feat(ballast): add Ballast switch-up leveller

Ballast gives every part of a bassline one gain that brings it to the target
loudness, with no compression inside a part. Parts start at note starts,
detected from the audio or taken from MIDI, or on the host's beat grid, so a
patch change on the same note counts too.

- Loudness is K-weighted over each part's first 100 ms, in 10 ms blocks with
  a relative gate, and every part is weighted from rest so the last part does
  not ring into it.
- The audio path is delayed by the tracker's lookahead, the window and a
  5 ms glide, so each gain is in place on its part's first sample.
- Learn takes the next part's loudness as the target. Amount, Range, Measure
  from (leave the sub out), Gate, Output, Bypass.
- Editor shows the last 32 parts in and out, the target, and the spread of
  the last 16 parts.
- Registered in the catalog, workflows, editor-check, README, chain and
  development docs, and the website copy.

tools/editor-check/src/main.rs

@@ -12,13 +12,13 @@ fn main() {
         .unwrap_or("rivet");
     if ![
         "rivet", "patina", "anvil", "crucible", "lathe", "temper", "weld", "knurl", "planish",
-        "braze", "quench",
+        "braze", "quench", "ballast",
     ]
     .contains(&plugin)
     {
         eprintln!(
             "Use --plugin rivet, patina, anvil, crucible, lathe, temper, weld, knurl, planish, \
-             braze or quench"
+             braze, quench or ballast"
         );
         std::process::exit(2);
     }
@@ -33,7 +33,10 @@ fn main() {
     let planish = plugin == "planish";
     let braze = plugin == "braze";
     let quench = plugin == "quench";
-    let (width, height) = if quench {
+    let ballast = plugin == "ballast";
+    let (width, height) = if ballast {
+        (ballast_ui::WIDTH, ballast_ui::HEIGHT)
+    } else if quench {
         (quench_ui::WIDTH, quench_ui::HEIGHT)
     } else if braze {
         (braze_ui::WIDTH, braze_ui::HEIGHT)
@@ -253,6 +256,37 @@ fn main() {
         }
         quench_state.accept_frame(engine.take_analyzer());
     }
+    let mut ballast_settings = ballast_core::Settings {
+        segment: ballast_core::Segment::Grid,
+        target: -16.,
+        ..Default::default()
+    };
+    let mut ballast_state = ballast_ui::State::default();
+    if ballast {
+        // A switch-up every quarter at 140 BPM, cycling four patches of different loudness.
+        let mut engine = ballast_core::Engine::new(48000., 2).unwrap();
+        engine.set_settings(ballast_settings).unwrap();
+        let mut saw = common_dsp::Saw::new(48000., 43.65);
+        let quarter = 48000. * 60. / 140.;
+        for i in 0..48000 * 9 {
+            if i % 512 == 0 {
+                engine.set_transport(Some(140.), Some(i as f64 / 48000. * 140. / 60.));
+            }
+            let part = (i as f32 / quarter) as usize;
+            let s = saw.sample();
+            let x = match part % 4 {
+                0 => (s * 4.).tanh() * 0.6,
+                1 => s * 0.15,
+                2 => (s * 2.).tanh() * 0.35,
+                _ => (s * 8.).tanh() * 0.9,
+            };
+            engine.process_sample([x, x]);
+            if i % 1600 == 0 {
+                ballast_state.accept_frame(engine.take_analyzer());
+            }
+        }
+        ballast_state.accept_frame(engine.take_analyzer());
+    }
     let mut weld_settings = weld_core::Settings::default();
     let mut weld_state = weld_ui::State::default();
     if weld {
@@ -382,7 +416,9 @@ fn main() {
     let session_motif = session.motifs[0].id;
     shared.replace(session).unwrap();
     let ctx = egui::Context::default();
-    if quench {
+    if ballast {
+        ballast_ui::style(&ctx);
+    } else if quench {
         quench_ui::style(&ctx);
     } else if braze {
         braze_ui::style(&ctx);
@@ -425,7 +461,9 @@ fn main() {
             },
             |ui| {
                 egui::CentralPanel::default().show(ui, |ui| {
-                    if quench {
+                    if ballast {
+                        ballast_ui::show(ui, &mut ballast_settings, &mut ballast_state);
+                    } else if quench {
                         quench_ui::show(ui, &mut quench_settings, &mut quench_state);
                     } else if braze {
                         braze_ui::show(ui, &mut braze_settings, &mut braze_state);