the resonance
ohm
Higher ohm = less resistance
false
more
what are the stages of pressure sores
Stage 1: redness, not swollen, can identify red spot
Stage 2: swelling, but not too much and redness
Stage 3: pressure sore that starts to fill with fluid, skin isn’t broken but swollen and raised, blister
Stage 4: skin breaks, can’t wear HA until it heals, open wound that needs managed
Course
Used to modify silicone
Need to use at least 25k to 20k RPM for best results
blue stone
For grinding acrylic or vinyl
Smaller one is for smaller areas
white stone
Removes large amounts of material fast
low grit
Removes less material and smoother finish
medium grit
Smooths and restores shine
Only used w/ lucite/acrylic molds
fine grit
Final edge smoothing
nail file
Review factors which may reduce battery life (environmental, and patterns of use)
Ear to Ear wireless transmission
FM signal processing
Tinnitus Masking Programs
Bluetooth streaming features
Low battery warnings
chemical dry out
Shelf life 2-3 years, maintains voltage for about 6 weeks.
Maintains stable 1.25Vm deteriorates rapidly at the end
zinc air
used to be common, recharge time 6 hours, life 10 hours (less than zinc air). Capacity fades over lifetime, manufacturer replacement about once a year. Cost comparable to disposables over the lifetime of the aid
nickel metal hydride
discontinued in 2020, 7 hour recharge, lasts for at least a day. Voltage runs higher than other batteries, needed voltage regulators to be installed before use
silver
zinc
agzn
Offered by all major manufacturers
Energy efficient, long life, fast charging – 30 mins = 6-7 hour life, lasts the life of the hearing aid
Disadvantages- faulty chargers are a huge pain, no replacement if battery loses its charge, must be replaced every 3-4 years.
lithium ion batteries (R)
what are pros for rechargeable
Convenience
No small batteries
No keeping track of batteries
More eco friendly
No buying batteries
what are pros of disposable
Convenience
Smaller HA size
Lower HA cost
Better reliability
what goes in s of soap note
Things you learn through talking w/ the patient and others
Must have reason that supports each diagnostic exam
what goes in o of soap note
documents your diagnostic test results
Describe specific findings from things you glean from observing, touching, testing
Otoscopy was normal, normal tymps, normal reflexes, normal OAeS
what goes in a of soap note
eviews what you think is causing the issue?
Interpretation statement based on your professional knowledge describing the relationship b/w subjective and objective findings
Theoretical analysis of the underlying cause based on the relationship b/w the subjective/objective findings
A clear statement of your interpretation of the findings as it relates to the symptoms
considering normal audiometric studies, it appears PT symptoms are result of occupational ____
what goes in p of soap note
management recommendations based on findings
What should the patient do next?
Describe recommendation of the next steps to take
Mrs. Hicks is a candidate for audiologic rehabilitation which may include bilateral amplification, auditory training, and group aural rehabilitation. It is recommended that she return to my office to complete a communication needs assessment.
plan
Frances Hicks, a 95-year-old female reports difficulty communicating, especially when in noisy environments. The patient denies symptoms of aural fullness, discomfort, tinnitus or balance concerns. A review of systems finds no other medical concerns.
subjective
Assessment results reveal Mrs. Hicks threshold loss is causing communication difficulties. Findings suggest loss of haircell function in the cochlea. There is no evidence of middle ear or retrocochlear pathology
assessment
Diagnostic studies reveal mild to moderate sensori-neural hearing loss bilaterally; tympanometric results show normal ear canal volume, peak pressure and static compliance in both ears; acoustic reflex thresholds were present ipsilaterally and contralaterally at reduced sensation levels, distortion product otoacoustic emissions were absent bilaterally.
objective
SBAR communication method to relay a call for action to another healthcare provider
Get to the point asap
Situation: brief statement of the problem you are facing
Background: follow up with pertinent case details
Assessment: statement of concern
Recommendation/request: what are you asking of them
Define patient centered care (PCC)
Active involvement from PTs and their families to design new care models in decision making about their options for treatment
Takes time & dont get reimbursed but we can for other services - need to bill & code effectively to be reimbursed for services we do provide
Define fiduciary as it relates to the PCC-based treatment plans audiologists recommend
Trust
a person places trust, confidence, and reliance on another to exercise discretion or expertise in acting on behalf of the client.
what is a cpt 4
describes diagnostic procedure
what is HCPCS
coes describing services & supplies
what are ICD 10
codes classifying diagnosis and/or symptoms
what are medical necessity
These are services that are provided for the diagnosis, treatment, cure, or relief of a health condition, illness, injury, or disease
Describe Medicare’s physician order requirements
Required for services in all settings except tests for non-acute hearing conditions
Once every 12 months
when will medicare reimburse
eval of cause of hearing tinnitus balance disorders
eval of change in hearing tinnitus or balance
finding how medicaiton, surgery or other effects PT
failure of screening test
when will medicare not reimburse
When the auditory/balance status is already known
When the reason for the hearing assessment is unrelated to hearing aids, or examinations for the purpose of prescribing, fitting, or modifying hearing aids
Understand how a carbon microphone works. Specifically, how it converts an acoustic signal to an electrical signal
sound waves come, hit diaphragm and compress it
when it moved in, the carbon balls are pushed together creating pos voltage flow, sound waves go back and forth so when it goes back so does the diaphragm so the balls decompress
compression and decompression of carbon creates a + and - electrical current
sound has positive peaks and negative
these hit d, compress/decompress the carbon balls, and because it created the +/- current flow, the electrical current matched the acoustic sign wave
input signal is blue and comes in it changed and what came out looks the same but it wasn’t sound
transferred acoustic signal to electric signal that looked identical
it is an analog electric signal
analog - the same, shape of signal that came out of the microphone is exactly the same as shape of signal that went into the microphone
now we have electric imitation of sound we can use it to do stuff but we do not have an amplifier yet
Define temporal resolution
The ability of the auditory system to detect time related changes in the acoustic stimuli over time
Needed in order to understand speech in noise
Ex: shutter speed = temporal resolution
If it is not fast enough the speech will be blurred or smeared like a photo
In a noisy environment it is hard to pick out what individual words are
Time related Cues
explain 3 processes that support temporal resolution
Gap detection
brief gaps of pauses between syllables, words, sentences, etc
Phonemic duration
some words are elongated, shortened etc. - distinguishes one word from another can vs cant
Temporal ordering (boots; boost)
Time related aspects of acoustic signal
boots vs boost
Suprasegmentals
Provides us with meaning (is it a question, a demand, etc.)
Patterns of stress
Intonation
rhythm
Explain binaural loudness summation. Its suprathreshold benefits and how this benefit supports hearing aid fitting strategies.
The auditory system increases the perception of loudness when auditory input signals are received from two ears
Increases threshold around 2-3 dB & increase suprathreshold around 6-8 dB
Results in PT perceiving greater loudness w/ bilateral devices
Less gain is needed to reach comfortable listening levels
Can fit a PT with less loudness in order for them to hear the words
What does a 6/8 IP rating suggest?
Dust light
Protects against long periods of liquid immersion
How easily the material flows before it cures; thickness
viscosity
Materials ability to return to shape after removal
stress relaxation
Shrinkage over 7 day period
contraction ratio
After cure hardness
shore value
Describe the cause of the occlusion effect (OE) and associated patient complaints. Describe the degree of LF threshold loss associated with OE concerns
Describe two management techniques used to reduce OE
Increased perception of one’s own voice when something is blocking the ear canal
Common complaint occurs when LF threshold is better than 50 dB
Causes
Dome closes off the ear
Mold with too small of a vent
Insufficient venting and/or insufficient canal length
non custom couplers result in less complaints of OE
Vent size & stabalizing the device in the bony canal are two management techniques to reduce OE
Move past cartilage to bony portion stopping vibrations & vent allows more energy to flow through
Describe the impact vent size has on high frequency output
Vent size impacts HF output
The larger the vent the less HF output you get from a HA
Define front-end distortion and its cause. Describe why digital HA’s have a lower mic dynamic range. Describe how front-end distortion is managed in digital hearing aids.
*mic has a dynamic range and FED happens when the input signal exceeds this
Distortion in analog - input >/= 115 dB SPL (anything louder sounds distorted)
Distortion in digital mic happens with input >/= 96 dB SPL (0-96, anything louder sounds distorted)
Real world snr is 2-3 because of head shadow and polar plots
If Signal was 76 and noise 74 what is SNR?
2 dB
Greatest directivity index
hypercartiod
Explain how raising/lowering TK input alters output of signals at or below the TK. Describe practical applications for this adjustment (include adjustments for high and low TKs)
lowering the TK to a softer input intensity will not change the output of the louder input signals
raising the TK to a loader input signal decreases the output of signals below the TK
lowering the TK to a softer input intensity increases the output of signals below the TK
Practically, shift TK down if a PT needs more clarity of soft consonant sounds & shift TK up to reduce audibility of soft low frequency background noise
Explain expansion & its purpose. List CR associated with it
ower output with very very soft sounds
as input increases amount of gain applied is reduced = compression
as input increases amount of gain applied is rapidly increasing too = expansion
Very soft acoustic signals below the first threshold kneepoint (TK) are attenuated by applying
Expansion
<.9:1 CR
