Those behind the first new hearing aid fitting formula in 15 years, the National Acoustic Laboratories’ NAL-NL3, discuss everything audiologists need to know about the updated formula, now featuring a suite of prescriptions rather than a one-size-fits-all solution.
Modern day audiology clinics face all kinds of complex problems, but there’s one patient cohort that creates a high degree of uncertainty and indecision.
Those with audiometrically normal hearing tests (minimal or no audiometric hearing loss) – who have trouble hearing in noise – are a particularly challenging set of patients who can be disillusioned after being told their hearing is ‘normal’.
The practitioner can be left wondering how they can optimally manage such patients.
It’s a problem the new NAL-NL3 hearing aid fitting formula hopes to address, along with a raft of other updates unveiled by the National Acoustic Laboratories (NAL), which has developed hearing aid fitting formulae used by clinicians globally.
Estimates suggest half of new clients walking into audiology clinics fit in this category (no audiometric hearing loss), Dr Padraig Kitterick, NAL head of audiological science who has overall responsibility for delivery of the project, told Hearing Practitioner Australia.
Another key change advises how to fit hearing aids to help other clients hear better in noise. “The point is making hearing aids acceptable and beneficial even if you’ve got little or no audiometric hearing loss, to help you hear better in noise,” Dr Kitterick said.
With NAL director Dr Brent Edwards, he revealed details and evidence behind the new program at the American Academy of Audiology conference in New Orleans on 28 March 2025.
Dr Edwards said: “I’m probably most excited about delivering the next generation of fitting prescription that will help hearing health companies and hearing care practitioners provide the best hearing aid fittings possible.”
Dr Kitterick told HPA: “We’re excited to provide not just the next generation of what has been a long line of evidence-based hearing aid fitting prescriptions but for the first time introduce brand new ways of fitting hearing aids.
“These new prescriptions will help clinicians address needs that they’re seeing in clients where they don’t have a really good evidence-based solution for fitting, particularly those with minimal hearing loss and those with difficulties in noise. It’s a whole new ball game.”
Dr Kitterick said NAL had been at the forefront of hearing aid fitting prescriptions for decades. Its NAL rule was launched in 1976, a revised rule in 1986 and in 1999 the NAL-NL1 algorithm was released.
“It was the first non-linear formula from NAL and was revolutionary because it started what is still used today, a process of using computer models to find the best way to program hearing aids to maximise speech understanding,” he said.
“That was superseded about 12 years later with NAL-NL2, which became the most popular and widely recognised fitting algorithms available globally, compatible with Windows or mobile apps.”
NAL-NL2 is the second generation of prescription procedures for fitting wide dynamic range compression instruments. Like its predecessor NAL-NL1, NAL-NL2 aims at making speech intelligible but without making sounds too loud. NAL-NL2 is the world’s most widely used fitting prescription for hearing aids to date.
“When NAL launched NL2 it was a huge step forward and kept with the same type of approach, using computer models and evidence to find the best targets,” Dr Kitterick said.
“It included a lot of information we had learned about fitting hearing aids, such as how we should adjust hearing aids based on somebody’s experience of using them, whether users are male or female, or they primarily listen to tonal languages versus non tonal languages like English.”
These empirical adjustments were learnt from decades of using NL1.
Dr Kitterick said NAL surveyed clinicians worldwide asking for use cases where NL2 was not providing the best solution for their clients.
“We got a lot of feedback and consistency across clinicians from around the world,” he said. “They said it worked really well for most clients, but they identified pain points.
“They told us that sometimes NL2 prescribes too much compression and can prescribe too much gain for specific kinds of hearing losses like mixed losses and reverse sloping losses. Data from hundreds of thousands of hearing aid fittings also suggested that often for many users, particularly new hearing aid wearers, NL2 prescribed too much high frequency gain that did not really improve intelligibility in a meaningful way.”
Apart from clinical pain points, there were a lot of hearing needs and use cases that NL2 didn’t address. “One is how to fit hearing aids to people with minimal or no audiometric hearing loss, and the other is how do we help our clients with hearing loss who use hearing aids listen more comfortably in noisy situations? These are two important needs we’re addressing for the first release of NL3 later this year,” Dr Kitterick said.
“A key new feature of NAL-NL3 is the shift from one prescription for everybody to a modular system that we will expand over time that contains a suite of different prescriptions to achieve different things.
Same approach as NL2 for quiet environments
Dr Kitterick said there are different philosophies and ways of solving the problem of how best to fit hearing aids. When fitting the best option for patients who want to listen and understand well in quiet environments, NL2 has remained the gold standard since its release 15 years ago.
“It is well validated and well understood. We’re keeping that same philosophy for quiet and are fixing pain points with it, making it even more effective by bringing the latest machine learning approaches and over a decade of experience with fitting NL2.”
“The minimum hearing loss module has a very different philosophy from NL2. All our prescriptions to date are based on the idea that you’re amplifying sounds to make them audible (compensate for hearing loss) and therefore make speech understandable,” Dr Kitterick explained.
“That’s the primary thing we’re trying to do when we fit hearing aids. But for people with minimal or no (audiometric) hearing loss, our existing solution in NL2 would provide no amplification because it was based on the assumption that the person using the hearing aid would have a hearing loss.
“Hearing aids are amazing devices that can remove noise and make it easier to listen. The minimum hearing loss module we’re introducing with NAL-NL3 adopts a completely different philosophy from NAL-NL2 on how sounds should be amplified by the hearing aid.”
The goal of the new module is to make hearing aids both acceptable to new hearing aid users with minimal or no audiometric hearing loss while also ensuring they help them to hear better in noise.
Dr Kitterick says practitioners often thought that telling these patients they have normal hearing was reassuring, but if they’re having problems in noise, what they often want is a recommendation for which solution could help address their listening difficulties. “We get lots of queries from around the world from practitioners who saw our research on the benefits of hearing aids for these individuals,” he said.
“Practitioners keep asking – but how do I fit them? And that’s what we’re going to solve with NAL-NL3’s minimum hearing loss module.”
Comfort in noise
Another feature of NAL-NL3 is a comfort in noise module. Dr Kitterick said every audiologist knows most people coming to their practice who are motivated to take up hearing aids are not sitting in quiet rooms all day. They want to use their hearing aids in the real world – and that world is a noisy place.
“We don’t believe NL2 is the best we can do to fit a hearing aid when the use case is listening in noise,” he said. “Our NL3 noise module maximises comfort in noise without sacrificing speech intelligibility. It gives a much more comfortable experience but maintains the focus on maximising speech understanding that has been at the core of NAL hearing aid prescriptions for decades.
“NL3 is both an evolution and a revolution. The evolution is that it provides a replacement for NL2 that builds on a solution which is widely validated and trusted, but we’re addressing pain points and making a better version. The revolution is the new modules that address specific unmet needs where existing prescription formulae do not provide a suitable solution.”
“We will grow and improve modules over time and have started to reach out and talk to practitioners, manufacturers and providers about what are other key use cases that are most important to address for future modules such as non-speech focused modules like listening to music.”
Practitioner demand
The changes were introduced due to practitioner demand and to address needs that were not being met. They were also driven by technology improvements. NL2 was based on computer models that maximised speech intelligibility and was a very early use of machine learning to maximise outcomes with hearing aids.
“With our noise module we want to make speech much more comfortable when listening in noisy environments without sacrificing intelligibility,” Dr Kitterick said. “Intelligibility is core of the key new parts of NL3 but importantly in two out of three cases, it’s intelligibility in noise to reflect how most people are using hearing aids today.”
NL3 is a team effort and one of the most important projects NAL has done. It involved every NAL employee including audiologists, signal processing engineers, and engineers with expertise in hearing aid design and manufacture, machine learning and artificial intelligence.
Promising results
Dr Kitterick has been involved in running in-house studies and in clinic studies for a while – and they’re seeing “exciting and important findings” that verify these new philosophies do deliver the benefits they’re seeking with the new modules.
“We have evidence from our trials to demonstrate the new minimum hearing loss module significantly improves speech understanding in noise, while not impairing speech clarity, naturalness and comfort of listening, making hearing aids acceptable to people with minimal hearing loss or normal (audiometric) hearing while delivering significant speech benefits,” he said.
” Our trials also show that our new noise module can significantly improve people’s comfort in noise. The way we have shown that is to send hearing aid users out into the real world and get them to report back which option they prefer – hearing aids fitted on our noise module or the existing quiet module from NL2 but improved in NL3.
“Our listeners showed significant preference for the noise module when listening in noise and our lab-based studies showed they received no detriment in their speech intelligibility from using the noise module. Trials are occurring using NL3 as a drop-in replacement for NL2’s general fitting formula. About 30 clinicians across more than 25 clinics have done almost 600 REM sessions with their clients using NL3.
“We’re getting feedback and learning a lot so when this new solution is released, it will be a tried, well tested and verified solution. It’s exciting to have the first patients being fit so we can get feedback from the clinical coalface that this is working as we would like it to.”
Hearing Australia clinics including its Innovation Centre, and Hearing Savers clinics, a member of the Hearing Business Alliance, have taken part in the trials.
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Groundbreaking new NAL-NL3 fitting formula reveals new ways of hearing aid fitting
