Initial commit

src/noise.rs

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+//! Colored noise generators.
+//!
+//! Transforms white noise into spectrally-shaped noise with different frequency
+//! characteristics. Both generators are stateful filters that process white noise
+//! sample-by-sample.
+//!
+//! # Noise Colors
+//!
+//! | Color | Slope      | Character                        |
+//! |-------|------------|----------------------------------|
+//! | White | 0 dB/oct   | Equal energy per frequency       |
+//! | Pink  | -3 dB/oct  | Equal energy per octave          |
+//! | Brown | -6 dB/oct  | Rumbling, emphasizes low freqs   |
+
+/// Pink noise generator using the Voss-McCartney algorithm.
+///
+/// Applies a parallel bank of first-order lowpass filters to shape white noise
+/// into pink noise with -3 dB/octave rolloff. The coefficients approximate an
+/// ideal pink spectrum across the audio range.
+///
+/// Also known as 1/f noise, pink noise has equal energy per octave, making it
+/// useful for audio testing and as a natural-sounding noise source.
+#[derive(Clone, Copy)]
+pub struct PinkNoise {
+    b: [f32; 7],
+}
+
+impl Default for PinkNoise {
+    fn default() -> Self {
+        Self { b: [0.0; 7] }
+    }
+}
+
+impl PinkNoise {
+    /// Processes one white noise sample and returns the corresponding pink noise sample.
+    ///
+    /// The input should be uniformly distributed white noise in the range `[-1, 1]`.
+    /// Output is scaled to approximately the same amplitude range.
+    pub fn next(&mut self, white: f32) -> f32 {
+        self.b[0] = 0.99886 * self.b[0] + white * 0.0555179;
+        self.b[1] = 0.99332 * self.b[1] + white * 0.0750759;
+        self.b[2] = 0.96900 * self.b[2] + white * 0.153852;
+        self.b[3] = 0.86650 * self.b[3] + white * 0.3104856;
+        self.b[4] = 0.55000 * self.b[4] + white * 0.5329522;
+        self.b[5] = -0.7616 * self.b[5] - white * 0.0168980;
+        let pink = self.b[0]
+            + self.b[1]
+            + self.b[2]
+            + self.b[3]
+            + self.b[4]
+            + self.b[5]
+            + self.b[6]
+            + white * 0.5362;
+        self.b[6] = white * 0.115926;
+        pink * 0.11
+    }
+}
+
+/// Brown noise generator using leaky integration.
+///
+/// Applies a simple first-order lowpass filter (leaky integrator) to produce
+/// noise with -6 dB/octave rolloff. Named after Robert Brown (Brownian motion),
+/// not the color.
+///
+/// Also known as red noise or random walk noise. Has a deep, rumbling character
+/// with strong low-frequency content.
+#[derive(Clone, Copy)]
+pub struct BrownNoise {
+    out: f32,
+}
+
+impl Default for BrownNoise {
+    fn default() -> Self {
+        Self { out: 0.0 }
+    }
+}
+
+impl BrownNoise {
+    /// Processes one white noise sample and returns the corresponding brown noise sample.
+    ///
+    /// The input should be uniformly distributed white noise in the range `[-1, 1]`.
+    /// Output amplitude depends on the integration coefficient.
+    pub fn next(&mut self, white: f32) -> f32 {
+        self.out = (self.out + 0.02 * white) / 1.02;
+        self.out
+    }
+}