Everything DeltaEQ does.

1 · What DeltaEQ is

DeltaEQ is a context EQ. It has everything you expect from a modern parametric — nine band types, dynamic bands, per-channel targeting, oversampling, linear phase — and one thing no other EQ has: its bands can see the rest of your mix. A band can duck only while another track needs the space, target the exact frequencies your sidechain spikes at, and show you where the mix is burying the track you're EQing.

It opens as a clean, blank analyzer — a live spectrum and nothing else. Every band you add starts from a click on the canvas.

2 · Install & formats

DeltaEQ is currently built as VST3; AU and CLAP are on the roadmap. The installer places the VST3 in C:\Program Files\Common Files\VST3 — rescan plugins in your DAW.

Beta builds are unsigned — Windows SmartScreen will show "Windows protected your PC" → More info → Run anyway. Expected for a beta.

3 · Quick start

1. Insert DeltaEQ on a track and play. You see the live spectrum.
2. Click anywhere on the canvas — a band is created and grabbed in one move. Drag it where you want it.
3. Alt-drag (or mouse-wheel) the handle to shape its Q.
4. Want it dynamic? Click DYN on the band bar — the band now ducks itself when energy hits it.
5. Want it mix-aware? Click the CTX pill's caret and pick what to duck against — the sidechain, or any other Delta track in your project.
6. A/B honestly: enable MATCH (level-match), then toggle BYP.

4 · The interface at a glance

5 · Working with bands

Adding

• Click empty canvas → a band is added and grabbed, so click-and-drag places it in one gesture. The type comes from where you click: the middle of the plot adds a Bell; the outer quarters add a Shelf (click above the 0 dB line) or a Cut (below it).
• Hover still for a moment and a faint type glyph (and after ~1 s, a dashed ghost of the would-be curve) previews what a click would add.
• Shift-click → drop a harmonic rake at the cursor (a Harm Bell seeded with your last tooth count). While Shift is held, a live preview of the rake's overtone beams follows the cursor.
• New bands are created on the channel you're viewing — the channel selector is your brush (§13).

Shaping

• Drag the handle — frequency and gain. You can also grab a band by its gain fill (the tinted area between the 0 dB line and its curve).
• Alt-drag or mouse-wheel — Q (up / wheel-up = sharper).
• On cuts, plain vertical drag adjusts the resonance directly (cuts have no gain).

Disable · reset · delete

• Double-click a handle — toggle the band off/on (it stays placed as a dim handle, ready to come back).
• Alt-double-click — reset the band to neutral.
• ✕ on the band bar — delete the selected band. Right-click the canvas for Disable all / Delete all.
• Escape (or clicking the selected handle again) dismisses the selection. ⌘/Ctrl-Z undoes gesture by gesture.

6 · The band bar

The floating glass row is the selected band's inspector. Drag the dotted grip at its left end to pin it anywhere (double-click the grip to snap it back to centre-bottom). Its chips, left to right:

7 · Band types

8 · Dynamic bands

Any bell, shelf or gain band becomes dynamic with the DYN pill. The first enable seeds a classic −6 dB duck so you immediately see it work.

• RANGE — the signed span the band may travel from its static gain: negative ducks down, positive expands up.
• THR — the threshold. It starts in AUTO (a rolling self-adjusting reference — zero knobs, just works). Drag it for a manual dB value; double-click flips AUTO ⇄ manual.
• ATT / REL — detector ballistics (1–100 ms / 20–1000 ms).

The canvas draws the whole story: the band's territory — a gradient from the static curve to its full reach, closed by a dashed outline — and inside it the live curve breathing with the music, with a Δ x.x dB readout at the handle showing the current travel. What's drawn is what's heard.

9 · Context ducking (CTX)

A dynamic band normally reacts to its own track. CTX makes it react to something else — that's the unmasking move: "duck my pad's 2 kHz only while the vocal is actually singing there."

• The CTX pill toggles context mode; the caret at its right end (or a right-click) opens the DUCK AGAINST picker.
• The picker shows a live mini-spectrum of the summed context with your band's listening region highlighted, and the sources: ALL (the rest of the mix), SIDECHAIN (the plugin's own SC input), and every live Delta track in your project — multi-select, with colour dots and names.
• SIDECHAIN (@SC) is special: it's fed sample-accurately from the audio itself, so the duck lands on the transient — kick-tight. Track scopes are contextual and smooth; the sidechain is surgical and instant.

10 · The Spectral band

The Spectral type takes context ducking to its logical end: instead of one bell you place, it runs a bank of up to MAX (1–12) narrow bells that find the key's spike frequencies themselves and duck exactly those — leaving everything in between untouched.

• Choosing the type auto-seeds everything it needs (narrow Q, DYN on, −12 dB range) — drop it and feed it a key.
• The KEY CURTAIN hangs the detected key spectrum upside-down from the top of the plot — the cause above, the bells beneath, each curtain spike directly over the bell it triggers.
• Each live bell draws at its current frequency with a dB tag; the filled sum is the actual response being applied.

The detector's discipline

The bells obey rules built for transparency, not just precision:

• Born-fixed: a bell's frequency is pinned from birth to silence — bells fade in and out in place, never sweep. (A moving narrow filter is a phaser; ours can't become one.)
• Presence-gated: the whole bank only acts while the key is audibly there. The gate follows the key's own recent loudness, so it works at any gain and true silence can never trigger a duck.
• Persistent peaks only: a spike must survive consecutive analysis frames before it earns a bell — single-frame flickers never duck anything.
• Sideband-safe: the deeper and narrower a bell, the gentler its maximum attack slope — a hard-edged narrow duck would smear energy around the notch (visible as a "wake" in DeltaMeter's ±dB view). The rhythm stays tight; the splatter doesn't happen.
• TIGHT (band bar, next to MAX) — the key compressor: it evens out how hard soft and loud key hits duck. At 0% depth follows the key's dynamics raw (this is your A/B); higher values let quiet hits reach musical depth sooner while loud hits stop over-ducking. Default 50%.

Hearing test: route white noise through the band, key it from a rhythmic source, and listen to the delta (the Δ monitor) — you should hear the key's rhythm, and nothing else. That test is how this detector was tuned.

11 · Pitch-Track & Harmonic Lens

• TRACK — the band's centre follows the detected note. Made for isolated mono sources (vocal, bass): the handle glides along the spectrum riding the pitch, with a note pill naming what it hears. GLIDE sets the chase speed, RANGE the lock window in semitones, and LOCK re-captures the ratio (so a band can track, say, the 3rd harmonic). When the source goes unvoiced the handle hollows and holds.
• STAB — the tracker's stability dial. The detector de-glitches every estimate and gives the current note an incumbent's advantage: a different note must win several confident frames in a row before the band moves (so a bass alternating two notes steps cleanly instead of flickering between them). 0% = hummingbird (instant, loose) · 100% = rock (wide deadband, patient switching). Default 50%; raise it if an isolated band's delta sounds warbly.
• Harmonic Lens — grab or hover any band and it reads the fundamental's note (+cents) and lights an overtone ladder whose beams brighten with the live energy at each harmonic. Free music theory with every drag.
• Pair TRACK with a Harm band and the whole rake stays in tune with the performance — a moving-target notch.

12 · Spectrum Freeze

The FREEZE pill holds the spectrum still (display only — the audio keeps playing). The frozen peaks get icy note guides, so you can park a band exactly on the resonance you spotted instead of chasing it. Once more than a moment is captured, a scrub strip appears along the bottom — drag through the captured window to find the exact frame. With TRACK active, LOCK captures against the frozen note.

13 · Channels & the Δ view

• MODE — view Stereo · L/R · M/S. In a pair mode a contextual SOLO pill appears (L/R in green/amber, Mid/Side in teal/magenta); nothing lit = both.
• The channel you're viewing is also the brush: new bands land on it. Bands are colour-coded — Stereo gold · L green · R amber · Mid teal · Side magenta — across the whole Delta family.
• The Δ pill cycles the delta view: off → Δ (one wet curve with the EQ's signed effect filled — green boost, magenta cut) → Δ + body (plus the wet spectrum body in the channel colour). The fastest honest answer to "what is this EQ actually doing?"
• The REAL pill draws the measured transfer — wet ÷ dry, computed from the actual audio, on the same gain axis as the theoretical curves. Where theory and measurement agree, the curves lie on top of each other; where the real world differs (dynamics acting, cramping, anything), you see it. It cycles off → REAL (teal, over the spectrum) → REAL SOLO (magenta — the spectrum steps aside and the measured truth stands alone). Ducking bands breathing, in real dB, live.

14 · Oversampling & phase

• OVERSAMPLING — OFF · 2× · 4× · 8×. Keeps high-frequency curves accurate up to Nyquist (cramping-free bells at 15 kHz).
• PHASE — ZERO (minimum-phase IIR, zero latency — tracking & live), NAT (natural: minimum-phase FIR, low latency), LIN (linear phase: zero phase shift, adds latency the host compensates). The dry reference is delayed to match, so the Δ views stay honest in every mode.

15 · Monitor, A/B, MATCH

16 · Presets

The centre-top bar is the house preset browser: ‹ › step alphabetically, clicking the name opens the menu — every preset plus Save As… · Overwrite · Rename… · Delete… · Reveal presets folder. Presets are plain files in Documents\DeltaEQ\Presets — share them, back them up. A preset stores the sound (all parameters), not the window layout.

17 · Settings

The ⚙ cog opens the settings flyout:

• Display — GPU rendering (default on) · 60 FPS refresh (default 30) · loudness rail with its dry-mirror and dB-scale sub-options.
• Styling — the spectrum's Reactivity, Smoothing, Shading and Stroke, plus a flat-fill toggle.

Two icon toggles live at the far left of the bar and survive everything: ZEN (hide the chrome, keep the EQ) and SPECTRUM-ONLY (hide the curves and handles for a bare analyzer). They combine.

18 · Interaction cheat-sheet

19 · Troubleshooting

• CTX does nothing. Check the scope: ALL needs other Delta instances alive in the project; SIDECHAIN needs a key routed to DeltaEQ's SC input. The picker's mini-spectrum shows exactly what the band hears — if it's flat, no context is arriving.
• The Spectral band sits idle. It ducks what the key spectrum spikes at — feed it a context (or the sidechain) with actual energy, and check MAX isn't at 1.
• TRACK jumps around. Pitch-tracking is built for isolated, mostly-mono sources. On dense material, narrow the RANGE window or use FREEZE + a static band instead.
• Linear phase feels laggy. That's its latency (host-compensated on playback). Use ZERO while tracking live input, LIN for mixdown decisions.
• A band disappeared. Double-clicking a handle disables (dim handle), it doesn't delete — double-click again. Deleted bands come back with ⌘/Ctrl-Z.
• My EQ sounds "better" every A/B. Enable MATCH — if it still wins level-matched, it's actually better.

DeltaEQ — EQ in context. 🖤