HAC Digital Signal Processing in Hearing Aids 2 — Questions and Answers
Question 1: What is the primary advantage of a multi-band compression system over single-band compression in hearing aids?
- It reduces battery consumption significantly
- It allows independent gain adjustments across different frequency regions (Correct answer)
- It eliminates feedback whistling completely
- It increases the maximum output sound pressure level
Correct answer: It allows independent gain adjustments across different frequency regions
Multi-band compression processes each frequency region independently, allowing precise gain fitting that matches the audiogram across frequencies.
Question 2: In DSP hearing aids, what does the term 'attack time' refer to in dynamic range compression?
- The time to switch between listening programs
- The delay before the microphone activates
- The time for the compressor to respond to a sudden loud sound (Correct answer)
- The processing delay introduced by the DSP chip
Correct answer: The time for the compressor to respond to a sudden loud sound
Attack time is how quickly the compression circuit reduces gain after detecting a sound that exceeds the compression threshold.
Question 3: Which sampling rate is most commonly used in modern digital hearing aids?
- 8 kHz
- 16 kHz
- 32 kHz (Correct answer)
- 44.1 kHz
Correct answer: 32 kHz
Most modern hearing aids sample at approximately 32 kHz, providing adequate bandwidth for speech and environmental sounds while managing power consumption.
Question 4: What is 'spectral subtraction' used for in digital hearing aid processing?
- Reducing feedback by subtracting the receiver output from the microphone
- Noise reduction by estimating and removing steady-state background noise (Correct answer)
- Equalizing the frequency response of the receiver
- Separating speech from music signals
Correct answer: Noise reduction by estimating and removing steady-state background noise
Spectral subtraction estimates the noise spectrum during quiet pauses and subtracts it from the incoming signal to reduce steady-state background noise.
Question 5: A patient reports that their hearing aid makes speech sound 'tinny' or metallic. Which DSP parameter adjustment would most likely address this complaint?
- Increasing high-frequency gain
- Reducing release time of the compressor
- Boosting low-frequency gain or reducing high-frequency emphasis (Correct answer)
- Increasing the compression ratio
Correct answer: Boosting low-frequency gain or reducing high-frequency emphasis
A tinny or metallic sound perception typically indicates excessive high-frequency gain or insufficient low-frequency energy, which can be corrected by adjusting the frequency shaping.
Question 6: What is the function of a 'notch filter' in digital hearing aid feedback management?
- It amplifies specific frequencies where hearing loss is greatest
- It attenuates a narrow frequency band where feedback oscillation occurs (Correct answer)
- It widens the dynamic range of the amplifier
- It delays the signal to match binaural processing
Correct answer: It attenuates a narrow frequency band where feedback oscillation occurs
A notch filter targets and attenuates the specific frequency at which feedback whistling is occurring, eliminating the oscillation.
Question 7: In hearing aid DSP, 'binaural coordination' between two hearing aids most commonly uses which wireless protocol?
- Wi-Fi 802.11n
- Near Field Magnetic Induction (NFMI) or Bluetooth Low Energy (Correct answer)
- AM radio frequency
- Infrared light transmission
Correct answer: Near Field Magnetic Induction (NFMI) or Bluetooth Low Energy
Most modern binaural hearing aid systems use NFMI or Bluetooth Low Energy (BLE) to wirelessly synchronize processing between the two devices.
HAC Digital Signal Processing in Hearing Aids 2
What is the primary advantage of a multi-band compression system over single-band compression in hearing aids?