Proprietary fitting formulas = recipes for success

Phonak’s proprietary fitting formula, Adaptive Phonak Digital (APD) 2.0, brings the sound of Audéo Paradise to life through three key changes designed to optimize your hearing aid fittings.

For those who know me, it is well established that I enjoy a cup of coffee (or three). As you would expect, I have received more recommendations for beans, brew methods, and coffee shops than I can count—which is not a complaint! I thoroughly enjoy exploring the recommendations that come my way, that is, except for one. Throughout my years of caffeine consumption, there has been a brand that is consistently recommended. I have been told to “give it another try!” time and time again, but, just as consistently, I have found myself disappointed. It was simply not my Java, or so I thought. Eventually, I realized the coffee filter I was using affected the flavor by preventing the natural oils of the coffee beans from seeping into my mug. To say I was shocked by the difference a simple filter could make would be an understatement! It turns out the popular coffee company everyone was recommending is my cup of Java. I just needed to use the right filter to bring out the flavor.

Much like my pursuit for the perfect cup, the pursuit for an optimal hearing aid fitting can be affected by a single choice—should you use the proprietary fitting formula or an industry standard, such as NAL-N2? You may be asking yourself, what are the differences between the two, and in what ways does the proprietary fitting formula affect device performance? If so, then grab a mug and read along as we dive into these questions and more!

Why choose a proprietary fitting formula?

In the simplest terms, the fitting formula determines the amount of gain that is applied based on the hearing loss programmed to the device. There are evidenced based fitting formulas that are commonly used in clinical practice with adult patients, and are the gold standard for pediatric fittings (DSLv.5a pediatric and NAL-NL2). These evidenced based formulas are designed to be used with any model or brand you are fitting to meet gain targets that are well established as essential indicators of speech intelligibility. Proprietary fitting formulas are developed with the product in mind, taking into account the signal processing and feature set of the device. The proprietary fitting formula enables the various aspects of the hearing aid to work collaboratively, and a well-constructed proprietary fitting formula not only ensures the device features are complementary, but that the amplification also meets industry standards for good clinical practice by closely aligning with evidenced based gain targets.

What is unique about APD 2.0?

Phonak updated their proprietary fitting formula from APD to APD 2.0 with the launch of Phonak Audéo Paradise. APD 2.0 features three key changes to improve the user experience by optimizing speech intelligibility while maintaining listening comfort.1

  1. Adaptive compression speed—It has been shown that slow-acting compression is perceived as more comfortable than fast-acting compression, while fast-acting compression results in better speech intelligibility2. APD 2.0 combines the best of both speeds in a single pathway compression strategy. This is achieved by using the hearing aid input to drive which compression speed to activate. Specifically, slow-acting compression is used until a steep signal onset activates fast-acting compression.  For example: You are standing outside a café with a friend and you are having a one-on-one conversation in a minimal amount of background noise. Slow-acting compression is active in this moment because this compression speed is subjectively more comfortable and speech intelligibility is not being threatened by competing noise. You then open the café door and go inside. As you enter the building, you are greeted by a sudden increase in noise and it becomes harder to understand your friend. Fast-acting compression is activated by the change in noise, which should then result in better speech intelligibility.
  2. Linearized high level gain—APD 2.0 introduces an additional kneepoint for loud inputs. Gain past this kneepoint is linear. Linear gain has been found to improve speech intelligibility when used with high intensity inputs3. In addition to the improved speech intelligibility, having this additional kneepoint allows the device output to more closely mimic the normal loudness growth function, reducing the effect of recruitment on listening comfort.
  3. New precalculation for mild-moderate hearing losses—The precalculation in APD 2.0 features small gain reductions for moderate and loud inputs (G65 is reduced up to 2dB and G80 by 4dB) for hearing losses up to and including an N3 standard hearing loss4. These changes do not affect the gain for soft inputs, so the audibility of soft sounds is preserved while moderate to loud inputs are less likely to become uncomfortably loud due to the gain reductions. Additionally, the modifications to the precalculation result in gain targets that are more aligned with the NAL-NL2 prescription, ensuring that, with APD 2.0, providers can program and verify Phonak Audéo Paradise devices with a fitting formula that optimizes the overall performance of the hearing aid without concern that they are compromising speech intelligibility.

Together, these key changes craft a balance between comfort and clarity that is sure to satisfy clients from the first fit.

What are the other benefits of using APD 2.0?

In addition to the individual benefits each of the key changes brings to APD 2.0, the cumulative effect of these changes was further assessed in a human subject study at the Hörzentrum Oldenburg, Germany. The study found that among 41 adult participants, APD 2.0 reduced listening effort, especially in noise, compared to its predecessor, APD, for individuals with mild to severe hearing loss5. Bundled together, the changes implemented in APD 2.0 results in clear, comfortable sound with less listening effort.

Meaning, we have an overall answer to our questions—the fitting formula does matter! And if you have shied away from proprietary formulas in the past, I encourage you to “give it another try.” You might be surprised by the outcome.


To read more about Phonak’s proprietary fitting formula, APD 2.0, please visit the Phonak Evidence Library.




  1. Woodward, J., Jansen, S., & Kühnel, V. (2020) Hearing inspired by nature: the new APD 2.0 fitting formula with adaptive compression. Phonak. Insight. Retrieved from Accessed October 20, 2020.
  2. Gatehouse, S., Naylor, G., & Elberling, C. (2006). Linear and nonlinear hearing aid fittings-1. Patterns of benefit. International Journal of Audiology, 45 (3), 130-152.
  3. Lopez-Poveda, E. A., Johannesen, P. T., Perez-González, P., Blanco, J. L., Kalluri, S., & Edwards, B. (2017). Predictors of hearing-aid outcomes. Trends in Hearing, 21, 1-28.
  4. Bisgaard, N., Vlaming, M. S., & Dahlquist, M. (2010). Standard audiograms for the IEC 60118-15 measurement procedure. Trends in Amplification, 14(2), 113–120.
  5. Wright, A. (2020). Adaptive Phonak Digital 2.0: Next-level fitting formula with adaptive compression for reduced listening effort. Phonak Field Study News. Retrieved from Accessed October 20, 2020.