Research Resources

This section shares benchmarking and related research information from inside Starkey Hearing Technologies, including detailed methodology used in data collection.

Added Stable Gain (ASG)

Background

Added stable gain (ASG) is the difference in a hearing aid's maximum stable gain (MSG) with its feedback cancellation algorithm turned off and its feedback cancellation algorithm turned on. In other words, it is the additional gain available to a hearing aid user when the hearing aid's feedback cancellation algorithm is activated. MSG is the highest amount of gain that can be provided in a hearing aid without audible feedback or degraded sound quality due to feedback oscillation (Johnson et al., 2007; Ricketts et al., 2008). For an in-depth definition and walk-through on measurement of MSG visit the link below.

Learn more about MSG

Traditionally, feedback management systems minimize feedback through gain reduction in specific frequency channels. A key disadvantage to the use of such feedback management systems is the possible compromise to speech audibility that may arise from gain reduction. Feedback cancellation (FBC), on the other hand, minimizes feedback by subtracting a signal that mimics the feedback signal from the input to the hearing aid. One advantage to FBC is that these algorithms can provide additional gain to the user without compromising speech audibility (Ricketts, 2008). Merks et al. (2006) provides an overview of current feedback cancellation technology. The author concludes that not all FBC algorithms are alike. One of several characteristics that can vary significantly from one FBC algorithm to another is ASG. In order for hearing healthcare professionals to make evidence-based decisions when recommending specific products to their patients, accurate characterization of FBC algorithms should be available. Objective measurement methods that are reliable and valid must be utilized to quantify benefit from FBC algorithms.

Chart showing Maximum Stable Gain with Feedback Control on and off An example of a clinically viable method of measuring ASG involves gradually raising the broadband gain of a hearing aid until the MSG (with FBC off) is obtained (Johnson et al., 2007; Ricketts et al., 2008). A real-ear aided response is recorded. Then the FBC algorithm is activated and the overall gain is increased until the MSG has been reached, and a second measurement is recorded. The difference in gain between the two measurements is the ASG. This relationship is shown in Figure 1, where maximum stable real-ear aided gain is plotted as a function of frequency for MSG with the feedback canceller activated and feedback canceller deactivated.

A disadvantage to the clinical evaluation of ASG is that MSG with FBC on is not always reached before the maximum output of the hearing aid is reached, resulting in a ceiling effect. A second problem is that it does not use an objective criterion to determine the MSG. In other words, the presence of feedback is subjectively observed by either the hearing aid wearer or the clinician. A third problem with this clinical method is that it requires extensive gain manipulation by the experimenter, which is time consuming and can compromise reproducibility. A fourth problem is that patients may be subjected to annoying feedback and/or excessive gain.

The ASG benchmarking protocol described below was developed in order to address shortcomings of traditional or clinical ASG measurement methods. The benchmarking technique described in this section has the following advantages over traditional methods: 1) it is free from ceiling effects, 2) it can be conducted on a KEMAR, 3) it is mostly automatic, and 4) it does not require measurements at gain settings close to audible feedback. When single number indices of ASG are discussed in literature from Starkey, the largest difference among the collected data, defined as the peak ASG, will be reported.

Methodology

References

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