Hearing Aid Prescription DSL, NAL-NL1 and NAL-NL2

Question 1

what is the difference between prescriptive and ‘experiential’ or ‘evaluative approach’ for a prescriptive fitting?

Answer 1

“A prescriptive approach to hearing aid fitting is one in which some characteristics of the hearing-impaired person are measured, and the required amplification characteristics are calculated from them” (Dillon 2001)

As opposed to “experiential” or “evaluative approach” where a number of hearing aids would be compared and an attempt made to find the best one

Question 2

What do prescription formulas for hearing aids typically use as a basis?

Answer 2

either audiometric thresholds or loudness measurements, such as Most Comfortable Loudness (MCL).

Question 3

What’s the goal of a prescriptive formula in hearing aid fitting?

Answer 3

To calculate an “ideal” target output based on the provided information, aiming to optimise amplification for the individuals hearing needs

Question 4

what are some examples of prescription rules?

Answer 4

• DSL (Desired Sensation Level):
  DSL i/o (Cornelisse, Seewald & Jamieson 1995)
• NAL-NL1 (National Acoustic Laboratories, version 1):
  NAL – NL1 (Byrne et al. 2001)
• NAL-NL2 (National Acoustic Laboratories, version 2):
  NAL-NL 2 (Keidser and Dhillon. 2022)

*Examples of others:
- The Cambridge method: Moore & Glasberg 1998
- FIG6: Gitles & Niquette 1996
IHAFF: Cox 1995
- Hearing aid manufacturer rules:
– E.g. Oticon ASA2, SKI, Widex Senso Diva etc

Question 4

what are the most commonly used prescriptive approaches in the UK?

Answer 4

-DSL
- NAL NL1
- NAL NL2

Question 4

what is NAL NL1 and its aim?

Answer 4

• NAL NL1 stands for National Acoustics Laboratory, Version 1.
• To maximize speech intelligibility at the listening level preferred by the hearing aid wearer, assuming intelligibility is maximized when all bands of speech are perceived to have the same loudness.

Question 4

what is DSL and its aim?

Answer 4

• DSL i/o stands for Desired Sensation Level.
• To make speech sufficiently audible to allow speech perception without discomfort for all degrees of hearing loss.

Question 5

what is NAL NL2 and its aim?

Answer 5

• NAL NL2 stands for National Acoustics Laboratory, Version 2.
• The aim of NAL NL2 is to make speech as intelligible as possible while ensuring comfortable loudness. This includes optimizing intelligibility, localization, tonal/non-tonal sounds, and maintaining naturalness across male and female voices.

Question 6

What does DSL i/o calculate?

Answer 6

DSL i/o calculates target output for different input levels, typically 40, 65, and 95 dBSPL.

Question 7

What principle is DSL i/o based on?

Answer 7

DSL i/o is based on the concept that speech must be amplified to a sufficient sensation level, ensuring a comfortable listening level to maximize intelligibility.

Question 8

What factors influence the targets set by DSL i/o?

Answer 8

Targets in DSL i/o are influenced by the Long Term Average Speech Spectrum (LTASS) and are adjusted to amplify speech to a comfortable level within the patient’s dynamic range. Initially designed for pediatric fitting, it has since been used across various age groups.

Question 9

What does NAL-NL1 calculate?

Answer 9

NAL-NL1 calculates target insertion gain for different input levels, typically 50, 65, and 80 dBSPL.

Question 10

What principle does NAL-NL1 operate on?

Answer 10

NAL-NL1 operates on the principle of equalizing loudness relationships across speech frequencies. It assumes that maximizing speech intelligibility requires amplifying all speech frequencies to be equally loud.

Question 10

How does NAL-NL1 differ from other fitting formulas in terms of target determination?

Answer 10

Unlike other formulas, NAL-NL1 considers “effective audibility” rather than sensation level. It provides less gain for low frequencies where speech is most intense, focusing on maximizing intelligibility rather than just making sounds audible.

Question 11

What are the key differences between NAL-NL1 and NAL-NL2?

Answer 11

• NAL-NL2 shares the same aim and process as NAL-NL1, aiming to maximize speech intelligibility through equalized loudness relationships across speech frequencies.
• However, NAL-NL2 incorporates improvements based on empirical data, a recent loudness model, and extensive evaluation, including patient preference and performance data.

Question 12

How does NAL-NL2 adjust gain compared to NAL-NL1?

Answer 12

• NAL-NL2 introduces changes in gain reduction based on tonal/non-tonal sounds, with a notable emphasis on the low frequencies.
• Overall, there’s a reduction in gain, particularly for adults, with a 4dB reduction for females and a 2dB reduction for males.

Question 13

How did NAL-NL2 account for the adaptation effect in users with different levels of hearing loss?

Answer 13

Evaluations revealed that new users with moderate hearing loss or greater preferred less gain, while new or experienced users with mild hearing loss showed no significant difference in preference.

Question 14

How does NAL-NL2 differ from NAL-NL1 regarding gain preferences for different levels of hearing loss?

Answer 14

In NAL-NL2, subjects with mild to moderate loss preferred higher gain for low input levels (50 dB) and lower gain for high input levels (80 dB) compared to NAL-NL1.

Question 15

How does NAL-NL2 adjust compression ratio (CR) for severe to profound losses?

Answer 15

NAL-NL2 restricts compression ratio (CR) for severe to profound losses.

Question 16

What changes did NAL-NL2 make in terms of gain adjustment for binaural listening compared to NAL-NL1?

Answer 16

NAL-NL2 still applies more gain for unilateral fittings compared to binaural fittings, but the difference is less pronounced than in NAL-NL1.

Question 16

Why is it important to listen to a patient’s feedback during the fitting process?

Answer 16

It’s crucial to listen to the patient’s feedback, particularly if they’re experienced hearing aid users, as they can provide valuable insight into the quality of sound and whether adjustments are needed.

Question 16

What role does a fitting rule play in hearing aid adjustment?

Answer 16

A fitting rule serves as a starting point for adjusting hearing aid settings.

Question 17

Why might patients require different settings for different listening situations?

Answer 17

Patients encounter various listening environments in daily life, each with unique acoustic characteristics, so they may need different hearing aid settings to optimize their hearing experience accordingly.

Question 18

What is Real Ear to Coupler Difference (RECD)?

Answer 18

• RECD is a measurement, in dB, of the difference between the response to a signal in the patient’s real ear and the same signal in a 2cc coupler, across different frequencies.
• It quantifies how much the patient’s ear differs from a standard 2cc coupler.

Question 19

How is RECD typically measured?

Answer 19

RECD can be measured using insert earphones with foam tips or custom earmolds.

• Measuring the coupler response of the insert earphone

Question 20

How is the Real Ear to Coupler Difference (RECD) used in fitting hearing aids?

Answer 20

• it serves as a correction factor to convert coupler dBSPL (sound pressure level) to dBSPL at the eardrum.
• Coupler dBSPL plus RECD equals dBSPL at the eardrum.
• This enables the testing of various hearing aids or settings to determine the best match to target outputs or insertion gain without the patient needing to be present.

Question 21

what are the advantages of Real Ear to Coupler Difference?

Answer 21

• Quick to perform
• Allows hearing aid to be set up & adjusted in the test box
• Can evaluate and compare different hearing aids
  without the patient having to be present

Question 22

What is the SPL-ogram?

Answer 22

The SPL-ogram is a graph where all dB scales are converted into identical units: dB SPL (Sound Pressure Level) at the eardrum, also known as TM (Tympanic Membrane) dB SPL.

Question 23

What does the SPL-ogram allow to be represented on the same graph?

Answer 23

The SPL-ogram enables representation of various audiological information, including normal thresholds, patient’s thresholds, Long Term Average Speech Spectrum (LTASS), Amplified Speech Spectrum, and Maximum Output.

Question 24

How are RECDs utilized in the context of the SPL-ogram?

Answer 24

RECDs are incorporated by adding them to coupler dBSPL, resulting in dBSPL at the eardrum, which allows for accurate representation of audiological information on the SPL-ogram.

Question 24

How is SPL used in the context of hearing aid fittings?

Answer 24

SPL is employed to display target outputs for hearing aids, originally in the DSL method but now commonly used for NAL targets as well.

Question 24

What information does SPL typically show?

Answer 24

SPL displays various data in dBSPL, including unaided thresholds, predicted uncomfortable loudness levels (ULLs), targets for aided conversational speech, and targets for the maximum output of the aid.