The Audibility Extender and how to individualise it

This bulletin describes the Audibility Extender program, the default settings in Compass, how to fine tune the Audibility Extender program as well as how to individualise it. The descriptions in this bulletin refer to the Graphics panel and the Audibility Extender settings panel in the Fine tuning window of the program in  Compass. Please refer to Compass in order to see the details of the screen. References will be found in the final section.

Audibility Extender default setting in Compass 

The Audibility Extender program uses linear frequency transposition and is developed for clients with little or no hearing in the high frequency area. Compass uses Sensogram data to set the start frequency of the transposed signals where normal aided speech cannot be made audible by normal amplification. The frequency range of the transposed signals is, by default, set to three frequency bands.



In the Fine tuning window in Compass you can see how the start frequency is automatically set, based on the Sensogram.

Fine tuning the Audibility Extender program

In the Fine tuning window, you can fine tune the Audibility Extender program. The elements that can be changed are:
The start frequency o • f the transposed signal
• The loudness of the transposed signal
• The frequency range of the transposed signal (Basic or Expanded)

Individualising the Audibility Extender program

Proper fine tuning ensures that the client is able to detect and discriminate relevant sounds. If a client
fitted with the Audibility Extender in the default setting has not benefitted from the program after a period of acclimatisation, it is recommendable to fine tune the start frequency and the Audibility Extender gain. One way to find the optimal setting is to make sure that the hearing aid user can hear the/s/ sound at normal speech level (approx. 30 dB HL). The energy of the /s/ sound lies in the range between 4 KHz and 6 KHz and is of great importance in speech understanding in many languages. It should therefore be in the transposed signal and be audible with the appropriate settings.

A simple method, based on this, is described below:

1. 
   
   Increase The start frequency three steps


2. 
   
   Check the audibility of the /s/. If audible end, if not audible proceed


3. 
   
   Adjust AE gain in steps


4. 
   
   Check the audibility of the /s/ after each step. If audible end, if not audible proceed


5. 
   
   Lower start frequency one step (reset AE gain to 0


6. 
   
   Repeat from step 2       

For clients who cannot hear the /s/ sound even at lowest start frequency, use the /sh/ sound (the energy
of this sound lies in the range from 2 KHz to 4 KHz). Be aware that it will normally take some time for the client to get used to the new sound. Several clinical trials have shown that benefit of the Audibility Extender improves over time (Kuk et al. 2008)

Frequently asked questions:

Who are candidates for the Audibility Extender?
Candidates for the Audibility Extender are both children and adults with an unaidable high frequency hearing loss. Clients who have hearing loss that is greater than 70 dB at and above the start frequency can often benefit from the Audibility Extender.

Verified fitting range for the Audibility Extender. From Kuk et al 2008

Is fine tuning always necessary?
If the client is satisfied with the Audibility Extender in the default setting, fine tuning is not necessary. If the client cannot get used to the sound in the Audibility Extender program after an acclimatisation period, fine tuning is necessary.

How long is the acclimatisation period in general?
Studies indicate that clients still improve in a speech discrimination test 6 weeks after being fitted with the Audibility Extender (Auriemmo et al 2008, Kuk et al 2007).

Can I make an objective evaluation of the settings of the Audibility Extender?
It is possible to make an objective evaluation of the settings in the Audibility Extender program by using SoundTracker: Say the /s/ sound and look at the bars of the transposed signals in SoundTracker. If the bars of the transposed signals exceed the thresholds, the sound should be audible. This is also a method that can be used if the client cannot provide a verbal response.

References and other relevant literature

Auriemmo, J., Kuk, K., & Stenger, P. (2008). Criteria for evaluating the performance of linear frequency
transposition in children. Hearing Journal, 61(4), 50, 51-54
Auriemmo, J., Thiele, N., Marshall, S., Quick, D., Pikora, M., & Strenger, P. (2008). Effect of linear
frequency transposition in school-aged children. AAA. American Academy of Audiology 2008, 1
Kuk, F, Keenan, D., Peeters, H., Korhonen, P., & Auriemmo, J. (2008). 12 Lessons learned about linear
frequency transposition. Hearing Review, 15(12), 32, 34, 36-38, 40-41
Kuk, F. (2007). Critical factors in ensuring efficacy of frequency transposition. Part 1: Individualizing
the start frequency. Hearing Review, 14(3), 60, 62-64, 66
Kuk, F., Keenan, D., Peeters, H., Lau, C., & Crose, B. (2007). Critical factors in ensuring efficacy of
frequency transposition part 2: Facilitating initial adjustment. Hearing Review, 14(4), 90, 92, 95-96.
Kuk, F., Korhonen, P., Peeters, H., Keenan, D., Jessen, A., & Andersen, H. (2006). Linear frequency
transposition: Extending the audibility of high-frequency information. Hearing Review, 13(11), 42,
44-46, 48.