In this paper, we propose an audio watermarking scheme based on the scalar Costa scheme specifically calibrated with a perceptual model allowing to increase the embedding power. For our study, this scheme is designed to be efficient for low bit-rate embedding with sufficient robustness to channel degradations. We present here the main characteristics of our scheme and the way for introducing perceptual models in such a Costa based watermarking scheme without introducing any noticeable artifacts. An evaluation of the robustness of the embedding system is also theoretically discussed by the way of the main channel attack : additive noise from low to high level. We illustrate its relevance in practice using Monte Carlo simulations.