oximedia-effects 0.1.7

Professional audio effects suite for OxiMedia
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138

//! Moog ladder filter simulation.

use crate::AudioEffect;

/// Moog ladder filter configuration.
#[derive(Debug, Clone)]
pub struct MoogConfig {
    /// Cutoff frequency in Hz.
    pub frequency: f32,
    /// Resonance (0.0 - 1.0).
    pub resonance: f32,
}

impl Default for MoogConfig {
    fn default() -> Self {
        Self {
            frequency: 1000.0,
            resonance: 0.3,
        }
    }
}

/// Moog ladder filter - classic 4-pole low-pass.
pub struct MoogFilter {
    // Four filter stages
    stage: [f32; 4],
    // Delay elements
    delay: [f32; 4],
    // Coefficients
    cutoff: f32,
    resonance: f32,
    config: MoogConfig,
    sample_rate: f32,
}

impl MoogFilter {
    /// Create new Moog filter.
    #[must_use]
    pub fn new(config: MoogConfig, sample_rate: f32) -> Self {
        let mut filter = Self {
            stage: [0.0; 4],
            delay: [0.0; 4],
            cutoff: 0.0,
            resonance: 0.0,
            config,
            sample_rate,
        };
        filter.update_coefficients();
        filter
    }

    fn update_coefficients(&mut self) {
        // Calculate cutoff coefficient
        let fc = self.config.frequency / (self.sample_rate * 0.5);
        self.cutoff = fc * 1.16;

        // Calculate resonance feedback
        self.resonance = self.config.resonance * 4.0;
    }

    /// Set cutoff frequency.
    pub fn set_frequency(&mut self, frequency: f32) {
        self.config.frequency = frequency.clamp(20.0, self.sample_rate * 0.4);
        self.update_coefficients();
    }

    /// Set resonance.
    pub fn set_resonance(&mut self, resonance: f32) {
        self.config.resonance = resonance.clamp(0.0, 1.0);
        self.update_coefficients();
    }

    fn tanh_approx(x: f32) -> f32 {
        if x < -3.0 {
            -1.0
        } else if x > 3.0 {
            1.0
        } else {
            x * (27.0 + x * x) / (27.0 + 9.0 * x * x)
        }
    }
}

impl AudioEffect for MoogFilter {
    fn process_sample(&mut self, input: f32) -> f32 {
        // Add resonance feedback
        let input_with_fb = input - self.resonance * self.stage[3];

        // Process through 4 stages
        for i in 0..4 {
            let stage_input = if i == 0 {
                input_with_fb
            } else {
                self.stage[i - 1]
            };

            self.stage[i] = self.delay[i]
                + self.cutoff * (Self::tanh_approx(stage_input) - Self::tanh_approx(self.delay[i]));
            self.delay[i] = self.stage[i];
        }

        self.stage[3]
    }

    fn reset(&mut self) {
        self.stage.fill(0.0);
        self.delay.fill(0.0);
    }
}

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

    #[test]
    fn test_moog_filter() {
        let config = MoogConfig::default();
        let mut filter = MoogFilter::new(config, 48000.0);

        let output = filter.process_sample(1.0);
        assert!(output.is_finite());
    }

    #[test]
    fn test_moog_resonance() {
        let config = MoogConfig {
            frequency: 1000.0,
            resonance: 0.8,
        };
        let mut filter = MoogFilter::new(config, 48000.0);

        for _ in 0..1000 {
            let output = filter.process_sample(0.5);
            assert!(output.is_finite());
            assert!(output.abs() < 10.0); // Should not explode
        }
    }
}