Real thunder (Gitea #4): six CC0 recordings, close cracks and distant rolls, in place of the synthesised rumble; a storm's flash is followed by a roll seconds later or a crack sooner, quieter indoors, and a strike on a tree cracks from the tree

tools/audio/make_audio.py

@@ -699,6 +699,44 @@ def _decode(src, sr, af=None):
     return [x * 0.06 / rms for x in left], [x * 0.06 / rms for x in right]
 
 
+def make_thunder():
+    """Thunder (0.6.2, Gitea #4): CC0 recordings (tools/audio/sources/
+    thunder_near_* and thunder_far_*, credited in assets/audio/CREDITS.md),
+    each cut round its loudest strike, faded out and evened out in level, into
+    assets/audio/sfx/thunder/thunder_near_N.ogg (a crack close by) and
+    thunder_far_N.ogg (a roll in the distance). Replaces the synthesised rumble."""
+    d = os.path.join(OUT, "sfx", "thunder")
+    os.makedirs(d, exist_ok=True)
+    print("thunder ->", os.path.relpath(d, ROOT))
+    sr = 44100
+    for kind, lead, most in (("near", 0.15, 7.0), ("far", 0.6, 10.0)):
+        for n, src in enumerate(sources("thunder_" + kind)):
+            raw = subprocess.run(["ffmpeg", "-v", "error", "-i", src, "-ac", "1", "-ar", str(sr), "-f", "s16le", "-"],
+                                 capture_output=True, check=True).stdout
+            x = [struct.unpack_from("<h", raw, i * 2)[0] / 32768.0 for i in range(len(raw) // 2)]
+            win = sr // 20
+            env = [math.sqrt(sum(v * v for v in x[i:i + win]) / win) + 1e-9 for i in range(0, len(x) - win, win)]
+            ip = max(range(len(env)), key=lambda i: env[i])
+            top = env[ip]
+            # Back from the loudest moment to where this strike starts (20 dB down).
+            j = ip
+            while j > 0 and env[j] > top * 0.1:
+                j -= 1
+            start = max(0, int((j * 0.05 - lead) * sr))
+            # On until it's died away (40 dB down), or `most` seconds.
+            k = ip
+            while k < len(env) - 1 and env[k] > top * 0.01 and (k - j) * 0.05 < most:
+                k += 1
+            end = min(len(x), int(k * 0.05 * sr) + win)
+            seg = x[start:end]
+            fade_in, fade_out = int(0.02 * sr), min(int(1.5 * sr), len(seg) // 3)
+            for i in range(fade_in):
+                seg[i] *= i / fade_in
+            for i in range(fade_out):
+                seg[-1 - i] *= i / fade_out
+            _encode(os.path.join(d, "thunder_%s_%d.ogg" % (kind, n)), [seg], sr, 5)
+
+
 def make_recorded(name, srcs=None):
     """A field-recorded ambience loop (assets/audio/ambience/<name>.ogg) from
     CC0 recordings (tools/audio/sources/<name>_*, or the files given): each
@@ -808,6 +846,9 @@ if __name__ == "__main__":
     if what in RECORDED:   # one recorded loop: birds | crickets
         make_recorded(what)
         sys.exit(0)
+    if what == "thunder":  # the recorded thunder (not part of "all": it's from sources/)
+        make_thunder()
+        sys.exit(0)
     if what in ("all", "sfx"):
         make_sfx()
     if what in ("all", "sfx", "voices"):