final exam with review topics Flashcards
explain the carbon microphone process and how it goes from acoustic signal to an electrical signal
the acoustic signal arrives to the microphone and vibrates the diaphragm which gets compressed and when it moves inward, the carbon balls get pushed together (positive voltage flow). the sound waves goes outward and will bring the diaphragm out with the carbon balls (negative signal)
-this back and forth direction results in an electrical wave that matches the input acoustic signal
overview of a carbon microphone
sound wave → arrives at microphone → pushes on diaphragm and compresses carbon balls → creates a analog signal as the sound wave continues → creates a analog electric signal → receiver picks up the electric signal and makes it back to an acoustic wave
temporal resolution
ability for the auditory system to detect small time related changes in the acoustic stimuli over time
-our system has the ability for these rapid changes and can process in order for speech intelligibility
how do time related cues affect auditory processing
gap detection, phonemic duration, temporal ordering and suprasegmentals
gap detection
being able to detect small gaps within words or between words/sounds
-such as spoon vs. soon
phonemic duration
being able to detect sharp endings of sound words or the voiceless sounds of other words
-length of words or statements or sounds
temporal ordering
are we able to retain the order of sounds as they are presented to us or do they get mixed up
-such as boots vs. boost
suprasegmentals
such as patterns of stress, intonation and rhythm
binaural loudness summation
action potentials within the brainstem increase loudness when two ears receive auditory input signals
how does binaural loudness summation impact normal threshold? supra-thresholds?
gain of around 2-3 dB ; gain of around 5-8 dB
ingress protection (IP) rating
how a device is protected from various materials or contaminants
-various degrees for protection against solids and liquids
-can look at different rates and select one based on the need of the patient
what does a 6/8 IP rating mean?
this is the top rating device
-6 is dust tight
-8 is protection against long immersion and good for max depth within water
viscosity
how easily it flows before it is cured
-high : thick, provides resistance, provides stretch to the aperture
-medium : provides some stretch to the aperture
-low : runny, loose, flows easily without resistance
why would you want a high viscosity material?
provides for the stretching of the aperture
-snugger fit
shore value
if it has the ability to remain its shape or if it will be altered after its cured
-silicone has high
-MM has low
why would you want a high shore value?
with lower values, there is a higher change for it to become damaged in the shipping process so with a higher shore value it ensure it is shipped without damage
stress relaxation
materials ability to return to its shape after removal from the ear
-high can be pulled out and will go back to its shape
-low will not bounce back
-silicone is superior and MM is inferior as the shape can be distorted
contraction ratio
shrinkage over a 7 day period, will the impression be the same in a few days or will it be altered
-silicone does not shrink, MM will shrink
occlusion effect
a common complaint when low frequency threshold loss is better than 50 dB HL
-voices can sound boomy, hollow or as if they are in a barrel
-insufficient venting or insufficient canal length can cause it
how does OE occur within the low frequencies
the skull transduces the low frequencies generated by the voice
-bone conduction signal becomes trapped within the canal
how to reduce the OE
venting and by extending the canal length
how can venting reduce OE
can release the lows out of the canal
-vocalized sounds that cause the OE are within the low frequencies so with venting it can release these frequencies
how can extending the canal length reduce the OE
by extending the canal length (canal portion of the mold) into the bony portion, the waves bouncing around are not able to make it to the cartilage therefore they cannot vibrate within the canal and the OE will not occur
-the waves will be bouncing around within the bony portion so this blocks off the cartilage portion and can reduce the OE
how does vent size impact high frequency output
increasing the vent size causes less high frequency output we get from the HA
occluding molds allow fro around ______ dB of gain
40
-supports audibility to around 80 dB HL
3 mm vent allows for around _____ dB HL of gain
30
-supports audibility to around 60 dB HL
open domes allow for around ______ dB HL of gain
25
-supports audibility to around 50 dB HL
front end distortion
occurs when the collected/incoming signal exceeds the microphones dynamic range
-complaints are due to loud music or to the users own voice
-planned for acoustical effects or unplanned
why do digital HA’s have a lower microphone dynamic range
due to using analog to digital converters (ADCs) which use a 16-bit converters allowing for a 96 dB dynamic range
-can lead to peak clipping
peak clipping
flattening out of the top of the sound wave, resulting in multiple points being stimulated in one area on the basilar membrane
-causes distortion
how is front end distortion managed within digital HA’s
they have the ability to shift their dynamic range to fit the listening situation
-when you raise the louder end, you raise the quieter end
-in loud environments it will shift upwards and you will get less within the quiet range
signal to noise ratio (SNR)
difference in volume level between the desired signal and the undesired signal
-normal hearing listeners require and ideal SNR of 2 dB (meaning speech is 2 dB louder than the noise)
-signal minus the noise
what is a null
point of maximum attenuation
-the microphone turns off
bi-directional polar plot
collection from the front and back, attenuation from 90 and 270
-used in specific situations
carotid polar plot
collecting sounds from the front and attenuating from the back
-null at 180
-DI of 4.8 dB SNR
super carotid polar plot
collecting from the front and back, attenuates at the sides (125)
-DI of 5.7 dB SNR
hyper carotid polar plot
collecting from front and back, attenuation from sides (110)
-DI of 6 dB SNR
what is the TK (threshold kneepoint)
the point of activation for the compressor to begin working
-signal for the compressor to alter or begin
shifting the TK down (smaller) causes the output to ______ for soft sounds
increase
shifting the TK up (bigger) causes the output to ________ of soft sounds
decrease
how can we either raise or lower the TK within a practical setting
if a patient can hear and perceive soft sounds as being soft, lowering would be beneficial whereas if a patient cannot hear perceive the soft sounds as anything besides noise increasing the TK may be beneficial
expansion
rapidly adds gain to very soft input signals until the first TK, which lowers output of those signals
-CRs lower than 1:1
-manages intensity of very soft input signals and circuit noise
analog to digital conversion (ADC)
chops sine waves into bits and assigns numbers to it
-taking the electrical signal and putting it into a digital word which is a series of 0s and 1s
what does ADC require in order to occur
sampling rates and quantization
sampling rates
they measure spaced moments of time along the electrical signal and DSP only uses these samples points and the other parts of the signal is ignored
-each cycle of the wave must be represented by at least two sampling points
quantization
bit resolution
-this rounds each sample and creates a digitized version of the signals that results in a less idealized representation of the analog input signal
digital to analog converter (DAC)
takes the digitized signal and transduces it back to an electrical signal
-digital to analog electrical signal that goes directly to the receiver
processing speed and DAC
the time it takes for it to occur can impact the quality of the sound
-can sound like an echo
what occurs as a result of quantization errors
can create soft random noise within the HA referred to as the noise floor
explain how an overlap exists between auditory filters
high frequency bands pick up lower frequency signals from adjacent critical bands
-as a result, noise masks signals within the adjacent critical band
what is the effect of low frequency masking to a damaged cochlea
the critical bands within the cochlea are organized by frequencies and so what occurs is one frequency range spills into another range, which is the upward spread of masking
-a 250 Hz noise can impact noise all the way up to around 1500 Hz
-meaning you have to manage noise under 1500 Hz to help manage the noise present
how is sound cleaning achieved within the spatial domain
through the usage of directional microphones
-automatic microphone switching (adaptive) and adaptive directional mics (null steering)
automatic microphone switching (adaptive)
automatically changing from omnidirectional to directional mic in the presence of background noise
-can be fixed directional or adaptive directional
-helps aid reduction of background noise
-occurs automatically and continuously, reverting back to omnidirectional in quiet
-there is a override switch that can be activated for the patient
fixed directional
one polar plot and is superior in the presence of multiple noise sources
-mic switches from omni to fixed with one set of polar plots, no steering of the null