Midterm Flashcards
Induction loop
Similar to phone
Emits electromagnetic signal
Looped system
With or without hearing aids
- individual headsets
- interference
- inexpensive
- installation/maintenance
Frequency modulated systems (FM)
Carry acoustic signals through FM radio waves from transmitter to receiver
865 MHz / 175 MHz wave length
Comprised of transmitter➡️ worn by speaker or at the source of interest
Signal sent from the transmitter to reciever through a FM signal
-eliminate distance
-improve communications
-highest SNR than any device ➡️
15-20 db
-optimal for classroom
FM systems for children
Default ➡️ FM-microphone
Hearing aid automatically detects FM signal when it is turned on
FM system on the voice closest to the transmitter will dominate
However child will still be at to hear around him
Receivers usually “eat level”- attached to the hearing aid
Assistive listening devices
Alternative ways of improving communication.
TV listening devices
Usually infrared technology
Cannot have obstructions ➡️ signal will be crappy
Used as far as 10 metres
Sometimes can modify volume and pitch
Amplified telephone
Volume
Pitch
Tone
CONTROL
Voice carryover phones (TTY versus VCO)
TTY ➡️ type message to voice
VCO ➡️ voice to text
Both:
- special phone
- call service number before hand
Tinnitus Maskers
Several expensive devices but realistically a radio with ocean sounds would work
Hearing instrument accessories
REMOTE CONTROLS: allow users to access the (potentially) multiple programs within their hearing instrument ie volume control
TV LISTENING DEVICES: connects to back of TV or say/cable receiver, wirelessly transmits audio signal to hearing instrument, someone’s need to wear a device, same idea as FM system
BLUETOOTH
CELLPHONES
True or false: hearing loss is linked to accelerated brain tissue loss
True
3 Technologies OTICON uses in their hearing aids to help reduce feedback
- Gain management
OTICONS proprietary prescriptive formula
VAC
Signs of hearing loss - adults
Report that people mumble Trouble hearing background noise Ask for repetition Usually picked up by family Require you to face them Cannot hear from a distance Report people speak too quickly Tinnitus Trouble on phone but not in person
Signs of hearing loss - children.
Language delays Issues with articulation Ask for repetition Require more effort to get attention Paren or teacher is usually the first one to raise concerns Issues with academic performance Ear pain
Hearing loss and newborns
Hearing screening at birth
Infant Hearing Program (IHP)
4 in 100 babies have hearing impairment
Goal IHP IS TO GET BABY AMPLIFIED BY 6 months-language normal if aided by 6mo
Early identification saves app. 400000 is special Ed costs
What is the goal of IHP?
To get the baby amplified by 6mo because language processes normal is aided by 6 mo
Effects of hearing loss
1 decreased audibility
2 decreased identification
3 decreased dynamic range
4 decreased ability to hear in noise
Decreased identification
“Pick up the black harp” vs “kick the cat hard”
Ability to distinguish sounds of differing frequency declines
Temporal processing declines
Decreased dynamic range
Soft sounds need to be louder to hear them
No change in audibility for loud sounds, sometimes increased sensitivity to loud sounds
Ex. Window thing
The bottom line
Individuals with hearing impairment, require the signal to be louder, come in at a slower rate, and have minimal competing signals
Leads to greater signal to noise ratio
Telecoils
Since '40's Small ➡ ️mini antenna Picks up electromagnetic signal given by a phone, etc. ➡️ lack of visual cues, feedback tendency Manual and automatic versions Interactions with looped buildings
What Makes Someone A Candidate For Amplification
Severity of hearing loss-more severe the loss, greater likelihood of amplification
Speech Intelligibility -can be affected by a variety of factors…-signal-to-noise ratio (SNR) plays a large role in an individual’s ability to derive benefit from amplification
Lifestyle-still working? concerns from family, reclusion/isolation
Assessing Candidacy
Lower Limit of Aidable Hearing Loss
Upper Limit of Aidable Hearing Loss
The Lower Limit of Aidable Hearing Loss
Severity of Hearing Loss Speech Comprehension Acceptance of Noise Environment, Needs, Expectation (ENE) Stigma Managing Hearing Instrument Age Personality Central Auditory Processing Disorders Tinnitus
Severity of Hearing Loss
Generally, the more severe the hearing loss, the greater the usage-the greater likelihood someone will pursue amplification
Pure tone thresholds alone cannot be used to determine hearing aid benefit
Speech Comprehension
Speech assessments (speech reception thresholds or word recognition scores) have shown no strong evidence to predict hearing instrument benefit Test conditions (sound treated audiology booth) are not consistent with the real world Signal-to-noise ratio loss is a way to assess an individual’s ability to understand speech in the presence of noise-HINT and QuickSIN
Acceptance of Noise
Individuals with untreated hearing loss, think the world is a lot quieter than it actually is
We can determine beforehand how “willing” someone is to follow conversation while there is background noise going on-Acceptable Noise Level (ANL) test
Environment, Noise, Expectations (ENE)
Hearing instruments are built for quiet environments, with one primary talker-greatest amount of benefit
The noisier the environment, the less amount of benefit-background noise limits low frequency hearing, hearing thresholds limits high frequency hearing
Outcome measures can assess (ENE) and hearing instrument technology can assist in noisy situations
Stigma
Some find hearing loss and hearing instruments to be associated with “being older”
Size of the hearing instrument matters, many studies have shown people’s willingness to pay more for smaller hearing aids (Abrams, et al. 2004, Kochkin 1994)
Many manufacturers provide different colours that match hair or skin tone
Managing of Hearing Instruments
Hearing instruments are very small
Low cognitive ability, dementia, etc. can cause difficulties with remembering how to operate the hearing aid
As a clinician it can impact which style of hearing instrument you select
Age
Indirectly affects candidacy
Overlaps with many issues previously discussed
Central processing disorders and signal to noise ratio loss increases with age
Satisfaction with hearing aids decreases as age increases (Hosford-Dunn & Halpern, 2001)
Personality
The traits possessed by a hearing instrument candidate can impact the amount of benefit
More agreeable and open minded more perceived benefit
Expectations play a huge role
Central Auditory Processing Disorders
Impacts how the acoustic signal is processed at the higher auditory centres (auditory nerve)-individuals with ADP can have normal hearing
Increases in prevalence with age
Assistive listening devices such as FM systems may be an option for those with ADP
Tinnitus
Many individuals with tinnitus may also have hearing loss-Related to neural reorganization of auditory centres in the brain
Hearing aids can provide relief by amplifying ambient noises in the environment-gives the brain something else to focus on
Upper Limit of Aidable Hearing Loss
These individuals will have profound hearing losses
Traditional hearing instruments may not be appropriate for these individuals
Options for upper limit of aidable hearing loss
Unilateral Cochlear Implant Bilateral Cochlear Implants Bimodal Hearing Instrument-one cochlear implant, one hearing aid Unilateral Hearing Instrument Bilateral Hearing Instruments Bone anchored devices-vibrations
Possible Medical Issues
Sudden hearing loss-if treated fast enough (with steroids) hearing can recover
Unilateral tinnitus that has a pulsing perception
Vertigo
Conductive hearing loss
Unilateral hearing loss that where the etiology is unknown
Cerumen impaction
What are some reasons people think hearing aids “suck”?
“too noisy”-individuals with long standing, uncorrected hearing loss may not “like” or appreciate how loud the world is
“can’t get it in my ear!”-poor manual dexterity, can’t see where you’re going, miniaturization of devices
expensive -hearing instruments can run upwards of $6000 for two
perception of technology-marketed as these complex high technical instruments
Factors that influence adoption of hearing instruments
- experience
- recommendation
- family
- $
- minimize need
- stigma
- attitude
- knowledge
- trust
What does Ally Cat think helps people get past the barriers against adoption?
- Family members (supportive or otherwise)-television is a source of conflict-family members can be in tune with how hearing impairment has effected their personality/demeanour
- Word of Mouth Referral -often times the best marketing tool
- “Connectors”-those individuals who want to remain connected
What does Ally Cat consider the biggest barriers against adoption?
- Financial-set of hearing aids cost anywhere from $3000 to $6000-better off investing in a pocket talker versus than buying two hearing aids for less than $1000
- Minimizing Need -form of denial-people need to “enunciate” their words -can be isolated, minimal interaction
- Stigma-many people still associate hearing instruments with getting older-”but I’m not even 60 yet!”-vanity
What they used to hear in the “dark ages”
-Cupping the ear with your hand-5-10dB gain for mid and high frequencies from the front-helps attenuate noise behind you
-Use of objects that would allow them to collect sound from a larger area than just their ear
-This practice dates back to the 18th century
Individuals also used speaking tubes, to funnel sound directly into one’s ear
What they used to hear by the 19th century
Acoustic headbands became very popular-better able to conceal them under hair, beards, and head swag
Electronic Hearing Instrument
- constructed after the invention of the telephone
- the first was called the “Akouphone” - 1898
- vacuum-tube hearing instrument introduced in the 1920’s
- high battery drain
Transistor Hearing Instruments
- Improvement in battery drain, sound quality, and size over their vacuum-tubed predecessors
- Introduced in the in 1950’s and were used up until the 1980’s
Digital hearing instruments
- First available as a body aid (1987)
- First digital behind-the-ear (BTE) hearing instrument was produced (early 1990’s)-programmed through “digital control”
- By 1995-1996 Oticon and Widex produced the first “all digital” hearing instruments-allowed hearing instruments to be programmed using computer software
- Using computer software to program hearing instruments enabled hearing care workers to…-save and load previous settings-increased control of the hearing instrument-introduction of automatic and advanced features (feedback management, noise reduction, etc.)
- you have more control over compression and frequency response of the hearing instrument
Accessories for digital hearing instruments
- The technology in digital hearing instruments has also enabled manufacturers to use bluetooth and other wireless signals to connect hearing instruments to cell phones, TV’s, remote microphones, amongst other things
- Two manufacturers (GN Resound and Starkey) allow their hearing instruments to be controlled directly through an iPhone
- Others manufacturers require a proprietary intermediate device
What are the styles of hearing instruments?
BIICO
- Behind-the-ear (BTE)
- In-the-ear (ITE)
- In-the-canal (ITC)
- Completely-in-the-canal (CIC)
- Open fit behind-the-ear
what is BTE appropriate for?
all hearing loss severities
What is BTE comprised of?
Casing that sits behind the ear, that is comprised of…
-one or two microphones
-receiver
-digital signal processing chip
-program button-volume control
-battery door
Earhook attaches to the casingon one end and earmold tubingon the other
what are the 4 advantages of BTE?
- bigger battery - longer life
- bigger - easy to manipulate
- can fit the widest range of hearing losses
- very durable
what are the 3 disadvantages of BTE?
- cosmetics
- tubing can be difficult to change - it hardens with humidity
- insertion can be difficult - 2 pieces - hearing aid & earmold
what is ITE appropriate for?
mild to severe hearing loss
what is ITE comprised of?
- Hard plastic casing that fills the concha bowl and helix for the user
- In the casing encompasses all the components of a hearing instrument
- A wax guard sits at the end of the ear canal portion
what are the 4 advantages of ITE?
- one piece - easy to insert and remove
- easy to manipulate due to the bigger size
- can fit a fairly wide range of hearing loss
- volume control and program button are easily accessible
what are the 3 disadvantages of ITE?
- cosmetics
- changing the wax guard can be difficult
- has to be sent down if it breaks down
What is ITC appropriate for?
mild to moderately severe/severe hearing loss
What is ITC comprised of?
- Hard plastic casing that fills the concha bowl
- In the casing encompasses all the components of a hearing instrument
- A wax guard sits at the end of the ear canal portion
what are the 3 advantages of ITC?
- one piece- easy to insert and remove
- cosmetics
- volume control and switch on the hearing device
what are the 2 disadvantages of ITC?
- has to be sent in if it breaks down
2. changing wax guard could be difficult for some
What is CIC appropriate for?
mild to moderately-severe hearing loss
What is CIC comprised of?
- Of hearing instruments that are readily available these are the most discrete ones
- Sit completely in the canal and can only be seen when a person looks directly into one’s ear canal
- Not all CIC’s have wireless capability-can’t connect to cellular phones, remote controls, or TV’s
- There are also Invisible-In-The-Canal(IIC) hearing instruments-sit deeper than a CIC
what are the 2 advantages of CIC?
- one piece - easy to insert and remove
2. cosmetics
What are the 4 disadvantages of CIC?
- changing the wax guard could be difficult for some
- may be inappropriate if hearing loss progresses
- discomfort
- more wax build up
What is open-fit BTE appropriate for?
all types of hearing loss
what is an open fit slim tube hearing instrument?
- These hearing instruments have the receiver in the hearing aid itself, and use a thin plastic tube to deliver the sound into the ear canal
Open Fit Behind-The-Ear Hearing Instruments
- By far the most popular style of hearing instrument for it’s cosmetic appeal and flexibility for a wide range of hearing loss
- Can be coupled to a variety of domes and custom molds depending on the needs of the hearing instrument wearer
- Can either have a receiver sitting in the canal (open fit receiver in the canal) OR have a slim tube
Open Fit Behind-The-Ear Hearing Instruments (Receiver in the ear)
Similar to a traditional BTE hearing instrument, there will be a microphone, DSP chip, and amplifier will sit behind the ear
The difference is the receiver will sit INSIDE the ear canal
Occlusion Effect
Occlusion effect=low frequency sound being “trapped” in your ear canal
- when you plug up your ears you may hear yourself more echo -y or hollow - unnatural sounding - The primary reason open fit hearing instruments are so popular is because they reduce the “occlusion effect” - With age related hearing loss we see a decrease in high frequency hearing sensitivity… - Good low frequency hearing + plug…can lead to occlusion
What are some considerations with open fits?
Type of Dome…
-mainly consider what the severity of the low frequency hearing loss is (more severe, more of an enclosed dome required)
Strength of Receiver
-more severe the hearing loss, greater the strength of receiver required
The vents (holes) in each dome going left to right get smaller and smaller, while the amount of material making up each domes increases
More vents=Less occlusion=More satisfied users
Will be dictated by the strength of the receiver-able to change these receivers on the hearing instrument
When open fit style hearing instruments are coupled to custom earmolds larger receivers can be added, and thus more power provided
what are the 4 advantages of open fit?
- cosmetics
- reduces occlusion effect
- most repairs can be done in clinic
- flexibility
what are the 3 disadvantages of open fit?
- changing the wax guard could be difficult
- inserting the hearing instrument
- liable to fall out much easier then other styles
What is an extended use hearing instrument?
- The Lyric is a hearing instrument developed by a hearing instrument manufacturer called Phonak
- It stays in the ear for 3 monthsat a time, and is bought on a1-3 year subscription
- Many contraindications to the Lyric
- straight ear canal, too much wax, sensitivity increases as you get closer to the tympanic membrane, can’t get wet
what are the 3 basic components of a hearing instrument?
- a receiver
- a microphone
- a microchip (digital signal processor)
the Microphone
- Where the sound will be picked up and enters the hearing instrument
- Many of today’s hearing instruments have two microphones -allows for directional hearing
the Signal Processor
- Analyzes the incoming signal-breaks it up and filters it
- Each hearing instrument manufacturer will have their own processing strategies-think Microsoft vs. Apple
- Advanced technology is embedded within the signal processor-directional microphones-feedback management-noise reduction
- It will modify the signal based on the environment the hearing instrument is in, the settings or parameters that have been created, and the severity of hearing loss it is programmed to
- The processor in the digital hearing instruments will take the sound waves picked up by the microphone, convert them into a digital signal, analyze them, distort/manipulate that signal, and then convert it back to an analog signal
- Makes use of binary code
the HI receiver
Transducer that converts the amplified, modified electrical signals back into sound
HI batteries
- All hearing instruments can run off zinc air batteries
- At least one hearing instrument manufacturer has rechargable batteries
- Like with every other battery there is a positive and negative side
- Hearing instruments are designed in a way that requires the battery to be properly orientated
- Different sizes
- Colour coded
- Life-span approximately 4 days to 3 weeks
- Stickers come attached to keep the battery fresh
What does an earmold do?
help a hearing instrument retain in someone’s ear
How do you choose a style of earmold?
- the severity of the hearing loss
- what can the individual get in their ear
- what will the individual tolerate in their ear
What are 3 styles of earmolds
- skeleton
- semi skeleton
- half shell
- canal mold
- non occluding
- canal lock
what are the types of ear mold materials?
- lucite - hard durable- could hurt - don’t fall
- heat-cured lucite - same as lucite but hypoallergenic
- Polyethylene - mild/severe HL - doesn’t shirck - best for ppl with allergies
- formaseal - softer then Lucite, durable-shrinkage-peds pop.
- silicone -soft- durable - hypoallergenic - doesn’t shrink
- new-sil - softest - doesn’t really shrink, selectively hypoallergenic, mod. durable
- flex-canal - lucite/silicone combo
Vents and Earmolds
Allows air to flow in and out of the ear through the earmold
Reduces occlusion
Size is dependent on the severity of the hearing loss
Hearing Instrument fitting Process
Audiologist and Hearing Instrument Specialists use a process called real ear verification when programming instruments
It involves a real ear machine, which is compromised of a speaker, 1 or 2 external microphones, probe tube(s) and a test box
Hearing instruments, programming devices, and programming software
Coupler Microphones
There are two different types of coupler microphones
HA2 HA1
These couplers are designed to “mimic” the acoustics of the “average” ear canal
Traditional BTE’s attach onto the HA2 Coupler
ITE’s, ITC’s, CIC’s, and open fit BTE’s with custom molds attach to the HA1 coupler
What are the two ways to verify?
- Verify in the test box-can be used for all hearing instruments besides those without custom molds
- Verify on the ear-all styles hearing instruments can be verified on the ear
What are the three test box benefits?
- the microphone does not move
- minimal artifact from ambient noise
- good for children
What is the test box disadvantage?
- does not include the patient in the process
what are the two benefits of real ear testing?
- patient is included
2. can be used as a way of trouble shooting
what are the three disadvantages of real ear testing?
- requires patient to stay still and quiet
- artifacts from the room, noise, reflections
- difficult for kids
hearing instrument fitting - before the patient comes
- make sure your microphones are calibrated
- measure your probe tubes
- enter the patients hearing threshold into real ear machine
- pre-set hearing instrument test box if possible
Probe tube measurements
- 31mm for adult males
- 28mm for adult females
- 20-25mm for children
hearing instrument fitting - once the patient has arrived
- Otoscopy-check for wax, can cause issues with feedback and getting accurate readings
- Place probe microphone module on their ear-want to insert the probe tube down their ear canal, goal is to be 5mm away from the ear drum
- Set the individual as close as possible to the external speaker and at least 5 feet away from any walls
What is speechmapping?
- This is a standardized passage of speech we use to verify hearing instruments-what will be played through the speaker
- It will gives us as audiologists a sense of how much amplification a hearing instrument user is receiving-is it loud enough across all the frequencies?-are there frequency ranges where the individual is underamplified? Overamplified?
Speechmap - Audiometry & RECD
Audiometry
-this is where we would insert the individual’s hearing thresholds
-can include bone conduction thresholds (if differ from air conduction)
-UCL=uncomfortable limits, can measure these during the hearing test or using average (predicted) values based on the hearing thresholds
RECD
-a measurement that compares the size of an individual’s ear canal to that of the “average” ear canal in the general population, allows for a more accurate hearing aid fitting
Speechmap - Verification & Targets
Verification
- the mode defines how we are measuring hearing aid performance (test box vs. real ear)
- fitting defines what style of hearing instrument we are measuring
Targets
- the rule used relates to which prescriptive formula you are following, this will determine where the targets (green crosses) come up in the speech map
- type indicates binaural or monaural hearing aid user
Speechmap - stimulus
The stimulus we use to measure/verify hearing aid performance is noted here. The stimulus can be speech at various volumes or various types of noises (broadband and narrowband). MPO stands for maximum power output and is a way to ensure the hearing aid does not further amplify very loud sounds that may cause pain or damage.
speechmap caveats
Making sure the volume of the hearing aid is “on target” is just a starting point
Not an exact science
Some people like their hearing aids to be above the targets, some people like it below
Need to balance what people like versus what they need…
Prescriptive Formulas
Give us a way to determine how much volume (gain) a given individual needs for their hearing loss
An objective way to measure hearing instrument performance
who creates prescriptive formulas?
Hearing instrument manufacturers: phonak, oticon, widex, siemens, unitron
Research centres: western, national acoustic labs - Australia
how do we know how much volume a person needs?
- the preferred amount of volume and individual recieves depends on the input signal –> So your input will always be the same, but depending on a) how loud the input is and b) the prescriptive strategy- used X may change
2,The preferred volume may depend on their suprathreshold loudness perception and their frequency resolution-cannot be determined with a hearing test
- The preferred volume may depend on how the individual currently “hears”
- How important the input signal is may determine the preferred volume -more important louder volume?
supra-threshold based prescriptions
SHAPIRO
CID (central institute for the deaf)
LGOB (loudness growth in half octave bands)
IHAFF contour (interdependent hearing aid fitting forum)
ScalAdapt
DSL i/o (desired sensation level input/output)
threshold based prescriptions
NAL, NAL 1, NAL 2 (national acoustic laboratories) Berger Pogo (prescription of gain and output) FIG6 CAMREST DSL m i/o
Targets
- each formula has a set of targets
- allow the clinician to manipulate the gain of the hearing instrument to”achieve” the formula
- Targets are where the “average” individual with that specific hearing loss needs the volume of their hearing instrument(s) to achieve the goal of the specific formula (NAL or DSL) that’s being implemented
where the targets fall on the graph is predicted on…
- Severity of the hearing loss
- Specific formula used
- Monaural or Binaural Fitting
- Conductive component
- Child or Adult
Why would a hearing instrument be set above the target?
Generally long term users
Usually more severe hearing losses
Conductive component
Why would a hearing instrument be set below the target?
extended auditory deprivation
what are the two most common prescriptive formulas
NAL & DSL
what is the goal of NAL?
- maximize spoeech intelligibility at a volume comparable to what someone with normal hearing would need
- achieves this by determining how various hearing losses impact speech intelligibility and the perception of loudness
What is the goal of DSL or desired sensation level?
- normalize loudness
- all sounds (soft, med, loud) would be the same for the hearing impaired as they would be for someone with normal hearing
what is DSLmi/o?
- the latest version of DSL
- m stands for multistage
thus
there are four stages:
1. expansion
2. linear amplification
3. compression
4. output limiting
what prescriptive formula is most often used for the adult population and why?
NAL
- it was originally designed for adults
- maximized speech intelligibility
what prescriptive formula is most often used foro the ped. population and why?
DSL
- normalized loudness
issues with prescriptive formulas
- acclimatization
- preferred loudness levels
- dead regions
- severe to high frequency losses
What are the 2 additional considerations regarding prescriptive formulas?
- unilateral hearing loss
- If any individual has hearing loss in both ears, but only wears a hearing instrument in one many prescriptive formula’s will add 3dB of volume on top of what would normally be prescribed
- Binaural summation
- 3dB increases are used, as we are able to perceptually notice the difference - infants and young children
- Prescribed more volume than adults with similar hearing losses because they are developing and learning
- Incidental learning, learning by hearing passively - conductive and mixed hearing losses
- attenuation of sound in middle ear cavity
Input
refers to he acoustic signal entering the microphone of the HI
output
refers to the amplified signal the ear recieves
gain
the difference between input and output
compression
the OUTPUT range is smaller then the INPUT range
compression threshold
the input level at which the compressor switches from linear amplification to non-linear amplification
compression ratio
determined by dividing the difference in input by the difference in output
multichannel compression
- Because hearing loss can vary across frequency it is prudent to have different compression ratios and compression thresholds
- This affords clinicians the ability to optimize the gain and frequency response of the hearing instrument to best suit a given individual’s hearing thresholds
- Gain and compression will not be the same across frequency, will be dependent on the severity of the hearing
linear amplification
For every 1dB increase in INPUT there is a corresponding 1dB increase in OUTPUT
Once the input reaches a certain point (80dB SPL) the output will no longer increase
non linear amplification
Occurs when the difference between the input and the output is not 1:1
Non-linear amplification is represented by compression ratios
Compression ratios are calculated by dividing the
difference in input by the difference in output
compression ratios
A compression ratio of 3:1 would indicate that once past the compression threshold an increase in 3dB input at the level of the microphone would represent a 1dB increase in output at the receiver of the hearing instrument
wide dynamic range compression
- most common
- gradual application of compression over a wide range of sugnals
attack and release times
- Protect against abrupt input changes (environmental sounds) - reality is that we aren’t always listening to sounds at the same volume
- If we go suddenly from very quiet environments to very loud environments we want to ensure the hearing instrument doesn’t overamplify and cause damage
- Once those loud sounds stop we want to ensure the hearing instrument is providing enough volume so the wearer doesn’t miss anything
attack time
the time it takes for compression to kick in
release time
time it takes for compression to turn off
why is compression good?
- Avoid Distortion, Discomfort, and Damage
- Optimize the Residual Dynamic Range and Restore Normal Loudness Perception
- Maintain Listening Comfort
- Maximize Speech Intelligibility
- Reduce Noise
directional microphones
Directional microphones allow the hearing instrument to amplify a specific area or direction with the hopes of improving speech intelligibility
- All hearing instruments have two microphone ports, one at the front and one at the back
- Hearing instruments have a database of different shapes (polar plots) that they will create based on the environment that the individual is in
omni directional microphones
Amplify sound all around the hearing instrument user
how does the HI know where to amplify?
Two things dictate what direction the microphones will amplify in
1. Port spacing-the distance between the front microphone and the back microphone-helps to distinguish sounds front vs. back
2. Internal delay-a low pass filter, analyzes low frequency sound waves
Based on the information gathered by the port spacing and the internal delay an amplification map forms
An amplification map shows which direction the hearing instruments amplify -these maps are referred to as polar plots
types of polar plots
- omni directional
- figure 8
- hyper cartoid
- cartoid
fixed versus adaptive directional microphones
Directional microphones can be set in a way that they are always amplifying in one (fixed) direction, or they can be programmed to adapt to their environment
Hearing instruments can have one or both of these settings
Adaptive directional microphones are frequency dependent -lots of low frequency from behind? Hearing instrument might automatically switch into a cardioid pattern
Adaptive directional microphones are better than fixed directional microphones when these three conditions exist
- dominant nearby noise source
- the dominant noise is stable for an extended period of time
- the dominant noise source is aligned in the area where the fixed directional microphone is not amplifying
things to consider with directional microphones
- signal to noise ratio
- benefit from directional microphones will not be as apparent in rooms with very little noise, or a strong signal
- conversely rooms with diffuse noise aren’t conducive to directional mics - room acoustics and distance
- anytime you increase the distance between the source and the hearing instrument user to introduce more reverberation which will reduce the benefit of directional microphones
what are the 4 drawbacks of directional microphones
- side or read amp.(most are front facing)
- decrease in low frequency amp. - directional mics are designed to naturally reduce low frequency amplification, can have unintended consequences in areas with low level noise
- reduced localization-reduce left and right localization when hearing instruments do not coordinate with each other
- wind noise-greater for directional versus omnidirectional
Noise Reduction (NR)
- provide less amp of noise, while not affecting amp toward speech sounds
- hearing instrument manufacturers use to reduce signal to noise ratio
How does NR work?
- HI detects the modulation in the signal
- HI have speech/non speech detector to determine between speech versus noise
- programs are able to detect amplitude differences and modulation depths of a signal
- also able to distinguish between feedback
what are the 2 most common ways to reduce noise through the output of the hearing instrument filter
- wiener filter
- spectral subtraction
- both have goals of decreasing the output of the hearing instrument in frequency bands with the poorest SNR
some caveats of NR
- Noise reduction algorithms depend on the ability to properly identify noise
- calculations are often done based on what is occurring in the preceding seconds
- Want to be careful to not reduce gain too much for individuals with very severe hearing impairments-want to maintain speech intelligibility as much as possible
what are the benefits of noise reduction?
- Many studies have shown that individuals prefer listening with their hearing instruments in noise with noise reduction processing on vs. off-no improvement in speech intelligibility
- Reduce the intensity of very loud impulse sounds or transient noises-dish hitting the floor -door slamming
what is feedback in HI?
- occurs when the output of the microphone (inut) of the hearing instrument
- causes a “whistling” sound
what are the main causes of feedback
- someone or something getting too close to the hearing aid (more likely with individuals wearing open domes, profound high frequency hearing loss)
- wax
- poorly inserted hearing aid
How do you control feedback?
- gain control
- phase control
- feedback path cancellation
Gain frequency response control
- -This method involves controlling the gain (output) the hearing instrument provides to the user
1. Reduce the overall volume-feedback is eliminated at the consequence of poorer speech intelligibility
2. Reduce the volume at specific frequencies-usually channel specific eg. Feedback at 3 kHz, in a channel that controls 2-4kHz…volume is reduced from 2-4 kHz just to eliminate feedback at 3 kHz
what is the drawback to gain frequency control?
- reducing the overall gain fro an HI will affect ability too hear
- frequency could changed depending on cause
phase control
- Goal of phase control is to detect the frequency that is causing the feedback and use an inverted phase response
- Phase control is a delayed response to the ongoing feedback so it is inefficient to use when multiple frequencies are involved
feedback phase cancellation
- Most popular method of feedback control in today’s hearing instruments
- Uses a completely internal feedback path that is created by the hearing instrument that is designed to prevent any external feedback path
- The hearing instrument will be able to continuously monitor the EXTERNAL feedback path
- Think of it as a hall monitor…
- If the external feedback path gets to the point where feedback will become noticeable to the hearing instrument user and those around them, the INTERNAL feedback path will kick in and cause a reduction to the external feedback path-leaves the overall gain unaffected
what are the benefits of feedback?
- some use it to tell if their hearing aids work
- limited benefit for new ones
- cup and hold method
frequency lowering
- Most individuals with hearing loss have poorer hearing in the high frequency region
- Limited ability to extract the necessary speech information from these regions
- Frequency lowering is the idea that you take high frequency information and move it to a lower more audible frequency range
If we can move high frequency sounds to a lower frequency region (with better hearing) chances are intelligibility will be greater because the individual will be able to extract more of that information
what are the three typpes of freedback lowering
- transposition
- compression
- translation
frequency compression
High frequency information is “compressed” into a lower frequency range-similar to how loud sounds get compressed to fit into a given individual’s dynamic range
frequency transposition
The shifted high frequency sounds overlap with lower frequency information
Only transposed when the processor detects an extensive amount of high frequency information
frequency translation
Takes high frequency information and processes so it becomes a lower frequency sound that is (hopefully) more audible
who is a canditate for frequency lowering
Anyone with a high frequency hearing loss (≥2kHz) that exceeds 80dB HL
Infants and young children
Those who have issues with feedback
frequency lowering can be a way to reduce feedback
what are two considerations of frequency lowering
- Adaptation -frequency lowering can cause an unique perception to speech
- Parameters Used-the more aggressive the compression, transposition, translation is the harder it will be for an individual to acclimatize to the signal-while optimized settings for a given hearing loss have been developed, different individuals (with the same loss) may perceive different levels of benefit
advanced features of frequency lowering
- speech cure enhancement
- de-reverberation and echo reduction
- environmental classification
- automatic telephone detection
- data logging
- occlusion reduction
- Used to compliment the gain provided by the hearing instrument
- Evidence for improved speech intelligibility is limited
- Evidence points towards making listening “easier”
- Lots of practice and knowledge required to maximize features
advantages of bilateral fittings
- speech intelligibility
a. head diffraction effects - speech on one side but noise on the other (good snr vs bad snr) - if speech on unaided side you lose good snr
b. binaural squelch- suppress interfering sounds and focus on speech within noise
c. binaural redundancy - reflections of hearing a signal twice - same signal in both ears = greater speech intelligibility - localization
- Better localization in both the horizontal and vertical planes
- Your ears and brain can compare timing and intensity cues, two hearing instruments maintain these cues
- Most effective for individuals with hearing losses that are moderate and greater - sounds quality
- Avoid Late-Onset Auditory Deprivation
disadvantages of frequency lowering
- cost
- binaural interference
- self-image
