sound: macOS-like two-hit shutter, Balatro clatter, bell arpeggio tail, even loudness, volume 0.9

README.md

@@ -116,7 +116,7 @@ backend = "builtin"   # or "satty"
 
 [sound]
 enabled = true
-volume = 0.6
+volume = 0.9
 combo_reset_secs = 5
 ```
 

docs/test-checklist.md

@@ -142,7 +142,7 @@ image, a cancel brought the thumbnail back, and a swipe still dismissed it.
 - [ ] Region: while dragging, a `W × H` label follows the pointer (physical pixels, same as the saved PNG), flipping near the edges.
 - [ ] Shift locks the dimension you move first; Alt grows from the centre; Space held moves the selection, and after letting go resizing continues without a jump; Space before a drag still switches to window mode.
 - [ ] `[capture] window_shadow = true`: window shots get a soft shadow following the rounded corners; preview, clipboard and file all have it.
-- [ ] Shots in quick succession play sounds 1 → 5 getting faster and brighter, then 6, 7, 6, 7 rising endlessly; after a 5 s pause it starts at 1 again. `valw __combo-demo` plays the whole sequence for tuning.
+- [ ] Each shot is a two-hit "ka-chunk" (macOS-like) with a metallic clatter that grows from shot 2; shots in quick succession play sounds 1 → 5 getting faster and brighter, then 6, 7, 6, 7 (a climbing bell arpeggio over a glide) rising endlessly; every shot about as loud; after a 5 s pause it starts at 1 again. `valw __combo-demo` plays the whole sequence for tuning.
 - [ ] `[sound] enabled = false`, `volume`, `combo_reset_secs` take effect; the toolbar's Play sound option overrides the config; no `pw-play` → no sound, capture still works (warning in the log).
 
 ### Known minors (deferred from the polish review)
@@ -152,7 +152,6 @@ image, a cancel brought the thumbnail back, and a swipe still dismissed it.
 - `__combo-demo` and a capture regenerating the same WAV at once can race on the temp file (one silent shot).
 - Without `XDG_RUNTIME_DIR` the sound cache and combo state in `/tmp` are shared between users.
 - `pipewire` on the wrapper's PATH adds its whole closure to the package.
-- Tuning by ear: shots 6–7 are about 9–10 dB louder than 1–5; adjust with `__combo-demo`.
 
 ## home-manager module
 

src/config.rs

@@ -84,7 +84,7 @@ impl Default for Sound {
     fn default() -> Self {
         Self {
             enabled: true,
-            volume: 0.6,
+            volume: 0.9,
             combo_reset_secs: 5,
         }
     }
@@ -292,7 +292,7 @@ mod tests {
     fn sound_defaults_and_bounds() {
         let s = Config::default().sound;
         assert!(s.enabled);
-        assert_eq!((s.volume, s.combo_reset_secs), (0.6, 5));
+        assert_eq!((s.volume, s.combo_reset_secs), (0.9, 5));
         for bad in ["volume = 1.5", "volume = nan", "volume = -0.1"] {
             let err = parse(&format!("[sound]\n{bad}\n")).unwrap_err();
             assert_eq!(

src/sound/synth.rs

@@ -1,11 +1,33 @@
 //! The shutter sounds, synthesised: no samples, no licences.
+//!
+//! A two-hit mechanical shutter with a pitched body ("ka-chunk"), a metallic
+//! clatter that grows with the combo, and on shots 6 and 7 a bell
+//! arpeggio over a Shepard glide that seems to rise forever.
 
 use std::f32::consts::TAU;
 
 pub const RATE: u32 = 44_100;
 const SPEEDS: [f32; 5] = [1.00, 1.12, 1.25, 1.40, 1.60];
 const LOOP_SPEED: f32 = 1.80;
-const GLIDE_SECS: f32 = 0.4;
+/// The shutter's second hit, after the first.
+const GAP: f32 = 0.150;
+/// How much clatter each of shots 1–5 carries (6 and 7 take the last).
+const CLATTER: [f32; 5] = [0.0, 0.08, 0.15, 0.22, 0.30];
+const CLATTER_HZ: f32 = 900.0;
+/// The clatter's partials: (ratio to its fundamental, amplitude, decay s).
+const CLATTER_PARTIALS: [(f32, f32, f32); 4] = [
+    (1.0, 1.0, 0.060),
+    (1.50, 0.7, 0.050),
+    (4.40, 0.9, 0.030),
+    (22.1, 0.25, 0.012),
+];
+/// Every sound is scaled to this short-term loudness (RMS).
+const LOUDNESS: f32 = 0.30;
+/// The tail of shots 6 and 7, relative to [`LOUDNESS`].
+const TAIL_LOUDNESS: f32 = 0.8;
+const TAIL_SECS: f32 = 0.30;
+const ARPEGGIO_NOTES: usize = 3;
+const ARPEGGIO_STEP: f32 = 0.075;
 /// The Shepard tone: octave-spaced partials from BASE Hz under a bell
 /// centred on CENTRE Hz (log scale).
 const BASE: f32 = 55.0;
@@ -29,32 +51,138 @@ fn secs(n: usize) -> f32 {
     n as f32 / RATE as f32
 }
 
-/// A two-part mechanical "tak-shk", about 150 ms.
-pub fn shutter() -> Vec<f32> {
-    let len = (0.150 * RATE as f32) as usize;
-    let mut noise = Noise(0x1234_5678);
-    let (mut low, mut high_prev, mut high) = (0.0f32, 0.0f32, 0.0f32);
-    let mut out = Vec::with_capacity(len);
-    for i in 0..len {
-        let t = secs(i);
-        let n = noise.next();
-        // Click: bright, 0.5 ms attack, ~6 ms decay.
-        let click = n * (t / 0.0005).min(1.0) * (-t / 0.006).exp();
-        // "shk": band-passed noise from 60 ms, ~30 ms decay, softer.
-        low += 0.25 * (n - low);
-        high = 0.9 * (high + low - high_prev);
-        high_prev = low;
-        let u = t - 0.060;
-        let shk = if u >= 0.0 {
-            high * 0.9 * (u / 0.002).min(1.0) * (-u / 0.03).exp()
-        } else {
-            0.0
-        };
-        out.push(click * 0.8 + shk);
+fn samples(secs_long: f32) -> usize {
+    (secs_long * RATE as f32) as usize
+}
+
+/// Adds `src` times `gain` into `dst` from `at` seconds, growing `dst`.
+fn mix(dst: &mut Vec<f32>, src: &[f32], at: f32, gain: f32) {
+    let start = samples(at);
+    if dst.len() < start + src.len() {
+        dst.resize(start + src.len(), 0.0);
     }
-    fade_out(&mut out, 0.010);
-    normalise(&mut out, 0.9);
-    out
+    for (d, s) in dst[start..].iter_mut().zip(src) {
+        *d += s * gain;
+    }
+}
+
+/// A damped resonance at `f` Hz with a small downward pitch blip and an
+/// inharmonic overtone: the body of a hit.
+fn thunk(f: f32, decay: f32) -> Vec<f32> {
+    let (mut p1, mut p2) = (0.0f32, 0.0f32);
+    (0..samples(decay * 7.0))
+        .map(|i| {
+            let t = secs(i);
+            let env = (t / 0.0008).min(1.0) * (-t / decay).exp();
+            let fi = f * (1.0 + 0.25 * (-t / 0.006).exp());
+            p1 = (p1 + TAU * fi / RATE as f32) % TAU;
+            p2 = (p2 + TAU * fi * 2.76 / RATE as f32) % TAU;
+            env * (p1.sin() + 0.35 * p2.sin() * (-t / (decay * 0.4)).exp())
+        })
+        .collect()
+}
+
+/// A burst of high-passed noise; `bright` (0–1) tames the very top.
+fn burst(decay: f32, seed: u32, bright: f32) -> Vec<f32> {
+    let mut noise = Noise(seed);
+    let (mut low, mut high_prev, mut high) = (0.0f32, 0.0f32, 0.0f32);
+    (0..samples(decay * 7.0))
+        .map(|i| {
+            let t = secs(i);
+            low += bright * (noise.next() - low);
+            high = 0.92 * (high + low - high_prev);
+            high_prev = low;
+            high * (t / 0.0005).min(1.0) * (-t / decay).exp()
+        })
+        .collect()
+}
+
+fn hit(f: f32, seed: u32, noise: f32) -> Vec<f32> {
+    let mut s = thunk(f, 0.035);
+    mix(&mut s, &burst(0.018, seed, 0.9), 0.0, noise);
+    s
+}
+
+/// The mechanical "ka-chunk": two hits [`GAP`] apart, the second a fifth up.
+pub fn shutter() -> Vec<f32> {
+    let mut s = hit(260.0, 0x0123_4567, 0.55);
+    mix(&mut s, &hit(390.0, 0x0765_4321, 0.65), GAP, 1.1);
+    s
+}
+
+/// One metallic strike of the clatter at `f` Hz.
+fn ping(f: f32) -> Vec<f32> {
+    let mut phases = [0f32; CLATTER_PARTIALS.len()];
+    (0..samples(0.35))
+        .map(|i| {
+            let t = secs(i);
+            let mut v = 0.0;
+            for (p, (ratio, amp, decay)) in phases.iter_mut().zip(CLATTER_PARTIALS) {
+                *p = (*p + TAU * f * ratio / RATE as f32) % TAU;
+                v += amp * p.sin() * (-t / decay).exp();
+            }
+            v * (t / 0.0004).min(1.0)
+        })
+        .collect()
+}
+
+/// A coin-like clatter: four quick, fading metallic strikes.
+fn clatter(f: f32) -> Vec<f32> {
+    let mut s = Vec::new();
+    for (j, (at, amp)) in [(0.0, 1.0), (0.035, 0.7), (0.080, 0.5), (0.135, 0.35)]
+        .into_iter()
+        .enumerate()
+    {
+        mix(&mut s, &ping(f * (1.0 + 0.012 * j as f32)), at, amp);
+        mix(
+            &mut s,
+            &burst(0.006, 0x9e37_79b9 + j as u32, 0.6),
+            at,
+            0.35 * amp,
+        );
+    }
+    s
+}
+
+/// The shutter with clatter `level` (1–5): more of it, and two semitones
+/// higher, each level.
+fn shot(level: usize) -> Vec<f32> {
+    let mut s = shutter();
+    let amount = CLATTER[level - 1];
+    if amount > 0.0 {
+        let f = CLATTER_HZ * 2f32.powf((level - 1) as f32 * 2.0 / 12.0);
+        mix(&mut s, &clatter(f), GAP, amount);
+    }
+    s
+}
+
+/// The loudest 20 ms of `s` (RMS): what the ear compares between shots.
+pub fn loudness(s: &[f32]) -> f32 {
+    let window = samples(0.020).min(s.len()).max(1);
+    let mut sum: f32 = s[..window.min(s.len())].iter().map(|v| v * v).sum();
+    let mut best = sum;
+    for i in window..s.len() {
+        sum += s[i] * s[i] - s[i - window] * s[i - window];
+        best = best.max(sum);
+    }
+    (best.max(0.0) / window as f32).sqrt()
+}
+
+/// Scales `s` to `target` loudness through a soft limiter, keeps the peak
+/// under 0.95 and fades the end.
+fn finish(mut s: Vec<f32>, target: f32) -> Vec<f32> {
+    let gain = target / loudness(&s).max(1e-9);
+    for v in s.iter_mut() {
+        *v = (*v * gain * 1.2).tanh() / 1.2;
+    }
+    let max = s.iter().fold(0.0f32, |m, v| m.max(v.abs()));
+    if max > 0.95 {
+        for v in s.iter_mut() {
+            *v *= 0.95 / max;
+        }
+    }
+    fade_out(&mut s, 0.010);
+    s
 }
 
 /// `samples` played `factor` times faster (shorter and higher).
@@ -106,14 +234,50 @@ pub fn glide(from: f32, to: f32, secs_long: f32) -> Vec<f32> {
     out
 }
 
+/// One bell note of the Shepard scale at `position` octaves: octave
+/// partials with a short metallic overtone.
+fn bell(position: f32) -> Vec<f32> {
+    let partials = partials(position);
+    let mut phases = vec![(0f32, 0f32); partials.len()];
+    (0..samples(0.16))
+        .map(|i| {
+            let t = secs(i);
+            let mut v = 0.0;
+            for ((p, q), (f, a)) in phases.iter_mut().zip(&partials) {
+                *p = (*p + TAU * f / RATE as f32) % TAU;
+                *q = (*q + TAU * f * 4.4 / RATE as f32) % TAU;
+                v += a * (p.sin() + 0.25 * q.sin() * (-t / 0.015).exp());
+            }
+            v * (t / 0.0015).min(1.0) * (-t / 0.05).exp()
+        })
+        .collect()
+}
+
+/// [`ARPEGGIO_NOTES`] bell notes climbing from `from` towards `to`
+/// octaves, over a quiet Shepard glide.
+fn tail(from: f32, to: f32) -> Vec<f32> {
+    let mut notes = Vec::new();
+    for j in 0..ARPEGGIO_NOTES {
+        let position = from + (to - from) * j as f32 / ARPEGGIO_NOTES as f32;
+        mix(&mut notes, &bell(position), j as f32 * ARPEGGIO_STEP, 1.0);
+    }
+    let pad = glide(from, to, TAIL_SECS);
+    let gain = 0.45 / loudness(&pad);
+    let mut s: Vec<f32> = pad.iter().map(|v| v * gain).collect();
+    mix(&mut s, &notes, 0.0, 1.0 / loudness(&notes));
+    s
+}
+
 /// The sound for shot `n` of a combo (1–7).
 pub fn sound(n: u8) -> Vec<f32> {
     match n {
-        1..=5 => speed(&shutter(), SPEEDS[n as usize - 1]),
+        1..=5 => finish(speed(&shot(n as usize), SPEEDS[n as usize - 1]), LOUDNESS),
         6 | 7 => {
-            let mut s = speed(&shutter(), LOOP_SPEED);
+            let mut s = finish(speed(&shot(5), LOOP_SPEED), LOUDNESS);
             let half = if n == 6 { (0.0, 0.5) } else { (0.5, 1.0) };
-            s.extend(glide(half.0, half.1, GLIDE_SECS));
+            let t = tail(half.0, half.1);
+            let gain = LOUDNESS * TAIL_LOUDNESS / loudness(&t);
+            s.extend(t.iter().map(|v| v * gain));
             s
         }
         _ => sound(1),
@@ -175,15 +339,48 @@ mod tests {
         s.iter().fold(0.0, |m, v| m.max(v.abs()))
     }
 
+    fn rms(s: &[f32], from_ms: f32, to_ms: f32) -> f32 {
+        let at = |ms: f32| ((ms / 1000.0 * RATE as f32) as usize).min(s.len());
+        let seg = &s[at(from_ms)..at(to_ms)];
+        (seg.iter().map(|v| v * v).sum::<f32>() / seg.len().max(1) as f32).sqrt()
+    }
+
     #[test]
-    fn the_shutter_is_short_and_never_clips() {
+    fn the_shutter_is_two_hits_and_never_clips() {
         let s = shutter();
         let ms = s.len() as f32 * 1000.0 / RATE as f32;
-        assert!((140.0..=160.0).contains(&ms), "{ms} ms");
-        assert!(peak(&s) <= 0.95 && peak(&s) > 0.3);
+        assert!((300.0..=450.0).contains(&ms), "{ms} ms");
+        let (first, between, second) = (
+            rms(&s, 0.0, 20.0),
+            rms(&s, 115.0, 140.0),
+            rms(&s, 150.0, 170.0),
+        );
+        assert!(first > 3.0 * between, "{first} vs {between}");
+        assert!(
+            second > 3.0 * between,
+            "a second hit at 150 ms: {second} vs {between}"
+        );
         assert!(s.last().unwrap().abs() < 0.01, "ends quietly (no pop)");
     }
 
+    #[test]
+    fn every_shot_is_about_as_loud() {
+        let db: Vec<f32> = (1..=7)
+            .map(|n| 20.0 * loudness(&sound(n)).log10())
+            .collect();
+        let (lo, hi) = db
+            .iter()
+            .fold((f32::MAX, f32::MIN), |(lo, hi), v| (lo.min(*v), hi.max(*v)));
+        assert!(hi - lo < 1.5, "{db:?}");
+    }
+
+    #[test]
+    fn every_shot_ends_quietly() {
+        for n in 1..=7 {
+            assert!(sound(n).last().unwrap().abs() < 0.01, "sound {n} pops");
+        }
+    }
+
     #[test]
     fn faster_is_shorter() {
         let s = shutter();
@@ -192,8 +389,16 @@ mod tests {
 
     #[test]
     fn sounds_escalate_then_loop() {
-        let lens: Vec<usize> = (1..=5).map(|n| sound(n).len()).collect();
-        assert!(lens.windows(2).all(|w| w[1] < w[0]), "{lens:?}");
+        assert!(SPEEDS.windows(2).all(|w| w[1] > w[0]) && LOOP_SPEED > SPEEDS[4]);
+        for n in 1..=5u8 {
+            let s = sound(n);
+            let at = GAP * 1000.0 / SPEEDS[n as usize - 1];
+            let (before, hit) = (rms(&s, at - 25.0, at - 5.0), rms(&s, at, at + 15.0));
+            assert!(
+                hit > 2.0 * before,
+                "shot {n}: second hit at {at} ms ({hit} vs {before})"
+            );
+        }
         assert!(sound(6).len() > sound(5).len(), "6 adds the glide");
         assert_eq!(sound(6).len(), sound(7).len());
         for n in 1..=7 {