Watermarking is a technique used to transmit hidden information by modifying an audio signal in an imperceptible manner. The transmission must be possible in spite of subsequent imperceptible alterations (attacks) of the watermarked signal. We propose a unitary approach of watermarking and attack algorithms by defining them in a similar manner, using sets and sets' mappings. The algorithms are then sorted out in several classes characterized by the number and the role of the defined (or known in case of attacks) sets and transforms. The interdependence between the characteristics of the defined sets and transforms is found out, for each class, by an analysis in the framework of metric spaces theory. This approach strongly addresses the interdependence between the information transmission aspects of these algorithms and the psycho acoustical characteristic of audio signals.