## 1 Introduction
This approach was implemented by using Lorenz and Rossler systems. Furthermore, the author in [32] proposed a new chaotic map, named tent delay-sine cascade with logistic map (TDSCL), for image encryption. In [33], the authors developed a long-distance encryption system using the chaos masking technique, employing three cascaded lasers, called vertical-cavity surface-emitting lasers (VCSELs), to develop the proposed system. More references related to cascaded chaotic systems are listed in Table 1.  
The ideal number of cascaded levels has not been thoroughly discussed in the aforementioned references in Table 1. They mainly focused on using a specific number of cascaded systems without taking into consideration the general performance and the cost of a secure communication system. Although the use of multiple cascaded chaotic systems increases the key-space and the complexity of encrypted signals, it also increases the execution time and the cost of the system. Recognizing the ideal quantity of cascaded tiers is essential as it directly impacts the system's security and resource efficiency. Achieving a bal \begin{table}
\begin{tabular}{c c c} \hline \hline
**Ref.** & **Used Chaotic Systems** & **Levels of Masking** \\ \hline
[34] 2012 & Lorenz System & 1, 2 \\
[35] 2014 & Seed map & 2 \\
[33] 2017 & Optical chaos with TD signature suppression & 3 \\
[25] 2017 & Lur’e system & 1, 2 \\
[36] 2018 & Quantum cascade lasers & 2 \\
[32] 2020 & Tent Delay-Sine cascade with Logistic Map & 2 \\
[26] 2020 & Rossler chaotic flow system & 1, 2 \\
[29] 2021 & discrete memristive maps & 2, 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Related work for cascaded chaotic masking. ance between optimizing security and reducing resource overhead is crucial, with practical consequences for sectors that depend on secure, fast data transfer. In light of this conflict, further research is required to determine the effects of changing the number of cascaded levels on system efficiency and security. Our work aims to bridge this gap by conducting a practical study that examines the impact of increasing the number of cascaded levels on the system's overall performance and resource utilization. In this paper, we propose a secure communication system for voice encryption based on the cascaded structure using the 4D unified hyperchaotic system, we illustrate the efficiency of using different number of cascaded levels, (from N = 1 to N = 20), on the quality of encryption. Various security metrics are then applied to test the performance of the systems such as Correlation coefficient analysis, Signal-to-Noise Ratio (SNR), Peak Signal-to-Noise Ratio (PSNR), Percent Residual Deviation (PRD), and timing analysis. Moreover, the proposed systems are realized on FPGA in order to determine the implementation cost. Finally, to evaluate the whole performance of the communication systems, we propose a new metric, termed Value-Based Performance Metrics (VBPM), which integrates multiple metrics for a holistic assessment. This metric is used to compare different cascaded chaotic systems that employ different values of N levels. The main contributions of this paper are summarized as follows:  
1. Introduce a novel N-level cascaded chaotic-based secure communication system for voice encryption using the 4D unified hyperchaotic system. 2. Investigate the effect of increasing the number of cascaded levels on encryption quality. 3. Implement the proposed system on FPGA and analyze its performance using various parameters. 4. Analyze the effect of increasing the number of cascaded levels from N = 1 to N = 20 to reach the best performance by measuring various of metrics. 5. Introduce VBPM as a new performance metric for evaluating the system's overall performance. 6. Demonstrate the superiority of the proposed system compared to other related works in terms of security and efficiency. The remainder of this paper is organized as follows. The architecture of the proposed N-levels cascaded chaotic-based secure communication system is presented in Section 2.