Abstract: A selectable band-pass filtering apparatus for use at the input of analysis instrumentation, such as a spectrum analyzer for testing a multi-channel communication system, comprises a high-pass filter section including a plurality of separate high-pass filters, each characterized by a respective high-pass cut-off frequency within a predetermined input frequency spectrum characterizing the communication system and a low-pass filter section including a plurality of separate low-pass filters each characterized by a corresponding low-pass cut-off frequency within the input frequency spectrum. The apparatus further comprises switching devices capable of connecting a selected high-pass filter In series with a selected low-pass filter in order to select passband having center frequency and bandwidth characteristics defined by corresponding high-pass cut-off frequency and low-pass cut-off frequency.