Perscriptive Formulas, Compression And Hearing Software Flashcards
What are the four challenges regarding knowing how much volume is needed?
- The preferred amount of volume received depends on input volume
- Preferred volume depends on suprathreshold loudness perception and frequency resolution
- Preferred volume may depend on how they currently “hear”
- How important the input signal may determine preferred volume
What are the suprathreshold based prescriptions
SHAPIRO
CID (central institute for the deaf)
LGOB (loudness growth in half octave bands)
IHAFF/contour (independent hearing aid fitting formula)
ScalAdapt
DSL I/o (desired sensation level)
What Re the threshold based formulas
NAL (national acoustic laboratories) Berger POGO (prescription of gain and output) FIG6 CAMREST DSLm i/o
What does the “target” do
Allows you to manipulate the gain of the hearing instrument to achieve the formulas
What predicts where the targets fall on the graph
- Severity of the hearing loss
- Specific formulas used
- Monaura or binaural fitting
- Conductive component
- Child or adult
What do the targets represent
Where the average individual with a specific hearing loss needs the volume of their hearing aids to achieve a specific formula
Why would you aim for above target?
If they are long term users
If they have a more severe hearing loss
Conductive component
Why would you aim for below target?
If they have had extended auditory deprivation
What does the prescriptive formula do?
Gives us a way to determine how much volume an individual needs for their hearing loss
What is the goal from the NAL, NL2, and NL1`
Goal of the non linear prescription is to maximize speech intelligibility at a volume comparable to what someone with normal hearing would need
How does the NAL achieve the goal
they determine how various hearing losses impact speech intelligibility and the perception of loudness
What is the goal of the DSL
Goal of this prescription is to normalize loudness
How does the DSL achieve their goal
all sounds would be the same for hearing impaired individuals as it would be for someone with normal hearing
What are the stages in the DSL m[i/o]
- Expansion
- Linear amplification
- Compression
- Output limiting
Who typically prefers the NAL vs the DSL
NAL - Adults
DSL - pediatrics
Is the DSL adult better for an adult with congenital hearing loss than another?
Nope
What are the four issues with prescriptive formulas and expand
- Acclimatization
- the more severe the loss and the longer they have gone through auditory deprivation acclimatizing to their HA volume is harder - Preferred loudness levels
- different people with the same loss have different preferred levels - Dead regions
- inner hari cells in cochlea stop functioning: amplify one octave higher in the dead region is appropriate - Severe to profound high frequency losses
- excessive high frequency information may lead to reduction in speech intelligibility
Additional considerations for unilateral hearing loss
If a hearing loss in both ears but only wears one hearing aid you can increase formula by 3db (this is where we can perceptually hear a difference)
Additional considerations for infants and young children
More volume than adults with similar losses because thy are developing and learning
Additional considerations for conductive and mixed hearing losses
They have an attenuation of sound in their middle ear cavity
Many prescriptions add gain to overcome the conductive component
“Power junkies” they like the volume higher then clinicians would like
What is the dynamic range
Range of sounds a given individual can hear
Cannot hear very soft sounds
Tolerance for loud sounds doesn’t change
What is compression used for
To increase intelligibility we need to increase volume of softer sounds without overamplifying medium and loud sounds
Allows you to take a wide range of input volume and place these sounds comfortably into a smaller range
Define input
Refers to the acoustic signal entering the microphone of the hearing instrument
Define output
Refers to the amplified signal the ear receives
