The NAL-NL3 system marks a transformative step in hearing aid fitting, shifting from a one-size-fits-most prescription to a modular, patient-centred approach. Developed by the National Acoustic Laboratories, this new system integrates a core audiogram-based prescription with targeted modules to address individual listening needs, enabling more personalised and effective hearing care.
For decades, hearing aid fitting has revolved around a single prescription – a one-size-fits-most approach. While effective for many, this model has limitations in meeting the nuanced needs of diverse users. With the introduction of NAL-NL3, we shift from a singular prescriptive algorithm to a modular system, designed to better individualise hearing aid fittings and reflect modern patient-centred hearing healthcare principles.
A brief history of hearing aid prescriptions
Hearing aid ‘prescription’ is defined as a systematic, evidence-based approach to selecting gain and output based on an individual’s audiogram. The concept of using a ‘prescription’ in hearing aid fitting emerged in the 1970s. Before this, fittings were often guided by clinician intuition or manufacturer defaults, with limited standardisation across providers. These early methods lacked the clinical rigour needed to ensure consistent outcomes, especially as devices became more sophisticated.
Several landmark approaches helped define the modern era of prescriptive fitting:
- NAL (National Acoustic Laboratories): First introduced in the late 1970s in Australia, the original NAL prescription (now NAL-R) sought to maximise speech intelligibility while ensuring comfort at preferred listening levels. This core concept was to balance audibility with loudness comfort, and became foundational to subsequent NAL prescriptions.
- FIG6: Developed by Denis Byrne in the 1970s, FIG6 offered a tabulated set of gain recommendations based on audiometric thresholds. It represented one of the first attempts to formalise fitting rules in a clinically applicable way.
- DSL (Desired Sensation Level): Introduced in the 1980s by Richard Seewald and colleagues, DSL was particularly influential in paediatric audiology. It aimed to make speech sounds audible and comfortable for children, accounting for developmental and physiological differences in younger populations.
Prescriptive methods have continued to evolve with successive generations of technology and clinical research. NAL-NL1 and later NAL-NL2 introduced non-linear gain strategies aligned with wide dynamic range compression, reflecting real-world listening demands. DSL evolved into DSL v5.0, incorporating loudness normalisation and speech mapping technologies for more precise fitting. These modern prescriptions, now global standards, share a common aim: to provide audiogram-driven recommendations that maximise intelligibility and comfort. However, their focus remains on treating hearing loss as defined by audiometric thresholds.
Yet as the audiological landscape has evolved, so too has our understanding of what constitutes meaningful hearing support. It is now widely acknowledged that hearing difficulties cannot be adequately captured by the audiogram alone. Individuals with identical audiometric profiles often report vastly different experiences in daily life, shaped by factors such as cognitive ability, lifestyle demands, listening environments, personal preferences and psychological adaptation. For example, some users may struggle significantly in background noise despite having only mild hearing loss, while others with similar thresholds report minimal functional impact.
In this context, a single, population-derived prescription, however well-validated, can no longer meet the full spectrum of individual needs. What’s required is an approach that allows for adaptation, not just to audiometric configuration, but to the real-world communication goals and functional limitations of the user. NAL-NL3 responds directly to this challenge by introducing a modular system that maintains the integrity of a core diagnostic-based prescription, while enabling evidence-informed tailoring through purpose-built modules. This structure empowers clinicians to move beyond a ‘best-fit average’ and instead provide hearing aid fittings that are personalised, context-aware and responsive to the complexities of everyday listening.
Introducing NAL-NL3: a modular system
NAL-NL3 retains a familiar foundation: the NAL-NL3 Prescription, derived from audiometric data and grounded in diagnostic treatment. This is the direct successor to NAL-NL2, refined for today’s devices and users. However, NAL-NL3 is more than just a prescription; it is a system.
At its core is the NAL-NL3 Prescription, the recommended gain and output settings based on a user’s audiogram and other clinical data. This is what aligns most closely with the traditional definition of a ‘prescription’, a clinician’s management plan for a diagnosed condition.
NAL-NL3 represents a significant advancement over NAL-NL2 in its core prescription by addressing limitations in how previous algorithms handled atypical or edge-case audiometric configurations. NAL-NL2 was designed using population-average data and performed well for common hearing loss profiles, such as gently sloping sensorineural losses. However, it sometimes struggled with more complex or less prevalent patterns. For example, individuals with rising configurations (better hearing in the high frequencies), notches (often associated with noise exposure), mixed losses, reverse slopes or cookie bite (congenital) losses - in keeping with the consistent descriptors you’ve provided for the other losses frequently received gain targets that either overamplified certain frequencies or underdelivered speech cues, resulting in poor sound quality, low speech intelligibility or discomfort. The NAL-NL3 Prescription was developed through deep learning models trained on a vast database of millions of hearing aid fittings, specifically calibrated to better accommodate this wider spectrum of hearing loss profiles. By refining how gain and output are calculated across the frequency range and incorporating updated modelling of real-world speech perception, NAL-NL3 offers more accurate and comfortable fittings across diverse audiometric shapes. The new NAL-NL3 Prescription was trialled across 30 sites in Australia, with 170+ clients and 600 REMs, which showed improved clinician usability and patient preference. Clinicians can now have greater confidence that the NAL-NL3 base prescription will perform effectively without the need for extensive manual fine-tuning for these less common audiometric configurations.
Surrounding this core prescription are NAL-NL3 Modules – distinct, purpose-built extensions that modify the base prescription to address specific functional challenges, user preferences or listening contexts. The first two launched include:
- The NAL-NL3 Comfort in Noise Module – Tailored to those needing greater comfort in complex environments or with specific noise sensitivity profiles.
- The NAL-NL3 Minimal Hearing Loss Module – Designed for individuals with normal audiograms but documented functional difficulties, such as speech-in-noise challenges.
These modules do not replace the prescription. Instead, they build upon it, allowing clinicians to tailor fittings using evidence-based tools aligned with patient needs.
Why ‘prescription’ still matters
Clarifying terminology is essential. Only the NAL-NL3 Prescription is a true ‘prescription’. It is diagnostic-based and guides treatment for a health condition – hearing loss. In contrast, the modules provide optional adaptations based on preferences, performance goals or specific contexts, and are not prescriptive in the medical sense.
This distinction is important. Prescriptions treat a diagnosed condition. Modules solve problems that may fall outside the boundaries of a clinical diagnosis but are crucial for functionality, comfort and satisfaction.
For example, the Comfort in Noise Module adjusts the base prescription to suit personal comfort levels in noisy environments, addressing listening effort, sound quality and tolerance, rather than hearing loss per se. This module is designed for individuals who may report that noisy environments are overwhelming or fatiguing, even if their hearing thresholds do not suggest a need for increased gain. By strategically modifying the gain and output characteristics of the NAL-NL3 Prescription, often by reducing gain in certain frequency regions or by adjusting compression characteristics, it provides a more comfortable listening experience in complex soundscapes. Importantly, speech understanding is retained, ensuring that the wearer still receives the core benefit of amplification without unnecessary auditory strain. The module empowers clinicians to manage user preferences for noise tolerance in an evidence-based way, rather than relying solely on fine-tuning or ad hoc adjustments.
Likewise, the Minimal Hearing Loss Module provides targeted audibility enhancements for individuals who have normal audiograms but experience real-world communication difficulties, particularly in environments with poor signal-to-noise ratios. These users may score highly on self-report measures such as the Hearing Handicap Inventory for the Elderly (HHIE), indicating functional impairment despite clinically normal thresholds. The module works by applying a carefully limited gain strategy that supports the operation of advanced features such as directional microphones and speech-in-noise algorithms, ensuring that these features are audible and effective, while preserving comfort and avoiding over-amplification. Because it does not aim to treat a diagnosed hearing loss, it is not classified as a ‘prescription’. Rather, it is a solution-oriented design that addresses the needs of underserved groups, such as those with hidden hearing loss or auditory processing difficulties, and represents a new frontier in proactive, needs-based care.
Together, these modules reflect a shift from deficit-based treatment to functional support, offering clinicians evidence-informed options that better match the diversity of needs seen in modern audiological practice.
Enabling person-centred, personalised audiology
NAL-NL3 aligns with the increasing emphasis on person-centred care. While the NAL-NL3 Prescription incorporates some patient factors, the modular structure allows clinicians to further personalise fittings and address users’ lived experiences.
This is particularly important in light of rising expectations for healthcare to be tailored, inclusive and outcome driven. As clinicians adopt NAL-NL3 and its modules, they’re better-equipped to understand and meet individual needs, going beyond audibility to address participation, quality of life and real-world success.
Conclusion
NAL-NL3 represents a paradigm shift from a single prescription to a modular system that embraces individualisation. By preserving the integrity of the prescription while offering modular enhancements, NAL-NL3 equips clinicians with a structured yet flexible approach to person-centred hearing device fitting. It honours our profession’s clinical roots while embracing a future of personalised, evidence-based hearing healthcare.
As more modules are developed and validated, the NAL-NL3 system will continue to expand, supporting clinicians in delivering care that is not only effective, but also responsive, empowering and person-centred.
Further reading
1. Keidser G, Dillon H, Flax M, et al. The NAL-NL2 Prescription Procedure. Audiol Res 2011;1(1):e24.
2. Seewald R, Moodie S, Scollie S, Bagatto M. The DSL Method for Pediatric Hearing Instrument Fitting: Historical Perspective and Current Issues. Trends Amplif 2005;9(4):145–57.
3. Byrne D, Dillon H. The National Acoustic Laboratories’ (NAL) new procedure for selecting the gain and frequency response of a hearing aid. Ear Hear 1986;7(4):257–65.
Declaration of competing interests: The National Acoustic Laboratories (NAL), where the authors are employed, has received research funding and / or resources from several hearing healthcare companies for projects not directly related to the research described here, including Sonova, GN ReSound, Oticon, WS Audiology, Cochlear and Interacoustics. In addition, NAL currently licenses the NAL-NL2 prescription and has recently commenced licensing of the new NAL-NL3 prescription to organisations internationally.
