This International Standard provides performance requirements and methods for testing the performance of analogue@ sampled-data@ and digital implementations of band-pass filters that comprise a filter set or spectrum analyser. The extent of the passband region of a filterapos;s relative attenuation characteristic is a constant percentage of the midband frequency for all filters of a given bandwidth. An instrument complying with the requirements of this International Standard may contain any number of bandpass filters covering any desired frequency range.Performance requirements are provided for three filter classes designated class 0@ class 1@ and class 2. Allowed tolerances increase as the class number increases.Bandpass filters complying with the performance requirements of this standard may be part of various measurement systems or may be an integral component of a specific instrument and shall operate in real time. Performance requirements apply to any method that is selected by the manufacturer to implement the design of the filters.Instruments complying with the requirements of this standard are capable of providing frequency-band-filtered spectral information for a wide variety of signals@ for example@ time-varying@ intermittent@ and steady; broadband and discrete frequency; and long and short durations. For applications involving transient signals@ different realizations of filters meeting the requirements of this standard may give different results.