Chapter 6 59
The DSL/NAL-NL1 Module
The DSL/NAL-NL1 test window was designed to help fit non-linear hearing aids
according to the DSL or NAL-NL1 fitting formulas. Both formulas are highly
adaptable and have many different settings that will allow you to fine-tune your
hearing aid fittings.
The University of Western Ontario developed the Desired Sensation Level (DSL)
method of hearing aid fitting. The goal of the DSL method is to make amplified
speech audible. The DSL method differs from many traditional methods; it uses
an SPL-o-gram rather than insertion gain and, when necessary, incorporates 2-cc
coupler measurements made in the sound chamber into the hearing aid fitting.
DSL was originally designed to expedite fitting hearing aids for young children
and to improve the accuracy of those fittings.
The NAL-NL1 fitting formula is the natural non-linear extension to the NAL-
R linear formula that has been dominant in the hearing aid industry for many
years. NAL-NL1 is based on insertion gain measurements, and it takes into
account many factors including the number of channels of the hearing aid,
whether the patient has a binaural or monaural fitting, and even what type of
output limiting is present on the hearing aid.
To enter the DSL/NAL-NL1 test window:
1. Click Test Menu in the Main Menu.
2. Locate the client you want to test. See Section 4.1.3.
3. Select the client’s name in the right column of the Test Menu. This will
bring up the client test selection window.
4. Choose DSL/NAL-NL1 Test
.
The DSL/NAL-NL1 test has four windows: The Audiometry window, DSL win
-
dow, NAL-NL1 window, and the Info window. The Audiometry window is used
to input audiometric information such as thresholds and upper limit values. You
can also use it to perform RECD and REDD transforms or input existing data.
The DSL and NAL-NL1 windows are used for taking real-ear and coupler mea
-
surements and compare them to the displayed targets. The Info window records
the date the test is taken, the clinician performing the fitting, and the equipment
used to take the measurements. The DSL 2-cc coupler derivations are also dis
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played in this window; they are generally used when ordering a hearing aid to
match the patient’s hearing loss.
6.1 General Information
General operations of the DSL/NAL-NL1 test such as opening existing tests,
creating new tests, changing clients, printing results, and saving defaults are
described in this section.
