That has been discussed here before. From the way Giobbi and others referred to it, I believe the room where they waited (coordinated) the interrogations is located near the interrogation rooms where Knox and Soloecito were being interrogated separately. (Giobbi said he could hear Knox's screams.) The room may have been the office (or near the office) from where interrogation room activity is overseen and from where the on/off switches and modern recording machines (computers) are located.
The police headquarters is a very modern police building with cameras and concealed microphones built-in interrogation rooms and hallway waiting areas. Such devices would be controlled from a control room.
A year ago, while googling various information, I came across information on an Italian firm that cited their role in installing the recording systems in Perugia police headquarters.
Apparently, then, there is evidence that the interrogations could have been readily recorded with the installed audiovisual setup (not that any reasonable person would doubt that an ad hoc system could have been used). This may be significant to the ECHR case; the failure to produce an audio or audiovisual recording of the interrogations becomes more suggestive of police and prosecution misconduct when there is a built-in system.