The MDS / ADS decoder converts the MDS system from the general input to the ADS system of the interior blocks. One MDS / ADS decoder per block is required. The MDS / ADS decoder can manage from 1 to 199 homes per block. From the MDS general entrance, communication can be established with any home in the different blocks. The MDS / ADS Decoder, in addition to the interface between the two systems, acts as an audio changer, which when idle (without communication with a general entrance or MDS concierge) allows communication to be established between the ADS interior panels and the houses in the corresponding block. In this way it is possible to hold simultaneous conversations in different blocks, each with its internal plate, in addition to a block with the general entrance.