Crate resonators 

A Rust implementation of Alexandre François’s Resonate algorithm for low-latency spectral analysis.

The primary type is ResonatorBank, a collection of independent resonators each tuned to a fixed frequency. Feed samples in one at a time with process_sample or in chunks with process_samples. Read per-bin magnitudes, powers, phases, or complex values at any time. For one-shot processing of a full signal into a spectrogram-like output, use resonate.

Resonator is the single-resonator analogue, useful when only one bin is needed.

In addition to its frequency, each resonator has two EWMA coefficients: alpha sets the time constant, and beta smooths the output. See ResonatorConfig for parameter details, or the paper for the full algorithm.

Example

The following example uses the common case, where both alpha and beta default to a per-frequency heuristic.

use resonators::ResonatorBank;

let sample_rate = 44_100.0;
let freqs = [110.0, 220.0, 440.0, 880.0];
let mut bank = ResonatorBank::from_frequencies(&freqs, sample_rate);

bank.process_samples(&vec![0.0f32; 1024]);
let magnitudes = bank.magnitudes();
assert_eq!(magnitudes.len(), 4);

The following example shows the equivalent with explicit ResonatorConfig values, useful when you need custom alpha or beta.

use resonators::{ResonatorBank, ResonatorConfig, heuristic_alpha};

let sample_rate = 44_100.0;
let configs: Vec<_> = [110.0, 220.0, 440.0, 880.0]
    .iter()
    .map(|&freq| {
        let alpha = heuristic_alpha(freq, sample_rate);
        let beta = alpha;
        ResonatorConfig::new(freq, alpha, beta)
    })
    .collect();
let mut bank = ResonatorBank::new(&configs, sample_rate);

bank.process_samples(&vec![0.0f32; 1024]);

Structs

Resonator

A single resonator tuned to a fixed frequency.

ResonatorBank

A bank of independent resonators, each tuned to a fixed frequency.

ResonatorConfig

Parameters for a single resonator.

Functions

alpha_from_tau

Converts an EWMA time constant tau (in seconds) to an alpha coefficient.

heuristic_alpha

Returns a reasonable default alpha (EWMA coefficient) for a resonator at the given frequency, using the per-frequency heuristic from the paper.

heuristic_alphas

Returns heuristic_alpha applied to each frequency in freqs.

midi_to_hz

Converts a MIDI note number to a frequency, in Hz, given a tuning reference for A4 (MIDI 69).

tau_from_alpha

Converts an alpha coefficient to an EWMA time constant tau, in seconds.