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(jsfft
Small, efficient Javascript FFT implementation for node or the browser.
Usage
JSFFT ships with ComplexArray which can be operated on:
const fft = require('jsfft');
// Use the in-place mapper to populate the data.
const data = new fft.ComplexArray(512).map((value, i, n) => {
value.real = (i > n/3 && i < 2*n/3) ? 1 : 0;
});
Including the fft module attaches FFT methods to ComplexArray. FFT and
InvFFT perform in-place transforms on the underlying data:
const frequencies = data.FFT();
// Implement a low-pass filter using the in-place mapper.
frequencies.map((frequency, i, n) => {
if (i > n/5 && i < 4*n/5) {
frequency.real = 0;
frequency.imag = 0;
}
});
Alternatively, frequency-space filters can be implemented via the frequencyMap:
const filtered = data.frequencyMap((frequency, i, n) => {
if (i > n/5 && i < 4*n/5) {
frequency.real = 0;
frequency.imag = 0;
}
});
Conventions
JSFFT uses the normalization convention that is symmetric between the forward and
reverse transform. With N data points, the transform is normalized by a factor of √N:
1 N-1 2πik/N
fft(k) = - ∑ f(j) ?
√N j=0
Other Implementations
DSP is a full featured Digital Signal
Processing library in JS which includes a JS FFT implementation.