FB-20: make the two filters and patch bay work together

Start with the space between the filters

FB-20 combines two oscillators with resonant high-pass and low-pass filtering, envelopes and a virtual patch bay. It is useful for a biting bass, a wiry lead or a sequence whose tonal contour becomes part of the rhythm. Begin with a normalled patch and a phrase that already has a clear role.

The high-pass and low-pass decisions are related but different. One chooses the lower boundary and its emphasis, while the other shapes the upper edge. A useful sound can come from the changing space between them rather than sweeping both controls together.

Choose the model and performance behaviour first

Diode and OTA filter choices provide different starting behaviour. Mono, Legato and Poly voice modes change the way notes interact, with further voice and unison settings available. Establish these structural choices before trying to make every patch respond like the same instrument.

The virtual patch bay offers envelopes, modulation waves, noise, sample-and-hold, velocity, pressure and external-signal-processor sources. A destination can replace a normal connection, so begin with one route and a restrained amount. A quiet modulation often reveals more than a fully raised route.

Workflow one: a bass with a moving upper boundary

Use the actual bass line with the kick and a harmonic reference.

1. Choose a simple oscillator balance and set the high-pass low enough to retain the intended foundation.
2. Set the low-pass cutoff and envelope amount for the attack and body of each note.
3. Compare the filter models on the full phrase, including its lowest and highest notes.
4. Choose Mono or Legato behaviour and portamento for the intended overlaps.
5. Bring additional drive or effects in only after the basic note shape works.

If the bass loses weight as its tone becomes more animated, revisit the high-pass and resonance rather than adding another low layer automatically. A resonant emphasis can make one note dominate; check the whole line before committing.

Workflow two: pressure makes a lead open

Use a controller and host route that actually deliver the intended MIDI expression.

1. Build a stable lead with the oscillator and filter panel before patching.
2. Route pressure or another available performance source to a useful filter destination with a small amount.
3. Play both short notes and a sustained phrase to establish a usable response.
4. Add sample-and-hold or another modulation only when it supplies a separate role.
5. Check that the route's intermediate values remain musically useful.

A performance route should make the line easier to play expressively. If it becomes difficult to maintain pitch or tone, reduce the amount and separate the destinations. Changing several strong routes at once makes an unintended response harder to identify.

A creative use: let percussion shape the synth

With a real host audio route to the plugin input, use the external signal processor's envelope or trigger information from a percussion source to influence the synthesiser. Begin with an audible, stable synth patch and a simple rhythmic input. This creates a relationship between the recorded rhythm and the generated tone.

The external signal processor needs actual audio; MIDI notes alone do not provide an external waveform. Confirm the route and source level before setting extreme controls. Treat pitch-derived control as an experiment on suitable material rather than assuming clean note extraction from a full mix.

Revisit the normal connections before printing

Hear the patch through the complete phrase, its quiet notes and its ending. If a route creates silence or an unstable register, restore the normal connection and rebuild that choice deliberately. Keep the source and effect levels sensible during the comparison.

Keep FB-20 when its two filters and selected patch routes give the performance a useful contour. A clear bass or expressive lead with one purposeful connection is a strong result without filling the whole virtual patch bay.