Procedural sound kit: the whole game has audio, no recordings

Every WAV is synthesized from maths by tools/gen_sounds.py (run through Blender
for its bundled numpy) -- sines, noise and envelopes, seeded and reproducible,
licence-free by construction. Loops (engine, skid, boost, siren) are built from
integer-Hz components over exactly 1 s so the seam is mathematically silent;
noise beds get a crossfaded seam. Seam continuity is verified numerically.

Wiring: pitch-tracked engine loop on every car (idle burble to top-end scream,
bump while boosting), skid loop off slip, player boost whoosh, small/big crash
by jolt with glass on wrecks, two-tone siren on pursuit cops (derby brawlers
stay silent), Crashbreaker boom, gearbox clunk/bog, win/lose stings on
takedowns, outruns, escapes, busts and derby eliminations.

Loop flags live in code (sfx.gd), not per-file .import settings, so a
regenerated wav never silently loses its loop.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -261,8 +261,33 @@ Visual check (opens a window, saves a PNG):
 /Applications/Godot.app/Contents/MacOS/Godot --path . --script tests/screenshot.gd -- car=datto_120y mode=crash frames=280 out=shot.png
 ```
 
+## Sound
+
+Every WAV in `assets/sounds/` is synthesized from maths by
+[tools/gen_sounds.py](tools/gen_sounds.py) — sines, noise and envelopes, no
+recordings, so the whole kit is licence-free by construction and reproducible
+from its seed like everything else in this repo. (Run it through Blender: it's
+only there for the bundled numpy, no bpy involved.)
+
+Loop discipline: anything the game loops (engine, skid, boost, siren) is built
+from integer-Hz components over exactly 1 s so the seam is mathematically
+silent; noise beds get a crossfaded seam. Loop flags are set in code
+([sfx.gd](src/sfx.gd)), not per-file import settings, so a regenerated wav never
+silently loses its loop.
+
+Wiring: every car runs a pitch-tracked engine loop (the arcade law: idle burble
+at rest, screaming near top speed, a bump while boosting) plus a skid loop off
+the slip value; the player adds a boost whoosh. Crashes pick small/big by jolt
+strength with glass on a wreck, pursuit cops wail a two-tone siren (derby
+brawlers don't), the Crashbreaker booms, the gearbox clunks or bogs, and event
+results sting up or down.
+
+If the kit ever wants sweetening beyond synthesis, use **CC0 sources only**
+(kenney.nl, OpenGameArt filtered to CC0) — CC-BY means shipping attribution
+forever and NC-licensed audio doesn't belong in this repo at all.
+
 ## Design doc
 
 `docs/BurnoutInfinityShitbox.pdf` — research report on the original game. Still to come:
-crash deformation (control-hull vertex displacement, equations in the PDF), oncoming-lane
-boost, Road Rage mode, sound, real level GLBs from Blender.
+oncoming-lane boost, Road Rage mode, a DEM elevation pass (so the Story Bridge deck
+actually rises), and hand-picked crossings for the two scenery-crash junctions.

assets/sounds/bog.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://qbn0cilhfqwj"
+path="res://.godot/imported/bog.wav-8f1da2786c55aeefbeb106dc868c91db.sample"
+
+[deps]
+
+source_file="res://assets/sounds/bog.wav"
+dest_files=["res://.godot/imported/bog.wav-8f1da2786c55aeefbeb106dc868c91db.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/boom.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://dnwpk58ldx1ky"
+path="res://.godot/imported/boom.wav-ce80ab5026d9de2164088103d22abe14.sample"
+
+[deps]
+
+source_file="res://assets/sounds/boom.wav"
+dest_files=["res://.godot/imported/boom.wav-ce80ab5026d9de2164088103d22abe14.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/boost.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://da0fblx1gdv5u"
+path="res://.godot/imported/boost.wav-810a94b056a1e46df7bb29aadebe3719.sample"
+
+[deps]
+
+source_file="res://assets/sounds/boost.wav"
+dest_files=["res://.godot/imported/boost.wav-810a94b056a1e46df7bb29aadebe3719.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/clunk.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://bypon8wahkl6m"
+path="res://.godot/imported/clunk.wav-39e9719aa8e918e8eeb10576b0be4c5d.sample"
+
+[deps]
+
+source_file="res://assets/sounds/clunk.wav"
+dest_files=["res://.godot/imported/clunk.wav-39e9719aa8e918e8eeb10576b0be4c5d.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/crash_big.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://bcxbcnytwk7pj"
+path="res://.godot/imported/crash_big.wav-4b192579a3fd4414c388af2e6de59ed6.sample"
+
+[deps]
+
+source_file="res://assets/sounds/crash_big.wav"
+dest_files=["res://.godot/imported/crash_big.wav-4b192579a3fd4414c388af2e6de59ed6.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/crash_small.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://ceeyt53afugxp"
+path="res://.godot/imported/crash_small.wav-94e44666608124db8d2651ef7b97a9aa.sample"
+
+[deps]
+
+source_file="res://assets/sounds/crash_small.wav"
+dest_files=["res://.godot/imported/crash_small.wav-94e44666608124db8d2651ef7b97a9aa.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/engine.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://cybkeltoy7j3a"
+path="res://.godot/imported/engine.wav-d6786269ebfd2ada75bdd079c2e17f80.sample"
+
+[deps]
+
+source_file="res://assets/sounds/engine.wav"
+dest_files=["res://.godot/imported/engine.wav-d6786269ebfd2ada75bdd079c2e17f80.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/glass.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://cttvhh5nm5j1m"
+path="res://.godot/imported/glass.wav-8cd29b0619eb51b1e55ea8a7e038a004.sample"
+
+[deps]
+
+source_file="res://assets/sounds/glass.wav"
+dest_files=["res://.godot/imported/glass.wav-8cd29b0619eb51b1e55ea8a7e038a004.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/siren.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://cwrt3oul3vs3m"
+path="res://.godot/imported/siren.wav-847d6fbddcbf15b051f8f55cc9265888.sample"
+
+[deps]
+
+source_file="res://assets/sounds/siren.wav"
+dest_files=["res://.godot/imported/siren.wav-847d6fbddcbf15b051f8f55cc9265888.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/skid.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://xhfwat50fi7v"
+path="res://.godot/imported/skid.wav-2935abfa7678803791f7dd569a3dc250.sample"
+
+[deps]
+
+source_file="res://assets/sounds/skid.wav"
+dest_files=["res://.godot/imported/skid.wav-2935abfa7678803791f7dd569a3dc250.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/sting_lose.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://dw8p7p4q4y413"
+path="res://.godot/imported/sting_lose.wav-6123e9e6785ae293e80b5df7e1e06e37.sample"
+
+[deps]
+
+source_file="res://assets/sounds/sting_lose.wav"
+dest_files=["res://.godot/imported/sting_lose.wav-6123e9e6785ae293e80b5df7e1e06e37.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

assets/sounds/sting_win.wav.import

@@ -0,0 +1,24 @@
+[remap]
+
+importer="wav"
+type="AudioStreamWAV"
+uid="uid://dskukm4ylh7n7"
+path="res://.godot/imported/sting_win.wav-99ef8cb7f30234f01743fb8f02166015.sample"
+
+[deps]
+
+source_file="res://assets/sounds/sting_win.wav"
+dest_files=["res://.godot/imported/sting_win.wav-99ef8cb7f30234f01743fb8f02166015.sample"]
+
+[params]
+
+force/8_bit=false
+force/mono=false
+force/max_rate=false
+force/max_rate_hz=44100
+edit/trim=false
+edit/normalize=false
+edit/loop_mode=0
+edit/loop_begin=0
+edit/loop_end=-1
+compress/mode=2

src/car.gd

@@ -43,6 +43,9 @@ var _prev_lv := Vector3.ZERO
 var _impact_cd := 0.0
 var _parts: Array[Node] = []
 var _deform: Deformer = null
+var _snd_eng: AudioStreamPlayer3D
+var _snd_skid: AudioStreamPlayer3D
+var _snd_boost: AudioStreamPlayer3D
 
 @onready var wheels: Array[Node] = [$FL, $FR, $RL, $RR]
 
@@ -71,6 +74,13 @@ func _ready() -> void:
 		var bm := BoxMesh.new()
 		bm.size = Vector3(stats.width, 1.0, stats.length)
 		$Body.mesh = bm
+	# the player's own engine sits front and centre; everyone else's is scenery
+	_snd_eng = Sfx.looper(self, "engine", -9.0 if is_player else -17.0)
+	if _snd_eng:
+		_snd_eng.play()
+	_snd_skid = Sfx.looper(self, "skid", -7.0 if is_player else -14.0)
+	if is_player:
+		_snd_boost = Sfx.looper(self, "boost", -8.0)
 
 func _physics_process(delta: float) -> void:
 	if is_player:
@@ -123,6 +133,25 @@ func _physics_process(delta: float) -> void:
 	if boosting:
 		boost = maxf(boost - BOOST_DRAIN * delta, 0.0)
 
+	if _snd_eng:
+		# arcade pitch law: idle burble at rest, screaming near top speed
+		_snd_eng.pitch_scale = clampf(0.55 + linear_velocity.length() / 26.0, 0.55, 2.5) \
+			+ (0.25 if boosting else 0.0)
+		_snd_eng.volume_db = (-9.0 if is_player else -17.0) + absf(throttle_in) * 4.0
+	if _snd_skid:
+		var skidding := grounded >= 2 and absf(slip) > 4.0 and linear_velocity.length() > 8.0
+		if skidding and not _snd_skid.playing:
+			_snd_skid.play()
+		elif not skidding and _snd_skid.playing:
+			_snd_skid.stop()
+		if skidding:
+			_snd_skid.pitch_scale = clampf(0.85 + absf(slip) / 40.0, 0.85, 1.4)
+	if _snd_boost:
+		if boosting and not _snd_boost.playing:
+			_snd_boost.play()
+		elif not boosting and _snd_boost.playing:
+			_snd_boost.stop()
+
 	var jolt := linear_velocity - _prev_lv
 	_prev_lv = linear_velocity
 	_impact_cd = maxf(_impact_cd - delta, 0.0)
@@ -136,6 +165,10 @@ func earn_boost(amount: float) -> void:
 func _impact(jolt: Vector3) -> void:
 	var dv := jolt.length()
 	crashed.emit(dv)
+	Sfx.shot(self, "crash_big" if dv > 8.0 else "crash_small",
+		-2.0, randf_range(0.9, 1.1))
+	if dv > WRECK_DV:
+		Sfx.shot(self, "glass", -4.0)
 	var side := (global_basis.inverse() * -jolt).normalized()
 	if _deform:
 		# no contact manifold from the jolt heuristic, so approximate the strike

src/cop.gd

@@ -9,9 +9,18 @@ extends Car
 
 var target: Node3D
 var power_boost := 1.0     # scales with heat: more wanted = more committed
+var siren := true          # pursuit cops wail; derby brawlers don't
 
 var _stuck := 0.0
 var _unstick := 0.0
+var _snd_siren: AudioStreamPlayer3D
+
+func _ready() -> void:
+	super()
+	if siren:
+		_snd_siren = Sfx.looper(self, "siren", -8.0)
+		if _snd_siren:
+			_snd_siren.play()
 
 func _physics_process(delta: float) -> void:
 	if target and not wrecked:

src/game.gd

@@ -203,6 +203,7 @@ func _ready() -> void:
 			var d: Cop = (load("res://src/cop.tscn") as PackedScene).instantiate()
 			d.stats = load(pool[randi() % pool.size()])
 			d.power_boost = 1.0
+			d.siren = false     # brawlers, not police
 			# a wreck is an elimination: without this car.gd's 2.2 s _recover
 			# timer stands them back up and the field never empties
 			d.hold_wreck = true
@@ -594,6 +595,7 @@ func _derby_down(d: Cop) -> void:
 		derby_kills += 1
 		car.boost_max = minf(car.boost_max + 0.5, Car.BOOST_CAP)
 		car.boost = car.boost_max
+		Sfx.shot(car, "sting_win", -4.0)
 		_msg("WRECKED 'EM! x%d" % derby_kills, 46)
 
 func _derby_tick(delta: float) -> void:
@@ -642,10 +644,12 @@ func _drag_tick(delta: float) -> void:
 		if Input.is_action_just_pressed("boost"):
 			if revs >= SHIFT_LO and revs < REDLINE:
 				clean_shifts += 1
+				Sfx.shot(car, "clunk", -2.0)
 				_msg("CLEAN SHIFT", 34)
 			else:
 				blown_shifts += 1
 				bog = 0.9
+				Sfx.shot(car, "bog", -2.0)
 				_msg("MISSED IT", 34)
 			gear += 1
 			revs = 0.28 if gear <= DRAG_GEARS else 1.0
@@ -727,9 +731,11 @@ func _end_pursuit(escaped: bool) -> void:
 		escapes += 1
 		car.boost_max = minf(car.boost_max + 0.5, Car.BOOST_CAP)
 		car.boost = car.boost_max
+		Sfx.shot(car, "sting_win", -4.0)
 		_msg("LOST 'EM! x%d" % escapes, 52)
 	else:
 		busts += 1
+		Sfx.shot(car, "sting_lose", -4.0)
 		_msg("BUSTED", 52)
 
 func _pursuit_tick(delta: float) -> void:
@@ -831,8 +837,10 @@ func _outrun_end(won: bool, why: String) -> void:
 		outruns_won += 1
 		car.boost_max = minf(car.boost_max + 0.5, Car.BOOST_CAP)  # takedown-tier reward
 		car.boost = car.boost_max
+		Sfx.shot(car, "sting_win", -4.0)
 		_msg("OUTRUN WON! x%d%s" % [outruns_won, tail], 52)
 	else:
+		Sfx.shot(car, "sting_lose", -4.0)
 		_msg("OUTRUN LOST%s" % tail, 44)
 
 func _race_tick() -> void:
@@ -894,6 +902,7 @@ func _rival_wrecked(r: Rival) -> void:
 		return
 	car.boost_max = minf(car.boost_max + 0.5, Car.BOOST_CAP)
 	car.boost = car.boost_max
+	Sfx.shot(car, "sting_win", -4.0)
 	_msg("TAKEDOWN!", 56)
 
 func _traffic_smashed(impulse: float) -> void:
@@ -927,6 +936,7 @@ func _crashbreaker() -> void:
 		else:
 			(b as RigidBody3D).apply_central_impulse(dir * strength * (b as RigidBody3D).mass)
 	car.apply_central_impulse(Vector3.UP * car.mass * 7.0)
+	Sfx.shot(car, "boom", 0.0)
 	_msg("CRASHBREAKER!", 52)
 	var boom := MeshInstance3D.new()
 	var sm := SphereMesh.new()

src/sfx.gd

@@ -0,0 +1,51 @@
+class_name Sfx
+## Tiny audio utility over the procedural kit in assets/sounds (tools/gen_sounds.py).
+## Loops are flagged here rather than in per-file .import settings so a wav
+## regenerated by the tool never silently loses its loop flag.
+
+const DIR := "res://assets/sounds/%s.wav"
+const LOOPS := ["engine", "skid", "boost", "siren"]
+
+static var _cache := {}
+
+static func stream(name: String) -> AudioStream:
+	if _cache.has(name):
+		return _cache[name]
+	var path := DIR % name
+	if not ResourceLoader.exists(path):
+		return null
+	var s: AudioStream = load(path)
+	if s is AudioStreamWAV and name in LOOPS:
+		var w := s as AudioStreamWAV
+		w.loop_mode = AudioStreamWAV.LOOP_FORWARD
+		w.loop_begin = 0
+		w.loop_end = w.data.size() / 2   # 16-bit mono: 2 bytes per frame
+	_cache[name] = s
+	return s
+
+static func looper(parent: Node, name: String, db: float) -> AudioStreamPlayer3D:
+	## Persistent 3D player for a looped bed (engine, skid, siren). Not playing
+	## until the caller decides; returns null when the kit isn't generated yet.
+	var s := stream(name)
+	if s == null:
+		return null
+	var p := AudioStreamPlayer3D.new()
+	p.stream = s
+	p.volume_db = db
+	p.max_distance = 90.0
+	parent.add_child(p)
+	return p
+
+static func shot(parent: Node, name: String, db := 0.0, pitch := 1.0) -> void:
+	## Fire-and-forget one-shot at the parent's position.
+	var s := stream(name)
+	if s == null:
+		return
+	var p := AudioStreamPlayer3D.new()
+	p.stream = s
+	p.volume_db = db
+	p.pitch_scale = pitch
+	p.max_distance = 160.0
+	parent.add_child(p)
+	p.play()
+	p.finished.connect(p.queue_free)

src/sfx.gd.uid

@@ -0,0 +1 @@
+uid://bf8uwanb2pyhb

tools/gen_sounds.py

@@ -0,0 +1,156 @@
+"""Procedural sound kit: every WAV the game plays, synthesized from maths.
+
+Run:  /Applications/Blender.app/Contents/MacOS/Blender -b -P tools/gen_sounds.py
+      (Blender only for its bundled numpy -- no bpy used)
+
+Licence-free by construction: sines, noise and envelopes, no recordings.
+Deterministic (seeded), so a rebuild is byte-for-byte reproducible.
+
+Loop discipline: anything the game loops (engine, skid, boost, siren) is built
+from integer-Hz components over an exact 1 s so the seam is mathematically
+silent; noise beds get a crossfaded seam instead. One-shots just decay to zero.
+"""
+import math
+import os
+import wave
+
+import numpy as np
+
+SR = 22050
+OUT = os.path.join(os.path.dirname(os.path.abspath(__file__)), "..", "assets", "sounds")
+rng = np.random.default_rng(1982)
+
+
+def t(dur):
+    return np.arange(int(SR * dur)) / SR
+
+
+def env_exp(dur, tau):
+    return np.exp(-t(dur) / tau)
+
+
+def noise(dur):
+    return rng.standard_normal(int(SR * dur))
+
+
+def band(x, lo, hi, peaks=()):
+    """FFT bandpass with optional resonant peaks [(hz, width, gain)]."""
+    spec = np.fft.rfft(x)
+    f = np.fft.rfftfreq(len(x), 1 / SR)
+    mask = ((f >= lo) & (f <= hi)).astype(float)
+    edge = (hi - lo) * 0.15 + 1.0
+    mask = np.convolve(mask, np.hanning(9) / np.hanning(9).sum(), mode="same")
+    for hz, width, gain in peaks:
+        mask += gain * np.exp(-((f - hz) / width) ** 2)
+    return np.fft.irfft(spec * mask, len(x))
+
+
+def seam(x, fade=0.06):
+    """Crossfade the tail into the head so a noise bed loops cleanly."""
+    n = int(SR * fade)
+    w = np.linspace(0, 1, n)
+    x[:n] = x[:n] * w + x[-n:] * (1 - w)
+    return x[:-n]
+
+
+def norm(x, peak=0.85):
+    return x / (np.max(np.abs(x)) + 1e-9) * peak
+
+
+def write(name, x):
+    x16 = (np.clip(x, -1, 1) * 32767).astype("<i2")
+    with wave.open(os.path.join(OUT, name + ".wav"), "wb") as w:
+        w.setnchannels(1)
+        w.setsampwidth(2)
+        w.setframerate(SR)
+        w.writeframes(x16.tobytes())
+    print("%-14s %5.2fs  peak %.2f" % (name, len(x) / SR, np.max(np.abs(x))))
+
+
+os.makedirs(OUT, exist_ok=True)
+
+# engine: integer-Hz harmonic stack of 56 Hz with a firing-pulse AM -- the
+# arcade "brap". All components integer Hz over exactly 1 s = seamless loop.
+tt = t(1.0)
+eng = np.zeros(len(tt))
+for h, a in ((1, 1.0), (2, 0.62), (3, 0.42), (4, 0.30), (6, 0.16), (8, 0.09)):
+    eng += a * np.sin(2 * math.pi * 56 * h * tt + h)
+eng += 0.5 * np.sin(2 * math.pi * 28 * tt)                     # sub
+eng *= 1.0 + 0.38 * np.sin(2 * math.pi * 28 * tt - 0.7)        # firing pulses
+bed = band(noise(1.0), 40, 900)
+eng[: len(seam(bed))] += 0.10 * norm(seam(bed), 1.0)[: len(eng)]
+write("engine", norm(eng, 0.7))
+
+# skid: screechy banded noise with resonances and a 15 Hz tremolo
+sk = band(noise(1.0), 900, 3200, peaks=((1250, 90, 6.0), (1900, 120, 4.0)))
+sk *= 1.0 + 0.3 * np.sin(2 * math.pi * 15 * t(1.0))
+write("skid", norm(seam(sk), 0.6))
+
+# boost: airy rushing band with a slow 6 Hz surge
+bo = band(noise(1.0), 250, 1600) + 0.5 * band(noise(1.0), 2500, 6000)
+bo *= 1.0 + 0.25 * np.sin(2 * math.pi * 6 * t(1.0))
+write("boost", norm(seam(bo), 0.55))
+
+# siren: Aussie two-tone, 620/470 Hz halves with soft crossfades, odd harmonics
+tt = t(1.0)
+gate = 0.5 * (1 + np.tanh(np.sin(2 * math.pi * 1 * tt) * 24))  # smooth 0/1 square
+si = np.zeros(len(tt))
+for f0, g in ((620, gate), (470, 1 - gate)):
+    tone = sum(np.sin(2 * math.pi * f0 * k * tt) / k for k in (1, 3, 5))
+    si += g * tone
+write("siren", norm(si, 0.5))
+
+# crashes: thump sweep + banded burst (+ clatter echoes on the big one)
+def thump(dur, f_hi, f_lo, tau):
+    ph = 2 * math.pi * np.cumsum(np.linspace(f_hi, f_lo, int(SR * dur))) / SR
+    return np.sin(ph) * env_exp(dur, tau)
+
+cs = thump(0.35, 150, 48, 0.09)
+cs += 0.8 * band(noise(0.35), 200, 4200) * env_exp(0.35, 0.05)
+cs += 0.25 * (np.sin(2 * math.pi * 810 * t(0.35)) + np.sin(2 * math.pi * 1130 * t(0.35))) * env_exp(0.35, 0.03)
+write("crash_small", norm(cs, 0.8))
+
+cb = thump(0.9, 120, 34, 0.22)
+cb += 0.9 * band(noise(0.9), 120, 3800) * env_exp(0.9, 0.13)
+for d, a in ((0.16, 0.4), (0.29, 0.3), (0.45, 0.2)):           # clatter
+    i = int(SR * d)
+    burst = band(noise(0.12), 400, 3000) * env_exp(0.12, 0.03) * a
+    cb[i:i + len(burst)] += burst
+write("crash_big", norm(cb, 0.9))
+
+# glass: a shower of tiny bright pings over a sizzle
+gl = 0.25 * band(noise(0.6), 4000, 9500) * env_exp(0.6, 0.12)
+for _ in range(42):
+    at = rng.uniform(0, 0.4)
+    f = rng.uniform(3800, 8800)
+    ping = np.sin(2 * math.pi * f * t(0.05)) * env_exp(0.05, 0.012) * rng.uniform(0.2, 0.55)
+    i = int(SR * at)
+    gl[i:i + len(ping)] += ping
+write("glass", norm(gl, 0.6))
+
+# crashbreaker: deep sweep + saturated noise whomp
+bm = thump(1.2, 95, 28, 0.35)
+bm += 1.2 * band(noise(1.2), 30, 700) * env_exp(1.2, 0.18)
+write("boom", norm(np.tanh(bm * 2.2), 0.95))
+
+# stings: little square arpeggios (win up, lose down)
+def sting(notes, dur=0.16, gap=0.02):
+    parts = []
+    for f in notes:
+        tone = sum(np.sin(2 * math.pi * f * k * t(dur)) / k for k in (1, 3)) * env_exp(dur, 0.09)
+        parts += [tone, np.zeros(int(SR * gap))]
+    return np.concatenate(parts)
+
+write("sting_win", norm(sting([392, 523, 659, 784]), 0.55))
+write("sting_lose", norm(sting([392, 311, 233], dur=0.22), 0.5))
+
+# gearbox: clean clunk vs blown-shift bog
+ck = thump(0.14, 95, 60, 0.03) + 0.5 * band(noise(0.14), 1500, 5000) * env_exp(0.14, 0.006)
+write("clunk", norm(ck, 0.7))
+
+ph = 2 * math.pi * np.cumsum(np.linspace(130, 55, int(SR * 0.45))) / SR
+bg = np.sign(np.sin(ph)) * env_exp(0.45, 0.16)
+bg *= 1.0 + 0.5 * np.sin(2 * math.pi * 27 * t(0.45))
+write("bog", norm(bg * 0.5 + 0.3 * band(noise(0.45), 80, 500) * env_exp(0.45, 0.1), 0.6))
+
+print("sound kit written to", os.path.abspath(OUT))