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Audiology 2-2 > Week 3 > Flashcards

Week 3 Flashcards

1
Q

How to microphones work?

A

All HI have 2 microphone ports and a database of different shapes of amplification patterns based on the environment. These shapes are called polar plots and tell microphones how to behave

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2
Q

What dictates the directions the microphones amplify in?

A

PORT SPACING: accuracy increases with distance between ports

INTERNAL DELAY: low pass filter analyzes noise to amplify away from it

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3
Q

What are the 4 main polar plots?

A

OMNIDIRECTIONAL: 360 around

CARDIOID: only amplify in front

FIGURE 8: front and behind, no sides

HYPER CARDIOID: mostly front focus with some amplification behind

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4
Q

What are the two kinds of directional microphones?

A

Fixed directional microphones and adaptive directional microphones.

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5
Q

Under what conditions are adaptive directional microphones better than fixed?

A
  1. Dominant nearby noise source
  2. Dominant noise is stable
  3. Dominant noise source in non amplified area
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6
Q

How do SNR and distance affect the effectiveness of directional microphones?

A

SNR; less benefit with higher ratio (little noise or a strong signal)

Distance: the great the distance between sound and listener the less benefit

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7
Q

What are the drawbacks of directional microphones

A

No side or rear amplification

Decease in low frequency listening

Reduced localization of HI don’t coordinate

Wind noise greater for directional mics

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8
Q

What is noise reduction?

A

The goal is to provide less amplification of noise while keeping the level of speech sounds the same. Aim to improve the SNR.

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9
Q

How does digital noise reduction work?

A

Listens for the modulation of a signal (fluctuation found in speech) and doesn’t reduce that sound

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10
Q

What are the 2 most common noise reduction algorithms?

A

Weiner filter

Spectral subtraction

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11
Q

What is feedback?

A

Feedback is the whistling sound when the output of a microphone gets back to the microphone input

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12
Q

List some causes of feedback

A
  • Someone/sth too close to mic
  • wax
  • HI poorly inserted
  • Poorly fit/sealed mild
  • Crack in shell or tubing
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13
Q

List the three types of feedback control

A
  1. gain frequency response control
  2. Phase control
  3. Feedback path cancellation
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14
Q

Describe gain frequency response control

A

Want to reduce the volume at a channel-specific group of frequencies to do to the output provided to the user

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15
Q

Describe phase control

A

Detect the frequency causing feedback and use inverted phase response to turn it down. This is inefficient if more than 1 frequency involved

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16
Q

Describe feedback path cancellation

A

Use internal feedback path created by HI. The HI monitors the external feedback path and if it makes the HI whistle then the internal path kicks in

17
Q

What is frequency lowering

A

Process where a HI takes HF information and moves it to a lower and more audible range

18
Q

What are the different types of frequency lowering?

A
  1. Frequency compression
  2. Frequency transposition
  3. Frequency translation
19
Q

Describe frequency compression

A

HF information compressed into LF range

20
Q

Frequency transposition

A

Shifted HF sounds overlap with LF information, so we get a mix of sounds at those channels

21
Q

Describe Frequency translation

A

Manipulate HF information to be at wowed frequency to make it more audible. The distorted sound is overlayed onto the other sound

22
Q

Who are good candidates for frequency lowering

A

HFHL (>2kHz) that exceeds 80 dB HL

Infants and young children

Those with feedback issues

23
Q

What are some advantages of bilateral hearing aids?

A
  1. Speech intelligibility
    1a- head diffraction effects
    1b- binaural squelch
    1c-binaural redundancy
  2. Localization
  3. Sound quality
  4. Avoid late onset auditory deprivation
24
Q

What are head diffraction effects?

A

In unilateral HI wearers, if the speech is on the bad side and the noise is on the good side you can lose your good SNR

25
Q

What is binaural squelch?

A

The ability of bilateral hearing aids to suppress interfering noise and focus on speech

26
Q

What is binaural redundancy?

A

Reflection of hearing a signal twice. In binaural microphones you hear the sound in both ears resulting in better speech intelligibility

27
Q

What are some disadvantages of binaural hearing aids?

A

Cost

Self esteem

Binaural interference

28
Q

What are the 2 types of microphones

A

DIRECTIONAL: allow HI to amplify specific area/direction

OMNIDIRECTIONAL: amplify sound in all directions

Audiology 2-2 (11 decks)

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