RP203 - NL3: The Next Generation Hearing Aid Fitting System

Abstract:
Best-practice hearing aid fitting involves the use of a prescriptive method to derive appropriate targets for gain and compression. NAL-NL2 continues to be the gold standard for the fitting of hearing aids in adults. However, the needs of clients and hearing aid technology has changed since the introduction of NAL-NL2, as has the science that underpins our existing approach to hearing aid prescription. NAL-NL3 represents a step change in hearing aid fitting and personalisation, providing tools to support the management of a broader range of client needs and support clinicians to help their clients achieve enhanced benefit from hearing aids.

Summary:
Rationale
Best-practice hearing aid fitting involves the use of a prescriptive method to derive appropriate gain and compression based on the audiometric and demographic characteristics of the client. NAL-NL2 continues to be the leading standard worldwide for the prescriptive method of choice for adults. However, the needs of today’s clients and hearing aid technology has changed since the introduction of NAL-NL2, as has the science that underpins our existing approach to hearing aid prescription.

Objectives
The purpose of this work was to develop the next generation NAL non-linear hearing aid prescription that better reflects the contemporary needs of clients and those clinicians who fit their hearing aids. In particular, the objective was to create an enhanced fitting solution that provides specific solutions that address unmet client needs.

Methods/design
The development of NAL’s new fitting solution has drawn on over a decade of experience with NL2 and an analysis of emerging client needs not well served by the philosophy of maximising intelligibility while not exceeding 'normal' loudness. The approach taken was founded on fitting philosophies that are appropriate to address those unmet client needs and developing algorithms that can be incorporated into fitting and verification software for routine use in the clinic. The development of the novel fitting philosophies was informed by reviews of existing published evidence and feedback from clinicians and hearing aid users for where current approaches fail to provide an appropriate solution. The development and validation of novel algorithms was informed by the analysis of large-scale data on the clinical fitting of hearing aids, the application of advances in machine learning and optimisation techniques, exploiting advances in psychoacoustic models of perception, and prospective testing with new and experienced hearing aid users.

Results
The novel fitting philosophies depart from the traditional approach to hearing aid gain prescription that seeks to maximise intelligibility based on the principle of restoring audibility. In particular, greater focus is placed on ensuring that a wider population can benefit from the advanced signal processing of modern hearing aids, and that the resulting amplification maximises the comfort of listeners under realistic listening conditions. As expected, the novel algorithms for determining the gain and compression settings for hearing aids generate prescriptive targets that depart significantly from the existing gold standard NAL-NL2. Prospective testing with new and existing hearing aid users confirmed the validity of this novel approach.

Conclusion
NL3 represents a step change in NAL’s approach to hearing aid fitting and personalisation, providing novel tools to support the management of hearing problems in a broader range of clients, and providing a practical clinical tool that can support clinicians to help their clients achieve enhanced benefit from hearing aids

Justification for level of instruction
This presentation is designed to describe the approach and outcomes from conducting research on developing a novel hearing aid fitting system. While it does require foundational knowledge of hearing aid fitting, it does not require attendees to have substantial knowledge or expertise in how existing hearing aid fitting prescriptions work.

Brief Summary of Clinical Takeaways:
The clinical takeaway for this session is that existing approaches to deriving prescriptive targets for hearing aids have limitations based on the fact that they focus primarily on maximising intelligibility, and alternative fitting philosophies better address the needs of specific client groups or specific use cases for modern hearing aids.