In this paper, an encryption approach for Speech communication based on direct chaotic modulation (non-autonomous
modulation) is presented, in which speech signal is injected into one variable of the master system (using Lorenz system) without changing the value of any control parameter. This approach is based on the change of chaotic signal by injecting Speech samples into one variable in chaotic system and hence generating a new chaotic signal. The Speech signal is then extracted from the chaotic signal on the receiver side. Furthermore, a high dimension chaotic system is used, which increases the security of the encrypted signal. Non-autonomous modulation technique is suitable for securing real-time applications. A comparative study of approach and Speech masking technique is also presented. Experimental results show that non-autonomous methods give better performance than their chaotic masking counterparts when they are analyzed against Signal-to-Noise-Ratio (-38.55 dB vs. -35.51 dB), Segmental signal-to-Noise-Ratio (-38.91 dB vs. -35.84 dB), Log-Likelihood Ratio (0.89 vs. 0.80), and Correlation Coefficient Analysis (0.0345 vs. 0.021). Non-autonomous techniques overcome the chaotic masking break and considered more secure.