What is it?
It is a software program to prescribe hearing aids using the NAL-NL1 selection procedure.

The National Acoustic Laboratories and the Cooperative Research Centre for Cochlear Implant, Speech and Hearing Research have derived a prescription formula that specifies the required performance characteristics for non-linear hearing aids, and have developed a software program that makes it easy for clinicians to use the new procedure.

Why is there a need for the new procedure?
Existing published procedures for non-linear hearing aids are based largely on the principle of normalizing loudness. That is, at each frequency, they aim for a hearing-impaired person to hear narrow-band test sounds at the same loudness that would be perceived by a normal-hearing person. Empirically, making all frequencies have their normal loudness contradicts decades of research into what is needed for maximum speech intelligibility.

The NAL-NL1 fitting procedure aims to provide the gain-frequency response that maximizes speech intelligibility while keeping overall loudness at a level no greater than that perceived by a normal-hearing person listening to the same sound. The calculations of speech intelligibility are based on extensive NAL research into how audibility relates to intelligibility.

Is there any evidence to support NAL-NL1?

Yes, both indirectly and directly.  Indirectly: NAL-NL1 prescribes a frequency/gain response for average input levels (65-70 dB SPL) that is very similar to that prescribed by NAL-RP.  This procedure has successfully been used as the basis of non-linear hearing aid fittings.  Directly: In a recent study conducted at NAL, it was found that hearing impaired people with both flat and sloping losses preferred and performed better with NAL-Nl1 than with a prescription based on loudness normalization.

Is the software program available to clinicians and others?
The software is available to clinicians and other people at a unit cost of A$205.00 (including GST) or US$139.00, with appropriate price reductions for multiple purchases. A User Manual will accompany every purchase.

Is it simple to use?
Yes.  The steps involved are:
Enter the audiogram. You can choose to enter other information such as an individual Real Ear to Coupler Difference, but age appropriate average values will be used by the program if you do not.

Specify whether the fitting is monaural or binaural, the type of hearing aid (CIC, ITC, ITE or BTE), the number of compression channels, and the earmold or earshell configuration.

Move to the target screen (see below) and look at the prescription in just about any format you would like.

Operating environment

486 or later (Pentium recommended) personal computer or compatible;

Microsoft Windows 95 or Windows NT 4 (or later);

Video display resolution of 800 x 600 or greater.

How to order?
To order the software program, Click the following link "Order form" and select either orders within Australia or outside Australia. On the order form select product number P4376, fill in the details and follow the instructions for sending it back to the National Acoustic Laboratories.

Message to manufacturers of hearing aids and real ear gain analysers

• A licence of the formula can be made available to manufacturers of hearing aids and real ear gain analysers. The formula prescribes insertion gain at each 1/3 octave frequency from 125 Hz to 8000Hz inclusive, for any input level of a broad-band, speech like, test signal. The formula indicates that compression extends down to extremely low input levels, so it will be necessary to impose a suitable compression threshold when using this formula. An ancillary formula indicates those combinations of frequency and level for which contributions to speech intelligibility will be minimal, and for which it is not therefore worth trying to meet the insertion gain target. The purchase price will depend on the number of copies of manufacturer software for which a licence is required. This purchase gives the manufacturer the right to use both formulae up to the specified number of copies, but not to divulge them to a third party. The purchase also entitles the manufacturer to any updates to the formula (should any occur) during the next two years.

• There is also the option of purchasing a licence covering a special version of the software for use within the purchaser's own fitting systems. This software would be made available as a .dll program. Manufacturers would have the choice of using our input and output screens, or using the information behind the screens as data for their own fitting programs. Any of the prescription information that can be accessed from the standard software's target screen could be made available. The software is based on the insertion gain formula, but provides a great deal more information, such as input-output curves at any 1/3 octave frequency, gain frequency responses, compression thresholds, compression ratios, maximum output, real-ear aided gain, coupler gain, cross-over frequencies, and other forms of output. The purchase price will depend on the number of copies of manufacturer software in which the program is to be included. This option also includes any upgrades that occur within the next two years. We anticipate providing continued support for the software past that time, at a reasonable fee.