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Auto Masking

 Interacoustics auto masking is available to ease the effort required in order to mask with correct masking levels. When auto masking is enabled, channel 2 is controlled by the system and is set to the appropriate intensity level.

 Auto masking is activated by selecting the icon that shows the mask with letter A. 

 Green indicates that masking is correctly applied.

 Amber indicates that masking is recommended louder and that extended range needs to be activated to allow setting channel 2 to the correct level.

 Purple indicates that masking would be needed, but is not possible practically.

Note: The auto masking feature is only available in the Diagnostic Suite – and not on the audiometer as a standalone.

Recommendations
Be aware that patients require proper instructions before audiometry with masking is undertaken. The switching on and off of the masking noise may be uncomfortable to some patients and cause them to become more fatigued. In some cases (when testing young children, some elderly patients or difficult to test patients), it is recommended not to use masking because confusion about the application of masking noise may lead to false responses.

When measuring the second test ear, more information becomes available and it is not guaranteed that the earlier measurements are still correct. By measuring the best ear first and completing air conduction on both ears before measuring bone conduction, most errors can be avoided.

Be careful when storing thresholds where masking was not possible. Masking not possible means that the risk for crossover hearing is high. In these cases it is recommended to store a no-response at the loudest intensity where masking was still possible (by pressing the N key).

Additional information
The masking help calculates answers to the following questions:

  • Is masking required?
  • Is the masking level too low?
  • Is the masking level too high?
  • Is masking impossible?

Terminology

AC AC test ear
ACc AC contra
BC BC test ear
BCc BC contra
IaA  Minimum interaural attenuation
IaAc  Minimum interaural attenuation contra transducer
Dial Dial setting test ear
Dialc Dial setting contra (masking level)

Is masking required?
Masking is recommended when the presentation at the test ear can be heard by at the contralateral side, or in a formula:

Dial – IaA ≥ lowest of ACc and BCc

Is the masking level too low?
The applied masking level is too low when the applied masking level does not match the intensity at which the test signal is heard in the contralateral ear, or in a formula:

Dialc – (ACc – BCc) < Dial – IaA

Is the masking level too high?
The applied masking level is too high when the masking level is so loud that it potentially is heard by the test ear, or in a formula:

Dialc – IaAc ≥ Dial – (AC – BC) when testing air conduction
Dialc – IaAc ≥ Dial when testing bone conduction

Is masking impossible?
Masking is not possible when the needed masking level results in overmasking at the same time: 

Dial + (ACc – BCc) – IaA ≥ Dial – (AC – BC) + IaAc  when testing air conduction
Dial + (ACc – BCc) – IaA ≥ Dial + IaAc  when testing bone conduction

or when the needed masking level is higher than the maximum level of the masking transducer:

Dial + (ACc – BCc) – IaA > maximum available Dialc

Recommended masking intensity
The masking help can indicate a recommended masking intensity. If masking is indeed required and also possible, the recommended masking intensity is given by the minimum required masking level plus a fixed preferred amount:

Recommended Dialc = Dial – IaA + (ACc – BCc) + preferred additional amount.

The recommended masking level is adjusted for values that cannot be reached by the masking transducer due to maximum values.
When the auto masking feature is used, masking intensities are set to the recommended intensity.
Of course if “extended range” is not switched on, the masking intensities are thereby limited accordingly.

Frequency specific inter-aural attenuation
The inter-aural attenuations used by the masking help are frequency specific and can be customized in the setup. The following table shows the default inter-aural attenuation values (IaA). These are partly based on recommendations from the Handbook of Clinical Audiology and are otherwise slightly more conservative then recent publications and will therefore allow for appropriate decision making.

Frequency(Hz)

125 250 500 750 1000 1500 2000 3000 4000 6000 8000
IaA Headphones (dB) 35 40 40 40 40 40 40 45 50 50 50

IaA Inserts (dB)

50 50 50 50 50 50 50 50 50 50 50

IaABone(dB)

0 0 0 0 0 0 0 0 0 0 0

Recommendations
Experienced audiologists are recommended not to use the option of viewing a suggested masking level.

The masking help indicates if masking is performed correctly with the information given at the time of the measurement. When measuring the second ear, more information becomes available and it is not guaranteed that the earlier measurements are still correct. By measuring the best ear first and completing air conduction on both ears before measuring bone conduction, most errors can be avoided.

Although clinicians do often not apply masking for bone conduction in the instance where the air-bone gap is less than 15dB in the better ear, it can be recommended to apply masking to make the measure ear specific. Despite that an experienced clinician would disagree, the masking will, in these cases recommend, that masking is needed. This figure illustrates such a situation. 

 

 
June 2016
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