max / audiofiles

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1	//! DC offset removal: compute mean amplitude and subtract it from all samples.
2
3	/// Remove DC offset from interleaved audio samples.
4	///
5	/// Computes the mean sample value (the DC component) and subtracts it,
6	/// centering the waveform around zero. Operates per-channel to handle
7	/// stereo files where channels may have different offsets.
8	pub fn apply_remove_dc_offset(samples: &mut [f32], channels: u16) {
9	if samples.is_empty() \|\| channels == 0 {
10	return;
11	}
12	let ch = channels as usize;
13	let num_frames = samples.len() / ch;
14	if num_frames == 0 {
15	return;
16	}
17
18	// Compute per-channel mean
19	let mut sums = vec![0.0f64; ch];
20	for frame in 0..num_frames {
21	for c in 0..ch {
22	sums[c] += samples[frame * ch + c] as f64;
23	}
24	}
25	let means: Vec<f32> = sums.iter().map(\|s\| (*s / num_frames as f64) as f32).collect();
26
27	// Subtract per-channel mean
28	for frame in 0..num_frames {
29	for c in 0..ch {
30	samples[frame * ch + c] -= means[c];
31	}
32	}
33	}
34
35	#[cfg(test)]
36	mod tests {
37	use super::*;
38
39	#[test]
40	fn removes_dc_offset_mono() {
41	let mut samples = vec![0.5, 0.6, 0.4, 0.5]; // mean = 0.5
42	apply_remove_dc_offset(&mut samples, 1);
43	let mean: f32 = samples.iter().sum::<f32>() / samples.len() as f32;
44	assert!(mean.abs() < 1e-6, "mean should be ~0, got {mean}");
45	assert!((samples[0] - 0.0).abs() < 1e-6);
46	assert!((samples[1] - 0.1).abs() < 1e-6);
47	}
48
49	#[test]
50	fn removes_dc_offset_stereo() {
51	// L channel: mean 0.5, R channel: mean -0.5
52	let mut samples = vec![0.5, -0.5, 0.5, -0.5];
53	apply_remove_dc_offset(&mut samples, 2);
54	// After removal, both channels centered at 0
55	assert!((samples[0]).abs() < 1e-6);
56	assert!((samples[1]).abs() < 1e-6);
57	}
58
59	#[test]
60	fn noop_on_already_centered() {
61	let original = vec![0.1, -0.1, 0.2, -0.2];
62	let mut samples = original.clone();
63	apply_remove_dc_offset(&mut samples, 1);
64	for (a, b) in samples.iter().zip(original.iter()) {
65	assert!((a - b).abs() < 1e-6);
66	}
67	}
68
69	#[test]
70	fn empty_input() {
71	let mut samples: Vec<f32> = vec![];
72	apply_remove_dc_offset(&mut samples, 1);
73	assert!(samples.is_empty());
74	}
75	}
76