Question
Is the ReSound Audiogram+ fitting rule based off NAL or DSL prescriptions?
Answer
Neither. In fact, Audiogram+ predates both the first versions of the most popular generic prescriptions for fitting nonlinear hearing aids from the National Acoustic Laboratories and the University of Western Ontario. ReSound developed the first multiband wide dynamic range compression hearing aid in the late 1980s, including a novel fitting system based on suprathreshold loudness judgments (Pluvinage, 1988). The procedure, LGOB, Loudness Growth in Octave Bands (Allen et al, 1988) was an automated test using narrowband noise to set parameters in the hearing aids to achieve dynamic range compression. The LGOB procedure took 10-15 minutes per ear to carry out. Hearing Care Professionals (HCPs) often opted to skip this time-consuming process and simply use the largely theoretically based initial fit (Villchur, 1973), but then struggled with what at the time was complicated fine-tuning. To accommodate the need for greater efficiency, a systematic analysis of thousands of ReSound hearing aid fittings, including audiometric data, fitting parameters, and user responses to a detailed questionnaire, was carried out. From this analysis, it was possible to create a fitting algorithm that provided a more appropriate starting point for initial fittings than what was originally introduced with the first fitting system (Pluvinage, 1994). This algorithm has since been further refined and became known as Audiogram+.
Because Audiogram+ is an independently developed fitting prescription, there is no systematic relationship between it and the peer-reviewed NAL-NL2 (Keidser et al, 2011) or DSLv5 (Scollie et al, 2005) prescriptions. That said, HCPs may note that both NAL-NL2 and DSLv5 tend to prescribe a more aggressive high-frequency response and that NAL-NL2 may also yield higher compression ratios. A single-blinded clinical comparison study between Audiogram+ and NAL-NL2 confirmed that, at least for mild-to-moderate hearing losses, Audiogram+ showed less high-frequency gain but slightly more loudness. The greater high-frequency emphasis of NAL-NL2 (Groth et al, 2023) did not lead to better speech recognition in noise performance for the test participants, and no strong preferences for either fitting rationale were found after a period of daily life wear. It was concluded that both provided viable starting points for fitting ReSound hearing aids.
ReSound Smart Fit fitting software provides NAL-NL2 and DSLv5 as selectable fitting prescriptions in addition to Audiogram+. The fitting prescription can be set or changed either in the “Patient” screen or from the “Fitting” menu, and the default prescription can be set in the “Preferences” dialog.
References
Allen, J. B., Chen, P. S., & Hall, J. L. (1990). Loudness growth in 1/2-octave bands (LGOB) - a procedure for the assessment of loudness. Journal of the Acoustical Society of America, 88(2), 745–753.
Groth, J., Koehler, E., & Jespersen, C. (2023). Comparing ReSound hearing aid fittings with Audiogram+ and NAL-NL2. ReSound white paper.
Keidser, G., Dillon, H., Flax, M., Ching, T., & Brewer, S. (2011). The NAL-NL2 prescription procedure. Audiology Research, 1(1), 88–90.
Pluvinage, V. (1988). New dimensions in diagnostics and fitting. Hearing Instruments, 39(8), 28–30, 39.
Pluvinage, V. (1994). Rationale and development of the ReSound system. In M. Valente (Ed.), Understanding digitally programmable hearing aids (pp. 15–39). Allyn & Bacon.
Scollie, S., Seewald, R., Cornelisse, L., Moodie, S., Bagatto, M., Laurnagaray, D., Beaulac, S., & Pumford, J. (2005). The desired sensation level multistage input/output algorithm. Trends in Amplification, 9(4), 159–197.
Villchur, E. (1973). Signal processing to improve speech intelligibility in perceptive deafness. Journal of the Acoustical Society of America, 53(6), 1646–1657.
