Waldorf
Waldorf Mini Works 4-Pole Used
Description stolen from another site:
The MiniWorks is a stand-alone 4-pole resonant analog filter and modulation module. Use it to create those Daft-Punk filter sweeps on entire drum & rhythm loops! Run any sounds, synthesizers or loops through it and filter them with a truly analog-like VCF (filter) that is not only very flexible but MIDI controllable as well! There are many modulation sources that can be programmed between the extensive VCF, VCA, envelope and LFO sections and these settings can be stored in the (20) user memory patches. The MiniWorks can also be overloaded for a lo-fi crunchy sound too! If it were a true stereo filter it would be perfect (input is mono, output is stereo), but in its price range it is the best analog filter module available!