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\section{Introduction}
\subsection{Motivation}
According to the World Health Organisation (WHO), around 1.6 billion people over 14 years worldwide suffer from any kind of hearing loss. Included in this 1.6 billion people, around 430 million suffer from disabling hearing loss (up to deafness), requiring rehabilitation. In the case of disabling hearing loss, the possiblity of using a Cochlear Implant (CI) has revolutionized auditory rehabilitation by restoring partial hearing. Despite a steady progress in implant technology over the past decades, the system still faces its limitations. Complex auditory environments, like static noises overlain by a person speaking, can still propose a considerable challenge for CI-users comapred to people with a healty hearing. \\ \\
The use of Adaptive Noise Reduction (ANR) in combination with implant technology, like it is already used in conusmer-hardware like headphones provide users with a better sound perception and greater listening comfort. The challenge in implementing ANR in
\subsection{Overview of auditory implants and their role in auditory assistance}
\subsection{Introduction to Cochlear Implant (CI) Systems and Audio Processors}
According to the World Health Organisation (WHO), around 1.6 billion people over 14 years worldwide suffer from any kind of hearing loss. Included in this 1.6 billion people, around 430 million suffer from disabling hearing loss (up to deafness), requiring rehabilitation. In the case of disabling hearing loss, the possiblity of using a Implant System has revolutionized auditory rehabilitation by restoring partial hearing. Despite a steady progress in implant technology over the past decades, the system still faces its limitations. Complex auditory environments, like static noises overlain by a person speaking, can still propose a considerable challenge for users of auditory implants comapred to people with a healty hearing. \\ \\
Therefore, the improvement of implant performance in regard to the suppresion of distrubance noises is therefore a crucial step in the development of more user-friendly implant solutions which provide users with more natural sound perception and greater listening comfort.
\\ \\
By addressing these challenges, this work aims to contribute to the next generation of cochlear implant technology, ultimately enhancing the auditory experience and quality of life for people with severe hearing impairments.
\subsection{Introduction Cochlear Implant (CI) Systems}
A Cochlear Implant (CI) System is a specialized form of hearing aid, used to restore partly or complete deafness. In contrary to standard hearing aids, CI's do not just amplify the audio signal received by the ear, but stimulate the auditory nerve itself directly through electric pulses.\\ \\
Usually, a CI System consists out of an external processor (''audio processor'') receiving the ambient audio signal, processing it, and then transmitting it inductively via a transmission coil through the skin to the cochlear implant itself, implanted on the patient's skull (see figure \ref{fig:fig_snychrony}). The CI stimulates the auditory nerves inside the cochlear through charge pulses, thus enabling the patient to hear the received audio signal as sound.\\
\begin{figure}
\begin{figure}[H]
\centering
\includegraphics[width=0.5\linewidth]{Bilder/fig_synchrony.png}
\includegraphics[width=0.6\linewidth]{Bilder/fig_synchrony.png}
\caption{Sketch of a MED-EL Synchrony Cochlear Implant with a Sonnet 3 Audio Processor \cite{source_synchrony}}
\label{fig:fig_snychrony}
\end{figure}
\\As for any head worn hearing aid, the audio processor of a CI system does not only pick up the desired ambient audio signal, but also any sort of interference noises from different sources. This circumstance leads to a decrease in the quality of the final audio signal. Reducing this interference noise through Adaptive Noise Reduction (ANR), implemented on a low-power Digital Signal Processor (DSP), which can be powered within the electrical limitations of a CI system, is the topic of this master's thesis.
The pulse transmission to the cochlear is realized through a silicone eletrode with embedded metal contacts. Said electrode is inserted into the cochlear through a drilled hole in the bone, where, depending on the insertion-depth, different contact-areas stimulate different parts of the frequency-spectrum of the hearing sense. The smaller end of the electrode-array inserted deep into the cochelar stimulate low-frequencies, whereas the larger beginning of the array stimulates high-frequencies. (see figure \ref{fig:fig_electrode}).
\begin{figure}[H]
\centering
\includegraphics[width=0.8\linewidth]{Bilder/fig_electrode.jpg}
\caption{Visualization of a MED-EL electrode inserted into a human cochlear. \cite{source_electrode}}
\label{fig:fig_electrode}
\end{figure}
As for any head worn hearing aid, the audio processor of a CI system does not only pick up the desired ambient audio signal, but also any sort of interference noises from different sources. This circumstance leads to a decrease in the quality of the final audio signal. Reducing this interference noise through Adaptive Noise Reduction (ANR), implemented on a low-power Digital Signal Processor (DSP), which can be powered within the electrical limitations of a CI system, is the topic of this master's thesis.
\subsection{Problem description: Interference signals mixed with the ambient audio signals
in Audio Processors}
A signal is a physical parameter (e.g. pressure, voltage) changing its value over time. The termn "Signal Interference" describes the overlapping of two or more signals resulting in a new signal. \\ \\A simple example of a desirable signal interference would be the sound generated by playing several strings of a guitar. Hitting one string results in a pure sine wave of a designated frequency (depending on which note is played), perceptible as sound. Hitting a chord (consisting of several strings), the seperate sine waves of the strings combine to a new signal through the process of signal interference - in this case a desired, harmonic sound. (see XXX)
\subsection{Formulation of the objective of the thesis: Implementation of Adaptive Noise
Reduction (ANR) on a dedicated low-power Digital Signal Processor (DSP)}