sva_samples/measure/
spectrum.rs

1// Concern: resolves every channel's samples into magnitudes, third-octave bands and peaks | Non-concern: naming a peak as a note (pitch.rs), choosing the window | IO: (planes, sample rate) -> Spectrum
2
3use crate::fft::fft;
4pub use crate::measure::peaks::{Peak, db, peaks};
5
6pub const MAX_FRAME: usize = 8192;
7pub const MIN_FRAME: usize = 64;
8
9/// One FFT's memory, which is all that bounds a caller's own frame.
10pub const MAX_PINNED_FRAME: usize = 1 << 20;
11
12/// A caller checks this against [`MAX_PINNED_FRAME`]: a shrunk frame is not a pinned one.
13pub fn pinned_frame(secs: f64, sample_rate: f64) -> usize {
14    let asked = (secs * sample_rate).round().max(0.0);
15    if !asked.is_finite() || asked > MAX_PINNED_FRAME as f64 {
16        return MAX_PINNED_FRAME * 2;
17    }
18    (asked as usize).next_power_of_two().max(MIN_FRAME)
19}
20
21#[derive(Clone, Copy, Debug, PartialEq)]
22pub struct Band {
23    pub lo_hz: f64,
24    pub hi_hz: f64,
25    pub db: f64,
26}
27
28#[derive(Clone, Debug, PartialEq)]
29pub struct Spectrum {
30    pub frame_size: usize,
31    pub frames: usize,
32    pub resolution_hz: f64,
33    pub rms: f64,
34    pub centroid_hz: f64,
35    pub rolloff85_hz: f64,
36    pub bands: Vec<Band>,
37    pub peaks: Vec<Peak>,
38}
39
40pub fn analyze(
41    planes: &[&[f64]],
42    sample_rate: f64,
43    max_peaks: usize,
44    frame_secs: Option<f64>,
45) -> Spectrum {
46    let Framed {
47        mags,
48        bin_hz,
49        frame_size,
50        frames,
51        spanned,
52    } = magnitudes_of(planes, sample_rate, frame_secs);
53    let power = one_sided(&mags);
54    let total: f64 = power.iter().sum();
55
56    let centroid_hz = if total > 0.0 {
57        power
58            .iter()
59            .enumerate()
60            .map(|(k, p)| k as f64 * bin_hz * p)
61            .sum::<f64>()
62            / total
63    } else {
64        0.0
65    };
66
67    let mut running = 0.0;
68    let mut rolloff85_hz = 0.0;
69    for (k, p) in power.iter().enumerate() {
70        running += p;
71        if total > 0.0 && running >= 0.85 * total {
72            rolloff85_hz = k as f64 * bin_hz;
73            break;
74        }
75    }
76
77    let rms = crate::measure::envelope::level(planes);
78
79    Spectrum {
80        frame_size,
81        frames,
82        resolution_hz: bin_hz,
83        rms,
84        centroid_hz,
85        rolloff85_hz,
86        bands: bands(
87            &power,
88            1.5 * frame_size as f64 / spanned as f64,
89            bin_hz,
90            sample_rate,
91        ),
92        peaks: crate::measure::peaks::resolved(&mags, bin_hz, spanned, max_peaks),
93    }
94}
95
96/// 0 and Nyquist alone have no mirror folded in.
97fn one_sided(mags: &[f64]) -> Vec<f64> {
98    let last = mags.len() - 1;
99    mags.iter()
100        .enumerate()
101        .map(|(k, m)| match k == 0 || k == last {
102            true => m * m / 2.0,
103            false => m * m,
104        })
105        .collect()
106}
107
108/// A full-scale sine reads 1.0 at its own bin. Without `frame_secs` the size follows the
109/// range, so two ranges land on two bin grids.
110pub fn magnitudes(
111    samples: &[f64],
112    sample_rate: f64,
113    frame_secs: Option<f64>,
114) -> (Vec<f64>, f64, usize, usize) {
115    let f = magnitudes_of(&[samples], sample_rate, frame_secs);
116    (f.mags, f.bin_hz, f.frame_size, f.frames)
117}
118
119pub struct Framed {
120    pub mags: Vec<f64>,
121    pub bin_hz: f64,
122    pub frame_size: usize,
123    pub frames: usize,
124    /// The samples the Hann spans, fewer than `frame_size` where the range is.
125    pub spanned: usize,
126}
127
128pub fn magnitudes_of(planes: &[&[f64]], sample_rate: f64, frame_secs: Option<f64>) -> Framed {
129    let len = crate::measure::held(planes);
130    let frame_size = match frame_secs {
131        Some(secs) => pinned_frame(secs, sample_rate).min(MAX_PINNED_FRAME),
132        None => len.next_power_of_two().clamp(MIN_FRAME, MAX_FRAME),
133    };
134    let bins = frame_size / 2 + 1;
135    let spanned = len.clamp(1, frame_size);
136    let window = crate::stft::hann_periodic(spanned);
137
138    let starts = starts(len, frame_size);
139    let mut acc = vec![0f64; bins];
140    for start in &starts {
141        for samples in planes {
142            let mut re = vec![0f64; frame_size];
143            let mut im = vec![0f64; frame_size];
144            for (n, w) in window.iter().enumerate() {
145                re[n] = samples.get(start + n).copied().unwrap_or(0.0) * w;
146            }
147            fft(&mut re, &mut im);
148            for (k, a) in acc.iter_mut().enumerate() {
149                *a += re[k] * re[k] + im[k] * im[k];
150            }
151        }
152    }
153
154    let scale = 4.0 / spanned as f64;
155    let averaged = (starts.len() * planes.len()) as f64;
156    Framed {
157        mags: acc.iter().map(|p| (p / averaged).sqrt() * scale).collect(),
158        bin_hz: sample_rate / frame_size as f64,
159        frame_size,
160        frames: starts.len(),
161        spanned,
162    }
163}
164
165/// Whole frames, first sample to last, evenly at most half a frame apart.
166fn starts(len: usize, frame: usize) -> Vec<usize> {
167    let Some(past) = len.checked_sub(frame).filter(|past| *past > 0) else {
168        return vec![0];
169    };
170    let gaps = past.div_ceil(frame / 2);
171    (0..=gaps)
172        .map(|i| (2 * i * past + gaps) / (2 * gaps))
173        .collect()
174}
175
176/// Third-octave from 20 Hz up.
177pub fn third_octave_edges(sample_rate: f64) -> Vec<(f64, f64)> {
178    let nyquist = sample_rate / 2.0;
179    let ratio = 2f64.powf(1.0 / 3.0);
180    let mut out = Vec::new();
181    let mut lo = 20.0;
182    while lo < nyquist {
183        let hi = (lo * ratio).min(nyquist);
184        out.push((lo, hi));
185        lo = hi;
186    }
187    out
188}
189
190/// Over `enbw`, the noise bandwidth in bins, a band reads as the one sine carrying its power.
191fn bands(power: &[f64], enbw: f64, bin_hz: f64, sample_rate: f64) -> Vec<Band> {
192    let mut out = Vec::new();
193    for (lo, hi) in third_octave_edges(sample_rate) {
194        let sum: f64 = power
195            .iter()
196            .enumerate()
197            .filter(|(k, _)| {
198                let hz = *k as f64 * bin_hz;
199                hz >= lo && hz < hi
200            })
201            .map(|(_, p)| p)
202            .sum();
203        out.push(Band {
204            lo_hz: lo,
205            hi_hz: hi,
206            db: db((sum / enbw).sqrt()),
207        });
208    }
209    out
210}
sva_samples/measure/spectrum.rs

sva_samples/measure/
spectrum.rs
