Hearing Aid Technology

Question 1

what is signal processing?

Answer 1

Signal processing is anything that manipulates the sound signal,
including:

– Amplifying
– Filtering
– Peak-clipping
– Compression: output limiting, WDRC, etc
– Frequency lowering
– Anything else where the signal is changed

Question 2

what are the benefits of signal processing?

Answer 2

• Allows better fitting of the audiogram:
• Multichannel hearing aids
• Multiple compression ratios, dynamic compression,
  expansion
• Improves the signal to noise ratio:
• Directional microphone systems
• Noise Reduction
• Feedback cancellation

Question 2

What is the difference between analogue and digital multichannel hearing aids?

Answer 2

• Analogue Hearing Aids: These typically split the frequency content into 2 frequency bands.
• Digital Hearing Aids: These can have more than 20 channels, providing much finer control over sound processing and better customization.

Question 3

What are multichannel hearing aids, and how do they work?

Answer 3

Multichannel hearing aids split the frequency content of sounds into different frequency bands or channels.

This design allows different frequency areas to undergo distinct sound processing, improving the overall hearing experience.

Question 4

How do multichannel hearing aids benefit people with hearing loss?

Answer 4

• Frequency Band Processing: Different frequency areas can be processed differently, enhancing sound quality and clarity.
• Customization: They allow for varying gain, maximum output, and compression levels in each frequency band, which means a better fit to the individual’s specific hearing loss.

Question 4

How do multiple channels in hearing aids work like a graphic equalizer?

Answer 4

Multiple channel aids function similarly to a graphic equalizer by allowing the user to adjust various sound parameters (such as gain and compression) in each frequency band independently.

This ensures that the hearing aid can be finely tuned to the user’s specific hearing loss profile.

Question 5

What are the benefits of having two channels for high-frequency (HF) losses?

Answer 5

Two channels can specifically address high-frequency losses by:

• Enhancing the clarity of high-frequency sounds.
• Improving speech comprehension in noisy environments.

Question 5

Can the frequency crossover points in multichannel hearing aids be adjusted?

Answer 5

Yes, it is often possible to adjust the frequency at which the channels cross over.

This adjustment allows for more precise fitting of the hearing aid to the user’s specific hearing loss.

These adjustments are usually made using programming software.

Question 6

What is compression in digital hearing aids, and why is it important?

Answer 6

Compression in digital hearing aids is a feature that reduces the dynamic range of sounds, making softer sounds more audible while preventing louder sounds from becoming uncomfortably loud.

This process enhances the user’s ability to hear a wide range of sounds comfortably and clearly.

Question 6

How does changing the frequency crossover points improve hearing aid performance?

Answer 6

Adjusting the crossover points ensures that the hearing aid processes different frequencies more accurately according to the user’s hearing loss pattern.

This results in better sound quality and a more natural listening experience.

Question 7

How does compression work in digital hearing aids?

Answer 7

Compression works by applying different amounts of gain to sounds of varying loudness.

It can compress different frequency bands by different amounts, which helps tailor the hearing aid’s response to the user’s specific hearing loss.

Question 8

What are the types of compression that can be applied in digital hearing aids?

Answer 8

• Wide Dynamic Range Compression (WDRC): Enhances softer sounds while maintaining the clarity of louder sounds.
• Output Limiting Compression: Prevents sounds from becoming too loud, protecting the user’s hearing.
• Dynamic Compression: Adjusts in real-time with varying attack and release times, which can include:
• Syllabic Compression: Fast-acting compression suitable for speech sounds.
• Average Detection: Adaptive compression that changes based on the average input levels.

Question 8

What is expansion, and how does it differ from compression?

Answer 8

Expansion is the reverse of compression.

It reduces the gain for very quiet inputs, then rapidly increases gain as the input level rises until the compression kneepoint is reached.

This is useful for reducing internal hearing aid noise for users with good low-frequency hearing.

Question 9

How does compression work in multiple channel digital hearing aids?

Answer 9

In multiple channel digital hearing aids, different frequency bands can be compressed by varying amounts.

This allows for more precise adjustments across different frequencies, improving the customization and effectiveness of the hearing aid.

Question 9

What are the specific types of WDRC used in hearing aids?

Answer 9

• Base Increase at Low Levels (BILL): Applies WDRC to low frequencies, enhancing softer sounds in the bass range.
• Treble Increase at Low Levels (TILL): Applies WDRC to high frequencies, improving the audibility of softer treble sounds.

Question 9

Why is compression important for hearing aid users?

Answer 9

Compression is crucial because it helps users hear a wide range of sounds more comfortably and clearly.

It ensures that soft sounds are audible without making loud sounds uncomfortable, thereby improving overall hearing quality and speech comprehension.

Question 10

What is the purpose of using Base Increase at Low Levels (BILL) in hearing aids?

Answer 10

The aim of using BILL is to provide good listening for speech in background noise.

It is particularly beneficial for patients with significant low-frequency hearing loss.

Question 10

What are the kneepoints in BILL, and how do they function?

Answer 10

In BILL, there is a low kneepoint for low frequencies and a higher kneepoint for high frequencies. This configuration ensures that low-frequency sounds are compressed more, enhancing the audibility of higher-frequency speech sounds.

Question 10

How does BILL improve speech clarity in background noise?

Answer 10

BILL works by compressing low-frequency background noise more than higher frequencies. This reduces the interference from low-frequency noise, thereby improving speech clarity.

Question 11

What is the purpose of using Treble Increase at Low Levels (TILL) in hearing aids?

Answer 11

The purpose of TILL is to ensure sounds are not over-amplified for individuals with a reduced dynamic range, particularly those with mild to moderate high-frequency hearing loss.

Question 12

How does TILL help patients with high-frequency hearing loss?

Answer 12

TILL compresses high-frequency sounds more than lower frequencies. This keeps the hearing aid output within the wearer’s dynamic range, preventing over-amplification of high-frequency sounds and maintaining sound quality.

Question 13

What are the kneepoints in TILL, and how do they function?

Answer 13

In TILL, there is a high kneepoint for low frequencies and a low kneepoint for high frequencies. This ensures that high-frequency sounds are compressed more, making them comfortable for the user while preserving the audibility of lower frequencies.

Question 13

What is noise reduction in the context of hearing aids?

Answer 13

Noise reduction refers to the process of reducing or eliminating unwanted background noise that interferes with the listener’s ability to perceive speech. The goal is to diminish these unwanted sounds without significantly affecting the speech signals that the hearing aid user wants to hear.

Question 14

What is expansion in hearing aids, and how does it differ from compression?

Answer 14

Expansion is the opposite of compression. The gain increases as the input level increases, meaning softer sounds are amplified less than loud ones.

Question 15

Who can benefit from expansion in hearing aids?

Answer 15

• People with good low-frequency hearing and moderate loss at mid and high frequencies, as it reduces internal hearing aid noise.
• Individuals who find low-level background noise distracting.

Question 15

What is a disadvantages of using expansion in hearing aids?

Answer 15

A drawback of expansion is that it can negatively affect hearing for speech in low-level noise environments, making it harder to hear soft speech sounds.

Question 16

Why might it be helpful to use multiple types of compression simultaneously in hearing aids?

Answer 16

Using multiple types of compression, such as WDRC and output limiting compression or expansion, can provide a more tailored and effective hearing solution. Combining these methods can address different aspects of hearing loss and environmental challenges, offering a more comprehensive hearing experience.

Question 17

What are some common methods of noise reduction in hearing aids?

Answer 17

• Spectral Subtraction: Estimates the frequency spectrum of the noise and subtracts it from the speech spectrum. However, if the noise overlaps too much with the speech spectrum, some speech signals may be lost.
• Phase Cancellation: Measures the exact waveform of the noise and cancels it by producing a sound with an identical but reverse phase (180° phase to the original sound). This method is challenging because accurately measuring the noise waveform amid competing speech can result in some speech signal loss.
• Compression: Applied to long-term, moderate to loud, low-frequency sounds to reduce their impact.
• Speech Synthesis: An algorithm detects speech cues in background noise and adds artificial speech sounds to enhance recognition. This method can struggle with background noise that consists of speech and may produce unnatural-sounding speech.

Question 18

Why is noise reduction important for hearing aid users?

Answer 18

Noise reduction is crucial because one of the most common complaints among hearing aid users is difficulty hearing in noisy environments. Reducing background noise enhances the clarity of speech, making it easier for users to understand conversations.

Question 18

How does speech synthesis work for noise reduction, and what are its limitations?

Answer 18

Speech synthesis algorithms detect speech cues in background noise and add artificial speech sounds to enhance recognition. This method can struggle when background noise includes speech, and it may produce speech that sounds unnatural.

Question 19

How does spectral subtraction work in noise reduction?

Answer 19

Spectral subtraction estimates the frequency spectrum of the background noise and subtracts it from the overall sound spectrum, ideally leaving the speech signals intact. However, if the noise frequency overlaps significantly with the speech frequency, it can lead to some loss of the speech signal.

Question 19

What is phase cancellation, and what are its challenges?

Answer 19

Phase cancellation involves measuring the exact waveform of the noise and producing a sound with an identical but reverse phase to cancel out the noise. The main challenge is accurately measuring the noise waveform in the presence of competing speech, which can result in some loss of the speech signal.

Question 20

What role does compression play in noise reduction?

Answer 20

Compression in noise reduction is typically applied to long-term, moderate to loud, low-frequency sounds. By compressing these sounds, their impact is reduced, making it easier for the user to hear speech.

Question 21

What are the benefits and limitations of noise reduction techniques in hearing aids?

Answer 21

The benefits include reducing the wearer’s annoyance from background noise and sometimes improving speech recognition when the noise level is constant. However, limitations include the potential loss of some speech signals, challenges with overlapping noise and speech frequencies, and the unnatural sound that can result from speech synthesis methods.

Question 22

What do most hearing aids use for noise reduction, and why?

Answer 22

Most hearing aids use a form of spectral subtraction for noise reduction, based on the assumption that most background noise is low frequency. This method is effective in many cases, but it may not work as well if the noise overlaps significantly with speech frequencies. Some hearing aids also use spectral enhancement to further improve the clarity of speech signals.

Question 23

What is feedback cancellation in hearing aids, and why is it important?

Answer 23

Feedback cancellation is a crucial process in hearing aids, especially important for open molds or open-ear fittings. It helps eliminate the whistling or squealing sound (feedback) that occurs when amplified sound from the hearing aid speaker is picked up by the microphone and re-amplified.

Question 23

What are the types of feedback detection in hearing aids?

Answer 23

There are two main types of feedback detection:

• Static Detection: Performed at the initial switch-on of the hearing aid.
• Dynamic Detection: Involves continuous monitoring of the hearing aid’s output for feedback.

Question 24

What methods are used for feedback cancellation?

Answer 24

• Notch Filtering: Reduces the gain in a narrow frequency range where feedback occurs.
• Phase Cancellation: Produces a sound in reverse phase to the feedback noise to cancel it out.

Question 25

How does notch filtering work in hearing aids?

Answer 25

*Notch filtering uses filters to reduce the gain at the frequencies where feedback occurs. There are two types of notch filtering:

• Static Notch Filtering: Set by running a check with the hearing aid programming software, identifying the frequency bands where feedback occurs. It has limitations as the feedback frequency can change over time.
• Active Notch Filtering: Continuously monitors the hearing aid’s output for feedback. When feedback is identified, the hearing aid creates a notch filter at the appropriate frequency. Active filtering is more effective but can be slow to adapt to changes in noise.

Question 25

What is phase cancellation, and how does it work?

Answer 25

Phase cancellation involves the hearing aid’s microphone picking up the feedback signal (a constant high-frequency tone). The hearing aid processor then generates a signal that is 180° out of phase with the feedback signal. This reversed signal is emitted by the transducer, effectively canceling out the feedback.

Question 26

What are the advantages of phase cancellation in feedback removal?

Answer 26

Phase cancellation can remove several feedback tones simultaneously without affecting the quality of the speech sound through the hearing aid. However, its effectiveness depends on the processing power of the hearing aid and battery life.

Question 26

Why is active notch filtering more effective than static notch filtering?

Answer 26

Active notch filtering continuously adapts to feedback by monitoring the hearing aid’s output in real-time. When feedback is detected, it dynamically creates a notch filter at the appropriate frequency, making it more responsive to changes compared to static filtering, which is set once and may not adapt to shifting feedback frequencies.

Question 26

Can feedback cancellation affect the quality of speech sounds?

Answer 26

Effective feedback cancellation methods, like phase cancellation and active notch filtering, are designed to minimize the impact on speech quality. Phase cancellation, in particular, can handle multiple feedback tones without degrading speech sound quality, depending on the hearing aid’s processing capabilities.

Question 26

What is the purpose of directional microphones in hearing aids?

Answer 26

Directional microphones are used to improve the signal-to-noise ratio by picking up more sound from the front of the hearing aid user than from other directions. This enhances the user’s ability to hear speech in noisy environments.

Question 27

How do directional microphone systems traditionally improve the signal-to-noise ratio?

Answer 27

Traditional directional microphone systems increase the signal-to-noise ratio by focusing on sounds coming from the front of the wearer and reducing sounds from other directions.

Question 27

How can digital signal processing (DSP) enhance the performance of directional microphones?

Answer 27

*DSP can enhance directional microphones by:

• Controlling the shape of the polar plot, which maps the area from which the microphone collects sound.
• Automatically switching between directional and omnidirectional modes based on the listening environment.

Question 27

What is a polar plot in the context of directional microphones?

Answer 27

A polar plot is a graphical representation that maps the area from which the hearing aid microphone collects sound around the wearer, indicating the microphone’s sensitivity in different directions.

Question 28

How do automatically activated fixed directional systems differ from standard fixed directional systems?

Answer 28

Automatically activated fixed directional systems have a fixed polar plot, but they automatically switch to the directional mic setting when background noise is detected. This makes it easier for the wearer as the hearing aid automatically selects the appropriate program for different listening situations.

Question 28

What are fixed directional microphone systems?

Answer 28

Fixed directional microphone systems have a static polar plot that does not change once set. Different polar plots can be stored in different programs, but the settings remain fixed. This system is effective in specific situations but lacks adaptability to changing environments.

Question 29

What are automatically activated adaptive directional microphone systems?

Answer 29

These systems turn the directional microphone on and off as needed and can change the polar plot in response to the listening environment. For example, if a noise source moves closer, the hearing aid adjusts the polar plot to maintain the best possible signal-to-noise ratio. This allows the hearing aid to adapt to changing noise levels without user intervention.

Question 30

How does wireless communication benefit users with bilateral hearing aids?

Answer 30

• Control Convenience: It allows control of both hearing aids using just one control, such as adjusting the volume.
• Signal Comparison: It enables the comparison of signals across both hearing aids, which can be useful for noise reduction and improving overall sound quality.

Question 30

What are frequency-specific directional microphones?

Answer 30

Frequency-specific directional microphones use digital processing to make microphones directional at different frequencies. This allows for multi-channel directional microphones, where the frequency and location of noise determine the polar plot. This provides improved signal-to-noise ratios for multiple sources of noise. The processing needs to be fast for this to be effective.

Question 30

What is a common problem for people with precipitous high-frequency hearing loss when using hearing aids?

Answer 30

People with precipitous high-frequency hearing loss often miss high-frequency information when wearing hearing aids because a large amount of gain is required at high frequencies, leading to feedback, and the high-frequency hearing loss may be caused by a “dead region” in the cochlea.

Question 31

What is the benefit of wireless communication in hearing aids?

Answer 31

Wireless communication allows sound signals to be streamed directly to hearing aids, which reduces the effect of background noise, enhancing the user’s listening experience.

Question 31

What are “dead regions” in the cochlea, and how do they affect hearing aid amplification?

Answer 31

Dead regions in the cochlea are areas where the hair cells are no longer functioning. Amplifying sounds in these regions is ineffective because the dead hair cells cannot process the amplified sound, and high levels of gain in these regions can reduce frequency discrimination for other sounds.

Question 31

What is frequency lowering, and how does it help with high-frequency hearing loss?

Answer 31

Frequency lowering is a technique that moves high-frequency sounds to a lower frequency range to improve their audibility. This method helps individuals with severe to profound high-frequency losses, especially if they have good hearing in the mid frequencies.

Question 31

What are the different types of frequency lowering aids?

Answer 31

• Frequency Transposition Aids: These aids transpose a specific high-frequency area down by 1 or 2 octaves and mix it with the sound in the lower frequency area.
• Frequency Compression Aids: These aids take high-frequency sounds above a certain frequency and apply a frequency compression ratio to them, effectively compressing the high-frequency sounds into a lower frequency range.
• Frequency Translation Aids: These aids use an adaptive algorithm to identify high-frequency components likely to be speech, copy the sounds, and present them at a lower frequency.

Question 31

Why is the ability to control both hearing aids with one control advantageous?

Answer 31

Controlling both hearing aids with one control simplifies the user experience, making it easier to adjust settings like volume without needing to adjust each hearing aid individually. This can be especially beneficial for those with limited dexterity or vision issues.

Question 32

What are the potential benefits and drawbacks of frequency lowering aids?

Answer 32

Frequency lowering aids can be helpful for those with severe to profound high-frequency losses who have good mid-frequency hearing. However, there is not enough research to indicate clear benefits universally. Some hearing aid wearers may find the sound quality more acceptable, while others might find the changes unhelpful.

Question 32

How does wireless streaming help reduce background noise?

Answer 32

Wireless streaming directly transmits sound signals to the hearing aids, bypassing much of the background noise that would otherwise be picked up by the hearing aid microphones. This direct transmission results in clearer sound quality and better speech understanding in noisy environments.

Question 32

Why is there often no benefit from amplifying in the dead regions of the cochlea?

Answer 32

Amplifying in dead regions provides no benefit because the hair cells in these areas are damaged or dead, meaning they cannot process the amplified sound. Additionally, applying high levels of gain in these regions can negatively impact the ability to discriminate frequencies in other parts of the hearing range.

Question 33

How does comparing signals across hearing aids improve noise reduction?

Answer 33

Comparing signals across hearing aids allows the devices to share information about the acoustic environment, which can enhance noise reduction algorithms. By processing and comparing input from both ears, the hearing aids can more effectively distinguish between speech and background noise, improving the user’s ability to understand conversations in noisy settings.