sound-check.mjs

1	/**
2	* Render twelve seconds of the synthesized ice sound without playing it, and draw its
3	* spectrogram, so that the sound can be looked at beside the film's and a change to it
4	* can be seen as well as heard.
5	*
6	* npm run sound-check writes docs/sound/synth.png and docs/sound/synth.wav
7	*
8	* The skater strides as in the app, on ice 4.1 cm thick as in the film for six seconds,
9	* and then onto ice thinning to 2.8 cm, so the note should hold near 740 Hz and then
10	* climb past 1 kHz. Three cracks, 150, 500 and 60 m away. Needs ffmpeg.
11	*/
12	import { spawnSync } from 'node:child_process'
13	import { mkdirSync, writeFileSync } from 'node:fs'
14	import { chromium } from 'playwright'
15	import { createServer } from 'vite'
16
17	const OUT = 'docs/sound'
18	const SECONDS = 12
19	const RATE = 44100
20
21	mkdirSync(OUT, { recursive: true })
22	// The dev server, because it serves the source modules one by one and the page can then
23	// import the synthesizer by its path.
24	const server = await createServer({ server: { port: 4318, strictPort: true }, logLevel: 'error' })
25	await server.listen()
26	const browser = await chromium.launch()
27	let samples
28	try {
29	const page = await browser.newPage()
30	await page.goto(server.resolvedUrls.local[0])
31	samples = await page.evaluate(async ({ SECONDS, RATE }) => {
32	const { IceSound } = await import('/src/audio/iceSound.ts')
33	const { mulberry32 } = await import('/src/world/lake.ts')
34	const { strideSeconds } = await import('/src/skater.ts')
35	const ctx = new OfflineAudioContext(2, SECONDS * RATE, RATE)
36	const random = mulberry32(1)
37	const ice = new IceSound(ctx, random)
38	const thickness = (t) => (t < 6 ? 0.041 : 0.041 - (0.013 * (t - 6)) / 6)
39	const strikes = []
40	for (let t = 0.2, n = 0; t < SECONDS; t += strideSeconds(n++)) {
41	strikes.push(t)
42	ice.strike(thickness(t), t, 0.75 + 0.5 * random())
43	}
44	for (let t = 0; t < SECONDS; t += 0.02) {
45	const since = t - (strikes.findLast((s) => s <= t) ?? -Infinity)
46	ice.glide(thickness(t), Math.exp(-since / 0.5), t)
47	}
48	ice.crack(thickness(2.5), 150, 2.5, -0.5)
49	ice.crack(thickness(4.6), 500, 4.6, 0.6)
50	ice.crack(thickness(9.3), 60, 9.3, 0)
51	const rendered = await ctx.startRendering()
52	const left = rendered.getChannelData(0)
53	const right = rendered.getChannelData(1)
54	return Array.from(left, (v, i) => [v, right[i]]).flat()
55	}, { SECONDS, RATE })
56	} finally {
57	await browser.close()
58	await server.close()
59	}
60
61	let peak = 0
62	let power = 0
63	for (const v of samples) {
64	peak = Math.max(peak, Math.abs(v))
65	power += v * v
66	}
67	const db = (x) => (20 * Math.log10(x)).toFixed(1)
68	console.log(` peak ${db(peak)} dBFS, average ${db(Math.sqrt(power / samples.length))} dBFS`)
69
70	const data = Buffer.alloc(samples.length * 2)
71	samples.forEach((v, i) => data.writeInt16LE(Math.round(Math.max(-1, Math.min(1, v)) * 32767), i * 2))
72	const header = Buffer.alloc(44)
73	header.write('RIFF', 0)
74	header.writeUInt32LE(36 + data.length, 4)
75	header.write('WAVEfmt ', 8)
76	header.writeUInt32LE(16, 16)
77	header.writeUInt16LE(1, 20)
78	header.writeUInt16LE(2, 22)
79	header.writeUInt32LE(RATE, 24)
80	header.writeUInt32LE(RATE * 4, 28)
81	header.writeUInt16LE(4, 32)
82	header.writeUInt16LE(16, 34)
83	header.write('data', 36)
84	header.writeUInt32LE(data.length, 40)
85	writeFileSync(`${OUT}/synth.wav`, Buffer.concat([header, data]))
86
87	const drawn = spawnSync('ffmpeg', ['-v', 'error', '-y', '-i', `${OUT}/synth.wav`, '-lavfi',
88	'aformat=channel_layouts=mono,showspectrumpic=s=1600x600:legend=1:scale=log:fscale=lin:stop=8000',
89	`${OUT}/synth.png`])
90	if (drawn.status !== 0) throw new Error(`ffmpeg: ${drawn.stderr}`)
91	console.log(` ${OUT}/synth.wav\n ${OUT}/synth.png`)