88 lines
3.2 KiB
Python
88 lines
3.2 KiB
Python
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#!/usr/bin/env python3
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"""Generates the game's sound effects, from scratch.
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Forgejo #146 asked for free SFX sources, and the ones worth using are listed
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in the ticket - Kenney's CC0 packs, OpenGameArt's CC0 sets, Freesound's CC0
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filter. What ships here is synthesised instead, for one reason: a generated
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sound has no licence, no attribution to keep track of, and no binary in the
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repository whose provenance nobody can check a year from now.
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It also means the sounds are DATA rather than assets. If a shot is too sharp
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or an explosion too short, the fix is a number in this file and a re-run,
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not a hunt through a sound library.
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Run: python3 audio/make_sfx.py
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"""
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import math
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import random
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import struct
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import wave
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RATE = 44100
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def _write(name, samples):
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peak = max(1e-9, max(abs(s) for s in samples))
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frames = b"".join(struct.pack("<h", int(max(-1.0, min(1.0, s / peak * 0.89)) * 32767))
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for s in samples)
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with wave.open("audio/%s.wav" % name, "w") as w:
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w.setnchannels(1)
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w.setsampwidth(2)
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w.setframerate(RATE)
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w.writeframes(frames)
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print("audio/%s.wav %5.2fs %6d bytes" % (name, len(samples) / RATE, len(frames)))
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def _env(i, n, attack, decay_power):
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"""Fast attack, curved decay. `attack` is a fraction of the whole."""
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a = max(1, int(n * attack))
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if i < a:
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return i / a
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return (1.0 - (i - a) / max(1, n - a)) ** decay_power
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def shot(seconds=0.16, start_hz=1500.0, end_hz=320.0):
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"""A short descending zap. The fleet's guns are energy weapons, so this
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is a swept tone rather than a crack - it has to sit under a stream of
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itself without turning into noise."""
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n = int(RATE * seconds)
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out = []
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phase = 0.0
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for i in range(n):
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t = i / n
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hz = start_hz * (end_hz / start_hz) ** t
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phase += 2.0 * math.pi * hz / RATE
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# A little square in it, so it reads as synthetic rather than as a flute.
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tone = 0.7 * math.sin(phase) + 0.3 * (1.0 if math.sin(phase) > 0 else -1.0)
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out.append(tone * _env(i, n, 0.02, 2.2))
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return out
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def explosion(seconds, low_hz, brightness, rumble_hz):
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"""Noise through a one-pole low-pass, plus a falling sine underneath it.
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The sine is what gives it a size: without it a burst of noise is a hiss,
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however loud."""
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n = int(RATE * seconds)
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out = []
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last = 0.0
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phase = 0.0
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rng = random.Random(7)
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for i in range(n):
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t = i / n
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# The filter opens for an instant and closes as it decays, which is
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# what a real blast does - the crack first, the roar after.
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cutoff = brightness * (1.0 - t) ** 1.6 + 0.02
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last += cutoff * (rng.uniform(-1.0, 1.0) - last)
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hz = low_hz * (rumble_hz / low_hz) ** t
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phase += 2.0 * math.pi * hz / RATE
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body = 0.55 * math.sin(phase)
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out.append((last * 1.4 + body) * _env(i, n, 0.004, 1.7))
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return out
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if __name__ == "__main__":
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_write("sfx_shot", shot())
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# A vessel: sharp, bright, over quickly.
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_write("sfx_ship_death", explosion(0.85, 220.0, 0.55, 45.0))
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# A structure: slower, deeper, and it keeps falling down afterwards.
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_write("sfx_building_death", explosion(1.6, 130.0, 0.34, 26.0))
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