phonic 0.16.0

Audio playback library
Documentation 
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//! DSP tools, musical unit conversion functions and related UI tools.

// -------------------------------------------------------------------------------------------------

pub(crate) mod dsp;
pub(crate) mod event;
pub(crate) mod fader;
pub(crate) mod resampler;
pub(crate) mod time;

pub mod ahdsr;
pub mod buffer;
#[cfg(feature = "fundsp")]
pub mod fundsp;
pub mod smoothing;
pub mod waveform;

// -------------------------------------------------------------------------------------------------

/// dB value, which is treated as zero volume factor
const MINUS_INF_IN_DB: f32 = -200.0f32;

// -------------------------------------------------------------------------------------------------

/// Convert a linear volume factor to dB.
pub fn linear_to_db(value: f32) -> f32 {
    const LIN_TO_DB_FACTOR: f32 = 20.0 / std::f32::consts::LN_10;
    if value < 0.0 || value.is_nan() {
        return f32::NAN;
    } else if value == 1.0 {
        return 0.0; // avoid rounding errors at exactly 0 dB
    } else if value > 1e-12f32 {
        return value.ln() * LIN_TO_DB_FACTOR;
    }
    MINUS_INF_IN_DB
}

// -------------------------------------------------------------------------------------------------

/// Convert volume in dB to a linear volume factor.
pub fn db_to_linear(value: f32) -> f32 {
    const DB_TO_LIN_FACTOR: f32 = std::f32::consts::LN_10 / 20.0;
    if value.is_nan() {
        return f32::NAN;
    } else if value == 0.0 {
        return 1.0f32; // avoid rounding errors at exactly 0 dB
    } else if value > MINUS_INF_IN_DB {
        return (value * DB_TO_LIN_FACTOR).exp();
    }
    0.0f32
}

// -------------------------------------------------------------------------------------------------

/// Convert a \[-1,1\] ranged pan factor to a constant power L/R channel volume factors
pub fn panning_factors(pan_factor: f32) -> (f32, f32) {
    const POWER: f32 = std::f32::consts::FRAC_1_SQRT_2; // 1/√2
    let normalized = (pan_factor.clamp(-1.0, 1.0) + 1.0) / 2.0;
    let left = (1.0 - normalized).sqrt() / POWER;
    let right = (normalized).sqrt() / POWER;
    (left, right)
}

// -------------------------------------------------------------------------------------------------

/// Calculate playback speed from a MIDI note, using middle C (note number 60) as base note.
pub fn speed_from_note(midi_note: u8) -> f64 {
    // Middle Note C6 = MIDI note 60
    pitch_from_note(midi_note) / pitch_from_note(60)
}

// -------------------------------------------------------------------------------------------------

/// Calculate Hz from a MIDI note with equal tuning based on A4 = a' = 440 Hz.
pub fn pitch_from_note(midi_note: u8) -> f64 {
    // A4 = MIDI note 69
    440.0 * 2.0_f64.powf((midi_note as f64 - 69.0) / 12.0)
}

// -------------------------------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;

    macro_rules! assert_eq_with_epsilon {
        ($x:expr, $y:expr, $d:expr) => {
            if !($x - $y < $d || $y - $x < $d) {
                panic!();
            }
        };
    }

    #[test]
    fn lin_db_conversion() {
        assert_eq!(linear_to_db(1.0), 0.0);
        assert_eq!(linear_to_db(0.0), MINUS_INF_IN_DB);
        assert_eq!(db_to_linear(MINUS_INF_IN_DB), 0.0);
        assert_eq!(db_to_linear(0.0), 1.0);
        assert_eq_with_epsilon!(linear_to_db(db_to_linear(20.0)), 20.0, 0.0001);
        assert_eq_with_epsilon!(linear_to_db(db_to_linear(-20.0)), -20.0, 0.0001);
        assert!(db_to_linear(f32::NAN).is_nan());
        assert!(linear_to_db(-1.0).is_nan());
    }
}