dataviz engineer w/ passion for algorithms, maps & music
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Edited
Sep 25, 2024
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function DTF(samples) {
const N = samples.length;
const frequencies = [];
// for each harmonic k...
for (let k = 0; k < N; k++) {
// ...spin the signal backwards k times (in radians)
const rate = -1 * (2 * Math.PI) * k;
let re = 0;
let im = 0;
// for every point in time...
for (let t = 0; t < N; t++) {
// How far around the circle have we gone at time = t?
const time = t / N;
const distance = rate * time;
// datapoint * e^(-i*2*pi*f) is complex, store each part
const re_part = samples[t] * Math.cos(distance);
const im_part = samples[t] * Math.sin(distance);
// add this data point's contribution
re += re_part;
im += im_part;
}
// Close to zero? You're zero.
if (Math.abs(re) < 1e-10) {
re = 0;
}
if (Math.abs(im) < 1e-10) {
im = 0;
}
// Average contribution at this harmonic
re = re / N;
im = im / N;
frequencies[k] = {
re: re,
im: im,
freq: k,
amp: Math.sqrt(re * re + im * im),
phase: (Math.atan2(im, re) * 180) / Math.PI // in degrees
};
}
return frequencies;
}
Purpose-built for displays of data
Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
