# Application of Electrical Network Frequency of Digital Recordings for Location-Stamp Verification
## 2 Enf Extraction and Database Formation Based on Location Specific Recordings
### Classification Model
Figure 5 presents the hierarchical structure for 50 Hz power signals. This hierarchical classification structure provides better results than the two conventional ways of multiclass SVM classifier. Table 8 presents the performance comparisons of the classification techniques for 50 Hz power data. A similar hierarchical classification technique is developed and employed for 50 Hz audio data. Table 9 presents the performance comparisons of the classification methods for 50 Hz audio data and Figure 6 presents the hierarchical structure for decision making purpose. However, for three 60 Hz grids, the trained models are developed using possible combinations of the three classes taking two at a time. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Power** & \multicolumn{2}{c}{**Audio**} \\ \hline \(\mathbf{F_{c}=60\) Hz} & \(\mathbf{F_{c}=50\) Hz} & \(\mathbf{F_{c}=60\) Hz} & \(\mathbf{F_{c}=50\) Hz} \\ \hline
1. _AC_ & 1. \(BF\) & 1. _AC_ & 1. \(BF\) \\
2. _AI_ & 2. \(HF\) & 2. _AI_ & 2. \(DE\) \\
3. _CI_ & 3. \(EF\) & 3. \(CI\) & 3. \(GH\) \\ - & 4. \(DF\) & - & - \\ - & 5. \(GF\) & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Trained support vector machine (SVM) Models for 60 Hz and 50 Hz Power and Audio Recordings. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **One vs. All Classifier** & **All Possible Combinations Classifier** & **Proposed Method** \\ \hline Training Accuracy (\%) & 66.09 & 86.27 & 100.00 \\ Testing Accuracy (\%) & 47.37 & 52.63 & 94.74 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Comparison of Different Classification Techniques for 50 Hz Power Data. ### Performance Analysis

The ground truths of the testing dataset are available in Reference [23]. Table 10 presents the classification accuracies (%) for different systems. From the results it can be observed that all the grids are identified correctly in training for only power signals. In case of testing for only power signals, all 3 grids of 60 Hz are identified correctly with 100% accuracy, whereas for 50 Hz power testing, approximately 95% accuracy is obtained for 6 grids. However, in case of only audio training, approximately 96% accuracy is obtained for 60 Hz grids and more than 89% accuracy is achieved for 50 Hz grids. In case of only audio testing, the correctness of the authenticity for 60 Hz grids is found to be more than 87% and for 50 Hz grids it is more than 83%. For the overall (power + audio) training data, the system is 97.42% accurate, whereas for the overall (power + audio) testing data, the system is 92.00% accurate. Table 11 presents the confusion matrix considering the power and audio ENF testing data. The confusion matrix is computed in terms of testing accuracies (%) of grid classification. The performance evaluations underscore the efficacy and reliability of the proposed ENF based location-stamp authentication system. Figure 5: Proposed hierarchical structure for classifying 50 Hz power data. \begin{table}
\begin{tabular}{l c c c} \hline \hline  & **One vs. All Classifier** & **All Possible Combinations Classifier** & **Proposed Method** \\ \hline Training Accuracy (\%) & 77.78 & 86.11 & 89.66 \\ Testing Accuracy (\%) & 25.0 & 41.66 & 83.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparison of Different Classification Techniques for 50 Hz Audio Data. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{6}{c}{**Power**} & \multicolumn{6}{c}{**Audio**} \\ \hline \multicolumn{6}{c}{\(F_{c}\) = 60 Hz} & \multicolumn{2}{c}{\(F_{c}\) = 50 Hz} & \multicolumn{2}{c}{\(F_{c}\) = 60 Hz} & \multicolumn{2}{c}{\(F_{c}\) = 50 Hz} \\ \hline
**Training** & **Testing** & **Training** & **Testing** & **Training** & **Testing** & **Training** & **Testing** \\ \hline
100.00 & 100.00 & 100.00 & 94.74 & 96.05 & 87.50 & 89.66 & 83.33 \\ \hline \multicolumn{6}{c}{Power + Audio Training} & \multicolumn{6}{c}{Power + Audio Testing} \\ \hline \multicolumn{6}{c}{97.42} & \multicolumn{6}{c}{92.00} \\ \hline \hline \end{tabular}
\end{table}