Abstract: A second order section of an electronic filter comprises three cascaded amplifier stages and a compensating amplifier stage coupled between the first and second amplifier stages. The compensating stage introduces a leading phase shift at high frequencies so that the normalized transfer function of the circuit, for different frequencies, is substantially identical.

Abstract: A spectrum analyzer using digital filters for providing third octave spectrum analysis comprises means for breaking up input information into a plurality of digital data blocks, each block being of a given time duration and being within respective frequency ranges, means for weighting the information contained in the data blocks and means for digitally filtering the weighted digital data blocks with digital filtering devices having at least one center frequency falling within the frequency range represented by each of the data blocks, each of the data blocks comprising N samples satisfying the following equation-N >Kf.sub.o/ B.sub.nWhere K is a constant which is a function of the sampling rate and the falloff rate of the skirt of filter characteristic, B.sub.n is the filter bandwidth and f.sub.o is the center frequency of the filter.