Have you heard the saying “the problem is the solution”? It seems to originate in the permaculture movement, but it can apply equally well to electronics. Take the problem [shiura] ...
Filters 24dB/Octave Low Pass Filter with Resonance, 24dB/Octave switchable Low Pass/High Pass Filter with Resonance. Configurable in parallel (HP/LP), stereo (LP/LP), and series (HP/LP) Modulation ...