A unified approach to synchronization based on adaptive observers and passification is extended to nonpassifiable nonlinear systems, particularly to systems with relative degree greater than one. A synchronization scheme based on augmented error adaptive observer is proposed. Conditions of parametric convergence of the parameter estimation are established for the noiseless case. Robustness of the scheme to the bounded measurement error is established. The results are illustrated by examples of text and image transmission by means of chaotic Lorenz system.