Fitting Formula

Pro Fit offers a variety of prescriptive approaches for fitting hearing aids. These approaches can be categorized as Linear or Non-Linear in nature. Linear fitting formulas were designed to prescribe gain for hearing aids with fixed gain and frequency responses across input levels. Non-Linear fitting formulas prescribe different amounts of gain depending upon input level and were developed to fit wide dynamic range compression hearing aids.

 

The Non-Linear and Linear fitting formulas available within Pro Fit are described below. Only the fitting formulas selected via Target Preferences are available in the drop-down list from most Fitting screens.

  • e-STAT 2.0 (default) - e-STAT 2.0 is a proprietary fitting algorithm. Its predecessor, e-STAT, originated as a less compressive version of NAL-NL1 and has since been empirically optimized over several years based on the preferences of real patients wearing Starkey hearing aids. e-STAT 2.0 is tailored to Starkey's compression architecture with target gains defined at the system’s critical kneepoints. Also unique to e-STAT 2.0 is the ‘minimize vent interaction’ feature, which changes target gain based on vent size. This feature aims to reduce the potential for audible artifacts by minimizing the region over which amplified sound, and direct path sound are at about the same level. Expect e-STAT 2.0 to provide a good starting point from which further fine tuning adjustments may be needed.
  • DSL v5 - Specific objectives of DSL v5 include:
    • Avoidance of loudness discomfort during hearing aid use
    • Hearing aid prescription that ensures audibility of important acoustic cues in conversational speech as much as possible
    • Prescription of hearing aid compression that is appropriate for the degree and configuration of the hearing loss but that attempts to make a wide range of speech inputs available to the listener
    • Accommodation for the different listening requirements within quiet and noisy listening environments

A detailed description can be found at http://www.dslio.com.

 

Real Ear Aided Response (REAR) pure-tone DSL v5 targets generated in Pro Fit can be expected to closely match the DSL v5 stand alone version. Slight discrepancies can be accounted for by the fact that Pro Fit always uses soft speech compression thresholds whereas DSL v5 may prescribe slightly different compression thresholds.

 

'DSL v5' is only available if the patient's audiogram has at least two thresholds between 250 and 6000 Hz.

  • NAL-NL2 - This formula maintains the same aim as NAL-NL1: to make speech intelligible and overall loudness comfortable. In general, NAL-NL2 provides more gain in low and high frequencies and less gain through the mid-frequency region. The National Acoustics Laboratory reports that NAL-NL2 will provide better speech intelligibility without increasing loudness.

A detailed description can be found at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4040825/.

  • NAL-R - This linear prescriptive formula aims to amplify speech so that all frequency bands contribute equally to its loudness. Modifications for listeners with severe to profound hearing loss are also included.

A detailed description can be found at https://www.nal.gov.au/.

  • WFA - This linear formula provides more high-frequency gain and is a proprietary fitting formula (William F. Austin) only available in Pro Fit.
  • Music - This formula is only available with the Music program and cannot be selected. It was developed specifically for music and music listening. It restores both overall loudness of loud music with flat gain, and audibility of soft music with shaped, compressive gain.