# Fusion of Linear and Mel Frequency Cepstral Coefficients for Automatic Classification of Reptiles
## 4 Experimental Procedure
### Results and Discussion  
In order to validate the proposed data fusion, the features have been analyzed individually to compare their performance. At the same time, the acoustic features have been combined with the classification algorithms to seek the best model. The algorithms have been run 100 times to obtain significant results. Additionally, the dataset has been randomly scrambled in each repetition, dividing the data 50/50 for training and testing purposes. In Table 2, the experimental results show that MFCCs are more suitable for the identification of reptile calls than LFCCs. Mel features present more resolution at the lowest frequencies, emphasizing these spectrum regions where most reptile acoustic energy occurs. In fact, most of the sounds produced by reptiles are in the range 0.1 to 4 kHz. However, some reptiles--mainly lizards--can generate harmonic components at high frequency even into the ultrasound range (>20 kHz). At these \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Scientific Name**} & \multirow{2}{*}{**Family**} & \multirow{2}{*}{**Number of**} & \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Scientific Name**} & \multirow{2}{*}{**Family**} & \multicolumn{2}{c}{**Number of**} \\  & & & & & & & **Syllables (Ns)** \\ \hline
1 & _Crotalus legislus_ & Squamata & 12 & 2 & _Crotalus molassus_ & Squamata & 33 \\
3 & _Crotalus oregmus helleri_ & Squamata & 34 & 4 & _Crotalus tigris_ & Squamata & 22 \\
5 & _[PERSON]_ & Squamata & 5 & 6 & _Crotalus atrav_ & Squamata & 6 \\
7 & _Crotalus scututallus_ & Squamata & 64 & 8 & _Crotalus oregmus elegans_ & Squamata & 18 \\
9 & _Gainan crocodilis_ & Crocodilis & 5 & 10 & _Chudududis nigra_ & Testadines & 6 \\
11 & _Crotalus molassus_ & Squamata & 10 & 12 & _Crorochdys sustata_ & Testadines & 29 \\
13 & _Testado lorsefidili_ & Testadines & 20 & 14 & _Gekbo gocko_ & Gekkkonidae & 16 \\
15 & _Alligator sinensis_ & Crocodilis & 18 & 16 & _Alligator missispensis_ & Crocodilis & 5 \\
17 & _Crotalus dvississus_ & Squamata & 51 & 18 & _Crotalus horridus_ & Squamata & 53 \\
19 & _Kinizys belliana_ & Testadines & 13 & 20 & _Gecchalcone chilensis_ & Testadines & 14 \\
21 & _Testado lebirium_ & Testadines & 95 & 22 & _Gecchalcone chironaria_ & Testadines & 17 \\
23 & _Gecchudone chentiulata_ & Testadines & 115 & 24 & _Crotalus cernastes_ & Squamata & 642 \\
25 & _Heldorma susceptrun_ & Squamata & 383 & 26 & _Hamidactylus turcicu_ & Squamata & 199 \\
27 & _Ophiopbas human_ & Squamata & 10 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dataset classes. frequencies, MFCCs hold insufficient information because the area under the triangular filters used in the mel-filterbank analysis increases at higher frequencies. Therefore, LFCCs are more suitable to model these reptile calls, since no frequency warping is applied. Thus, LFCC surpasses MFCC in some experiments, for instance in class 19 (_Kinixys belliana_ or Hinge-back tortoise), where the mating calls contain high levels of low frequency noise. It can also be observed that _Alligator sinensis_ (class 15) was poorly classified in all experiments, as this class was created by appending several audio recordings because each of them only contains one or two sample calls. Therefore, it presents diverse types of calls, which hinders the classification process. The distress calls emitted by the alligator present a complex harmonic pattern in a wide bandwidth (see Figure 2), occasionally extending over 15 kHz. Hence, the linear cepstral coefficients show a superior performance in both classifiers on class 15. On the other hand, _Crotalus durissus_ (South American rattlesnake) also achieved low recognition rates, caused by its distinctive rattle noise that overlaps with the hissing call in several syllables. On the other hand, nine species reached a classification accuracy of 100%, regardless of the features used, due to the spectrum distribution of those reptile species being clearly different from others.