Abstract : Improving realism in simulations is a critical issue. In some air traffic control (ATC) simulations we use a pseudo-pilot which pilots up to fifteen aircraft. Thus, having the same voice for different aircraft in the case of pseudo-pilot decreases the realism of the simulation and may be confusing for the controllers especially in study context. In research context, a virtual aircraft piloted in a flight simulator is sometime needed in addition to the pseudo pilot. For simulation needs, the flight simulator aircraft must be merged with pseudo-pilot's one. This is not possible without voice modification since the controller can distinguish the pilot voice. In this paper we propose a method for transforming the voices of the pilot and the pseudo-pilot in order to have one particular voice and cabin noise for each aircraft. The two experiments that have been conducted show that, through our voice modification algorithm, the realism of the simulation is enhanced and the voice biases disappear.