An homage to a legendary 1U analogue club filter. A valve drive stage feeds a state-variable VCF whose filter-type buttons combine, exactly like the classic hardware idea:
| HI + LO | the notch - sweep it for phasing |
| HI + BAND + LO | the "all pass" - subtle to dramatic with Resonance |
none selected clean passthrough (our one deviation - the hardware mutes here; we hand the dry signal back instead)
A fresh Filter arrives switched off - a transparent wire - so dropping one into a chain changes nothing until you press the button.
The pots
| VCF Freq | 20 Hz - 20 kHz, the big sweep. |
| Res | gentle roll-off to synth-peaky. ARC (automatic resonance control) eases it back at high programme levels and low cut-offs, so full-tilt sweeps stay speaker-safe. |
| Valve | the overdrive: 2nd-harmonic warmth first, soft clip, then hard clip as you push - with make-up gain riding along so the level stays put. |
| Env Foll | the input's intensity opens the cut-off; Decay picks the fast or slow release. EF>OD re-routes the envelope into the valve instead - intensity-modulated overdrive. |
| LFO/Depth | 0.2 Hz to 10 kHz sweep, Triangle glides, Square gates. Past a few hundred hertz the sweep itself turns into tone - the growling sideband trick from the filterbank tradition. |
| Sync | locks the sweep to the transport instead of the LFO knob; Beats sets the cycle length (1 = one beat, 4 = a bar of 4/4). |
Switches
| Filter On | soft-switched true bypass - off is a clean straight wire. |
| 24dB MONO | the rear-panel trick: both channel filters in series from the left input - 24 dB/octave, doubled resonance, both outputs fed. |
| INV | rear "mix + invert filter": outputs dry MINUS filtered - cancellation effects, lovely into a reverb or delay. |
All switching is click-free (soft-switched), so ride the buttons in a performance like the original. Patches from the single-mode Filter era (Mode lowpass/highpass/bandpass) load with the matching band selected and the filter on - they sound as they did.