bass-foundry/plugins/knurl/core/src/lib.rs

//! Knurl: texture per cycle of the played note. A cycle clock follows the tracked pitch and
//! restarts at every note; each cycle gets its own step gain (a repeating pattern that
//! makes subharmonics), a random level and timing, and a noise burst tuned to the note.
//! Every amount is counted in cycles, so the texture has the same grain on every note.
//!
//! The audio path is delayed by the tracker lookahead plus the timing-jitter headroom, so
//! the clock already knows each note when its attack leaves the plugin. Allocation-free
//! after `new`; mono-safe (both channels get the same treatment).
mod settings;
use common_dsp::svf::{Svf, SvfCoef};
use common_dsp::tracker::{PitchFollower, Tracker, TrackerConfig};
use common_dsp::{coefficient, db_to_gain, hz_to_midi};
pub use settings::{Seed, Settings, Source, GRIT_OFF, PATTERNS, STEPS, STEP_MIN};

/// Cycles kept for the editor's scope, and points per cycle.
pub const SCOPE_CYCLES: usize = 8;
pub const SCOPE_POINTS: usize = 64;
/// Timing jitter can move a cycle by at most this share of the lowest period.
const JITTER_HEADROOM: f32 = 0.125;
/// Effects fade in and out with the note over this time.
const FADE_MS: f32 = 20.;
/// The grit filter is retuned this often, in samples.
const RETUNE: usize = 16;
/// Level follower for scaling the grit to the input.
const LEVEL_MS: f32 = 30.;

#[derive(Clone, Copy, Debug)]
pub struct AnalyzerFrame {
    /// Fundamental the clock follows, 0 before the first note.
    pub hz: f32,
    /// Sounding note, rounded; None between notes.
    pub note: Option<u8>,
    /// Pattern step of the newest cycle.
    pub step: usize,
    /// Output of the last `SCOPE_CYCLES` cycles, oldest first, each resampled to
    /// `SCOPE_POINTS` points.
    pub scope: [[f32; SCOPE_POINTS]; SCOPE_CYCLES],
    /// True when the scope holds cycles of a sounding note.
    pub scope_valid: bool,
    pub input_db: f32,
    pub output_db: f32,
    pub latency: u32,
    pub sample_rate: f32,
}
impl Default for AnalyzerFrame {
    fn default() -> Self {
        Self {
            hz: 0.,
            note: None,
            step: 0,
            scope: [[0.; SCOPE_POINTS]; SCOPE_CYCLES],
            scope_valid: false,
            input_db: -120.,
            output_db: -120.,
            latency: 0,
            sample_rate: 48000.,
        }
    }
}

/// Deterministic per-cycle randomness: a hash of (stream, note seed, cycle).
fn hash(stream: u64, seed: u64, cycle: u64) -> u64 {
    let mut z = stream
        .wrapping_mul(0x9E37_79B9_7F4A_7C15)
        .wrapping_add(seed.wrapping_mul(0xBF58_476D_1CE4_E5B9))
        .wrapping_add(cycle.wrapping_mul(0x94D0_49BB_1331_11EB));
    z = (z ^ (z >> 30)).wrapping_mul(0xBF58_476D_1CE4_E5B9);
    z = (z ^ (z >> 27)).wrapping_mul(0x94D0_49BB_1331_11EB);
    z ^ (z >> 31)
}
fn uniform(stream: u64, seed: u64, cycle: u64) -> f32 {
    (hash(stream, seed, cycle) >> 40) as f32 / (1u64 << 24) as f32
}
/// Approximately normal, clamped to ±3 (sum of four uniforms, unit variance).
fn normal(stream: u64, seed: u64, cycle: u64) -> f32 {
    let s: f32 = (0..4).map(|i| uniform(stream, seed, cycle * 4 + i)).sum();
    ((s - 2.) * 3f32.sqrt()).clamp(-3., 3.)
}
/// Raised-cosine weight of the next cycle's value: 0 until `1 − width` of the cycle, then
/// rising to 1 at the boundary.
fn edge(frac: f32, width: f32) -> f32 {
    let t = ((frac - (1. - width)) / width).clamp(0., 1.);
    0.5 - 0.5 * (std::f32::consts::PI * t).cos()
}

const LEVEL: u64 = 1;
const TIME: u64 = 2;
const NOISE: u64 = 3;

/// What the clock needs, delayed by the jitter headroom so it lines up with the audio.
#[derive(Clone, Copy, Default)]
struct Pitch {
    hz: f32,
    start: bool,
    sounding: bool,
}

pub struct Engine {
    rate: f32,
    channels: usize,
    settings: Settings,
    /// Tracker lookahead.
    lookahead: usize,
    /// Largest timing offset in samples, either way.
    headroom: usize,
    tracker: Tracker,
    pitch: PitchFollower,
    pitch_line: Vec<Pitch>,
    pitch_at: usize,
    audio: Vec<[f32; 2]>,
    audio_at: usize,
    // Cycle clock.
    phase: f64,
    cycle: u64,
    note_seed: u64,
    notes: u64,
    noise_at: u64,
    amount: f32,
    fade: f32,
    // Grit.
    grit_coef: SvfCoef,
    grit_filter: Svf,
    countdown: usize,
    level: f32,
    level_coef: f32,
    // Smoothed controls.
    smooth: f32,
    mix: f32,
    output: f32,
    bypass: f32,
    fresh: bool,
    // Editor.
    scope: [[f32; SCOPE_POINTS]; SCOPE_CYCLES],
    scope_valid: bool,
    meter_in: f64,
    meter_out: f64,
    meter_count: usize,
}

impl Engine {
    pub fn new(rate: f32, channels: usize) -> Result<Self, &'static str> {
        if !(rate.is_finite() && (8000.0..=768000.).contains(&rate)) {
            return Err("unsupported sample rate");
        }
        if !(1..=2).contains(&channels) {
            return Err("unsupported channel count");
        }
        let tracker = Tracker::new(rate, TrackerConfig::BASS);
        let lookahead = tracker.latency();
        let headroom = (JITTER_HEADROOM * rate / TrackerConfig::BASS.min_hz).ceil() as usize;
        let settings = Settings::default();
        let mut e = Self {
            rate,
            channels,
            settings,
            lookahead,
            headroom,
            tracker,
            pitch: PitchFollower::default(),
            pitch_line: vec![Pitch::default(); headroom + 1],
            pitch_at: 0,
            // Reads reach `lookahead + 2·headroom` back, plus the interpolation taps.
            audio: vec![[0.; 2]; lookahead + 2 * headroom + 4],
            audio_at: 0,
            phase: 0.,
            cycle: 0,
            note_seed: 0,
            notes: 0,
            noise_at: 0,
            amount: 0.,
            fade: coefficient(rate, FADE_MS),
            grit_coef: SvfCoef::IDENTITY,
            grit_filter: Svf::default(),
            countdown: 0,
            level: 0.,
            level_coef: coefficient(rate, LEVEL_MS),
            smooth: coefficient(rate, 10.),
            mix: 1.,
            output: 1.,
            bypass: 0.,
            fresh: true,
            scope: [[0.; SCOPE_POINTS]; SCOPE_CYCLES],
            scope_valid: false,
            meter_in: 0.,
            meter_out: 0.,
            meter_count: 0,
        };
        e.set_settings(settings)?;
        e.fresh = true;
        Ok(e)
    }
    pub fn latency_samples(&self) -> u32 {
        (self.lookahead + self.headroom) as u32
    }
    pub fn channels(&self) -> usize {
        self.channels
    }
    pub fn settings(&self) -> Settings {
        self.settings
    }
    pub fn set_settings(&mut self, s: Settings) -> Result<(), &'static str> {
        s.validate()?;
        self.tracker.set(s.source == Source::Midi, s.gate, false);
        self.settings = s;
        if std::mem::take(&mut self.fresh) {
            self.mix = s.mix * 0.01;
            self.output = db_to_gain(s.output);
            self.bypass = f32::from(s.bypass);
        }
        Ok(())
    }
    pub fn reset(&mut self) {
        self.audio.fill([0.; 2]);
        self.pitch_line.fill(Pitch::default());
        self.pitch = PitchFollower::default();
        self.tracker.reset();
        self.grit_filter.reset();
        self.phase = 0.;
        self.cycle = 0;
        self.notes = 0;
        self.note_seed = 0;
        self.noise_at = 0;
        self.amount = 0.;
        self.level = 0.;
        self.countdown = 0;
        self.scope_valid = false;
        self.fresh = true;
    }
    pub fn note_on(&mut self, note: u8) {
        self.tracker.note_on(note);
    }
    pub fn note_off(&mut self, note: u8) {
        self.tracker.note_off(note);
    }
    /// The audio `back` samples (fractional) before the newest one, cubic Hermite.
    #[inline]
    fn read(&self, back: f32) -> [f32; 2] {
        let len = self.audio.len();
        let whole = back.floor();
        let t = back - whole;
        let base = whole as usize;
        let at = |back: usize| self.audio[(self.audio_at + len - back % len) % len];
        // y0 is one sample newer than y1; y2 and y3 are older.
        let (newer, p1, p2, p3) = (at(base.max(1) - 1), at(base), at(base + 1), at(base + 2));
        let mut out = [0.; 2];
        for c in 0..2 {
            let (y0, y1, y2, y3) = (newer[c], p1[c], p2[c], p3[c]);
            let c1 = 0.5 * (y2 - y0);
            let c2 = y0 - 2.5 * y1 + 2. * y2 - 0.5 * y3;
            let c3 = 0.5 * (y3 - y0) + 1.5 * (y1 - y2);
            out[c] = ((c3 * t + c2) * t + c1) * t + y1;
        }
        out
    }
    pub fn process_sample(&mut self, x: [f32; 2]) -> [f32; 2] {
        let mono = if self.channels == 2 {
            0.5 * (x[0] + x[1])
        } else {
            x[0]
        };
        let (pitch, snap) = (&mut self.pitch, self.settings.snap);
        self.tracker.process(mono, |e| pitch.event(snap, e));
        let (hz, jump) = self.pitch.step(1.);
        // Tracker events are timed for `lookahead`; the audio leaves `headroom` later.
        let len = self.pitch_line.len();
        self.pitch_line[self.pitch_at] = Pitch {
            hz,
            start: jump,
            sounding: self.tracker.sounding(),
        };
        self.pitch_at = (self.pitch_at + 1) % len;
        let p = self.pitch_line[self.pitch_at];

        let len = self.audio.len();
        self.audio_at = (self.audio_at + 1) % len;
        self.audio[self.audio_at] = x;
        let centre = (self.lookahead + self.headroom) as f32;
        let dry = self.read(centre);

        // Cycle clock.
        if p.start {
            self.phase = 0.;
            self.cycle = 0;
            self.notes += 1;
            self.noise_at = 0;
            self.note_seed = match self.settings.seed {
                Seed::Same => 0,
                Seed::Free => self.notes,
            };
            self.countdown = 0;
        }
        let active = p.sounding && p.hz > 0.;
        self.amount += (f32::from(active) - self.amount) * self.fade;
        let s = self.settings;
        let frac = self.phase.fract() as f32;
        let c = self.cycle;
        let seed = self.note_seed;
        let step = |k: u64| (k % s.steps as u64) as usize;

        // Pattern and level jitter, crossfaded into the next cycle.
        let w = edge(frac, s.edge * 0.01);
        let jitter_w = edge(frac, 0.5);
        let pattern = |k: u64| db_to_gain(s.pattern[step(k)]);
        let wobble = |k: u64| db_to_gain(s.level_jitter * normal(LEVEL, seed, k));
        let gain = (pattern(c) * (1. - w) + pattern(c + 1) * w)
            * (wobble(c) * (1. - jitter_w) + wobble(c + 1) * jitter_w);
        let gain = 1. + self.amount * (gain - 1.);

        // Timing jitter: an offset per cycle, blended across the whole cycle.
        let period = if p.hz > 0. { self.rate / p.hz } else { 0. };
        let shift = |k: u64| normal(TIME, seed, k) * s.time_jitter * 0.01 * period;
        let tw = edge(frac, 1.);
        let offset = (shift(c) * (1. - tw) + shift(c + 1) * tw) * self.amount;
        let offset = offset.clamp(-(self.headroom as f32), self.headroom as f32);
        let moved = if offset == 0. {
            dry
        } else {
            self.read(centre + offset)
        };

        // Grit: noise above `tone` harmonics, in a sin² window at `position` of each cycle.
        let mut grit = 0.;
        if s.grit > GRIT_OFF && p.hz > 0. && s.grit_steps[step(c)] {
            if self.countdown == 0 {
                let f = (s.tone * p.hz).min(0.45 * self.rate);
                self.grit_coef = SvfCoef::highpass(self.rate, f, std::f32::consts::FRAC_1_SQRT_2);
                self.countdown = RETUNE;
            }
            self.countdown -= 1;
            self.noise_at = self.noise_at.wrapping_add(1);
            let n = 2. * uniform(NOISE, seed, self.noise_at) - 1.;
            let hp = self.grit_filter.process(&self.grit_coef, n * 3f32.sqrt());
            let d = (frac - s.position * 0.01).rem_euclid(1.);
            let l = s.length * 0.01;
            if d < l {
                let window = (std::f32::consts::PI * d / l).sin().powi(2);
                grit = hp * window * self.level.sqrt() * db_to_gain(s.grit) * self.amount;
            }
        }
        let m = if self.channels == 2 {
            0.5 * (dry[0] + dry[1])
        } else {
            dry[0]
        };
        self.level += (m * m - self.level) * self.level_coef;
        // Advance the clock.
        if p.hz > 0. {
            self.phase += (p.hz / self.rate) as f64;
            let whole = self.phase.floor() as u64;
            if whole > 0 {
                self.phase -= whole as f64;
                self.cycle += whole;
                self.scope
                    .rotate_left(whole.min(SCOPE_CYCLES as u64) as usize);
                self.scope[SCOPE_CYCLES - 1] = [0.; SCOPE_POINTS];
            }
        }

        self.mix += (s.mix * 0.01 - self.mix) * self.smooth;
        self.output += (db_to_gain(s.output) - self.output) * self.smooth;
        self.bypass += (f32::from(s.bypass) - self.bypass) * self.smooth;
        let mut out = [0.; 2];
        for ch in 0..self.channels {
            let wet = moved[ch] * gain + grit;
            let mixed = (self.mix * wet + (1. - self.mix) * dry[ch]) * self.output;
            out[ch] = mixed * (1. - self.bypass) + dry[ch] * self.bypass;
        }
        let o = if self.channels == 2 {
            0.5 * (out[0] + out[1])
        } else {
            out[0]
        };
        if active {
            let i = ((frac * SCOPE_POINTS as f32) as usize).min(SCOPE_POINTS - 1);
            self.scope[SCOPE_CYCLES - 1][i] = o;
            self.scope_valid = true;
        }
        self.meter_in += (m * m) as f64;
        self.meter_out += (o * o) as f64;
        self.meter_count += 1;
        out
    }
    /// Editor data; levels are averaged since the previous call.
    pub fn take_analyzer(&mut self) -> AnalyzerFrame {
        let n = self.meter_count.max(1) as f64;
        let db = |p: f64| (10. * (p / n).max(1e-12).log10()).max(-120.) as f32;
        let mut f = AnalyzerFrame {
            hz: self.pitch.hz(),
            note: None,
            step: (self.cycle % self.settings.steps as u64) as usize,
            scope: self.scope,
            scope_valid: self.scope_valid,
            input_db: db(self.meter_in),
            output_db: db(self.meter_out),
            latency: self.latency_samples(),
            sample_rate: self.rate,
        };
        if self.tracker.sounding() && f.hz > 0. {
            f.note = Some(hz_to_midi(f.hz).round().clamp(0., 127.) as u8);
        }
        self.meter_in = 0.;
        self.meter_out = 0.;
        self.meter_count = 0;
        f
    }
}