bass-foundry/plugins/knurl/core/tests/dsp.rs

use common_dsp::{midi_to_hz, Saw};
use knurl_core::{Engine, Seed, Settings, Source, GRIT_OFF, PATTERNS};

const RATE: f32 = 48000.;

/// A tanh saw bass at `note`, as the prototype used.
fn bass(note: u8, n: usize) -> Vec<f32> {
    let mut saw = Saw::new(RATE, midi_to_hz(note as f32));
    (0..n).map(|_| (2.2 * saw.sample()).tanh() * 0.5).collect()
}
fn plain() -> Settings {
    let mut s = Settings {
        source: Source::Midi,
        level_jitter: 0.,
        time_jitter: 0.,
        grit: GRIT_OFF,
        ..Settings::default()
    };
    s.apply_pattern(PATTERNS[0].2);
    s
}
/// Runs one held note from sample 0 and returns the output, aligned to the input.
fn run(settings: Settings, note: u8, input: &[f32]) -> Vec<f32> {
    let mut engine = Engine::new(RATE, 1).unwrap();
    engine.set_settings(settings).unwrap();
    let latency = engine.latency_samples() as usize;
    engine.note_on(note);
    let mut out: Vec<f32> = input
        .iter()
        .chain(std::iter::repeat_n(&0., latency))
        .map(|&x| engine.process_sample([x, 0.])[0])
        .collect();
    out.drain(..latency);
    out
}
/// Level of the component at `hz` (single-bin DFT with a Hann window), dB.
fn level(x: &[f32], hz: f32) -> f64 {
    let n = x.len();
    let (mut re, mut im) = (0f64, 0f64);
    for (i, &v) in x.iter().enumerate() {
        let w = 0.5 - 0.5 * (std::f64::consts::TAU * i as f64 / n as f64).cos();
        let a = std::f64::consts::TAU * hz as f64 * i as f64 / RATE as f64;
        re += w * v as f64 * a.cos();
        im -= w * v as f64 * a.sin();
    }
    10. * (re * re + im * im).max(1e-30).log10()
}
fn subharmonic(out: &[f32], note: u8, divisor: f32) -> f64 {
    let f = midi_to_hz(note as f32);
    let seg = &out[4800..out.len() - 4800];
    level(seg, f / divisor) - level(seg, f)
}
fn max_step(x: &[f32]) -> f32 {
    x.windows(2).map(|w| (w[1] - w[0]).abs()).fold(0., f32::max)
}

#[test]
fn everything_off_is_the_delayed_input() {
    let input = bass(29, 24000);
    let out = run(plain(), 29, &input);
    assert_eq!(out, input);
}

#[test]
fn patterns_make_tuned_subharmonics_without_clicks() {
    let input = bass(29, 48000);
    let base = run(plain(), 29, &input);
    assert!(subharmonic(&base, 29, 2.) < -50.);
    for (pattern, divisor, expected) in [(1, 2., -8.2), (2, 3., -10.7)] {
        let mut s = plain();
        s.apply_pattern(PATTERNS[pattern].2);
        let out = run(s, 29, &input);
        let sub = subharmonic(&out, 29, divisor);
        assert!(
            (sub - expected).abs() < 0.5,
            "{}: {sub}",
            PATTERNS[pattern].0
        );
        assert!(
            max_step(&out) <= 1.05 * max_step(&input),
            "{}",
            PATTERNS[pattern].0
        );
    }
}

#[test]
fn the_texture_is_the_same_on_every_note() {
    let mut s = plain();
    s.apply_pattern(PATTERNS[1].2);
    let low = run(s, 29, &bass(29, 48000));
    let high = run(s, 36, &bass(36, 48000));
    let (a, b) = (subharmonic(&low, 29, 2.), subharmonic(&high, 36, 2.));
    assert!((a - b).abs() < 0.3, "F1 {a} C2 {b}");
}

#[test]
fn same_seed_repeats_every_note_and_free_does_not() {
    for (seed, identical) in [(Seed::Same, true), (Seed::Free, false)] {
        let s = Settings {
            source: Source::Midi,
            seed,
            ..Settings::default()
        };
        let mut engine = Engine::new(RATE, 2).unwrap();
        engine.set_settings(s).unwrap();
        let latency = engine.latency_samples() as usize;
        let note = bass(29, 12000);
        let mut out = Vec::new();
        let starts = [0, 36000];
        for i in 0..72000 + latency {
            if starts.contains(&i) {
                engine.note_on(29);
            }
            if i == starts[0] + 12000 || i == starts[1] + 12000 {
                engine.note_off(29);
            }
            let k = starts
                .iter()
                .filter(|&&s| i >= s)
                .map(|&s| i - s)
                .min()
                .unwrap();
            let x = note.get(k).copied().unwrap_or(0.);
            out.push(engine.process_sample([x, x])[0]);
        }
        let first = &out[latency..latency + 12000];
        let second = &out[starts[1] + latency..starts[1] + latency + 12000];
        let largest = first
            .iter()
            .zip(second)
            .map(|(a, b)| (a - b).abs())
            .fold(0f32, f32::max);
        if identical {
            assert!(largest < 1e-4, "{seed:?}: {largest}");
        } else {
            assert!(largest > 1e-2, "{seed:?}: {largest}");
        }
        assert!(out.iter().all(|v| v.is_finite()));
    }
}

#[test]
fn grit_follows_the_input_level_and_stops_with_the_note() {
    let mut s = plain();
    s.grit = -6.;
    let input = bass(29, 24000);
    let out = run(s, 29, &input);
    let noise: f64 = out
        .iter()
        .zip(&input)
        .skip(4800)
        .map(|(o, i)| ((o - i) as f64).powi(2))
        .sum::<f64>()
        / (out.len() - 4800) as f64;
    let signal: f64 = input
        .iter()
        .skip(4800)
        .map(|v| (*v as f64).powi(2))
        .sum::<f64>()
        / (out.len() - 4800) as f64;
    let ratio = 10. * (noise / signal).log10();
    // −6 dB bursts over 12 % of each cycle; the sin² window keeps 3/8 of the power:
    // −6 + 10·log10(0.12 · 0.375) = −19.5 dB.
    assert!((ratio + 19.5).abs() < 1.5, "{ratio}");

    // Silence in, silence out: no grit without a note, and no NaN.
    let mut engine = Engine::new(RATE, 2).unwrap();
    engine.set_settings(Settings::default()).unwrap();
    for _ in 0..48000 {
        let out = engine.process_sample([0., 0.]);
        assert_eq!(out, [0., 0.]);
    }
}

#[test]
fn audio_source_finds_the_note_and_reports_latency() {
    let mut s = plain();
    s.source = Source::Audio;
    s.apply_pattern(PATTERNS[1].2);
    let mut engine = Engine::new(RATE, 1).unwrap();
    engine.set_settings(s).unwrap();
    let latency = engine.latency_samples() as usize;
    // About 67 ms of lookahead plus 4.2 ms of jitter headroom.
    assert!((latency as f32 / RATE - 0.071).abs() < 0.005, "{latency}");
    let input = bass(29, 48000);
    let mut out: Vec<f32> = input
        .iter()
        .map(|&x| engine.process_sample([x, 0.])[0])
        .collect();
    out.drain(..latency);
    let frame = engine.take_analyzer();
    assert_eq!(frame.note, Some(29));
    assert!(frame.scope_valid);
    let sub = subharmonic(&out[..out.len() - 4800], 29, 2.);
    assert!(sub > -14., "{sub}");
}

#[test]
fn invalid_settings_are_rejected() {
    let mut engine = Engine::new(RATE, 2).unwrap();
    for bad in [
        Settings {
            steps: 0,
            ..Settings::default()
        },
        Settings {
            edge: 60.,
            ..Settings::default()
        },
        Settings {
            grit: f32::NAN,
            ..Settings::default()
        },
        Settings {
            time_jitter: 11.,
            ..Settings::default()
        },
    ] {
        assert!(engine.set_settings(bad).is_err());
    }
    let mut s = Settings::default();
    s.pattern[3] = -30.;
    assert!(engine.set_settings(s).is_err());
    assert!(Engine::new(1000., 2).is_err());
    assert!(Engine::new(48000., 3).is_err());
    let json = serde_json::to_string(&Settings::default()).unwrap();
    assert_eq!(
        serde_json::from_str::<Settings>(&json).unwrap(),
        Settings::default()
    );
}