Abstract: An active band-reject filter of the state-variable type is tuneable over a broad frequency range (three decades) while maintaining a substantial notch depth (50-80 db) which is essentially independent of component value or matching. The filter uses active amplifiers in the inverting mode only, to thereby enable use of inexpensive amplifiers which can be feed-forward compensated to increase their open loop gain and bandwidth. Low-pass, band-pass, and high-pass outputs are also provided, with the gain of the bandpass output at the center frequency being essentially flat over three decades of tuning. Provision is made for compensating for non-ideal behavior of both the active (amplifiers) and passive (capacitors) elements.