Spectral Shadow

A noise-vocoder that resynthesizes your input entirely out of filtered hiss. It tracks the spectral shape and rhythm of whatever you feed it, then rebuilds that motion using bandpass noise — a breathy "ghost" of the source that keeps the timing and frequency contour but discards the original timbre. Drums become hiss-bursts, tones become filtered hiss, voice becomes whispered formants.

How it works

An STFT analyzes the incoming sound and parses the spectrum into 24 log-spaced bands from roughly 60 Hz to 12 kHz. Each band's loudness drives a matching bandpass-filtered white-noise generator: where the input has energy, that band's noise swells; where it's quiet, the noise fades. There is no inverse FFT, so none of the original waveform survives — only its spectral silhouette, painted in noise. The analysis is a shared mono sum, but the two output channels are filled with independent noise streams, so the ghost spreads into a wide stereo fog rather than a mirrored mono.

Controls

  • Color — spectral tilt across the band stack. At the bottom the ghost is dark and sub-heavy; centered (0) it's flat; at the top it's airy and hissy. Use it to push the texture toward rumble or breath.
  • Smear — the release time of the band envelopes, from 0.05 s (snappy, tracks transients) up to 2 s (frozen, smeary wash). Low values follow drums tightly; high values blur everything into a sustained cloud.
  • Mix — dry/wet blend. Fully up is pure ghost; ease it back to haunt the live input with its own noisy shadow.
  • Focus — the bandwidth, or Q, of each band's noise filter, from a broad 1.5 Q fog up to a narrow 20 Q whistle. Low values let the bands overlap into diffuse, airy hiss; high values pull them into pitched, singing whistles that track the input's tones.
  • Drive — pre-clip makeup gain into the final soft-clipper, from a clean 1x up to a saturated 16x. Push it for a denser, grittier ghost that compresses as it clips; back it off for cleaner, more dynamic hiss.

Inputs & outputs

  • In L / In R — the stereo source to analyze. Both channels are summed for analysis, so anything works as a mono feed too.
  • Color / Smear / Mix / Focus / Drive CV — voltage control over each knob; patch an LFO or envelope to animate the tilt, release time, dry/wet blend, band Q, or drive.
  • Out L / Out R — the resynthesized noise ghost, decorrelated for real stereo width — patch both, don't mirror one.

Tips

  • Feed it a drum loop with Smear low for ghostly hi-hat and snare bursts that lock to the groove.
  • Crank Smear toward 2 s on a vocal or pad for an evolving, breathy ambient wash.
  • Sweep Smear CV with an envelope or LFO to morph between tight rhythmic hiss and a frozen drone.