This section shares benchmarking and related research information from inside Starkey Hearing Technologies, including detailed methodology used in data collection.
Maximum Stable Gain (MSG)
Measures of Maximum Stable insertion Gain (MSG) are valuable in that they represent the effectiveness of a hearing aid's feedback cancellation algorithm as well as the quality of the instrument' mechanical design.
Real-ear responses are measured using either an Audioscan Verifit or a Frye Electronics Fonix 6500. A composite noise is presented at 60 dB SPL using the manufacturer's recommended distance and seating position. Software settings for all evaluated devices are standardized, within available limits. All devices are programmed to a linear fitting configuration. All adaptive features are disabled to ensure that there is no interaction between a feature such as digital noise reduction and the composite test stimulus. Each hearing aid is fixed to a single program with the microphone set to an omnidirectional configuration. Prior to data collection the output characteristics of each device are analyzed to ensure that there is no visible gain adaptation to the test stimulus. In the case of a closed fitting configuration, custom earmolds with a specified vent size will be used. In the case of an open-canal fitting, testing is completed without the manufacturers included eartips. The elimination of eartips provides the most open fitting configuration available and avoids any confounds that may rise from different amounts of occlusion provided by different manufacturers' eartips. Each hearing aid is placed on the listener's ear and first fit to a single audiogram. Though arbitrary the starting audiogram is used to generate a consistent starting point for gain adjustments. All evaluated hearing aids are programmed to the default first fit settings, with all patients registered as adult, experienced hearing aid users.
When the initial fit is complete, overall gain will be increased using a broadband gain control. Feedback is identified as an audible whoop by the tester who monitors hearing aid output through supra-aural headphones plugged into the monitoring system of the real-ear equipment. When audible feedback is detected, each hearing aid's feedback cancellation protocol is initialized. After feedback cancellation has been initialized gain will be systematically increased in each available frequency band. The process of increasing gain begins at the lowest available frequency band control and proceeds to the highest frequency band control. Gain is increased until audible feedback is heard or maximum output is reached. When audible feedback is detected the channel gain is reduced until feedback is no longer audible. Once the system has stabilized or maximum output has been reached the tester will adjust the next channel and repeat the same process. This cycle of gain adjustment continues in each available frequency band until maximum stable gain or maximum available output has been reached. At the completion of these adjustments a measure of insertion gain is recorded.
Below is an example of how clinical measures of MSG may be used:
The following is an excerpt from: Galster, J.A., Yanz, J.L, and Freeman, B.A. In the Zōn: Excellence and innovation in hearing aid design. Technology Update, 2008.
Figure 1. Mean insertion gain as a function of frequency for the Starkey Zōn and the three closest competitors.…maximum stable gain (MSG) of Zōn and the competing RIC products was measured in the right ear of twenty subjects, with feedback cancellers on. MSG is defined as the maximum insertion gain that can be achieved without audible feedback oscillation. The only subject-selection criterion was that the participants' ear canals not be occluded by cerumen. Receivers of all instruments were placed in the canals without earbuds to ensure the most open fitting possible and avoid variability created by different earbud designs. The instruments were programmed to linear gain, and adaptive features were disabled. The initialization procedure of each feedback cancellation algorithm was performed, and the feedback canceller was turned on. To determine MSG, gain was systematically increased in each available band in each instrument, beginning at the lowest frequency and proceeding to each successively higher frequency band. Gain was increased until feedback was detected or maximum output was reached. When feedback occurred, band gain was reduced to a stable level, just below the point of feedback. This sequence of gain adjustments by frequency continued until each channel reached its maximum stable gain or maximum available output.
At the completion of these adjustments, at the MSG limit, insertion gain as a function of frequency was measured with a Fonix 6500 real-ear measurement system, using conventional real-ear measurement procedures. Results for Zōn and its three closest competitors are shown in Figure 1. In the mid to high frequencies, MSG in Zōn exceeds that of the competition by an average of 8.5 dB, with a maximum difference of 13 dB. The gain shown here reinforces the class leading performance of the AFI in Zōn, in agreement with prior evaluations in Destiny (Banerjee, 2006; Merks et al., 2006).