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

use quench_core::{shape, Engine, Monitor, Settings};
use std::f64::consts::TAU;

const RATE: f32 = 48000.;
/// Partials of the top: not harmonics of the sub, so their clipping products can be told
/// apart from the sub's own harmonics.
const TOPS: [f64; 5] = [437., 611., 1013., 1597., 2399.];

fn top(t: f64) -> f64 {
    TOPS.iter()
        .enumerate()
        .map(|(i, f)| (TAU * f * t + i as f64).sin())
        .sum::<f64>()
        / 4.2
}
/// Mono render of `seconds` of `signal`, returned as the left channel.
fn render(
    engine: &mut Engine,
    seconds: f32,
    monitor: Monitor,
    signal: impl Fn(f64) -> f64,
) -> Vec<f32> {
    let n = (seconds * RATE) as usize;
    (0..n)
        .map(|i| {
            let v = signal(i as f64 / RATE as f64) as f32;
            engine.process_sample([v, v], monitor)[0]
        })
        .collect()
}
fn engine(s: Settings) -> Engine {
    let mut e = Engine::new(RATE, 2).unwrap();
    e.set_settings(s).unwrap();
    e
}
/// Amplitude of `hz` over a whole number of its periods at the end of `x`.
fn amplitude(x: &[f32], hz: f64) -> f64 {
    let n = (RATE as f64 / hz * (0.5 * hz).floor()) as usize;
    let x = &x[x.len() - n..];
    let (mut re, mut im) = (0., 0.);
    for (i, &v) in x.iter().enumerate() {
        let a = TAU * hz * i as f64 / RATE as f64;
        re += v as f64 * a.cos();
        im += v as f64 * a.sin();
    }
    2. * (re * re + im * im).sqrt() / n as f64
}
/// Hann-windowed spectrum magnitude of the last half second, 2 Hz bins up to `top_bin`.
fn spectrum(x: &[f32], top_bin: usize) -> Vec<f64> {
    let n = RATE as usize / 2;
    let x = &x[x.len() - n..];
    let w: Vec<f64> = (0..n)
        .map(|i| 0.5 - 0.5 * (TAU * i as f64 / n as f64).cos())
        .collect();
    let norm: f64 = w.iter().sum();
    (0..=top_bin)
        .map(|b| {
            let (mut re, mut im) = (0., 0.);
            for i in 0..n {
                let a = TAU * b as f64 * i as f64 / n as f64;
                re += x[i] as f64 * w[i] * a.cos();
                im += x[i] as f64 * w[i] * a.sin();
            }
            2. * (re * re + im * im).sqrt() / norm
        })
        .collect()
}
/// Everything below 110 Hz except the 50 Hz sub, against the sub, in dB.
fn low_junk(x: &[f32]) -> f64 {
    let s = spectrum(x, 55);
    let junk: f64 = s
        .iter()
        .enumerate()
        .filter(|(b, _)| !(22..=28).contains(b) && *b > 0)
        .map(|(_, v)| v * v)
        .sum();
    let sub: f64 = s[22..=28].iter().map(|v| v * v).sum();
    10. * (junk / sub).log10()
}
fn db(r: f64) -> f64 {
    20. * r.log10()
}

#[test]
fn below_the_ceiling_the_signal_passes_unchanged() {
    let mut e = engine(Settings::default());
    let signal = |t: f64| 0.3 * (TAU * 50. * t).sin() + 0.2 * (TAU * 1000. * t).sin();
    let out = render(&mut e, 1., Monitor::Quench, signal);
    for (hz, a) in [(50., 0.3), (1000., 0.2)] {
        let got = db(amplitude(&out, hz) / a);
        assert!(got.abs() < 0.02, "{hz} Hz: {got:.3} dB");
    }
    let f = e.take_analyzer();
    assert_eq!(f.top_clip, 0.);
    assert_eq!(f.safety, 0.);
    let mut e = engine(Settings::default());
    let delta = render(&mut e, 0.2, Monitor::Delta, signal);
    assert!(delta.iter().all(|v| v.abs() < 1e-4));
}

#[test]
fn the_output_never_passes_the_ceiling() {
    let mut seed = 1u32;
    let noise: Vec<f64> = (0..RATE as usize)
        .map(|_| {
            seed = seed.wrapping_mul(1664525).wrapping_add(1013904223);
            (seed >> 8) as f64 / (1u32 << 24) as f64 * 2. - 1.
        })
        .collect();
    for ceiling in [-6., -0.3, 0.] {
        for soft in [0., 50., 100.] {
            for monitor in [Monitor::Quench, Monitor::Plain] {
                let mut e = engine(Settings {
                    drive: 24.,
                    ceiling,
                    soft,
                    ..Settings::default()
                });
                let out = render(&mut e, 1., monitor, |t| {
                    let i = ((t * RATE as f64) as usize).min(noise.len() - 1);
                    0.4 * (TAU * 41. * t).sin() + 0.3 * top(t) + 0.2 * noise[i]
                });
                let limit = 10f32.powf(ceiling / 20.) * (1. + 1e-6);
                let peak = out.iter().fold(0f32, |m, v| m.max(v.abs()));
                assert!(
                    peak <= limit,
                    "{ceiling} dB, soft {soft}, {monitor:?}: {peak}"
                );
            }
        }
    }
}

#[test]
fn the_sub_keeps_its_level_and_the_low_band_stays_clean() {
    // A quiet sub under a top that peaks far over the ceiling: the hard case for a clipper.
    let signal = |t: f64| 0.3 * (TAU * 50. * t).sin() + 2. * top(t);
    let mut results = Vec::new();
    for monitor in [Monitor::Quench, Monitor::Plain] {
        let mut e = engine(Settings::default());
        let out = render(&mut e, 1.5, monitor, signal);
        let sub = db(amplitude(&out, 50.) / 0.3);
        results.push((sub, low_junk(&out)));
    }
    let [(q_sub, q_junk), (p_sub, p_junk)] = [results[0], results[1]];
    assert!(q_sub.abs() < 0.2, "Quench changes the sub by {q_sub:.2} dB");
    assert!(
        p_sub < -0.8,
        "a plain clip should squash the sub: {p_sub:.2} dB"
    );
    assert!(
        q_junk < p_junk - 10.,
        "low-band products: Quench {q_junk:.1} dB, plain {p_junk:.1} dB"
    );
}

#[test]
fn the_meter_shows_how_much_less_the_low_band_changes() {
    let mut e = engine(Settings::default());
    render(&mut e, 1.5, Monitor::Quench, |t| {
        0.3 * (TAU * 50. * t).sin() + 2. * top(t)
    });
    let f = e.take_analyzer();
    assert!(
        f.low_quench < f.low_plain - 10.,
        "Quench {:.1} dB, plain {:.1} dB",
        f.low_quench,
        f.low_plain
    );
    assert!(f.top_clip > 6.);
    // The oversampled clip leaves the safety clip after the downsampler almost idle.
    assert!(f.safety < 0.2, "{}", f.safety);
    let mut e = engine(Settings::default());
    render(&mut e, 0.5, Monitor::Quench, |t| {
        0.5 * (TAU * 1000. * t).sin()
    });
    assert!(
        e.take_analyzer().low_quench.is_nan(),
        "no sub, nothing to compare"
    );
}

#[test]
fn a_sub_over_the_ceiling_leaves_no_room_and_is_still_limited() {
    let mut e = engine(Settings {
        ceiling: -6.,
        ..Settings::default()
    });
    let out = render(&mut e, 1., Monitor::Quench, |t| {
        0.8 * (TAU * 50. * t).sin() + 0.3 * top(t)
    });
    let f = e.take_analyzer();
    assert!(f.sub_peak > -6., "{}", f.sub_peak);
    assert!(f.safety > 0.);
    let peak = out.iter().fold(0f32, |m, v| m.max(v.abs()));
    assert!(peak <= 0.5012 * (1. + 1e-6));
    let room = f.scope_room.iter().fold(0f32, |m, v| m.max(*v));
    assert_eq!(room, 0., "the held sub peak is over the ceiling");
}

#[test]
fn the_held_peak_keeps_the_tops_room_steady_through_the_cycle() {
    let room_ripple = |hold: f32, hz: f64| {
        let mut e = engine(Settings {
            hold,
            ..Settings::default()
        });
        render(&mut e, 1., Monitor::Quench, |t| {
            0.5 * (TAU * hz * t).sin() + 0.3 * top(t)
        });
        let f = e.take_analyzer();
        let (lo, hi) = f
            .scope_room
            .iter()
            .fold((f32::MAX, f32::MIN), |(a, b), v| (a.min(*v), b.max(*v)));
        (hi - lo) / hi
    };
    // 30 Hz: the sub peaks every 16.7 ms.
    let held = room_ripple(60., 30.);
    let short = room_ripple(10., 30.);
    assert!(held < 0.01, "{held}");
    assert!(short > 0.1, "{short}");
}

#[test]
fn bypass_is_the_input_delayed_by_the_latency() {
    let mut e = engine(Settings {
        bypass: true,
        drive: 12.,
        ..Settings::default()
    });
    let latency = e.latency_samples() as usize;
    let x: Vec<f32> = (0..4800)
        .map(|i| (0.9 * (TAU * 50. * i as f64 / RATE as f64).sin()) as f32 + 0.5)
        .collect();
    let out: Vec<f32> = x
        .iter()
        .map(|&v| e.process_sample([v, v], Monitor::Quench)[0])
        .collect();
    for i in latency..x.len() {
        assert_eq!(out[i], x[i - latency]);
    }
}

#[test]
fn mono_works_and_the_shape_never_passes_its_limit() {
    let mut e = Engine::new(44100., 1).unwrap();
    e.set_settings(Settings {
        drive: 12.,
        ..Settings::default()
    })
    .unwrap();
    for i in 0..44100 {
        let v = (TAU * 55. * i as f64 / 44100.).sin() as f32;
        let o = e.process_sample([v, 0.], Monitor::Quench);
        assert!(o[0].abs() <= 0.9661 && o[1] == 0.);
    }
    for knee in [0., 0.3, 1.] {
        for h in [-5., -1., -0.2, 0., 0.5, 0.99, 3.] {
            let y = shape(h, 0.8, knee);
            assert!(y.abs() <= 0.8 && y * h >= 0.);
        }
    }
    assert_eq!(shape(0.5, 0.8, 0.), 0.5);
    assert_eq!(shape(0.5, 0., 0.), 0.);
}

#[test]
fn settings_are_validated_and_serialise() {
    assert!(Settings::default().validate().is_ok());
    for bad in [
        Settings {
            drive: -1.,
            ..Settings::default()
        },
        Settings {
            ceiling: 0.5,
            ..Settings::default()
        },
        Settings {
            split: 20.,
            ..Settings::default()
        },
        Settings {
            hold: f32::NAN,
            ..Settings::default()
        },
    ] {
        assert!(bad.validate().is_err());
        assert!(Engine::new(RATE, 2).unwrap().set_settings(bad).is_err());
    }
    let s = Settings {
        drive: 9.,
        soft: 40.,
        ..Settings::default()
    };
    let json = serde_json::to_string(&s).unwrap();
    assert_eq!(serde_json::from_str::<Settings>(&json).unwrap(), s);
    assert!(serde_json::from_str::<Settings>(r#"{"drive":0,"oops":1}"#).is_err());
}