feat: live operating-point fill + -6 dB refs on the gain curve

Add a per-channel input_level meter (post pre-gain, peak-with-decay) and use it
to shade the gain curve: a translucent fill under the curve from the floor up to
the current input, its right edge riding the curve (width = input, height =
output), plus a dot at the operating point. Add -6 dBFS reference lines on both
axes with a tick label.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -34,9 +34,9 @@ Built with **Rust** + **NIH-plug** (VST3 + CLAP output) + **egui** for the UI.
 ```
 Input
   └─ Crossover filterbank (Linkwitz-Riley LR4 @ each crossover freq)
-       ├─ Band 1 (low)   → pre-gain → look-ahead delay → compressor VCA → makeup ─┐ (bypassable)
+       ├─ Band 1 (low)   → pre-gain → look-ahead delay → compressor VCA → makeup ─┐ (dry/wet mix)
-       ├─ Band 2 (mid)   → pre-gain → look-ahead delay → compressor VCA → makeup ─┤ (bypassable)
+       ├─ Band 2 (mid)   → pre-gain → look-ahead delay → compressor VCA → makeup ─┤ (dry/wet mix)
-       └─ Band 3 (high)  → pre-gain → look-ahead delay → compressor VCA → makeup ─┤ (bypassable)
+       └─ Band 3 (high)  → pre-gain → look-ahead delay → compressor VCA → makeup ─┤ (dry/wet mix)
                                                                                   │
        Sum of bands ◄─────────────────────────────────────────────────────------┘
          └─ 'All' channel → pre-gain → look-ahead delay → compressor VCA → makeup
@@ -71,7 +71,7 @@ a first-class mode, not an afterthought.
 ### 'All' Aggregate Channel
 - Structurally **identical to a per-band compressor** — reuse the same comp/lim code/params, just fed the summed signal instead of a filtered band
 - Runs after the three bands are summed, before the output brickwall limiter
-- Bands are individually bypassable; with all three bypassed the (phase-coherent) crossover sum equals the dry input, so the 'All' channel alone acts as a full-band comp/lim
+- Bands have a per-channel dry/wet **mix** (parallel compression); at 0% (or all three dry) the (phase-coherent) crossover sum equals the dry input, so the 'All' channel alone acts as a full-band comp/lim
 - Has its own look-ahead; the plugin reports a single **constant** total latency (the fixed band + 'All' look-ahead), set once — see Latency below
 ### Output Limiter
 - Brickwall, ceiling = 0 dBFS or user-defined (`output_ceiling`). Look-ahead + sliding-max peak detection + a ceiling clamp guarantee the output never exceeds the ceiling
@@ -91,16 +91,24 @@ a first-class mode, not an afterthought.
 - `look_ahead_ms` — look-ahead time (0–5 ms). Reported latency is **constant** (the max look-ahead); the knob only moves the detector tap within that fixed delay, so it is safe to adjust during playback (changing reported latency mid-stream crashes some hosts, FL included)
 - `crossover_low_hz` — low/mid crossover frequency
 - `crossover_high_hz` — mid/high crossover frequency
+
+> **Crossover automation caveat:** the lo ≤ hi limit is enforced in the **editor only** (the two
+> are independent params). Host automation writes them directly, so it can drive lo past hi and
+> momentarily invert the mid band. The DSP clamps to a monotonic split so it won't break audio,
+> but FL's automation can misbehave once inverted. Not fixed by design — just don't automate the
+> two across each other.
 ### Per-Channel Compressor (× 4: low, mid, high, **all** — one `#[nested]` params struct reused)
 - `pre_gain_db` — drive into the compressor (−24…+36 dB, smoothed)
 - `detection` — peak / RMS level detection
+- `low_slope` — low-level shaper slope at the silence floor (1 = unity, >1 fans up/boost, <1 fans down/cut). **Serial**: reshapes the level *before* the threshold, so a boost can lift quiet material up into compression
+- `low_curve` — bends the low shaper toward a bounded saturation (0% = straight line) so the serial composition doesn't run away
 - `threshold_db`
 - `ratio` — 1.0 (off) to ∞ (limiting)
+- `knee_db` — soft knee width
 - `attack_ms`
 - `release_ms`
-- `knee_db` — soft knee width
 - `makeup_db` — makeup gain (−24…+24 dB)
-- `bypass` — per-channel bypass (bypassing low+mid+high = simple full-band comp via the 'all' channel)
+- `mix` — per-channel dry/wet mix (parallel compression); 0% = dry (a clean bypass), 100% = fully processed. Bands at 0% → simple full-band comp via the 'all' channel
 
 The 'all' channel uses the same struct so its UI and DSP are identical to a band; it just sits after the band sum.
 ---
@@ -124,21 +132,22 @@ src/
     oversampler.rs  # ✅ 4x polyphase oversampler for true-peak detection (detection-only)
 ```
 
-The editor's meters and plot are currently drawn directly with egui's `Painter` inline in
+The editor lives in an `editor/` module — one file per visualiser widget (each owns its GUI
-`editor.rs`. When the UI is redesigned (gain curve, draggable crossover, real layout), the plan is
+state), with `mod.rs` as the aggregator/layout. Drawn directly with egui's `Painter`.
-to split it into a widget module so each visualiser is self-contained and reusable:
 
 ```
 src/
   editor/
-    mod.rs            # editor assembly + layout (replaces editor.rs)
+    mod.rs            # aggregator: create(), EditorState, layout, placeholder slider columns
-    widgets/
+    meter.rs          # |L | GR | R| level + gain-reduction bars + per-channel ceiling lamp
-      meter.rs        # |L | GR | R| level + gain-reduction cluster (extract from editor.rs)
+    plot.rs           # rolling in/out/GR scope (200 Hz ring feed) + ceiling-hit markers
-      plot.rs         # rolling in/out/GR scope (extract from editor.rs)
+    crossover.rs      # log-freq strip with draggable crossover handles + number boxes
-      gain_curve.rs   # static gain-curve display per channel (threshold/ratio/knee)  — planned
+    gain_curve.rs     # static gain-curve display (out vs in) for the selected channel
-      crossover.rs    # frequency display with draggable crossover handles            — planned
 ```
 
+Remaining UI work: replace the placeholder per-channel slider columns in `mod.rs` with the real
+layout.
+
 Deferred until the redesign — no need to split prematurely while the layout is still a placeholder.
  
 ---
@@ -189,12 +198,13 @@ is essential — without it FL silently skips a plugin it has seen before.)
  
 Work through these stages in order — each stage produces a loadable, audible plugin.
 
-**Status (2026-06-23):** Stages 1–4 done — the full signal chain works: 3-band LR4 crossover →
+**Status (2026-06-25):** Stages 1–4 done — the full signal chain works: 3-band LR4 crossover →
-per-band pre-gain + compressors (peak/RMS) → 'All' channel → **true-peak brickwall limiter** (4×
+per-band pre-gain + compressors (peak/RMS) → per-channel dry/wet mix → 'All' channel → **true-peak
-oversampled detection). `lib.rs` has been split into `params.rs`, `editor.rs`, and `meters.rs`.
+brickwall limiter** (4× oversampled detection). `lib.rs` is split into `params.rs`, `meters.rs`, and
-Stage 6 metering is underway: per-channel **|L | GR | R| meters**, a **latching ceiling lamp**, and
+an `editor/` widget module. Stage 6 visualisers are essentially complete: per-channel **|L | GR | R|
-a **rolling in/out/gain-reduction plot** (per-channel tabs + flow-speed selector). **Next: gain-curve
+meters** + **per-channel ceiling lamps**, a **rolling in/out/GR plot** (200 Hz ring feed, flow-speed,
-display and draggable crossover handles, then replace the placeholder slider UI.**
+ceiling-hit markers), **draggable crossover handles**, and a **static gain-curve display**. **Next:
+replace the placeholder slider columns with the real UI layout.**
  
 ### Stage 1 — Skeleton plugin ✅
 - [x] NIH-plug "passthrough" compiling and loading in DAW
@@ -224,14 +234,14 @@ display and draggable crossover handles, then replace the placeholder slider UI.
 ### Stage 5 — Basic egui UI  *(basic version done early)*
 - [x] Add `nih_plug_egui` editor
 - [x] Sliders for all current parameters (`ParamSlider` grid)
-- [x] Per-band bypass toggles
+- [x] Per-channel dry/wet mix (parallel compression; replaced the bypass toggle)
 - [x] Confirm UI controls update DSP in real time
 ### Stage 6 — Custom visualisations
 - [x] Per-channel level meters (output level, `|L | GR | R|` cluster)
 - [x] Per-channel gain-reduction meters (vertical bars) + latching ceiling lamp
 - [x] Rolling in/out/gain-reduction plot (per-channel tabs, flow-speed selector)
-- [ ] Static gain-curve display per band (threshold/ratio/knee)
+- [x] Static gain-curve display (out vs in; includes pre-gain + makeup) for the selected channel
-- [ ] Draggable crossover handles on a frequency display
+- [x] Draggable crossover handles on a log-frequency display (with number boxes)
 - [ ] Replace the placeholder slider columns with the real UI
 ---
  

src/dsp/compressor.rs

@@ -26,6 +26,16 @@ const MAX_CHANNELS: usize = 2;
 /// ~ -240 dBFS; keeps `log10` away from zero without affecting audible levels.
 const LEVEL_EPS: f32 = 1e-12;
 
+/// Silence-floor anchor for the below-threshold shaping: at/below this level the gain change is 0
+/// (silence stays silence), and the low region fans up/down from here toward the threshold. Matches
+/// the editor gain-curve's display floor.
+const LOW_ANCHOR_DB: f32 = -60.0;
+
+/// Max bulge (dB) the low-shaper curvature adds at the MIDDLE of the low region, at `|low_curve|`=1.
+/// Bipolar: positive bulges up (boost the quiet middle), negative bulges down (suppress). Zero at
+/// both ends (silence floor and the knee), so it never moves those anchors.
+const LOW_BULGE_MAX_DB: f32 = 12.0;
+
 /// Hardcoded RMS averaging window (one-pole time constant). Deliberately small; can be
 /// promoted to a parameter later.
 const RMS_WINDOW_MS: f32 = 5.0;
@@ -40,6 +50,11 @@ pub struct CompressorSettings {
     pub threshold_db: f32,
     pub ratio: f32,
     pub knee_db: f32,
+    /// Low shaper slope at the silence floor (1 = unity; >1 fans up/boost, <1 fans down/cut).
+    /// Reshapes the level the compressor sees (serial), anchored at the floor.
+    pub low_slope: f32,
+    /// Low shaper curvature, 0..1 (0 = straight line, 1 = max bend toward bounded saturation).
+    pub low_curve: f32,
     /// One-pole coefficient for the attack ramp (see [`Compressor::time_to_coef`]).
     pub attack_coef: f32,
     /// One-pole coefficient for the release ramp.
@@ -50,7 +65,9 @@ pub struct CompressorSettings {
     pub lookahead_samples: usize,
     /// `true` = RMS detection (running power average), `false` = naive sample peak.
     pub use_rms: bool,
-    pub bypass: bool,
+    /// Dry/wet blend, 0..=1. 1 = fully compressed (incl. makeup), 0 = dry passthrough (bypass).
+    /// Parallel: dry and wet share the same delayed input, so the mix is phase-aligned.
+    pub mix: f32,
 }
 
 pub struct Compressor {
@@ -67,7 +84,8 @@ pub struct Compressor {
     mean_sq: f32,
     rms_coef: f32,
 
-    /// Smooth decoupled peak-detector state, expressed as dB of **attenuation** (>= 0).
+    /// Smooth decoupled peak-detector state, in dB of attenuation (signed: usually >= 0, but can go
+    /// negative = boost when `low_slope < 1`). The `max()` recurrence makes cut fast / boost slow.
     y1: f32, // release branch (peak-with-decay)
     yl: f32, // attack-smoothed output
 }
@@ -129,24 +147,56 @@ impl Compressor {
         }
     }
 
-    /// Static compressor curve. Returns gain reduction in dB (<= 0) for an input `level_db`.
+    /// Pure compressor transfer (threshold / ratio / quadratic soft knee). Returns gain reduction
-    /// Quadratic soft knee of width `knee_db`, centred on `threshold_db`.
+    /// in dB (<= 0) for an input `level_db`.
-    fn gain_computer(level_db: f32, threshold_db: f32, ratio: f32, knee_db: f32) -> f32 {
+    fn comp_gain_db(level_db: f32, threshold_db: f32, ratio: f32, knee_db: f32) -> f32 {
         let slope = 1.0 / ratio - 1.0; // <= 0 for ratio >= 1
         let over = level_db - threshold_db;
-
         if knee_db > 0.0 && 2.0 * over.abs() <= knee_db {
-            // Inside the knee: a parabola joining the two regions with a continuous slope.
             let x = over + knee_db * 0.5; // 0..knee
             slope * x * x / (2.0 * knee_db)
         } else if over > 0.0 {
-            // Above the knee (also covers the hard-knee case): linear region.
             slope * over
         } else {
             0.0
         }
     }
 
+    /// Low-level shaper gain in dB. Anchored at BOTH the silence floor ([`LOW_ANCHOR_DB`]) and the
+    /// knee (threshold). `low_slope` tilts the straight line between those anchors (1 = unity);
+    /// `low_curve` (-1..1) bulges that line in the middle without moving either endpoint — positive
+    /// bulges up (boost the quiet middle), negative down (suppress). Reshapes the level the
+    /// compressor then sees.
+    fn low_gain_db(level_db: f32, threshold_db: f32, low_slope: f32, low_curve: f32) -> f32 {
+        let d = level_db - LOW_ANCHOR_DB;
+        if d <= 0.0 {
+            return 0.0;
+        }
+        let span = (threshold_db - LOW_ANCHOR_DB).max(1.0); // floor -> threshold width
+        let t = (d / span).min(1.0); // normalized position, clamped at the knee
+        // Straight line anchored at the floor (t=0 -> 0) and the knee (t=1 -> (slope-1)*span).
+        let slope_line = (low_slope - 1.0) * span * t;
+        // Bipolar bulge: 0 at both ends, peaks (4·t·(1-t) = 1) at the middle.
+        let bulge = low_curve * LOW_BULGE_MAX_DB * 4.0 * t * (1.0 - t);
+        slope_line + bulge
+    }
+
+    /// Full static curve, **serial**: the low shaper reshapes the level, then the compressor's
+    /// threshold sees the shaped level. Returns total gain in dB (signed: negative = cut, positive
+    /// = boost). `gain = low + comp(level + low)`. Shared with the editor's gain-curve display —
+    /// single source of truth.
+    pub fn gain_computer(
+        level_db: f32,
+        threshold_db: f32,
+        ratio: f32,
+        knee_db: f32,
+        low_slope: f32,
+        low_curve: f32,
+    ) -> f32 {
+        let low = Self::low_gain_db(level_db, threshold_db, low_slope, low_curve);
+        low + Self::comp_gain_db(level_db + low, threshold_db, ratio, knee_db)
+    }
+
     /// The plugin's fixed reported latency in samples (the constant audio delay).
     pub fn latency(&self) -> u32 {
         self.fixed_delay as u32
@@ -188,18 +238,22 @@ impl Compressor {
             peak = peak.max(self.delay[ch][det_pos].abs());
         }
 
-        // 4) Gain computer + ballistics. On bypass we keep the delay aligned (so toggling
+        // 4) Gain computer + ballistics. The detector ALWAYS runs (even at mix 0) so metering
-        //    bypass doesn't shift timing) but apply unity gain and no makeup.
+        //    reflects the wet gain reduction regardless of the dry/wet blend.
-        let gain_lin = if set.bypass {
+        //    RMS = running mean of the linked squared level over a fixed window. Updated whenever
-            1.0
+        //    active (regardless of mode) so switching peak<->RMS is seamless.
-        } else {
-            // RMS = running mean of the linked squared level over a fixed window. Updated
-            // whenever active (regardless of mode) so switching peak<->RMS is seamless.
         self.mean_sq = self.rms_coef * self.mean_sq + (1.0 - self.rms_coef) * peak * peak;
         let detector = if set.use_rms { self.mean_sq.sqrt() } else { peak };
         let level_db = 20.0 * (detector + LEVEL_EPS).log10();
         // Desired attenuation in dB, as a positive quantity.
-            let target = -Self::gain_computer(level_db, set.threshold_db, set.ratio, set.knee_db);
+        let target = -Self::gain_computer(
+            level_db,
+            set.threshold_db,
+            set.ratio,
+            set.knee_db,
+            set.low_slope,
+            set.low_curve,
+        );
 
         // Smooth, decoupled peak detector (Giannoulis eq. 17–18) on the attenuation:
         //   y1 = max(target, release-smoothed y1)   (fast up / slow down "peak hold")
@@ -207,13 +261,14 @@ impl Compressor {
         self.y1 = target.max(set.release_coef * self.y1 + (1.0 - set.release_coef) * target);
         self.yl = set.attack_coef * self.yl + (1.0 - set.attack_coef) * self.y1;
 
-            let total_db = set.makeup_db - self.yl;
+        let wet_gain = 10.0f32.powf((set.makeup_db - self.yl) / 20.0);
-            10.0f32.powf(total_db / 20.0)
-        };
 
-        // 5) Output = delayed input (always `fixed_delay` old) * gain.
+        // 5) Dry/wet mix (parallel compression). Both paths use the same delayed input, so the
+        //    blend is phase-aligned. mix = 0 -> dry passthrough (clean bypass), mix = 1 -> wet.
+        let mix = set.mix.clamp(0.0, 1.0);
+        let blend = (1.0 - mix) + mix * wet_gain;
         for ch in 0..n {
-            output[ch] = self.delay[ch][out_pos] * gain_lin;
+            output[ch] = self.delay[ch][out_pos] * blend;
         }
 
         // 6) Advance the write head.
@@ -241,20 +296,41 @@ mod tests {
             makeup_db: 0.0,
             lookahead_samples: 0,
             use_rms: false,
-            bypass: false,
+            mix: 1.0,
+            low_slope: 1.0,
+            low_curve: 0.0,
         }
     }
 
     #[test]
     fn below_threshold_is_untouched() {
         // -30 dB input, -20 dB threshold -> no reduction.
-        assert_eq!(Compressor::gain_computer(-30.0, -20.0, 4.0, 6.0), 0.0);
+        assert_eq!(Compressor::gain_computer(-30.0, -20.0, 4.0, 6.0, 1.0, 0.0), 0.0);
+    }
+
+    #[test]
+    fn low_shaper_serial_slope_and_bipolar_bulge() {
+        let thr = -18.0;
+        // Serial slope-only (no curve): boost lifts -30 by 30 dB to 0 dB -> 18 dB over threshold,
+        // comp pulls back (1/4 - 1)*18 = -13.5 -> net 16.5.
+        assert_close(Compressor::gain_computer(-30.0, thr, 4.0, 0.0, 2.0, 0.0), 16.5, 1e-3);
+        // Cut (slope 0.5) -> -15 dB; shaped to -45, still below threshold -> net -15.
+        assert_close(Compressor::gain_computer(-30.0, thr, 4.0, 0.0, 0.5, 0.0), -15.0, 1e-3);
+
+        // Curvature is a BIPOLAR bulge at the middle of the low region (unity slope here).
+        let mid = -39.0; // middle of [-60, -18]
+        let flat = Compressor::gain_computer(mid, thr, 4.0, 0.0, 1.0, 0.0);
+        let up = Compressor::gain_computer(mid, thr, 4.0, 0.0, 1.0, 1.0);
+        let down = Compressor::gain_computer(mid, thr, 4.0, 0.0, 1.0, -1.0);
+        assert!(up > flat && flat > down, "bipolar bulge expected: {down} < {flat} < {up}");
+        // Endpoints are unaffected by curvature (silence anchored).
+        assert_close(Compressor::gain_computer(-60.0, thr, 4.0, 0.0, 1.0, 1.0), 0.0, 1e-6);
     }
 
     #[test]
     fn above_knee_follows_ratio() {
         // 10 dB over threshold at 4:1 -> output only 2.5 dB over -> 7.5 dB reduction.
-        let r = Compressor::gain_computer(-10.0, -20.0, 4.0, 0.0);
+        let r = Compressor::gain_computer(-10.0, -20.0, 4.0, 0.0, 1.0, 0.0);
         assert_close(r, -7.5, 1e-4);
     }
 
@@ -263,11 +339,11 @@ mod tests {
         // At the upper knee edge the soft-knee and linear formulas must agree.
         let (t, ratio, knee) = (0.0, 4.0, 6.0);
         let edge = t + knee / 2.0;
-        let knee_val = Compressor::gain_computer(edge, t, ratio, knee);
+        let knee_val = Compressor::gain_computer(edge, t, ratio, knee, 1.0, 0.0);
         let linear_val = (1.0 / ratio - 1.0) * (edge - t);
         assert_close(knee_val, linear_val, 1e-4);
         // At the lower edge there is still no reduction.
-        assert_close(Compressor::gain_computer(t - knee / 2.0, t, ratio, knee), 0.0, 1e-6);
+        assert_close(Compressor::gain_computer(t - knee / 2.0, t, ratio, knee, 1.0, 0.0), 0.0, 1e-6);
     }
 
     #[test]
@@ -336,7 +412,7 @@ mod tests {
         for &l in &[0usize, d / 2, d] {
             comp.reset();
             let mut set = settings(0.0, 1.0, 0.0);
-            set.bypass = true; // unity gain -> isolate the delay behaviour
+            set.mix = 0.0; // dry passthrough -> isolate the delay behaviour
             set.lookahead_samples = l;
 
             let mut out = [0.0f32];

src/editor/crossover.rs

@@ -0,0 +1,141 @@
+//! Draggable crossover handles — replaces the two plain crossover sliders.
+//!
+//! A horizontal log-frequency strip split into LOW / MID / HIGH by two draggable handles, plus a
+//! number box per crossover (double-click to type an exact value). The handles enforce a dynamic
+//! limit: lo/mid can never exceed mid/hi (and vice-versa), on top of each param's own range.
+
+use nih_plug::prelude::*;
+use nih_plug_egui::egui::{
+    self, pos2, vec2, Align2, Color32, CornerRadius, DragValue, FontId, Painter, Rect, Sense, Stroke,
+};
+
+use crate::params::Codename206Params;
+
+/// Height of the handle strip.
+const GRAPH_H: f32 = 54.0;
+/// Displayed frequency axis (log), independent of the params' own ranges.
+const DISP_MIN_HZ: f32 = 20.0;
+const DISP_MAX_HZ: f32 = 20_000.0;
+
+fn log_span() -> f32 {
+    DISP_MAX_HZ.ln() - DISP_MIN_HZ.ln()
+}
+
+fn fmt_hz(hz: f32) -> String {
+    if hz >= 1000.0 {
+        format!("{:.2} kHz", hz / 1000.0)
+    } else {
+        format!("{:.0} Hz", hz)
+    }
+}
+
+pub(super) fn draw(ui: &mut egui::Ui, params: &Codename206Params, setter: &ParamSetter) {
+    let lo = params.crossover_low_hz.value();
+    let hi = params.crossover_high_hz.value();
+    // Each param's own min/max (normalized 0/1 map to the range ends).
+    let lo_min = params.crossover_low_hz.preview_plain(0.0);
+    let lo_max = params.crossover_low_hz.preview_plain(1.0);
+    let hi_min = params.crossover_high_hz.preview_plain(0.0);
+    let hi_max = params.crossover_high_hz.preview_plain(1.0);
+    // Dynamic limits so the two never cross: lo <= hi.
+    let lo_upper = lo_max.min(hi);
+    let hi_lower = hi_min.max(lo);
+
+    ui.label("Crossover");
+
+    let (rect, _) =
+        ui.allocate_exact_size(vec2(ui.available_width(), GRAPH_H), Sense::hover());
+    let p = ui.painter_at(rect);
+    let (left, right, top, bottom) =
+        (rect.left() + 2.0, rect.right() - 2.0, rect.top() + 2.0, rect.bottom() - 2.0);
+    let width = right - left;
+    let x_for = |hz: f32| left + (hz.max(1.0).ln() - DISP_MIN_HZ.ln()) / log_span() * width;
+    let xlo = x_for(lo);
+    let xhi = x_for(hi);
+
+    // Three band regions.
+    p.rect_filled(Rect::from_min_max(pos2(left, top), pos2(xlo, bottom)), CornerRadius::ZERO, Color32::from_rgb(28, 38, 52));
+    p.rect_filled(Rect::from_min_max(pos2(xlo, top), pos2(xhi, bottom)), CornerRadius::ZERO, Color32::from_rgb(30, 48, 36));
+    p.rect_filled(Rect::from_min_max(pos2(xhi, top), pos2(right, bottom)), CornerRadius::ZERO, Color32::from_rgb(52, 38, 30));
+
+    let band_label = |cx: f32, t: &str| {
+        p.text(pos2(cx, top + 2.0), Align2::CENTER_TOP, t, FontId::proportional(11.0), Color32::from_gray(160));
+    };
+    band_label((left + xlo) * 0.5, "LOW");
+    band_label((xlo + xhi) * 0.5, "MID");
+    band_label((xhi + right) * 0.5, "HIGH");
+
+    handle(ui, &p, setter, "xover_lo", xlo, lo, &params.crossover_low_hz, lo_min, lo_upper, left, width, top, bottom, Color32::from_rgb(120, 170, 230));
+    handle(ui, &p, setter, "xover_hi", xhi, hi, &params.crossover_high_hz, hi_lower, hi_max, left, width, top, bottom, Color32::from_rgb(230, 150, 120));
+
+    // Number boxes (double-click to type). Clamped to the same dynamic limits.
+    ui.horizontal(|ui| {
+        ui.label("Lo/Mid");
+        let mut v = lo as f64;
+        if ui
+            .add(DragValue::new(&mut v).range(lo_min as f64..=lo_upper as f64).speed(0.5).suffix(" Hz"))
+            .changed()
+        {
+            set_clamped(setter, &params.crossover_low_hz, v as f32, lo_min, lo_upper);
+        }
+        ui.add_space(16.0);
+        ui.label("Mid/Hi");
+        let mut v = hi as f64;
+        if ui
+            .add(DragValue::new(&mut v).range(hi_lower as f64..=hi_max as f64).speed(2.0).suffix(" Hz"))
+            .changed()
+        {
+            set_clamped(setter, &params.crossover_high_hz, v as f32, hi_lower, hi_max);
+        }
+    });
+}
+
+/// One draggable vertical handle. Drives `param` from the pointer's x (log-frequency), clamped to
+/// `[min, max]` (which already encodes the dynamic lo<=hi limit), with proper begin/end gestures.
+#[allow(clippy::too_many_arguments)]
+fn handle(
+    ui: &egui::Ui,
+    p: &Painter,
+    setter: &ParamSetter,
+    id_salt: &str,
+    x: f32,
+    hz: f32,
+    param: &FloatParam,
+    min: f32,
+    max: f32,
+    left: f32,
+    width: f32,
+    top: f32,
+    bottom: f32,
+    color: Color32,
+) {
+    let hit = Rect::from_min_max(pos2(x - 5.0, top), pos2(x + 5.0, bottom));
+    let resp = ui
+        .interact(hit, ui.id().with(id_salt), Sense::drag())
+        .on_hover_cursor(egui::CursorIcon::ResizeHorizontal);
+
+    if resp.drag_started() {
+        setter.begin_set_parameter(param);
+    }
+    if resp.dragged() {
+        if let Some(pos) = resp.interact_pointer_pos() {
+            let frac = ((pos.x - left) / width).clamp(0.0, 1.0);
+            let new = (DISP_MIN_HZ.ln() + frac * log_span()).exp().clamp(min, max);
+            setter.set_parameter(param, new);
+        }
+    }
+    if resp.drag_stopped() {
+        setter.end_set_parameter(param);
+    }
+
+    let col = if resp.dragged() || resp.hovered() { Color32::WHITE } else { color };
+    p.line_segment([pos2(x, top), pos2(x, bottom)], Stroke::new(2.0, col));
+    p.text(pos2(x, bottom - 1.0), Align2::CENTER_BOTTOM, fmt_hz(hz), FontId::proportional(10.0), Color32::from_gray(220));
+}
+
+/// Set a param to `value` clamped to `[min, max]`, wrapped in its own gesture (for the number box).
+fn set_clamped(setter: &ParamSetter, param: &FloatParam, value: f32, min: f32, max: f32) {
+    setter.begin_set_parameter(param);
+    setter.set_parameter(param, value.clamp(min, max));
+    setter.end_set_parameter(param);
+}

src/editor/gain_curve.rs

@@ -0,0 +1,106 @@
+//! Static gain-curve display: output level vs input level for the channel currently selected in
+//! the plot. Plots the wet transfer `out = (in + pre_gain) + gain_reduction(...) + makeup` (mix not
+//! folded in; output clamped at 0 dBFS), plus a live **operating-point fill** under the curve up to
+//! the channel's current input level — its right edge rides the curve (width = input, height = out).
+
+use nih_plug::prelude::util;
+use nih_plug_egui::egui::{self, pos2, vec2, Align2, Color32, CornerRadius, FontId, Sense, Stroke};
+use std::sync::atomic::Ordering;
+
+use crate::dsp::compressor::Compressor;
+use crate::meters::Meters;
+use crate::params::Codename206Params;
+
+/// Side length of the square plot.
+const CURVE_SIZE: f32 = 150.0;
+/// dB extent of both axes (bottom/left = FLOOR_DB, top/right = 0 dBFS).
+const FLOOR_DB: f32 = -60.0;
+
+pub(super) fn draw(ui: &mut egui::Ui, params: &Codename206Params, selected: usize, meters: &Meters) {
+    let labels = ["LOW", "MID", "HIGH", "ALL"];
+    let ch = selected.min(3);
+    let cp = match ch {
+        0 => &params.low,
+        1 => &params.mid,
+        2 => &params.high,
+        _ => &params.all,
+    };
+    let pre = cp.pre_gain_db.value();
+    let threshold = cp.threshold_db.value();
+    let ratio = cp.ratio.value();
+    let knee = cp.knee_db.value();
+    let low_slope = cp.low_slope.value();
+    let low_curve = cp.low_curve.value();
+    let makeup = cp.makeup_db.value();
+
+    ui.label(format!("Curve: {}", labels[ch]));
+    let (rect, _) = ui.allocate_exact_size(vec2(CURVE_SIZE, CURVE_SIZE), Sense::hover());
+    let p = ui.painter_at(rect);
+    p.rect_filled(rect, CornerRadius::ZERO, Color32::from_rgb(16, 16, 20));
+
+    let inset = 2.0;
+    let (left, right, top, bottom) =
+        (rect.left() + inset, rect.right() - inset, rect.top() + inset, rect.bottom() - inset);
+    let w = right - left;
+    let h = bottom - top;
+    let x_for = |db: f32| left + (db - FLOOR_DB) / -FLOOR_DB * w;
+    let y_for = |db: f32| bottom - (db - FLOOR_DB) / -FLOOR_DB * h;
+
+    // -6 dBFS reference lines on both axes.
+    let g6 = Color32::from_gray(38);
+    let x6 = x_for(-6.0);
+    let y6 = y_for(-6.0);
+    p.line_segment([pos2(x6, top), pos2(x6, bottom)], Stroke::new(1.0, g6));
+    p.line_segment([pos2(left, y6), pos2(right, y6)], Stroke::new(1.0, g6));
+
+    // Unity reference (out = in), bottom-left to top-right.
+    p.line_segment([pos2(left, bottom), pos2(right, top)], Stroke::new(1.0, Color32::from_gray(45)));
+    // Threshold marker on the input axis — shifted left by pre-gain (the comp sees in + pre).
+    let tx = x_for((threshold - pre).clamp(FLOOR_DB, 0.0));
+    p.line_segment([pos2(tx, top), pos2(tx, bottom)], Stroke::new(1.0, Color32::from_rgb(80, 60, 45)));
+
+    // Full wet transfer: drive into the comp, then makeup. (Mix not folded in.)
+    let n = 96;
+    let mut pts = Vec::with_capacity(n + 1);
+    for i in 0..=n {
+        let in_db = FLOOR_DB + (i as f32 / n as f32) * -FLOOR_DB; // external input, -60..0
+        let driven = in_db + pre;
+        let gr = Compressor::gain_computer(driven, threshold, ratio, knee, low_slope, low_curve); // signed dB
+        let out_db = (driven + gr + makeup).clamp(FLOOR_DB, 0.0);
+        pts.push(pos2(x_for(in_db), y_for(out_db)));
+    }
+    // Operating-point fill: shade under the curve from the floor up to the current input level.
+    let driven_now = util::gain_to_db(meters.input_level[ch].load(Ordering::Relaxed));
+    let ext_in = (driven_now - pre).clamp(FLOOR_DB, 0.0); // external input -> curve x
+    let x_now = x_for(ext_in);
+    let fill_col = Color32::from_rgba_unmultiplied(120, 200, 160, 45);
+    for seg in pts.windows(2) {
+        let a = seg[0];
+        let mut b = seg[1];
+        if a.x >= x_now {
+            break;
+        }
+        if b.x > x_now {
+            let f = ((x_now - a.x) / (b.x - a.x)).clamp(0.0, 1.0); // clip the last quad at x_now
+            b = pos2(x_now, a.y + (b.y - a.y) * f);
+        }
+        p.add(egui::Shape::convex_polygon(
+            vec![pos2(a.x, bottom), a, b, pos2(b.x, bottom)],
+            fill_col,
+            Stroke::NONE,
+        ));
+    }
+
+    p.add(egui::Shape::line(pts, Stroke::new(1.6, Color32::from_rgb(120, 200, 160))));
+
+    // Operating-point dot, on the curve at the current input.
+    let driven = ext_in + pre;
+    let gr = Compressor::gain_computer(driven, threshold, ratio, knee, low_slope, low_curve);
+    let out_op = (driven + gr + makeup).clamp(FLOOR_DB, 0.0);
+    p.circle_filled(pos2(x_now, y_for(out_op)), 3.0, Color32::from_rgb(235, 240, 235));
+
+    // Corner dB ticks + the -6 dB reference.
+    p.text(pos2(left + 1.0, top + 1.0), Align2::LEFT_TOP, "0", FontId::proportional(9.0), Color32::from_gray(90));
+    p.text(pos2(left + 1.0, bottom - 1.0), Align2::LEFT_BOTTOM, "-60", FontId::proportional(9.0), Color32::from_gray(90));
+    p.text(pos2(x6 + 2.0, bottom - 1.0), Align2::LEFT_BOTTOM, "-6", FontId::proportional(9.0), Color32::from_gray(80));
+}

src/editor/mod.rs

@@ -19,6 +19,8 @@ use crate::meters::Meters;
 use crate::params::{Codename206Params, CompressorParams};
 use crate::Codename206;
 
+mod crossover;
+mod gain_curve;
 mod meter;
 mod plot;
 
@@ -45,10 +47,15 @@ pub(crate) fn create(params: Arc<Codename206Params>, meters: Arc<Meters>) -> Opt
 
             // One column of controls for a single compressor channel (placeholder layout).
             let band_col = |ui: &mut egui::Ui, title: &str, p: &CompressorParams| {
+                // Roughly in signal order: input drive -> low shaper -> compressor -> output.
                 ui.strong(title);
                 ui.label("Pre-gain");
                 ui.add(widgets::ParamSlider::for_param(&p.pre_gain_db, setter));
                 ui.add(widgets::ParamSlider::for_param(&p.detection, setter));
+                ui.label("Low Slope");
+                ui.add(widgets::ParamSlider::for_param(&p.low_slope, setter));
+                ui.label("Low Curve");
+                ui.add(widgets::ParamSlider::for_param(&p.low_curve, setter));
                 ui.label("Threshold");
                 ui.add(widgets::ParamSlider::for_param(&p.threshold_db, setter));
                 ui.label("Ratio");
@@ -61,7 +68,8 @@ pub(crate) fn create(params: Arc<Codename206Params>, meters: Arc<Meters>) -> Opt
                 ui.add(widgets::ParamSlider::for_param(&p.release_ms, setter));
                 ui.label("Makeup");
                 ui.add(widgets::ParamSlider::for_param(&p.makeup_db, setter));
-                ui.add(widgets::ParamSlider::for_param(&p.bypass, setter));
+                ui.label("Mix");
+                ui.add(widgets::ParamSlider::for_param(&p.mix, setter));
             };
 
             // Resizable window; vertical scroll so every control stays reachable even when the
@@ -73,16 +81,17 @@ pub(crate) fn create(params: Arc<Codename206Params>, meters: Arc<Meters>) -> Opt
                         ui.heading(Codename206::NAME);
                         meter::draw(ui, &meters, &mut state.meter);
                         ui.separator();
-                        plot::draw(ui, &meters, &mut state.plot);
+                        // Gain curve (left, square) beside the scrolling plot (right, fills the rest).
+                        let selected = state.plot.selected;
+                        ui.horizontal_top(|ui| {
+                            ui.vertical(|ui| gain_curve::draw(ui, &params, selected, &meters));
+                            ui.vertical(|ui| plot::draw(ui, &meters, &mut state.plot));
+                        });
+                        ui.separator();
+                        crossover::draw(ui, &params, setter);
                         ui.separator();
                         // Global controls stacked vertically so they never overflow sideways.
                         egui::Grid::new("globals").num_columns(2).show(ui, |ui| {
-                            ui.label("Xover Lo/Mid");
-                            ui.add(widgets::ParamSlider::for_param(&params.crossover_low_hz, setter));
-                            ui.end_row();
-                            ui.label("Xover Mid/Hi");
-                            ui.add(widgets::ParamSlider::for_param(&params.crossover_high_hz, setter));
-                            ui.end_row();
                             ui.label("Look-ahead");
                             ui.add(widgets::ParamSlider::for_param(&params.look_ahead_ms, setter));
                             ui.end_row();

src/editor/plot.rs

@@ -7,7 +7,7 @@
 //! (peak-preserving); `window_s` (the flow speed) sets how many buckets span each column.
 
 use nih_plug::prelude::*;
-use nih_plug_egui::egui::{self, pos2, vec2, Align2, Color32, CornerRadius, FontId, Sense, Stroke};
+use nih_plug_egui::egui::{self, pos2, vec2, Align2, Color32, CornerRadius, FontId, Rect, Sense, Stroke};
 
 use super::METER_FLOOR_DB;
 use crate::meters::{Meters, BUCKET_HZ, NUM_CHANNELS};
@@ -26,6 +26,8 @@ struct PlotHistory {
     in_db: [[f32; PLOT_N]; NUM_CHANNELS],
     out_db: [[f32; PLOT_N]; NUM_CHANNELS],
     gr_db: [[f32; PLOT_N]; NUM_CHANNELS],
+    /// Per-column flag: the output limiter hit the ceiling somewhere in this column.
+    hit: [bool; PLOT_N],
     write: usize,
     len: usize,
 }
@@ -36,6 +38,7 @@ impl Default for PlotHistory {
             in_db: [[METER_FLOOR_DB; PLOT_N]; NUM_CHANNELS],
             out_db: [[METER_FLOOR_DB; PLOT_N]; NUM_CHANNELS],
             gr_db: [[0.0; PLOT_N]; NUM_CHANNELS],
+            hit: [false; PLOT_N],
             write: 0,
             len: 0,
         }
@@ -43,13 +46,14 @@ impl Default for PlotHistory {
 }
 
 impl PlotHistory {
-    /// Append one column of (in_db, out_db, gr_db) per channel.
+    /// Append one column of (in_db, out_db, gr_db) per channel, plus the ceiling-hit flag.
-    fn push(&mut self, samples: &[(f32, f32, f32); NUM_CHANNELS]) {
+    fn push(&mut self, samples: &[(f32, f32, f32); NUM_CHANNELS], hit: bool) {
         for i in 0..NUM_CHANNELS {
             self.in_db[i][self.write] = samples[i].0;
             self.out_db[i][self.write] = samples[i].1;
             self.gr_db[i][self.write] = samples[i].2;
         }
+        self.hit[self.write] = hit;
         self.write = (self.write + 1) % PLOT_N;
         self.len = (self.len + 1).min(PLOT_N);
     }
@@ -58,8 +62,8 @@ impl PlotHistory {
 /// GUI-side state for the plot: selected channel, history ring, ring-drain cursor, and the
 /// column being assembled from drained buckets.
 pub(super) struct PlotState {
-    /// Channel shown in the plot (0..NUM_CHANNELS: low/mid/high/all).
+    /// Channel shown in the plot (0..NUM_CHANNELS: low/mid/high/all). Also drives the gain curve.
-    selected: usize,
+    pub(super) selected: usize,
     history: PlotHistory,
     /// Seconds of history shown across the full plot width — the flow speed (smaller = faster).
     window_s: f64,
@@ -67,6 +71,8 @@ pub(super) struct PlotState {
     cursor: Option<u64>,
     /// Per-channel max accumulator (in_db, out_db, gr_db) for the column currently being built.
     col_acc: [(f32, f32, f32); NUM_CHANNELS],
+    /// Ceiling-hit flag accumulated for the column currently being built.
+    col_hit: bool,
     /// Buckets folded into the current column so far (fractional — a column may span <1 bucket).
     col_fill: f64,
 }
@@ -79,6 +85,7 @@ impl Default for PlotState {
             window_s: 5.0,
             cursor: None,
             col_acc: [(METER_FLOOR_DB, METER_FLOOR_DB, 0.0); NUM_CHANNELS],
+            col_hit: false,
             col_fill: 0.0,
         }
     }
@@ -97,17 +104,20 @@ pub(super) fn draw(ui: &mut egui::Ui, meters: &Meters, state: &mut PlotState) {
         let cursor = state.cursor.get_or_insert(w0);
         let history = &mut state.history;
         let col_acc = &mut state.col_acc;
+        let col_hit = &mut state.col_hit;
         let col_fill = &mut state.col_fill;
-        meters.scope.drain(cursor, |in_lin, out_lin, gr_db| {
+        meters.scope.drain(cursor, |in_lin, out_lin, gr_db, hit| {
             for ch in 0..NUM_CHANNELS {
                 col_acc[ch].0 = col_acc[ch].0.max(util::gain_to_db(in_lin[ch]));
                 col_acc[ch].1 = col_acc[ch].1.max(util::gain_to_db(out_lin[ch]));
                 col_acc[ch].2 = col_acc[ch].2.max(gr_db[ch]);
             }
+            *col_hit |= hit > 0.5;
             *col_fill += 1.0;
             while *col_fill >= buckets_per_col {
-                history.push(col_acc);
+                history.push(col_acc, *col_hit);
                 *col_acc = [(METER_FLOOR_DB, METER_FLOOR_DB, 0.0); NUM_CHANNELS];
+                *col_hit = false;
                 *col_fill -= buckets_per_col;
             }
         });
@@ -133,6 +143,7 @@ pub(super) fn draw(ui: &mut egui::Ui, meters: &Meters, state: &mut PlotState) {
             // Cadence changed: start the history fresh so the time axis is consistent.
             state.history = PlotHistory::default();
             state.col_acc = [(METER_FLOOR_DB, METER_FLOOR_DB, 0.0); NUM_CHANNELS];
+            state.col_hit = false;
             state.col_fill = 0.0;
         }
         ui.separator();
@@ -197,5 +208,19 @@ pub(super) fn draw(ui: &mut egui::Ui, meters: &Meters, state: &mut PlotState) {
         draw_series(&state.history.out_db[c], &|db| db, COLOR_OUT, true);
         // GR hangs from the 0 dB line: a reduction of X dB is drawn at the -X gridline.
         draw_series(&state.history.gr_db[c], &|gr| -gr, COLOR_GR, false);
+
+        // Ceiling-hit markers: a short red tick at the TOP for any column where the output limiter
+        // hit the ceiling (global — shown on every channel's view). One column wide, so runs of
+        // hits merge into a continuous segment and a lone hit is just a dot. Nothing otherwise.
+        let dx = width / (PLOT_N - 1) as f32;
+        let marker = Color32::from_rgb(235, 45, 45);
+        for k in 0..len {
+            let idx = (write + PLOT_N - len + k) % PLOT_N;
+            if state.history.hit[idx] {
+                let pos = (PLOT_N - len + k) as f32 / (PLOT_N - 1) as f32;
+                let x = left + pos * width;
+                p.rect_filled(Rect::from_min_max(pos2(x, top), pos2(x + dx, top + 3.0)), CornerRadius::ZERO, marker);
+            }
+        }
     }
 }

src/lib.rs

@@ -46,11 +46,16 @@ struct Codename206 {
     scope_in: [f32; 4],
     scope_out: [f32; 4],
     scope_gr: [f32; 4],
+    /// Max output-limiter gain reduction seen in the current bucket (for the ceiling-hit marker).
+    scope_hit: f32,
     /// Samples accumulated into the current bucket, and the bucket length (= sample_rate / BUCKET_HZ).
     scope_samples: usize,
     scope_bucket_len: usize,
 }
 
+/// Limiter gain reduction (dB) above which a plot bucket is flagged as hitting the ceiling.
+const CEILING_HIT_GR_DB: f32 = 0.1;
+
 impl Default for Codename206 {
     fn default() -> Self {
         Self {
@@ -64,6 +69,7 @@ impl Default for Codename206 {
             scope_in: [0.0; 4],
             scope_out: [0.0; 4],
             scope_gr: [0.0; 4],
+            scope_hit: 0.0,
             scope_samples: 0,
             scope_bucket_len: 1,
         }
@@ -164,6 +170,7 @@ impl Plugin for Codename206 {
         self.scope_in = [0.0; 4];
         self.scope_out = [0.0; 4];
         self.scope_gr = [0.0; 4];
+        self.scope_hit = 0.0;
         self.scope_samples = 0;
     }
 
@@ -204,6 +211,7 @@ impl Plugin for Codename206 {
         let num_samples = buffer.samples();
         let mut lvl_l = [0.0f32; meters::NUM_CHANNELS];
         let mut lvl_r = [0.0f32; meters::NUM_CHANNELS];
+        let mut inp = [0.0f32; meters::NUM_CHANNELS]; // mono input level (detector / gain-curve x)
         let mut gr = [0.0f32; meters::NUM_CHANNELS];
         let mut lim_gr = 0.0f32;
 
@@ -237,6 +245,9 @@ impl Plugin for Codename206 {
                     band_in[b][ch] *= pre;
                 }
                 band_set[b].makeup_db = band_params[b].makeup_db.smoothed.next();
+                band_set[b].mix = band_params[b].mix.smoothed.next();
+                band_set[b].low_slope = band_params[b].low_slope.smoothed.next();
+                band_set[b].low_curve = band_params[b].low_curve.smoothed.next();
                 self.comps[b].process(&band_in[b][..n], &mut band_out[b][..n], &band_set[b]);
                 for ch in 0..n {
                     summed[ch] += band_out[b][ch];
@@ -245,7 +256,9 @@ impl Plugin for Codename206 {
                     let in_mono = band_in[b][0].abs().max(band_in[b][r].abs());
                     let out_l = band_out[b][0].abs();
                     let out_r = band_out[b][r].abs();
-                    let g = if band_set[b].bypass { 0.0 } else { self.comps[b].gain_reduction_db() };
+                    // Wet gain reduction (what the comp computes), independent of the mix.
+                    let g = self.comps[b].gain_reduction_db();
+                    inp[b] = inp[b].max(in_mono);
                     lvl_l[b] = lvl_l[b].max(out_l);
                     lvl_r[b] = lvl_r[b].max(out_r);
                     gr[b] = gr[b].max(g);
@@ -263,6 +276,9 @@ impl Plugin for Codename206 {
                 summed[ch] *= all_pre;
             }
             all_set.makeup_db = self.params.all.makeup_db.smoothed.next();
+            all_set.mix = self.params.all.mix.smoothed.next();
+            all_set.low_slope = self.params.all.low_slope.smoothed.next();
+            all_set.low_curve = self.params.all.low_curve.smoothed.next();
             self.comps[ALL].process(&summed[..n], &mut out_frame[..n], &all_set);
 
             // Output brickwall limiter.
@@ -272,7 +288,8 @@ impl Plugin for Codename206 {
                 let in_mono = summed[0].abs().max(summed[r].abs());
                 let out_l = out_frame[0].abs();
                 let out_r = out_frame[r].abs();
-                let g = if all_set.bypass { 0.0 } else { self.comps[ALL].gain_reduction_db() };
+                let g = self.comps[ALL].gain_reduction_db();
+                inp[ALL] = inp[ALL].max(in_mono);
                 lvl_l[ALL] = lvl_l[ALL].max(out_l);
                 lvl_r[ALL] = lvl_r[ALL].max(out_r);
                 gr[ALL] = gr[ALL].max(g);
@@ -284,14 +301,17 @@ impl Plugin for Codename206 {
                     self.scope_in[ALL] = self.scope_in[ALL].max(in_mono);
                     self.scope_out[ALL] = self.scope_out[ALL].max(out_l.max(out_r));
                     self.scope_gr[ALL] = self.scope_gr[ALL].max(g);
+                    self.scope_hit = self.scope_hit.max(self.limiter.gain_reduction_db());
 
                     // Emit a plot bucket every scope_bucket_len samples (~BUCKET_HZ).
                     self.scope_samples += 1;
                     if self.scope_samples >= self.scope_bucket_len {
-                        self.meters.scope.push(&self.scope_in, &self.scope_out, &self.scope_gr);
+                        let hit = if self.scope_hit > CEILING_HIT_GR_DB { 1.0 } else { 0.0 };
+                        self.meters.scope.push(&self.scope_in, &self.scope_out, &self.scope_gr, hit);
                         self.scope_in = [0.0; meters::NUM_CHANNELS];
                         self.scope_out = [0.0; meters::NUM_CHANNELS];
                         self.scope_gr = [0.0; meters::NUM_CHANNELS];
+                        self.scope_hit = 0.0;
                         self.scope_samples = 0;
                     }
                 }
@@ -310,6 +330,7 @@ impl Plugin for Codename206 {
             for i in 0..meters::NUM_CHANNELS {
                 meters::decay_store(&self.meters.level_l[i], lvl_l[i], w);
                 meters::decay_store(&self.meters.level_r[i], lvl_r[i], w);
+                meters::decay_store(&self.meters.input_level[i], inp[i], w);
                 meters::decay_store(&self.meters.gain_reduction_db[i], gr[i], w);
             }
             meters::decay_store(&self.meters.limiter_gr_db, lim_gr, w);

src/meters.rs

@@ -26,6 +26,9 @@ pub struct Meters {
     pub level_l: [AtomicF32; NUM_CHANNELS],
     /// Right output level per channel (== left for mono signals).
     pub level_r: [AtomicF32; NUM_CHANNELS],
+    /// Mono **input** level per channel (post pre-gain = what the compressor detects). Drives the
+    /// gain-curve operating-point fill. Peak-with-decay.
+    pub input_level: [AtomicF32; NUM_CHANNELS],
     /// Compressor gain reduction per channel in **dB (>= 0)**. Mono by design — detection is
     /// stereo-linked, so the same gain applies to both channels.
     pub gain_reduction_db: [AtomicF32; NUM_CHANNELS],
@@ -40,6 +43,7 @@ impl Default for Meters {
         Self {
             level_l: std::array::from_fn(|_| AtomicF32::new(0.0)),
             level_r: std::array::from_fn(|_| AtomicF32::new(0.0)),
+            input_level: std::array::from_fn(|_| AtomicF32::new(0.0)),
             gain_reduction_db: std::array::from_fn(|_| AtomicF32::new(0.0)),
             limiter_gr_db: AtomicF32::new(0.0),
             scope: ScopeRing::default(),
@@ -55,6 +59,7 @@ impl Meters {
         for i in 0..NUM_CHANNELS {
             self.level_l[i].store(0.0, Ordering::Relaxed);
             self.level_r[i].store(0.0, Ordering::Relaxed);
+            self.input_level[i].store(0.0, Ordering::Relaxed);
             self.gain_reduction_db[i].store(0.0, Ordering::Relaxed);
         }
         self.limiter_gr_db.store(0.0, Ordering::Relaxed);
@@ -85,6 +90,9 @@ pub struct ScopeRing {
     in_lin: Vec<AtomicF32>,
     out_lin: Vec<AtomicF32>,
     gr_db: Vec<AtomicF32>,
+    /// Per-bucket (not per-channel) flag: `1.0` if the output limiter hit the ceiling in this
+    /// bucket, else `0.0`. Indexed by `bucket_index % RING_N`.
+    hit: Vec<AtomicF32>,
     /// Monotonic count of buckets ever written.
     write: AtomicU64,
 }
@@ -92,7 +100,13 @@ pub struct ScopeRing {
 impl Default for ScopeRing {
     fn default() -> Self {
         let make = || (0..RING_N * NUM_CHANNELS).map(|_| AtomicF32::new(0.0)).collect();
-        Self { in_lin: make(), out_lin: make(), gr_db: make(), write: AtomicU64::new(0) }
+        Self {
+            in_lin: make(),
+            out_lin: make(),
+            gr_db: make(),
+            hit: (0..RING_N).map(|_| AtomicF32::new(0.0)).collect(),
+            write: AtomicU64::new(0),
+        }
     }
 }
 
@@ -103,14 +117,17 @@ impl ScopeRing {
         in_lin: &[f32; NUM_CHANNELS],
         out_lin: &[f32; NUM_CHANNELS],
         gr_db: &[f32; NUM_CHANNELS],
+        hit: f32,
     ) {
         let w = self.write.load(Ordering::Relaxed); // producer is the sole writer of `write`
-        let base = (w as usize % RING_N) * NUM_CHANNELS;
+        let slot = w as usize % RING_N;
+        let base = slot * NUM_CHANNELS;
         for ch in 0..NUM_CHANNELS {
             self.in_lin[base + ch].store(in_lin[ch], Ordering::Relaxed);
             self.out_lin[base + ch].store(out_lin[ch], Ordering::Relaxed);
             self.gr_db[base + ch].store(gr_db[ch], Ordering::Relaxed);
         }
+        self.hit[slot].store(hit, Ordering::Relaxed);
         // Publish the bucket: the Release pairs with the consumer's Acquire so the stores above are
         // visible before the new count.
         self.write.store(w + 1, Ordering::Release);
@@ -121,7 +138,7 @@ impl ScopeRing {
     pub fn drain(
         &self,
         cursor: &mut u64,
-        mut on_bucket: impl FnMut(&[f32; NUM_CHANNELS], &[f32; NUM_CHANNELS], &[f32; NUM_CHANNELS]),
+        mut on_bucket: impl FnMut(&[f32; NUM_CHANNELS], &[f32; NUM_CHANNELS], &[f32; NUM_CHANNELS], f32),
     ) {
         let w = self.write.load(Ordering::Acquire);
         if *cursor > w {
@@ -136,13 +153,15 @@ impl ScopeRing {
         let mut out_buf = [0.0f32; NUM_CHANNELS];
         let mut gr_buf = [0.0f32; NUM_CHANNELS];
         while *cursor < w {
-            let base = (*cursor as usize % RING_N) * NUM_CHANNELS;
+            let slot = *cursor as usize % RING_N;
+            let base = slot * NUM_CHANNELS;
             for ch in 0..NUM_CHANNELS {
                 in_buf[ch] = self.in_lin[base + ch].load(Ordering::Relaxed);
                 out_buf[ch] = self.out_lin[base + ch].load(Ordering::Relaxed);
                 gr_buf[ch] = self.gr_db[base + ch].load(Ordering::Relaxed);
             }
-            on_bucket(&in_buf, &out_buf, &gr_buf);
+            let hit = self.hit[slot].load(Ordering::Relaxed);
+            on_bucket(&in_buf, &out_buf, &gr_buf, hit);
             *cursor += 1;
         }
     }

src/params.rs

@@ -68,14 +68,22 @@ pub struct CompressorParams {
     pub ratio: FloatParam,
     #[id = "knee"]
     pub knee_db: FloatParam,
+    /// Low shaper slope at the silence floor (1 = unity; >1 fans up/boost, <1 fans down/cut).
+    #[id = "lowslope"]
+    pub low_slope: FloatParam,
+    /// Low shaper curvature (−1..1): bipolar mid-bulge, 0 = straight. +bulges up (boost quiet
+    /// middle), − bulges down (suppress). Endpoints (silence + knee) stay fixed.
+    #[id = "lowcurve"]
+    pub low_curve: FloatParam,
     #[id = "attack"]
     pub attack_ms: FloatParam,
     #[id = "release"]
     pub release_ms: FloatParam,
     #[id = "makeup"]
     pub makeup_db: FloatParam,
-    #[id = "bypass"]
+    /// Dry/wet mix (parallel compression). 100% = fully processed, 0% = dry (a clean bypass).
-    pub bypass: BoolParam,
+    #[id = "mix"]
+    pub mix: FloatParam,
 }
 
 impl Default for Codename206Params {
@@ -163,10 +171,23 @@ impl Default for CompressorParams {
                 s.split(':').next().and_then(|x| x.trim().parse::<f32>().ok())
             })),
 
-            knee_db: FloatParam::new("Knee", 6.0, FloatRange::Linear { min: 0.0, max: 24.0 })
+            knee_db: FloatParam::new("Knee", 6.0, FloatRange::Linear { min: 0.0, max: 30.0 })
                 .with_unit(" dB")
                 .with_value_to_string(formatters::v2s_f32_rounded(1)),
 
+            low_slope: FloatParam::new(
+                "Low Slope",
+                1.0,
+                FloatRange::Skewed { min: 0.5, max: 3.0, factor: FloatRange::skew_factor(-1.0) },
+            )
+            .with_smoother(SmoothingStyle::Linear(20.0))
+            .with_value_to_string(formatters::v2s_f32_rounded(2)),
+
+            low_curve: FloatParam::new("Low Curve", 0.0, FloatRange::Linear { min: -1.0, max: 1.0 })
+                .with_smoother(SmoothingStyle::Linear(20.0))
+                .with_value_to_string(formatters::v2s_f32_percentage(0))
+                .with_string_to_value(formatters::s2v_f32_percentage()),
+
             attack_ms: FloatParam::new(
                 "Attack",
                 10.0,
@@ -188,7 +209,10 @@ impl Default for CompressorParams {
                 .with_unit(" dB")
                 .with_value_to_string(formatters::v2s_f32_rounded(1)),
 
-            bypass: BoolParam::new("Bypass", false),
+            mix: FloatParam::new("Mix", 1.0, FloatRange::Linear { min: 0.0, max: 1.0 })
+                .with_smoother(SmoothingStyle::Linear(20.0))
+                .with_value_to_string(formatters::v2s_f32_percentage(0))
+                .with_string_to_value(formatters::s2v_f32_percentage()),
         }
     }
 }
@@ -203,11 +227,13 @@ pub fn build_settings(
         threshold_db: p.threshold_db.value(),
         ratio: p.ratio.value(),
         knee_db: p.knee_db.value(),
+        low_slope: p.low_slope.value(),
+        low_curve: p.low_curve.value(),
         attack_coef: Compressor::time_to_coef(p.attack_ms.value(), sample_rate),
         release_coef: Compressor::time_to_coef(p.release_ms.value(), sample_rate),
         makeup_db: 0.0,
         lookahead_samples: lookahead,
         use_rms: p.detection.value() == DetectionMode::Rms,
-        bypass: p.bypass.value(),
+        mix: p.mix.value(),
     }
 }