rill-router 0.4.0

Audio routing, mixing, and equalization for Rill
Documentation 
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//! Utility functions for EQ

/// Parse band parameter string like "band_0_freq" -> (0, "freq")
pub fn parse_band_param(name: &str) -> Option<(usize, &str)> {
    if name.starts_with("band_") {
        let rest = &name[5..];
        if let Some(underscore) = rest.find('_') {
            let (idx_str, param) = rest.split_at(underscore);
            let param = &param[1..]; // remove '_'

            if let Ok(idx) = idx_str.parse::<usize>() {
                return Some((idx, param));
            }
        }
    }
    None
}

/// Calculate logarithmic frequency spacing
pub fn log_spaced_frequencies(start_hz: f32, end_hz: f32, num_bands: usize) -> Vec<f32> {
    if num_bands == 0 {
        return Vec::new();
    }

    let start_log = start_hz.ln();
    let end_log = end_hz.ln();
    let step = (end_log - start_log) / (num_bands - 1) as f32;

    (0..num_bands)
        .map(|i| (start_log + i as f32 * step).exp())
        .collect()
}

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

    #[test]
    fn test_parse_band_param() {
        assert_eq!(parse_band_param("band_0_freq"), Some((0, "freq")));
        assert_eq!(parse_band_param("band_5_gain"), Some((5, "gain")));
        assert_eq!(parse_band_param("band_10_q"), Some((10, "q")));
        assert_eq!(parse_band_param("band_0"), None);
        assert_eq!(parse_band_param("output_gain"), None);
    }

    #[test]
    fn test_log_spaced_frequencies() {
        let freqs = log_spaced_frequencies(20.0, 20000.0, 5);
        assert_eq!(freqs.len(), 5);
        assert!((freqs[0] - 20.0).abs() < 0.1);
        assert!((freqs[4] - 20000.0).abs() < 0.1);

        // Should be increasing
        for i in 1..freqs.len() {
            assert!(freqs[i] > freqs[i - 1]);
        }
    }
}