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108 Cards in this Set

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  • Back
Environmental challenges faced by people with hearing loss
Distance: Intensity drops by 1/2 when distance doubles (drops by 6 dB SPL)
Noise: i.e. background and environmental noises
Reverberation: direct and reflected sound sources
Four main perceptual consequences of SNHL
1) Reduced audibility
2) Reduced hearing dynamic range
3) Reduced frequency resolution
4) Reduced temporal resolution
Reduced Audibility
All types of HL
Can result in reduced loudness. Reduced audibility results in reduced clarity because a high frequency HL means you are missing sound that help with the intelligibility of speech.
*Hearing aids can help.
Reduced Hearing Dynamic Range
Also known as recruitment. Can't hear soft sounds but loud sounds are too loud. The dynamic range of speech is 30 dB but with cochlear loss the hearing dynamic range is often less than 30 dB. This person would only be able to hear the peaks of speech.
*Hearing aids can help.
Reduced Frequency Resolution
"Smearing" of the spectral details of speech. Associated with difficulty understanding speech in background noise.
*Hearing aids can't help.
Reduced Temporal Resolution
"Smearing" of the time details of sound. E.g. VOT
*Hearing aids can't help.
What does the spectrum of sound show us?
Representation of sound showing the amplitude of sound (y-axis) as a function of frequency (x-axis).
What does the waveform of sound show us?
Representation of sound showing amplitude of sound (y-axis) as a function of time (x-axis).
Describe the LTASS
Long-term average speech spectrum.
The level of speech across different frequencies when averaged over a long period of time (e.g. 30 seconds or more).
Characteristics: The LTASS has more energy in the low frequencies. 6 dB/octave drop above 500 Hz.
Explain how sound intensity changes with distance. (Be able to provide an example.)
Intensity drops by 1/2 when distance doubles. 6 dB SPL change.
Speech Dynamic Range
The range of intensities from the strongest to the weakest speech sound for a given intensity level. Approx 30 dB.
Soft, Average and Loud speech levels
50 dB SPL
65 dB SPL
80 dB SPL
Dynamic Range of Speech
30 dB regardless of the speech signal level.
Hearing Dynamic Range
Intensity range between threshold and loudness discomfort level.
Symptoms of reduced hearing dynamic range
Difficulty hearing low-level sounds but loud sounds are "uncomfortable." When sound is adjusted not to be too loud only the peaks of speech will be heard. Can be fixed by fast acting compression.
Reduced audibility as a result of hearing loss results in reduced _____ and often (but not always) reduced ______.
Clarity, loudness.
What is needed to hear the full intensity range of the speech signal?
A hearing dynamic range of 30 dB or greater and appropriate amplification.
Loudness will be affected when hearing loss affects the ____ frequencies.
Low. Low frequency speech components contribute the most to loudness.
What frequencies are most important for understanding speech.
The high frequencies. Frequencies above 1000 Hz (1000-8000 Hz) contribute 60% to speech intelligibility, but only comprise 5% of the total speech energy.
Frequency Resolution
The auditory system's ability to separate complex sounds into its constituent components.
Temporal Resolution
The ability to hear time details of sound.
Reverberation
Occurs when reflected sound waves are delayed relative to the direct sound. Results in the addition of the direct and reflected sounds. Smears time and frequency details of sound.
RT60
Reverberation time.
Greater than .5 sec is undesirable.
Psychological factors that impact HA candidacy.
Motivation and expectations.
Cognitive factors.
Functional abilities that impact HA candidacy.
Adaptability and Dexterity.
Instrument-oriented possible goals
1) Audibility
2) Clarity
3) Comfort
Patient-oriented possible goals
Reduce the communicative impairment caused by the HL.
Cultural Competence
Sensitivity to issues related to culture, race, gender, sexual orientation, social class, economic situation, among other factors.
Be able to explain cultural differences related to conversation style and pacing, personal space, eye contact, touch, time orientation and other considerations.
See notes for examples.
Describe the basic principles (in a nutshell version) of hearing aid analysis.
1) Hearing aid placed in test box.
2) Signal delivered to hearing aid microphone.
3) Measurement mic detects/analyzes sound coming out of hearing aid.
Explain why electroacoustic analysis is done. i.e. what are the purposes?
Quality control (new aids) – check to make sure new aid is functioning according to specs
Troubleshooting – patient complaint: aid sounds fuzzy, weak ect. EAA can help us determine if aid needs repair.
Describe the basic elements of a hearing aid measurement system
Test space – sound absorbent walls. Reduces reflections inside test box. Reduces contamination from outside noise.
Loudspeaker – generates signal.
Regulation portion (control or reference mic)
Measurement portion (measurement mic)
Draw a flow chart illustrating the complete measurement process for basic hearing aid analysis and explain the basics of how this works.
HA mic at a fixed distance from sound source.
Output of HA attached to coupler or simulator.
SPL in coupler measured by calibrated microphone.
Output recorded as a function of frequency or analyzed in other ways (e.g. distortion)
Reference mic → Compression amplifier → Speaker(s) (sound) → Hearing aid mic → HA receiver → Coupler → Measurement mic → sound analyzer
Describe the functions of the reference (control) microphone and compression amplifier.
Control (reference) microphone: Placed next to HA microphone. Monitors SPL reaching hearing aid. Determines gain of compression amplifier.
Compression amplifier: adjusts intensity of sound from loudspeaker. Compensates for irregularities of SPL in test box. Want flat response in test box.
Explain the differences between the pressure method and equivalent substitution method of using the control microphone for hearing aid analysis.
Common to both methods: Control mic close to HA mic. Amplifier adjustment of levels (each frequency) during measurement.
Pressure method (Verifit): control mic monitors SPL (across freqs) during hearing aid measurement.
Equivalent substitution method (“Leveling”) (Fonix): control mic placed in test position before measurement. Control mic monitors SPL and stores discrepancies. Amplifier compensates for discrepancies during measurements but does not change during the measurement.
Describe a 2cc coupler, explain its function and describe the main differences between a 2cc coupler and the real ear
Connects hearing aid to measuring microphone. Intended to simulate EAC. Does not really simulate EAC. Larger cavity. Hard material, not soft like ear cavity.
Explain the difference between a 2 cc coupler and an ear simulator. How would you expect the electroacoustic analysis results to differ?
Ear simulator incorporates frequency variations attributed to the middle ear. Hearing aid produces same SPL in simulator as it does in (average) real ear. Not true of 2cc coupler. Greater high frequency response in ear simulator.
Explain the function of ANSI hearing aid tests in clinical practice
American National Standards Institute
Standard for FDA hearing aid labeling regulations
Manufactures must publish hearing aid specifications
Most specs: aids run on maximum settings
Specs for custom aids (ITE, ITC, ect.) – usually no specs provided because they differ
Pure-tone signals are used for ANSI tests
OSPL-90 (test-box measure)
Formerly “SSPL-90” (Saturation SPL-90)
ANSI 96 – changed term (Output SPL-90)
Measured for frequencies 200-5000 Hz.
2cc coupler – gain control full-on
Two values extracted
Maximum OSPL-90 (Tolerance = +3 dB SPL)
HFA OSPL-90 (Tolerance = +/- 4dB)
HFA average of 1k, 1.6k, 2.5k
HFA full-on gain
High Frequency Average
50 dB SPL input level (ANSI, 2003)
Volume control (gain setting) full-on
Average gain for 1k, 1.6k, 2.5k
Tolerance +/- 5 dB SPL
Reference test setting (RTS) or RTgain (No tolerance)
60 dB SPL input level (ANSI, 2003)
May reflect HFA gain with VC reduced (linear) or
May be same as HFA FOG (compression aids)
Purpose: avoid saturation for mid-level input
Frequency range measure
Measurement made in reference test position
Point of intersection 20dB below HFA gain
Tolerance: none – for information only
Equivalent input noise (EIN or EqN)
Relates to circuit noise generated by HA
Hearing aid related noise sources: 1) microphone, 2) amplifier
Only valid when ambient room noise is low
Measured in reference test position
Tolerance = + 3 dB
Distortion measures (harmonic distortion)
Tolerance = + 3% pts
Pure-tone input
Analyzing output to measure distortion components relative to total signal power
*Intermodulation distortion not included in ANSI tests, available in IEC tests – need 2 tones
Electroacoustic analysis of telecoils (ANSI) - TMFS
Telephone magnetic field simulator (test signal)
31.6 – mA/m magnetic field
Simulates strength of average hearing aid compatible phone
Electroacoustic analysis of telecoils (ANSI) - SPLITS
output frequency response using TMFS input
Telecoil mode, reference test gain
Test provides curve & HFA SPLITS
Tolerance +/- 6 dB
Electroacoustic analysis of telecoils (ANSI) - Acoustic vs. magnetic input
Compare SPLITS to HFA output for 60 dB SPL signal with HA at RTS (RGT)
Curves should be the same (no tolerance values)
RSETS (relative simulated equivalent telephone sensitivity – ANSI 2003) (or STS – simulated telephone sensitivity, ANSI 1996). The difference between the high frequency average of the acoustic response and the telecoil response. The HFA magnetic minus HFA acoustic output. Negative number indicates that the HFA magnetic output is lower than the HFA acoustic average.
Battery current
Gain: reference test position
Input: 65 dB SPL, 1000 Hz
Tolerance: +20%
Aid must be set that same way it was set when specs generated. This may mean setting compression aid in linear mode.
Be able to list the frequencies that are included in the high-frequency average (HFA) electroacoustic measures
1k, 1.6k, 2.5k
Describe the potential consequences of not plugging vent on a custom product ( ITE, ITC, or CIC aid) during electroacoustic measurement.
Creates an extra resonant cavity that participates in the response.
Describe the potential consequences of not adequately sealing the putty on the HA1 coupler during EAA of a custom product
A peak that shouldn’t be there. Anything sharp means a coupling problem.
List the tolerances of the ANSI tests
+ 3 dB Maximum peak OSPL-90
+/- 4 dB HFA OSPL-90
+/- 5 dB HFA gain (FOG full on gain)
+ 3 dB EIN
+ 3% pt. Distortion
+/- 6 telecoil
+20% battery
What do the abbreviations “RSETS” and “STS” stands for?
RSETS: relative simulated equivalent telephone sensitivity
STS: simulated telephone sensitivity
Describe how the RSETS (or STS) values are derived and what they means
The difference between the high frequency average of the acoustic response and the telecoil response. The HFA magnetic minus HFA acoustic output. Negative number indicates that the HFA magnetic output is lower than the HFA acoustic average.
Describe the basics of performing a Verifit directional microphone test in the test box. What evidence would indicate that the directional microphone is working?
Can be done on patient (on-ear) or in the test box
Not all directional mics are created equal
Some directional mics are installed backwards!
HA orientation – axis of microphone openings
Can test adaptive directional aids (w/ or w/out speech)
Front-back directionality only
Can generate polar plots in the test box.
Describe the basics of performing a Verifit noise reduction test. What evidence would indicate that the directional mic is working?
See what happens when the noise reduction is activated and when it isn’t.
What is meant by acoustic feedback? How does this occur?
When sound coming out of the aid (receiver) travels back into the microphone, oscillation occurs.
List the three types of hearing aid transducers
Microphone. Receiver. Telecoil.
Describe the function and basic characteristics of a microphone.
Function: takes in sound. Acoustic to electric.
Limitation: Major limitation-failure. Exposure to chemicals and moisture. Random electrical noise (worst: mics with steep low-frequency roll-off). Sensitivity to vibrations – when shaken can be amplified into annoying sound. Wind noise. Internal feedback-seal between receiver and microphone is bad.
Describe the function and basic characteristics of a receiver.
Function: Transduces electric energy to acoustic. Frequency response; one major peak – receiver’s resonance. Smaller peak – acoustic path. Extra peaks (BTE) – other resonance (tubing).
Limitations: Output is related to receiver size. Susceptibility to wax. Unwanted resonance – BTE aids. Can cause feedback and harsh quality.
Describe the function and basic characteristics of telecoils.
Function: Wire coil that produces voltage in response to magnetic field. Magnetic field generated by telephone. Can hear phone without background noise.
Limitations: Frequency response. 6 dB/octave cut-off in low frequencies. May not be enough low frequency gain for some people. Multi-memory solution. Produce noise – worse than microphones. Telecoil is directional. Telephone use – horizontal best. Loop systems – vertical best.
Gain
Output level minus input level. Amount added by the hearing aid.
Output
Level (in dB SPL) of sound at the output of the hearing aid (after amplification).
Saturation
The level (in dB SPL) at which a further increase in input no longer produces an increase in output.
Maximum power output
How the maximum output level of the hearing aid is measured. Using a signal of 90 dB SPL input to the hearing aid.
Peak Clipping
Effect of saturation on the waveform of the signal.
List the two main hearing aid microphone categories and explain the primary difference between them.
Directional: Suppress sound coming from some directions. Dependent on delays between HA front and back.
Omni-directional: Microphone sensitive to all directions.
Single Mic
One microphone, two ports (front and rear). Acoustic damper in rear part. Sounds from rear are delayed and partially canceled.
Dual Mic System
Two omnidirectional mics, each with a port. Output from mic #2 (rear) electronically delayed. Allows user to switch between directional and omnidirectional. (Omni-directional: rear mic off).
Microphone Arrays
More than two microphones. Can be accessory or built in. Advantages: Improves directivity. Limitations: Space, more mic noise.
Polar Plots
Indicate the directional sensitivity of microphones at ONE particular frequency. Response shape dependent on ratio of internal to external delay.
Directivity Index (DI)
Units in dB.
Ratio of sensitivity for front sounds as compared to sound for all directions.
Front-to-back ratio (FBR)
Units in dB.
Ratio of sensitivity for front sounds as compared to back sounds.
Describe the limitations of a single-mic, dual port directional microphone
Directivity may be limited by low-pass filter cut-off. Low frequency cut in gain. May need omni-directional microphone in some situations.
Describe the primary characteristics of a hearing air receiver’s frequency response
One major peak – receiver’s resonance
Smaller peak – acoustic path
Extra peaks (BTE) – other resonance (tubing)
Describe the three main limitations of receivers
1) Output is related to size
2) Susceptibility to wax
3) Unwanted resonances – BTE aids
Describe what a telecoil is
Wire coil that produces voltage in response to magnetic field.
Why does feedback sometimes occur with a microphone, but not with a telecoil?
Feedback is from the sound coming out of the hearing aid travels back into the microphone. No microphone is used with telecoil.
Explain three limitations of telecoils
1) Frequency response: 6 dB/octave cut-off in low frequencies. May not be enough low frequency gain for some people. Multi-memory solution.
2) Produce noise: worse than microphones
3)Telecoil is directional: Horizontal for phone. Vertical for loop systems.
Peak Clipping
Effect of saturation on the waveform of the signal.
Saturation Level
The level (in dB SPL) at which a further increase in input no longer produces an increase in output.
Distortion
Signal contains additional components that were not in the original signal.
Harmonic Distortion
Distortion products are harmonically related (occur at integral multiples of the signal frequency) to the frequency components of the signal. Can occur for pure-tone and complex signals.
Intermodulaition Distortion
Distortion products are combinations of the frequency components of the signal. (sum and difference tones). Only occurs for complex signals (signals with more than one frequency component).
Anderson (1996) refers to four types of non-linear distortion. What are these?
Crossover distortion, overload distortion, harmonic distortion (HD), and intermodulation distortion (IMD).
Class A amplifier
Simplest amplifier – inexpensive
Disadvantages: Inefficient – continuously draws battery current. Low battery life. Can be built designed with better batter life, but lower saturation level. Asymmetrical peak clipping. Saturation distortion.
Class H amplifier
“Sliding class A amplifier”
Class A with variable bias current. Varies with signal strength. (Strong signal=bias current increased)
Advantages: more efficient than A (less than D)
Disadvantages: Adds distortion to signal. Sliding too fast, changing bias current will be audible. Sliding too slow, peak clipping.
Class B amplifier
Consists of two separate amplifiers. One acts as positive phase on input signal. Other acts on negative phase. “Push-pull” amplifier.
Minimal current drawn when idle. Good for high power hearing aids.
Advantages over Class A: Less current drain – longer battery life. Higher saturation level. Symmetrical peak clipping – less objectionable than asymmetrical peak clipping.
Disadvantages: Cross-over distortion. Larger. More expensive.
Class D amplifier
Advantages: Very efficient use of battery current (best). High saturation levels (best). Symmetrical peak clipping at saturation. Small.
Disadvantages: More expensive than Class A, H, or B.
Tone control/filter
Changes the signal so that the output is different than the input.
Explain and identify what an “O-T-M” switch does (older model aids)
Off-Telecoil-Mic.
Switches between settings.
Explain the components/circuit configuration of a hearing aid with a single channel compression circuit
Gain controlled by linear gain amplifier. Level detector -- does level exceed compression threshold? If CT reached, message sent to amplifier to reduce gain. If CT not reached, no gain reduction occurs.
Static characteristics of compression aids
Compression threshold: the input level when input-output function departs from the linear slope by 2 dB. Or the level where HA starts compressing.
Compression ratio: Change in input level needed to produced 1 dB change in output level.
Dynamic characteristics of compression aids
Attack time: the time required for the compressor to fully activate once the threshold is reached (to stabilize within 2 dB of its steady-state value).
Release time: the time required for the hearing aid to de-activate the compressor after the level drops below the compression threshold.
A hearing aid has a compression ratio of 3:1 and the compression threshold of 50 dB SPL. At an input level of 30 dB SPL, the gain is 20.
What is the output and gain at for an input of 50 dB SPL?
What is the output and gain with an input of 59 dB SPL?
Answer: Output is 70. Gain is 20.
Answer: Output is 73. Gain is 14.
Compression Limiting hearing aid
Defining characteristic: High compression threshold (greater than 75 dB)
Operates linearly over much of its range.
High compression ratio >8:1
Attack/release times:
Short attack time <5ms
Short release time 50-100 ms
Wide Dynamic Range Compression (WDRC) hearing aids
Defining characteristics: low compression threshold (<60-65 dB), low compression ratio (< 5:1)
More gain for soft inputs.
Attack/release times:
Short attack time (<5 ms)
Short release time (10-100 ms)
Input compression
Compression before volume control. As the volume control increases, the compression threshold stays the same and maximum output increases.
Output compression
Compression after volume control. As the volume control increases, the compression threshold decreases and the maximum output increases.
FFR
Fixed Frequency Response.
Compression applied equally across frequency. Frequency response shape stays the same with change in level.
BILL
"Base Increase at Low Levels"
Low frequency gain varies with input. More compression in low frequencies.
TILL
"Treble Increase at Low Levels"
High frequency gain varies with input. More compression in high frequencies.
Origional rational underlying the design of the BILL processor
Noise dominated by low frequencies. Reduction of low frequencies at high inputs may help. Upward spread of masking. Low frequency speech sound scan mask high frequency speech sounds.
Origional rationale underlying the design of the TILL processor.
Most have greater HL in high frequencies. Require HF emphasis. Assumptions: maximum HF gain needed for soft HF consonant sounds. Less gain needed for higher input levels. If gain higher for soft consonants, should improve intelligibility.
What is a multi-channel compression hearing aid? Describe the potential advantages. Describe one potential disadvantage.
Multi-channel can potentially increase intelligibility (re single channel) because it increases audibility of speech. Multi-channel also decreases some of the essential differences between phonemes. Partially flatten spectral shapes making it harder to identify place cues.
Discuss general research findings on the BILL processor that demonstrates the benefit and lack of benefit patients receive from the processor (vs. a linear aid)
Testing in speech noise: no improvement in speech intelligibility when noise is speech (or has speech spectrum). Improvement in listening comfort.
Testing in low-frequency noise: Improvement in speech intelligibility when noise is low frequency.
Improvement in quality of own voice.
Describe general research findings that document the extent of benefit (if any) with TILL processing vs. other types of precessing (e.g. research with K-amp)
Very little research.
Speech intelligibility: No difference between linear and TILL. Improvement in final consonant recognition (low input level).
Preferences: No difference between preferences for linear vs. TILL (K-amp).
Subjective ratings: no differences.
Candidacy Considerations
Communication problems (most important)
-Self perceived
-Perceived by family/friends
Hearing loss
-Thresholds
-Speech recognition
Lifestyle/communication demands
Motivation/expectations