Spectral Gate

A stereo gate that works in the frequency domain instead of on the whole signal. Rather than opening and closing on level, it keeps or discards individual frequency bins by their magnitude — thinning a sound down to its loudest partials, or carving away those peaks to leave only the quiet residue.

How it works

Each analysis frame, the module runs an FFT, measures the magnitude of every frequency bin, and compares it to a threshold derived from that frame's loudest bin. Bins on the wrong side are silenced and the rest are resynthesised. Because the threshold tracks the signal's own peak, the effect stays musical as dynamics shift. The two channels run fully independent pipelines, so the stereo image is preserved.

Controls

  • Thresh — bipolar around the centre. At 0 the module is bypassed; turn toward -1 to gate (only the strongest bins survive, isolating a sound's core partials); turn toward +1 to anti-gate (the loudest bins are killed and only the quiet residue passes).
  • Tilt — skews the threshold across the spectrum by up to ±3 octaves, so the gating bites harder on the highs (positive) or the lows (negative); flat at the centre.
  • Mix — dry/wet blend; 100% is fully processed.
  • Smooth — sets how quickly each bin fades between gated and open, from 0.05 (smeary, reverberant, slow-breathing residue) up to 1 (snappy, chattery, glitchy). It's the gate's attack-and-release character: low values smear the transitions into a soft shimmer, high values let bins snap on and off for a stuttering, granular bite.

Inputs & outputs

  • In L / In R — stereo audio in; each channel runs its own FFT pipeline with no cross-feed.
  • Thresh / Tilt / Mix / Smooth CV — voltage control over each knob; patch an LFO or envelope to the threshold to make the spectrum shimmer and breathe, or sweep Smooth to morph from smooth gating into glitchy chatter.
  • Out L / Out R — the processed stereo pair.

Tips

  • Gentle gating (Thresh just left of centre) thins pads and reverbs to their loudest harmonics — a clean way to declutter a busy texture.
  • Anti-gate with a high Tilt scrapes off the bright transients and leaves a soft, hollow residue.
  • The spectral process adds about 21 ms of latency and cold-starts with a brief silent swell, so expect it on the first note in time-critical patches.