# Testing the Frequency Response Control Function of Level-Dependent Earplugs
## 4 Discussion  
Hearing protectors with electronic circuits can enhance the hearing of people wearing them in noisy environments [9; 10; 11]. Current existing solutions for improving the reception of sounds using electronic systems have predetermined characteristics of sound transmission frequencies, with no possibility of the user influencing their shape. The possibility of selecting the attenuation characteristics of the hearing protector would allow the user, through successive trials, to adapt the function of the hearing protector to their needs. For example, they could increase the amplification in the bands related to verbal communication or strengthen the band responsible for receiving warning signals. This type of functionality would therefore provide the possibility of influencing the operation of the electronic system to a much greater extent than is currently the case with level-dependent hearing protectors. Furthermore, it would be possible to configure the electronic system in such a way that the frequency characteristic of sound transmission under the hearing protector is as flat as possible, i.e., the effect of the smallest possible impact on the spectrum of the signal reaching this protector will be obtained. This is important for people who, on the one hand, have to protect their hearing, and on the other hand, whose quality of work depends on the impression related to the received sounds. The results of this study show that it is possible to design earplugs with the frequency control response function implemented using the ADAU1787 sound processor. The sound processor can be used to process signals representing sound for various purposes. The solution discussed in this article filters the signal delivered to the user of the hearing protector according to the preferences of that user, and at the same time, ensures hearing protection. The use of sound processors in hearing protection solutions has already been demonstrated, although not directly in a hearing protector but in a device designed for hearing ambient sounds, which simultaneously simulates hearing loss and includes a tinnitus simulator [23]. This is evidenced by the research results presented in Figures 3-5. The characteristics of filters with center frequencies of 125 Hz to 8000 Hz obtained using the electrical signal provided in Figure 3 show a high degree of compliance with the frequency characteristics of the class 2 octave filters according to EN 61260-1 [20]. However, filters intended for use in level-dependent earplugs do not constitute measuring equipment, and therefore, do not have to meet any of the filter class requirements. Therefore, despite the filter characteristics slightly exceeding the range of values defined by the standard at some points, the solution can be considered fully satisfactory and one that will fully realize its task. The ripples observed in Figure 3, which slightly exceeded the limits specified in the standard, occurred at a much lower level than the maximum characteristic and were at least 40 dB away from the value at the peak of the characteristic. In practice, due to such a large distance of the deviations from the maximum characteristic value, the measured deviations will not have a noticeable effect on the sound reaching the user. The results of the filter characteristics obtained using an acoustic signal are also satisfactory. Despite the fact that additional elements appeared in the measurement path, the characteristics of the filters measured using an acoustic signal were similar in a certain frequency and level range to the characteristics obtained using an electrical signal. Several factors will lead to certain differences between these characteristics. For example, due to the properties of level-dependent earplugs with limited passive attenuation, an external signal travels through the earplugs, bypassing the electronic sound transmission path, causing the filters to attenuate sound to about 30-40 dB in real conditions.