WinCHAP User’s Manual The DSL/NAL-NL1 Module 75
To do this, just follow the instructions for testing as described in Section 6.3.2.
In step 5, select the Source Type to
Composite. In step 6, set the Src. amplitude
to 0 (Spectrum Mode). Press Start to start the measurement. Now use the live
speech signal as the input source and see how the aid responds to it. Use the
noise reduction setting on the analyzer to control how much long-term averag
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ing the analyzer uses when displaying the measurements. When noise reduction
is set to OFF on the analyzer, the display will update very quickly in response to
all the changes in speech. When the noise reduction is set to 16X, the response
curve will update very gradually, showing the aid’s long-term response to the
speech signal. See your analyzer’s Operator’s Manual for details on setting the
noise reduction setting.
6.3.4 Adding the LTASS
The LTASS is a set of three curves based on the long-term, average speech
spectrum. The middle curve is the average, the upper curve is the average plus
12 dB and the lower is the average minus 18 dB. The LTASS curves show the
boundaries of average speech, and can be used as a counseling tool to show a
client how their hearing range relates to average speech sounds. It can be dis
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played in the DSL window in an SPL display.
6.3.5 Matching measurements with targets
DSL targets are dependent upon signal type and signal level. When adjustments
are made to the signal, the DSL target makes corresponding adjustments.
Each measurement is tied to a particular target; it is important to compare
appropriate targets to each measurement. Only measurements tied to the select
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ed targets will be displayed. That is, if you have taken a measurement at 65 dB
SPL, and then you change the target to 70 dB SPL, the 65 dB measurement will
be removed from the window but not deleted. You can redisplay the 65 dB mea
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surement by changing the target back to 65 dB.
6.3.6 Understanding Speech Weighting
The DSL method was designed around the LTASS speech weighting. However,
FONIX equipment normally uses the ANSI speech weighting, which rolls off the
high frequencies more gradually. When working in dB Gain, the speech weight
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ing differences have little effect because the speech-weighted input signal is
subtracted out to arrive at the gain values. However, when viewing targets and
measurements in dB SPL, the speech weighting is not subtracted out and has a
large impact on the displayed target.
In order for the FONIX measurements to be directly compared to the DSL tar
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gets, WinCHAP has altered the DSL targets to incorporate the FONIX speech
weighting. If you would like to view the targets in their non-altered state,
change the Signal Filter selection in the Settings window under the DSL tab.
You will not be able to take a measurement when this speech weighting is
selected.
