# Speech Enhancement Algorithms: A Systematic Literature Review
## 3 Method
### Study Selection Based on Inclusion and Exclusion Criteria  
Selection criteria aim to identify studies that provide direct evidence on the research topic. To minimize the potential for bias, selection criteria should be specified during the protocol definition phase and can be refined during the search process [47]. In this systematic review we identified target study papers based on specific formalized criteria. These criteria, collectively known as the eligibility criteria, should be specified carefully when searching for papers, as they help to narrow down the scope of the relevant topic. The criteria used for exclusion and inclusion set the boundaries of this paper, and were evaluated based on the details mentioned in Table 3. The first excluding step in this stage was to remove redundant papers, followed by screening the papers against the keywords and formulated research questions following the steps in [46; 48]. Any paper that was not expected to provide an accurate answer to the research questions was excluded. Next, papers were assessed against the inclusion and exclusion criteria based on the title, abstract, and full text. Included studies were from peer-reviewed journals, conferences, and workshop papers. In the event of multiple versions of a selected paper, only the most recently updated version was included; all other versions were excluded. Table 2 shows that the search string retrieved a total of 986 articles. In addition, fifteen papers were added from other surveys and overviews. Of 1001 papers, 78 were removed due to duplication, leaving 923 papers for further review. Subsequently, the retained papers were checked by authors based on the title, abstract, and keywords of the papers. The authors were considered the reviewers, and the number of retrieved records was 221. To assess the actual relevance of the studies, selection was performed on all potentially relevant studies by applying the set of inclusion and exclusion criteria. The criteria were applied to the retrieved records in order to assess them and make decisions about which retained papers were reviewed. The adopted exclusion and inclusion criteria are illustrated in Table 3.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Survey Sources** & **Data Access** & **Keywords** & **No. of Papers With Filter (by Selected Years)** & **No. of Papers with Filter (by Selected Years)** \\ \hline ACM Digital Library & 27/11/2024 & (“Enhancement” OR “noise reduction” OR “denoising”) AND (“wiener filtering” OR “deep learning”) & 40 & 38 \\ \hline IEEE Xplore & 26/11/2024 & (“speech”) AND (“noise reduction”) AND (“deep learning” OR “wiener filtering”) & 45 & 24 \\ \hline Springer Link & 27/11/2024 & (“Speech” OR “Voice” OR “Noise” OR “audio”) AND (“Enhancement” OR “Improvement” OR “Noise Reduction” OR “Denoising”) AND (“Wiener Filtering” OR “MMSE Estimation” OR “Deep Learning” OR “Spectral subtraction” OR “Algorithm”) & 68 & 36 \\ \hline Science Direct & 26/11/2024 & (“Enhancement”) AND (“Wiener Filtering”) AND (“Algorithm”) & 68 & 36 \\ \hline Google Scholar & 26/11/2024 & (“Speech” OR “Noise”) AND (“Enhancement” OR “Noise Reduction”) AND (“Wiener Filtering” OR “MMSE Estimation” OR “Deep Learning”) AND (“System” OR “Tool” OR “Technology or Technique” OR “Algorithm”) & 366 & 216 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Documentation of the search strategy with details of the online electronic databases.  
Based on [47; 49], two researchers evaluated each paper and reached agreement about whether to include or exclude it. In cases of disagreement, the matter was discussed and resolved based on the predefined criteria. The applied criteria further reduced the number of research papers to 50.