BBD modulation rack · Model SC-79 · v1.0.0

Swirl Chorus

Chorus, dimension, ensemble and vibrato for macOS and Windows

Four modulation effects inspired by the short bucket-brigade delays of late-70s rack units and pedals. Use Bass Protect to retain dry lows, set pitch motion in cents, and duck the wet signal around a lead. Soft Clip plus five drive voices add colour before or after the chorus. VST3, AU and CLAP for macOS; VST3 and CLAP for Windows.

  • VST3
  • AU
  • CLAP
  • Standalone
  • macOS
  • Windows
  • Coming soon
The complete Swirl Chorus window
Fig. 01The "Dimension II" starting point, with the new Motion & Mix controls and comparison tools.

ListenDry / wet, same take, rendered through the plugin

Electric piano

Preset

Silver 78

Dimension II uses 23 % Mix. Dimension Wide uses the same sweep at 50 %.

Clean guitar

Preset

Clean Amp

String synth

Preset

String Machine

All Ensemble mode: three voices per channel a third of a cycle apart.

Polysynth chords, mono source

Preset

Poly Pad

Mono source; stereo width is added by the plugin.

Electric bass

Preset

Bass Widener

Shallow sweep, 35 % mix and Bass Protect at 300 Hz to retain the low end.

Funk bass, drive presets

Preset

Germanium Pedal

Germanium at 83 % Drive before the chorus, 80 % in circuit.

Voice

Preset

Vocal Double

Bright doubling with 40 % Duck and Bass Protect at 160 Hz.

Organ chord

Preset

Organ Swirl

Ensemble at 1.1 Hz with some of the second sweep.

Recorded with the current development build, the named factory presets and HQ Drive enabled. Each dry/wet group uses the same source and input gain, with no separate wet normalization. Sources are CC0 recordings from freesound.org.

ModesChorus, Dimension, Ensemble and Vibrato

Chorus

One voice per channel · 5.5 ms centre · quarter-cycle stereo offset

The stereo chorus of the classic dual-BBD units: one delay line per channel, swept around 5.5 ms, with the right channel's sweep a quarter of a cycle behind the left. Rate runs from 0.02 to 8 Hz, free or locked to the host tempo.

Dimension

Opposite stereo sweeps · filtered wet path

Two channels sweep in opposite directions through a filtered wet path for stereo widening. The voicing is based on captures of a reference Dimension plugin. The Dimension Buttons menu provides four button settings and two combinations.

Ensemble

Three voices per channel at 0 / 120 / 240° · main sweep plus independent flutter

The string-machine arrangement: three voices per channel, spaced a third of a cycle apart. Flutter Hz sets the second sweep independently of the main Rate; Shimmer blends in that motion, and Size scales all the delay lines together.

Vibrato

One voice · optional depth in cents · used fully wet

A single voice for pitch movement at 100 % wet. Switch Depth to nominal cents to adjust speed while keeping a similar pitch excursion. Seasick uses 20 cents at 0.7 Hz; Pitch Drunk uses 60 cents at 4.2 Hz. Very slow rates or small Size settings can limit the excursion; Shimmer also changes the combined pitch movement.

The wet voices use BBD-inspired bandwidth and soft saturation. Longer delay settings darken the sound; Age blends in additional low-pass filtering, and Tone tilts the wet path.

DriveSoft Clip + five voices · pre or post

Swirl Chorus with Triode at 50 percent Drive, ahead of the Ensemble

Drive has its own enable switch and Mix control, before the chorus (Pre) or after it (Post). Choose Soft Clip or one of five voices informed by reference-plugin captures. The amount runs from 0 to 100 %, with zero clean. Level compensation is calibrated around −15 dBFS RMS input; changes in source level and dynamics still affect perceived loudness. HQ improves drive quality at a higher CPU cost. The chorus itself stays at the host sample rate.

  • Drive 0 – 100 %, with level compensation calibrated around −15 dBFS RMS input
  • Pre or Post routing, swapped by clicking the diagram
  • Drive Mix: dry/wet for the drive section on its own
  • Enable Drive switches the insert independently of chorus
  • Drive-only oversampling: 8× standard / 32× HQ at 44.1 and 48 kHz
Tape Pre
Two asymmetric stages add even harmonics, signal-dependent bias movement and low-end weight.
Console
A symmetric curve adds odd harmonics and rounds off peaks.
Germanium
A soft knee, moving bias and low-frequency emphasis.
Triode
Strong even harmonics with signal-dependent bias movement.
Pentode
Odd harmonics and flattened peaks, with compression that increases under sustained input.

Front panel

Voice and motion

  • Mode Init loads a starting preset; changing a mode alone keeps your other settings.
  • Rate, Depth, Width, Size and Mix; optional nominal depth in cents.
  • Sync the slow sweep while setting Flutter independently from 0.2 to 25 Hz.

Tone and mix

  • Bass Protect: Off or 40–500 Hz. Try 300 Hz for bass; drive can still colour the low end.
  • Duck reduces the wet contribution on louder notes, then restores it as the input falls.
  • Tone and Age shape wet colour; In and Out trims run ±12 dB.

Compare and recall

  • A/B keeps two temporary settings for comparison; the first click copies A into B.
  • Lock Mix and Lock Out keep those settings while you browse presets.
  • Mono checks the summed output. Bypass compares the original input at matched latency.

Value boxes accept typed input, double-click resets a knob, and Undo and Redo step through edits. The window resizes from 75 % to 200 %. Input and output meters show peak and RMS levels. Mode and drive changes use short fades to reduce switching clicks. Read the Swirl manual for setup and control details.

Presets53 factory presets · save your own

  • Basics3
  • Chorus13
  • Dimension11
  • Ensemble10
  • Vibrato8
  • Drive8

An asterisk marks an edited preset. Save your own presets as shareable XML files. A/B slots and Mix/Out locks last for the plugin instance and are not saved with the project. HQ, Bypass and Mono stay unchanged when loading a preset.

Specifications

Formats
VST3, AU, CLAP, Standalone (macOS) · VST3, CLAP, Standalone (Windows)
macOS
11 or later, Apple silicon and Intel (universal)
Windows
10 or later, 64-bit
Voices
Up to 3 per channel, BBD-modelled; Size 25 – 160 %
Rate
0.02 – 8 Hz free; 8 bars – 1/4 note synced
Flutter
0.2 – 25 Hz, independent of Rate and Sync
Drive
Soft Clip + 5 voices, 0 – 100 %, pre or post, own dry/wet
Sample rates
44.1 – 192 kHz; drive oversampling adapts to host rate
Latency
136 samples at either quality and in bypass (2.83 ms at 48 kHz); reported to the host
Price
£39 planned, with a 14-day trial

Buying and using Swirl

One purchase covers Mac and Windows for one person on up to five activated computers. Use it offline after activation. Version 1.x updates are included, with no subscription.

Trial and activation FAQLicence agreement14-day refund policy

Availabilityv1.0.0 · Sep 2026

Swirl Chorus is at version 1.0.0 and is being finished for release on macOS and Windows. The planned price is £39 with a 14-day trial. Downloads will appear here when it is released.