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

//! Harmonic EQ: bands sit on the harmonics of the played note instead of fixed frequencies,
//! so a cut on harmonic 3 stays on harmonic 3 on every note.
//!
//! The audio path is delayed by the tracker's lookahead, so the filters are already tuned to
//! a note when its attack leaves the plugin.
mod settings;
use common_dsp::meter::HarmonicMeter;
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::{Settings, Source, GAIN_MAX, GAIN_MIN, HARMONICS};

pub const MIN_HZ: f32 = TrackerConfig::BASS.min_hz;
pub const MAX_HZ: f32 = TrackerConfig::BASS.max_hz;
/// Harmonic bands plus the bands halfway between them.
const BANDS: usize = 2 * HARMONICS;
/// Filter coefficients are recomputed this often, in samples.
const RETUNE: usize = 16;
const GAIN_MS: f32 = 20.;

#[derive(Clone, Copy, Debug)]
pub struct AnalyzerFrame {
    /// Fundamental the filters are tuned to, 0 before the first note.
    pub hz: f32,
    /// Sounding note, rounded; None between notes.
    pub note: Option<u8>,
    /// Harmonic levels in dBFS of the delayed input and of the output (index 0 = fundamental).
    pub input: [f32; HARMONICS],
    pub output: [f32; HARMONICS],
    pub latency: u32,
    pub sample_rate: f32,
}
impl Default for AnalyzerFrame {
    fn default() -> Self {
        Self {
            hz: 0.,
            note: None,
            input: [-120.; HARMONICS],
            output: [-120.; HARMONICS],
            latency: 0,
            sample_rate: 48000.,
        }
    }
}

pub struct Engine {
    rate: f32,
    channels: usize,
    settings: Settings,
    latency: usize,
    delay: Vec<[f32; 2]>,
    delay_at: usize,
    tracker: Tracker,
    pitch: PitchFollower,
    hz: f32,
    hz_coef: f32,
    countdown: usize,
    coefs: [SvfCoef; BANDS],
    active: [bool; BANDS],
    gains: [f32; BANDS],
    state: [[Svf; BANDS]; 2],
    gain_coef: f32,
    smooth: f32,
    mix: f32,
    output: f32,
    bypass: f32,
    meter_in: HarmonicMeter,
    meter_out: HarmonicMeter,
    /// Smoothed controls start at the next settings instead of gliding from defaults.
    fresh: bool,
}

impl Engine {
    pub fn new(rate: f32, channels: usize) -> Result<Self, &'static str> {
        if !(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 latency = tracker.latency();
        let settings = Settings::default();
        let mut e = Self {
            rate,
            channels,
            settings,
            latency,
            delay: vec![[0.; 2]; latency + 1],
            delay_at: 0,
            tracker,
            pitch: PitchFollower::default(),
            hz: 0.,
            hz_coef: 1.,
            countdown: 0,
            coefs: [SvfCoef::IDENTITY; BANDS],
            active: [false; BANDS],
            gains: [0.; BANDS],
            state: [[Svf::default(); BANDS]; 2],
            gain_coef: coefficient(rate / RETUNE as f32, GAIN_MS),
            smooth: coefficient(rate, 10.),
            mix: 1.,
            output: 1.,
            bypass: 0.,
            meter_in: HarmonicMeter::new(rate, 85.),
            meter_out: HarmonicMeter::new(rate, 85.),
            fresh: true,
        };
        e.set_settings(settings)?;
        e.fresh = true;
        Ok(e)
    }
    pub fn latency_samples(&self) -> u32 {
        self.latency 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, s.smooth > 0.);
        self.hz_coef = coefficient(self.rate, s.smooth / 3.);
        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);
            self.gains = self.targets();
        }
        Ok(())
    }
    pub fn reset(&mut self) {
        self.delay.fill([0.; 2]);
        self.tracker.reset();
        for ch in &mut self.state {
            for f in ch.iter_mut() {
                f.reset();
            }
        }
        self.meter_in.reset();
        self.meter_out.reset();
        self.countdown = 0;
        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);
    }
    /// Gain targets in dB of every band for the current settings.
    fn targets(&self) -> [f32; BANDS] {
        let s = &self.settings;
        let mut t = [0.; BANDS];
        for k in 1..=s.harmonics as usize {
            t[k - 1] = s.effective(k);
            t[HARMONICS + k - 1] = s.between;
        }
        t
    }
    fn retune(&mut self, jump: bool) {
        let s = self.settings;
        let targets = self.targets();
        let width = s.width * 0.01;
        for b in 0..BANDS {
            self.gains[b] = if jump {
                targets[b]
            } else {
                self.gains[b] + (targets[b] - self.gains[b]) * self.gain_coef
            };
            if (self.gains[b] - targets[b]).abs() < 1e-4 {
                self.gains[b] = targets[b];
            }
            let order = if b < HARMONICS {
                (b + 1) as f32
            } else {
                (b - HARMONICS + 1) as f32 + 0.5
            };
            let centre = order * self.hz;
            let audible = self.hz > 0. && centre < 0.45 * self.rate;
            if audible && !self.active[b] {
                for ch in &mut self.state {
                    ch[b].reset();
                }
            }
            self.active[b] = audible && self.gains[b] != 0.;
            if self.active[b] {
                self.coefs[b] = SvfCoef::bell(self.rate, centre, order / width, self.gains[b]);
            }
        }
    }
    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 len = self.delay.len();
        self.delay[self.delay_at] = x;
        self.delay_at = (self.delay_at + 1) % len;
        let y = self.delay[self.delay_at];

        let first = self.hz == 0.;
        let (hz, jump) = self.pitch.step(self.hz_coef);
        let first = first && jump;
        self.hz = hz;
        if jump || self.countdown == 0 {
            self.retune(first);
            self.countdown = RETUNE;
        }
        self.countdown -= 1;

        let s = self.settings;
        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 c in 0..self.channels {
            let mut v = y[c];
            for b in 0..BANDS {
                if self.active[b] {
                    v = self.state[c][b].process(&self.coefs[b], v);
                }
            }
            let wet = (self.mix * v + (1. - self.mix) * y[c]) * self.output;
            out[c] = wet * (1. - self.bypass) + y[c] * self.bypass;
        }
        let hz = if self.tracker.sounding() { self.hz } else { 0. };
        let (dry, wet) = if self.channels == 2 {
            (0.5 * (y[0] + y[1]), 0.5 * (out[0] + out[1]))
        } else {
            (y[0], out[0])
        };
        self.meter_in.push(dry, hz);
        self.meter_out.push(wet, hz);
        out
    }
    pub fn take_analyzer(&self) -> AnalyzerFrame {
        let mut f = AnalyzerFrame {
            hz: self.hz,
            latency: self.latency as u32,
            sample_rate: self.rate,
            input: *self.meter_in.levels(),
            output: *self.meter_out.levels(),
            ..AnalyzerFrame::default()
        };
        if self.tracker.sounding() && self.hz > 0. {
            f.note = Some(hz_to_midi(self.hz).round().clamp(0., 127.) as u8);
        }
        f
    }
}