## 2 Materials and Methods
### Smartphone Application
#### 2.3.2 Self-Adjustment  
The application's self-adjustment function to change the daily listening experience is based on methods for modifying frequency-dependent gain parameters as described by [PERSON] et al. [9]. For this study, both the EQ user interface (EQ UI) and the 2D user interface (2D-Surface UI) were integrated into the self-adjustment workflow. These UIs empowered users to make frequency-specific adjustments, including modifications to bass, midrange, treble, and overall volume. All changes were applied to an initial expert setting, which was created during the first study appointment (see Section 2.5). Furthermore, in this study,  
Figure 2: (**a**) App environment for program selection: (**b**) naming a new program; (**c**) evaluation process of a saved adjustment. users had the ability to adjust beamforming strength, noise reduction, and wind noise reduction based on the AutoSens OS 3.0 program parameters at the moment the participant initiated the program creation for the first time. One of the two user interfaces (UIs) provided in this study was a classic equalizer and volume control interface (EQ UI), while the other followed a tactile 2D-Surface concept (2D-Surface UI) for manipulating frequency-specific sound parameters. The EQ UI, shown in Figure 3a, allowed participants to adjust three frequency ranges: low (centered at 172 Hz), medium (centered at 861 Hz), and high (centered at 4.5 kHz), along with overall volume. Adjustments could be made for both the HA and CI simultaneously or independently, if the two pointers for each slider were decoupled. Each slider offersreda range of \(\pm\)10 dB, and in combination with the volume control, total gain adjustments of \(\pm\)20 dB were possible. The 2D-Surface UI, depicted in Figure 3b is based on concepts developed by [PERSON] et al. [13], [PERSON] et al. [7], [PERSON] et al. [14] and further refined in the work of [PERSON] et al. [9]. In this interface, participants adjust sound parameters by moving a point within a square. As with the EQ UI, adjustments can be made simultaneously or independently for both the HA and CI if the points for the left and right sides are decoupled. Moving the point along the \(x\)-axis selects different gain-frequency curves focused on specific frequency ranges, while moving it along the \(y\)-axis allows for boosting or cutting these frequencies. Unlike the EQ UI, which utilizes three band-pass filters, the 2D-Surface UI combines a high-pass and a low-pass filter, with a gain range of \(\pm\)20 dB. In addition to the frequency adjustments, three additional sliders were incorporated, as shown in Figure 3c. These sliders allowed participants to adjust beamforming, noise reduction (HA only), and wind noise reduction. This expanded functionality enabled participants not only to amplify or attenuate specific frequency ranges but also to control the intensity of individual signal processing steps. During the adjustment process, the participant had the option to switch between the two UI's at any time. However, changing the UI resulted in the loss of previously made settings, as the parameter sets were not transferable between the UI's. Consequently, the sliders/points and their associated parameters were reset to their initial settings. To prevent this, a default UI could be set in the general settings of the application. In the event of a new adjustment, this UI would be displayed from the start. At any point of the adjustment process, the participant had the option to save the settings made or to cancel the customization and discarding all applied changes. In the case of modifying an existing program, the participant had to choose whether to irreversibly overwrite the old parameter  
Figure 3: App environment for creating and modifying programs: (**a**) 2D Surface user interface, (**b**) EQ Surface user interface, (**c**) slider to make changes to the strength of each signal processing step. Note: “L” refers to the left side, and “R” refers to the right side. set or to create a new program with updated settings.