01
Init
All defaults — a gentle Sine fold at 50%. A transparent-leaning starting point to build your own fold from.
Audubon · Plugins
CBL-001
·
v1.0.0
Harmonic Wavefolder
Crossbill.
Fold the wave. Grow the harmonics.
A west-coast harmonic wavefolder for growls and leads. Where a clipper flattens, Crossbill folds the waveform back on itself every time it crosses the threshold — sprouting dense, resonant, metallic overtones. The fold functions are bounded to full scale with unity slope at the origin, so it's transparent when you back off and it can never run away: harder drive adds folds, not level.
One-time · v1.1.0
$29
Free, full plugin. The output dips to silence every 30 seconds until you enter a serial — buying removes it, no reinstall needed.
01 — Overview
Not a clipper.
A folder.
A clipper or saturator squashes peaks flat. A wavefolder does the opposite: every time the signal exceeds the fold threshold, it reflects back on itself. Each fold adds a new pair of peaks — and a new burst of harmonics. Push the drive and the wave crosses the fold points more often, so the tone gets denser and brighter without ever getting louder. It's the west-coast (Buchla / Serge) sound: metallic, resonant, alive — perfect for dubstep and DnB growls and screaming leads.
The crossed bill of the bird mirrors the folded wave — harder drive adds folds, not level.
Crossbill runs on Crane-lineage 4× polyphase oversampling to keep fold aliasing in check. A pre-fold Tone tilt decides what hits the folder, Drive and Folds set how hard and how densely it folds, Symmetry biases the fold off-centre to slide between odd and even harmonics, and a post Smooth lowpass tames the fizz. The hero display is a live wave-shape scope — the faint input against the glowing copper folded output — plus a teal transfer-curve inset showing the exact input-to-output map and the current operating point.
02 — The Fold Engine
Bounded folds that can't run away.
Both fold functions — a sine wrap and a reflective period-4 triangle — are bounded to ±1 with unity slope at the origin. That means Crossbill is transparent at low drive (small signals pass through unchanged) and no combination of Drive and Folds can ever push the output past full scale. Instead of getting louder, the sound gets more folded: denser harmonics, brighter timbre, constant ceiling.
Drive Into The Folder
Drive (−12…+36 dB, default +3) is the input gain into the fold stage — it decides how hard you hit the fold points. More drive means the wave crosses the threshold more often, so more folds occur per cycle. Because the folder is bounded, this reads as brightness and density rather than level.
Folds — Density
Folds (0–100%, default 50) maps to a 1×–8× fold gain multiplier. At 0% the signal barely folds; at 100% it folds up to eight times per excursion, generating a thick stack of resonant overtones. This is the primary "how metallic" control, independent of Drive.
4× Oversampling
The fold stage is wrapped in Crane-class 4× polyphase oversampling, with a post-fold Smooth lowpass, to hold aliasing down even at maximum density. The dry path is delay-aligned to the oversampler so the Mix blend stays phase-coherent. Latency is a few samples, host-reported via PDC.
Transfer Curve, Live
The teal inset plots the actual input→output fold map, computed in the UI from the exact same maths as the C++ DSP. The moving operating point shows where your signal currently sits on the curve — so what you see is always what you hear, with no audio bridge required.
03 — Shape & Symmetry
Two fold shapes, and where they fold.
The Shape switch picks the fold function; Symmetry biases the fold point off-centre. Together they set the harmonic character — from round and vocal to sharp and metallic, and from pure-odd to a full odd-plus-even spectrum.
A — Sine
Round & West-Coast
The Sine fold wraps the signal through a smooth sinusoid. Folds are rounded, so the harmonics roll off more gently — the classic Buchla-style timbre. Warmer and more musical for leads, pads and softer growls.
B — Triangle
Sharp & Metallic
The Triangle fold uses a reflective period-4 triangle. The corners are sharper, so the harmonics extend further and buzz harder — the aggressive, metallic reese/growl side. Pair with a touch of Smooth to keep the top under control.
C — Symmetry
Odd ↔ Even Balance
Symmetry (−100…+100%, default 0) applies a pre-fold DC bias so the wave folds off-centre. Centred folding is purely odd-harmonic; biasing it introduces even harmonics for a hollower, more vocal, or brassier tone. A DC blocker after the fold keeps the output centred.
04 — Tone, Smooth & Mix
Voice the folder, then blend it.
Three controls shape the sound around the fold core: Tone decides what frequencies hit the folder, Smooth tames what comes out, and Mix parallels the folded signal against the delay-aligned dry.
A — Tone
Pre-Fold Tilt
Tone (−100…+100%, default 0) is a ±6 dB tilt about 700 Hz applied before the folder. Tilt bright to send more highs into the fold for a fizzier, more aggressive result; tilt dark to fold mostly low-end for a thicker, rounder growl. Because it's pre-fold, Tone changes which harmonics get generated, not just the output EQ.
B — Smooth
Post-Fold Lowpass
Smooth (0–100%, default 0) is a lowpass after the fold, sweeping 20 kHz down to 1.5 kHz. Use it to tame the fizz and harshness that dense folding creates — dial in just enough to sit the growl in a mix without dulling it.
C — Mix & Output
Parallel & Trim
Mix (0–100%, default 100) blends the wet fold against the dry — the dry copy is delay-aligned to the oversampler latency, so parallel folding stays phase-coherent. Output (±24 dB) is the final trim to match levels against bypass.
05 — Controls
Every parameter, grouped.
Eight controls, no menus. Ranges and defaults below trace directly to the plugin's parameter layout.
Drive
−12 to +36 dB · def +3
Input gain into the folder — how hard you hit the fold points. More drive = more folds per cycle = denser, brighter overtones. Bounded, so it never overshoots full scale.
Folds
0 – 100% · def 50
Fold density, mapping to a 1×–8× fold gain. The primary "how metallic" control — raise it for a thicker stack of resonant harmonics.
Symmetry
−100 to +100% · def 0
Pre-fold DC bias. Centred = pure odd harmonics; off-centre slides in even harmonics for a hollow or brassy character. DC-blocked after the fold.
Shape
Sine / Triangle · def Sine
The fold function. Sine = rounder, west-coast; Triangle = sharper, metallic with more extended harmonics.
Tone
−100 to +100% · def 0
Pre-fold tilt (±6 dB about 700 Hz). Decides which frequencies hit the folder — bright for fizz, dark for a thicker growl.
Smooth
0 – 100% · def 0
Post-fold lowpass (20 kHz → 1.5 kHz) to tame fold fizz and harshness. Blends the growl into a mix without dulling the body.
Mix
0 – 100% · def 100
Dry / wet blend. The dry path is delay-aligned to the oversampler, so any parallel setting stays phase-coherent.
Output
−24 to +24 dB · def 0
Final output trim after the blend, with a live Out meter. Match levels against bypass.
06 — Factory Presets
Seven folding starting points.
Each factory preset resets every parameter to default and then applies its overrides, so it's a clean, reproducible starting point. Save your own as .crossbillpreset files.
02
West Coast Lead
Moderate Sine folding with a touch of Symmetry and bright Tone. The classic Buchla-style singing lead.
03
Metal Reese
Dense Triangle folds with bright Tone and a little Smooth. Sharp, metallic reese territory.
04
Growl Teeth
Heavy Triangle folding, negative Symmetry for even-harmonic bite, Smooth to tame it, slightly parallel. Aggressive dubstep growl.
05
Sub Harmonics
Light Sine folds, no drive, heavily parallel. Adds gentle overtone weight to a sub without changing its level.
06
Parallel Fizz
Bright, dense Triangle folds blended low against the dry. A crushed-air fizz layer over a clean foundation.
07
Brass Bell
Sine folds with strong positive Symmetry and warm Tone. A hollow, brassy, bell-like resonance for melodic parts.
07 — Workflow
How to use it.
01
Drop it on a growl or lead. Crossbill loves harmonically simple sources — a saw, a sine sub, a basic reese. Start from Init and watch the scope: the faint line is your input, the copper glow is the folded output.
02
Set the character with Shape. Sine for rounder, musical leads; Triangle for sharp, metallic growls. This is the single biggest tonal decision, so make it first.
03
Fold with Drive and Folds. Push Folds for density and Drive for how hard it hits the fold points. Because the folder is bounded, keep pushing — it gets brighter and denser, never louder. Watch the transfer inset fill with fold ripples.
04
Shift the harmonics with Symmetry. Nudge Symmetry off centre to bring in even harmonics — hollow, vocal, or brassy depending on how far you go. This is where a static fold becomes a distinctive timbre.
05
Voice it with Tone and Smooth. Tilt Tone to choose what hits the folder (bright = fizz, dark = thick), then pull Smooth down from the top to tame any harsh fizz until the growl sits right.
06
Blend and trim. Use Mix for parallel folding — great for adding overtone weight to a sub while keeping its fundamental clean (see the Sub Harmonics preset). Set Output to match bypass, and automate Folds or Drive across a drop for a rising growl.
08 — Specifications
Everything, on one page.
Type
Harmonic wavefolder · west-coast (Buchla/Serge) style folding
Fold shapes
Sine (round) · Triangle (metallic) — both bounded to ±1 with unity slope at origin
Drive
−12 to +36 dB · default +3 dB
Folds
0 – 100% · default 50% · maps to 1×–8× fold gain
Symmetry
−100 to +100% · default 0 · pre-fold DC bias (odd↔even), DC-blocked after
Tone
−100 to +100% · default 0 · pre-fold tilt ±6 dB about 700 Hz
Smooth
0 – 100% · default 0 · post-fold lowpass 20 kHz → 1.5 kHz
Mix
0 – 100% · default 100% · delay-aligned dry path
Output
−24 to +24 dB · default 0 dB · live Out meter
Oversampling
4× polyphase (Crane-class) on the fold stage · dry delay-aligned
Latency
A few samples (oversampler) · host-reported via PDC
Format
VST3 · Windows 10 / 11 · macOS 10.13+ (Universal — Apple Silicon & Intel) · 64-bit
MIDI
None — audio effect only
Presets
7 factory · user presets saved to Documents (.crossbillpreset)
Version
1.1.0
09 — Fine Print
Documentation.
Operating System
Windows 10 or 11 (64-bit) — the editor uses WebView2, which is built into Windows 11 and most current Windows 10 installs. macOS 10.13 High Sierra or later — one Universal build runs natively on both Apple Silicon and Intel Macs.
DAW
Any VST3-compatible host — Ableton Live, FL Studio, Bitwig, Reaper, Studio One, Cubase. Insert on any mono or stereo track; best on bass, growls and leads. VST3 only — Logic Pro and GarageBand load Audio Units, not VST3, so they are not supported.
Latency
A few samples from the 4× oversampler, reported to the host and compensated automatically via PDC. The dry path is delay-aligned so Mix stays phase-coherent.
Activation
No iLok, no dongle — activation is offline with the serial from your Members Area. Your download stays accessible in your Members Area.
Personal & Commercial Use
One licence covers all your personal and commercial productions. No royalties, no project restrictions.
Terms & Refunds
See the Terms of Service and Refund Policy for full details.
No Redistribution
You may not resell or redistribute the plugin binary. Source code is not included.
v1.1.0 — Update check, from the logo
The Audubon Audio wordmark in Crossbill’s header is now a button. Click it and Crossbill asks audubonaudio.com one question — which build is current — then shows that number beside the one you are running, with a link straight to the members area if there is something newer and a plain “you have the current version” if there is not. If it cannot reach us it says so rather than claiming you are up to date. This is the only moment Crossbill touches the internet, it happens only on that click, and nothing about you goes with it — no serial, no licence, no machine id, not even your version or operating system. The comparison happens on your own machine.
v1.0.0 — Initial Release
Bounded harmonic wavefolder with Sine and Triangle fold functions (±1, unity slope at origin). Drive, Folds (1×–8×), Symmetry (odd↔even bias, DC-blocked), pre-fold Tone tilt, post-fold Smooth lowpass, delay-aligned Mix and Output. 4× polyphase oversampling. Live wave-shape scope with teal transfer-curve inset. 7 factory presets. WebView2 UI.
Full User Guide
A step-by-step guide covering every control, both fold shapes, how Drive and Folds interact, the odd↔even Symmetry axis, and four workflow recipes (west-coast lead, metallic growl, parallel sub-harmonics, brassy tonal fold).
Open User Guide →