sva_samples/measure/
onsets.rs

1// Concern: spectral flux onset detection, each onset placed at the sample its strike rises | Non-concern: a tempo grid, what an onset means musically | IO: (&[f64], rate, start) -> Onsets
2
3use crate::measure::spectrum::{MAX_PINNED_FRAME, magnitudes, pinned_frame};
4
5/// ~23ms: short enough to localize a transient, long enough for low percussion.
6const FRAME_SECS: f64 = 0.023;
7/// Strikes 25 ms apart peak a few hops from each other.
8const HOP_SECS: f64 = FRAME_SECS / 8.0;
9/// Below this two novelty peaks are one transient's attack and decay.
10const MIN_ONSET_GAP_SECS: f64 = 0.02;
11const ADAPTIVE_WINDOW_SECS: f64 = 0.115;
12/// A roll's flux peaks barely over its mean; the strike tells it from a swell.
13const THRESHOLD_MULTIPLIER: f64 = 1.0;
14const THRESHOLD_DELTA: f64 = 1e-6;
15const IOI_BUCKET_SECS: f64 = 0.025;
16const IOI_MAX_SECS: f64 = 2.0;
17/// Under this share of the loudest frame a rise is leakage.
18const LEVEL_FRACTION: f64 = 0.03;
19const STRIKE_SPAN_SECS: f64 = 0.012;
20/// ~5 dB over the span before, carried on as it moved: a strike jumps off a ring's fall.
21const JUMP_ENERGY_RATIO: f64 = 3.0;
22
23#[derive(Clone, Copy, Debug, PartialEq)]
24pub struct Onset {
25    pub t_secs: f64,
26    pub strength: f64,
27}
28
29#[derive(Clone, Copy, Debug, PartialEq)]
30pub struct IoiBucket {
31    pub lo_secs: f64,
32    pub hi_secs: f64,
33    pub count: usize,
34}
35
36#[derive(Clone, Debug, PartialEq)]
37pub struct Onsets {
38    pub onsets: Vec<Onset>,
39    pub ioi_histogram: Vec<IoiBucket>,
40    pub resolution_secs: f64,
41}
42
43struct SpectralFrame {
44    t_secs: f64,
45    mags: Vec<f64>,
46    span_secs: f64,
47}
48
49fn spectral_frames(samples: &[f64], sample_rate: f64, start_secs: f64) -> Vec<SpectralFrame> {
50    let frame_len = pinned_frame(FRAME_SECS, sample_rate).min(MAX_PINNED_FRAME);
51    let hop = ((HOP_SECS * sample_rate).round() as usize).max(1);
52    (0..samples.len())
53        .step_by(hop)
54        .map(|start| {
55            let end = (start + frame_len).min(samples.len());
56            let (mags, ..) = magnitudes(&samples[start..end], sample_rate, Some(FRAME_SECS));
57            SpectralFrame {
58                t_secs: start_secs + start as f64 / sample_rate,
59                mags,
60                span_secs: frame_len as f64 / sample_rate,
61            }
62        })
63        .collect()
64}
65
66pub fn detect(samples: &[f64], sample_rate: f64, start_secs: f64) -> Onsets {
67    let frames = spectral_frames(samples, sample_rate, start_secs);
68    let floor = LEVEL_FRACTION * frames.iter().map(|f| total(&f.mags)).fold(0.0, f64::max);
69    let flux = flux_of(&frames, floor);
70    let onsets = pick_peaks(
71        &flux,
72        &frames,
73        &Energy::of(samples, sample_rate, start_secs),
74        floor,
75    );
76    Onsets {
77        ioi_histogram: ioi_histogram(&onsets),
78        onsets,
79        resolution_secs: HOP_SECS,
80    }
81}
82
83fn total(mags: &[f64]) -> f64 {
84    mags.iter().sum()
85}
86
87/// The rise into each frame; nothing precedes the buffer, so one opening above the floor
88/// opens on a rise from silence.
89fn flux_of(frames: &[SpectralFrame], floor: f64) -> Vec<f64> {
90    let opens_on_sound = frames
91        .first()
92        .is_some_and(|f| floor > 0.0 && total(&f.mags) > floor);
93    (0..frames.len())
94        .map(|i| match i {
95            0 => match opens_on_sound {
96                true => total(&frames[0].mags),
97                false => 0.0,
98            },
99            _ => spectral_flux(&frames[i - 1].mags, &frames[i].mags),
100        })
101        .collect()
102}
103
104pub(crate) fn spectral_flux(prev: &[f64], curr: &[f64]) -> f64 {
105    prev.iter().zip(curr).map(|(&p, &c)| (c - p).max(0.0)).sum()
106}
107
108/// A candidate clears the threshold and the floor, peaks over the gap, and holds a strike;
109/// a frame past the buffer's end reads silence.
110fn pick_peaks(flux: &[f64], frames: &[SpectralFrame], energy: &Energy, floor: f64) -> Vec<Onset> {
111    let mut onsets: Vec<Onset> = Vec::new();
112    let window = (ADAPTIVE_WINDOW_SECS / HOP_SECS).round() as usize;
113    let reach = (MIN_ONSET_GAP_SECS / 2.0 / HOP_SECS).round().max(1.0) as usize;
114    for i in 0..flux.len() {
115        let lo = i.saturating_sub(window);
116        let hi = (i + window + 1).min(flux.len());
117        let local = &flux[lo..hi];
118        let mean = local.iter().sum::<f64>() / local.len() as f64;
119        let threshold = THRESHOLD_DELTA + THRESHOLD_MULTIPLIER * mean;
120        let near = &flux[i.saturating_sub(reach)..(i + reach + 1).min(flux.len())];
121        if flux[i] <= threshold || flux[i] < floor || near.iter().any(|&v| v > flux[i]) {
122            continue;
123        }
124        let Some(t) = energy.strike(frames[i].t_secs, frames[i].span_secs) else {
125            continue;
126        };
127        if onsets
128            .last()
129            .is_some_and(|o| t - o.t_secs < MIN_ONSET_GAP_SECS)
130        {
131            continue;
132        }
133        onsets.push(Onset {
134            t_secs: t,
135            strength: flux[i],
136        });
137    }
138    onsets
139}
140
141struct Energy {
142    running: Vec<f64>,
143    sample_rate: f64,
144    start_secs: f64,
145    reach: usize,
146    floor: f64,
147}
148
149impl Energy {
150    fn of(samples: &[f64], sample_rate: f64, start_secs: f64) -> Energy {
151        let mut running = Vec::with_capacity(samples.len() + 1);
152        running.push(0.0);
153        for s in samples {
154            let held = running[running.len() - 1];
155            running.push(held + s * s);
156        }
157        let reach = (STRIKE_SPAN_SECS * sample_rate).round().max(1.0) as usize;
158        let loudest = (0..samples.len())
159            .map(|n| running[(n + reach).min(samples.len())] - running[n])
160            .fold(0.0, f64::max);
161        Energy {
162            running,
163            sample_rate,
164            start_secs,
165            reach,
166            floor: LEVEL_FRACTION * LEVEL_FRACTION * loudest,
167        }
168    }
169
170    /// The energy of samples `[from, to)`, silence outside the buffer.
171    fn over(&self, from: usize, to: usize) -> f64 {
172        let last = self.running.len() - 1;
173        self.running[to.min(last)] - self.running[from.min(last)]
174    }
175
176    /// The sample whose energy after most outweighs the energy before it and the floor, if
177    /// by a strike's jump over that energy carried on as it moved.
178    fn strike(&self, from_secs: f64, span_secs: f64) -> Option<f64> {
179        let at = |secs: f64| {
180            ((secs - self.start_secs) * self.sample_rate)
181                .round()
182                .max(0.0) as usize
183        };
184        let (from, to) = (at(from_secs), at(from_secs + span_secs));
185        let before = |n: usize| self.over(n.saturating_sub(self.reach), n) + self.floor;
186        let mut best: Option<(f64, usize)> = None;
187        for n in from..to.min(self.running.len() - 1) {
188            let after = self.over(n, n + self.reach);
189            if before(n) == 0.0 {
190                continue;
191            }
192            let ratio = after / before(n);
193            if best.is_none_or(|(r, _)| ratio >= r) {
194                best = Some((ratio, n));
195            }
196        }
197        let (ratio, n) = best?;
198        let carried = before(n) / before(n.saturating_sub(self.reach));
199        (ratio / carried >= JUMP_ENERGY_RATIO)
200            .then(|| self.start_secs + n as f64 / self.sample_rate)
201    }
202}
203
204fn ioi_histogram(onsets: &[Onset]) -> Vec<IoiBucket> {
205    let n = (IOI_MAX_SECS / IOI_BUCKET_SECS).ceil() as usize + 1;
206    let mut counts = vec![0usize; n];
207    for w in onsets.windows(2) {
208        let ioi = w[1].t_secs - w[0].t_secs;
209        counts[((ioi / IOI_BUCKET_SECS) as usize).min(n - 1)] += 1;
210    }
211    counts
212        .into_iter()
213        .enumerate()
214        .map(|(i, count)| IoiBucket {
215            lo_secs: i as f64 * IOI_BUCKET_SECS,
216            hi_secs: if i + 1 == n {
217                f64::INFINITY
218            } else {
219                (i + 1) as f64 * IOI_BUCKET_SECS
220            },
221            count,
222        })
223        .collect()
224}
sva_samples/measure/onsets.rs

sva_samples/measure/
onsets.rs
