Swirl Chorus manual
Swirl provides Chorus, Dimension, Ensemble and Vibrato, with a separate drive section. This manual describes the current development build. The plugin is not yet on sale.
Start with a preset
Choose a factory preset from the preset bar, or choose a mode and press Mode Init. Clicking a mode button on its own keeps the other controls unchanged. Dimension Buttons loads one of four button settings or two combinations.
For chorus, start with a partial dry/wet mix. For vibrato without doubling, set Mix to 100%. Try Bass Widener on bass or Vocal Double on a lead vocal.
Voice and motion
| Control | What it does |
|---|---|
| Mode | Chorus uses one voice per channel. Dimension uses opposite stereo sweeps and a filtered wet path. Ensemble uses three voices per channel. Vibrato provides pitch movement and is usually used fully wet. |
| Rate | Main sweep speed, 0.02–8 Hz. With Sync on, select a division from eight bars to a quarter note. |
| Sync | Follows host tempo and song position. Bar divisions follow the time signature. Without host tempo, the fallback is 120 BPM. A transport seek resets the sweep immediately and can cause a pitch discontinuity. |
| Depth | The size of the delay-time sweep. |
| Depth in Cents | Changes Depth to nominal upward pitch excursion, 1–100 cents. Rate changes then adjust delay excursion to maintain a similar pitch range. Very slow rates and small Size settings can limit the available excursion. Downward deviation is slightly larger because cents are logarithmic. |
| Width | Changes the phase offset between the left and right modulation. Zero aligns the sweeps; it does not prevent cancellation between dry and delayed audio. Use Mono to check the result. |
| Size | Scales delay times from 25–160%. Outside Dimension mode, longer settings also darken the wet path. Small Size with high Depth can produce flanging as the sweep reaches its minimum delay. |
| Mix | Equal-power dry/wet blend. Intermediate settings can increase level or cause cancellation, depending on the source and delay settings. |
| Flutter Hz | Speed of the second sweep, 0.2–25 Hz, independent of Rate and Sync. Its speed includes a small random drift. |
| Shimmer | Blends the second sweep into the modulation. Ensemble includes some flutter even at zero. Shimmer changes the combined pitch movement, so a Depth value in cents describes only the nominal slow sweep. |
Dimension and the five named drive voices were developed using captures from reference plugins. They are not complete circuit models of the original hardware.
Tone and mix controls
Tone tilts the wet signal around 720 Hz. Age adds progressively more low-pass filtering. It controls darkening, not worn-chip dynamics.
Bass Protect retains the dry low end while applying chorus above a gradual crossover. Select Off or 40–500 Hz. Start at 300 Hz for bass; Bass Widener, Warm Bass and Mono Thick already use that setting. Some change remains near the crossover frequency. Drive can still affect bass according to its routing.
Duck reduces the chorus contribution when the input is loud, then restores it as the level falls. The detector is linked across stereo channels, with a 3 ms attack and 180 ms release. The amount of ducking depends on input level. Vocal Double provides a starting point at 40% Duck.
In and Out provide ±12 dB gain trims before and after processing. The header shows peak and RMS levels in dBFS. Input is measured after In trim; output includes bypass and mono audition. Red output text indicates a measured peak at or above 0 dBFS. These are sample-level meters, not true-peak or loudness meters.
Bypass compares the original input at the same latency, excluding both trims. Mono sends the summed output to both channels. Both controls survive preset changes and are saved as session parameters.
Drive
Enable Drive switches the drive section independently of chorus. Choose Soft Clip, Tape Pre, Console, Germanium, Triode or Pentode.
Drive runs from 0–100%. Zero is clean. The first quarter blends in the selected character; higher settings increase saturation. At maximum, Soft Clip receives 12 dB of gain and the five other voices receive 24 dB. Level compensation is calibrated around −15 dBFS RMS input. Source level and dynamics still affect output loudness, so use Out trim when comparing settings.
The drive section has its own Mix for parallel saturation. Pre processes the signal before chorus, including its dry component. Post processes the chorus output. Click the routing diagram to change order. The bar in that diagram displays final output level.
Voice, routing and quality changes use short fades and allow the new processing state to settle. Mode changes crossfade between chorus engines. These transitions reduce switching clicks, but the change in sound remains audible.
HQ Drive and latency
Only the drive section is oversampled; chorus runs at the host sample rate.
| Host sample rate | Standard drive | HQ Drive |
|---|---|---|
| 44.1 / 48 kHz | 8× | 32× |
| 88.2 / 96 kHz | 4× | 16× |
| 176.4 / 192 kHz | 2× | 8× |
HQ reduces drive aliasing at a higher CPU cost. Inactive drive skips oversampled processing.
Latency is 136 samples at either quality and in bypass, approximately 2.83 ms at 48 kHz. The plugin reports this to the host for compensation. Bypass keeps the effect running for a smooth return; disable Drive to avoid its oversampling cost.
Presets, A/B and locks
Swirl includes 53 factory presets. Save a user preset from the preset bar, or use Delete to remove a user preset. An asterisk beside the name indicates unsaved edits. User presets are XML files in the platform application-data folder under SwirlChorus/Presets.
Lock Mix and Lock Out keep those controls unchanged while browsing presets. The locks last for the plugin instance and are not saved with the project. HQ, Bypass and Mono are always preserved across preset loads.
A > B / B > A switches between two temporary settings. The first click copies A into B. Edit B, then switch back to compare; each slot retains its edits and preset identity. HQ, Bypass, Mono and window size stay with the session. The A/B slots are not saved with the project. Save a user preset if you need to keep an alternative setting.
Editing controls
Type directly into the value readouts. For a percentage control, 50 and 50 % both mean 50%. Double-click a knob to reset it. Undo and Redo step through edits made in the window. Resize from 75% to 200%; hover over a control for its tooltip.