Alera FAQs – DFS Ultra Whistle Control

Why not just set DFS Ultra to “Strong”?
The strong setting for DFS Ultra with built-in Whistle Control is more aggressive in what it identifies as potential feedback and will attack it more quickly.  In fact, it may reduce gain even in non-critical situations when the DFS Ultra feedback cancellation filters can easily eliminate feedback.  A strong setting is recommended for use in an acoustic phone program or when the gain is set near the maximum stable gain and the client will not accept occasional feedback.

When you put a phone up and DFS Ultra with built-in Whistle Control reduces gain, will it degrade the patient’s ability to understand speech on the phone?
If the DFS Ultra is activated, feedback will only occur in extreme situations where the adaptive feedback cancellation filter is not allowed to adapt to that extent (in order to keep it from attacking tonal and transient non-feedback sounds). Holding a phone up near the hearing aid is one of these situations. Essentially, there is some “leftover” feedback that DFS Ultra cannot get rid of, and this gets fed back into the amplifier, ultimately resulting in higher output in the ear canal for this feedback signal. The loop continues as that signal goes back to the mic. If you measured the sound in the ear canal you would see a big spike of gain beyond the desired response where the feedback is occurring. The Whistle Control knocks this spike out by taking the gain back down to where it is supposed to be. It does not reduce the gain below where it is supposed to be. So Whistle Control actually restores the correct gain rather than reducing gain; it is not reducing audibility and degrading sound quality. In actuality, it is maintaining audibility and improving sound quality compared to not having Whistle Control on. So the patient who puts the cell phone up to their ear is not going to get a drop in gain beyond where it was supposed to be so audibility should be maintained.

Does a hearing aid have to actually feedback for Whistle Control to take effect?
No.  The stronger settings of Whistle Control actually begin to manage the process of feedback before feedback even starts to occur.

Does Whistle Control default to off in Aventa?
Whistle Control is combined with DFS Ultra in one setting. Once the DFS Ultra calibration has been run, Whistle Control is activated at the mildest setting.  Changing the “DFS Ultra” setting actually changes the level of Whistle Control that accompanies the DFS Ultra.

Will DFS Ultra/Whistle Control change its setting automatically based on the calibration or is that the dispenser’s choice to make?
The default level is “mild” but the dispenser may choose to change the setting.

Describe how well each of the models works with the telephone?  Does DFS Ultra/Whistle Control solve the telephone issue?
With open BTEs, there is seldom a telephone issue in the first place. In the rare cases where feedback on the phone is problematic for this type of fitting, DFS Ultra/Whistle Control can be expected to solve it, although some experimenting with the level might be required. For closed BTE and custom products, DFS Ultra/Whistle Control may entirely solve any feedback on the phone issues but there will be some cases where feedback still occurs. In all cases, there will be significantly less feedback on the phone with DFS Ultra/Whistle Control than without and it will most likely be possible to obtain satisfactory phone performance.

How has DFS been improved, and what is “Whistle Control”?
DFS Ultra with built-in Whistle Control combines the most advanced feedback control systems available. The new algorithm models both the feedback path and the external input signal, to improve the accuracy in identification of feedback from other tonal input sounds.  Once it correctly separates feedback from other tonal input sounds, phase cancellation is applied to eliminate the feedback alone. The result is fewer sound quality artifacts, which can occur when traditional phase cancellation feedback control systems incorrectly try to cancel out tonal input sounds instead of feedback. In addition, new improvements to the precision and scaling in the models result in a more accurate feedback cancellation signal.

Whistle Control serves as an additional layer of feedback control, by reducing the occurrence of feedback that arises from dynamic, transient situations such as hugging and using the telephone. Feedback that manages to elude the DFS system is controlled via gain reduction in the frequency range of the feedback. The signal itself is unaffected while the extra gain from the feedback spike is reduced. Thus, Whistle Control serves as an emergency option, for the most difficult feedback-provoking events which are not completely resolved through DFS alone. These algorithms together, which comprise DFS Ultra, create a feedback control system that eliminates artifacts to provide the best sound quality without sacrificing user gain.

For Whistle Control, what do the settings mild, moderate and strong represent?
Regardless of whether Whistle Control is set to mild, moderate or strong, the actual gain reductions will be the same. The different Whistle Control settings indicate how often or how likely gain reduction will occur, not how much gain reduction there will be. With a mild setting, the sensitivity is weaker, and with a strong setting, the sensitivity is at its highest.

So, what Whistle Control gain setting should be chosen?
The setting defaults to “mild” when DFS is calibrated. If a patient experiences little to no feedback in all situations, nothing needs to be done. If the patient has feedback in many situations, such as while using a telephone, the setting may be changed to “moderate” or “strong.”

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