echogarden/dist/math/MedianFilter.js

An easy-to-use speech toolset. Includes tools for synthesis, recognition, alignment, speech translation, language detection, source separation and more.

export function medianOf5Filter(points) {
    // This function computes the moving median with a window of 5 elements.
    // I initialized the window such that at the edges of the range no median would be computed.
    // This is a form of optimization assuming that computing a median edge points
    // is less important.
    const pointCount = points.length;
    if (pointCount < 5) {
        return Float32Array.from(points);
    }
    const medians = new Float32Array(pointCount);
    medians[0] = points[0];
    medians[1] = points[1];
    medians[pointCount - 2] = points[pointCount - 2];
    medians[pointCount - 1] = points[pointCount - 1];
    for (let i = 2; i < pointCount - 2; i++) {
        medians[i] = medianOf5(points[i - 2], points[i - 1], points[i], points[i + 1], points[i + 2]);
    }
    return medians;
}
export function medianOf3Filter(points) {
    // This function computes the moving median with a window of 3 elements.
    // I initialized the window such that at the edges of the range no median would be computed.
    const pointCount = points.length;
    if (pointCount < 3) {
        return points;
    }
    const medians = new Float32Array(pointCount);
    medians[0] = points[0];
    medians[pointCount - 1] = points[pointCount - 1];
    for (let i = 1; i < pointCount - 1; i++) {
        medians[i] = medianOf3(points[i - 1], points[i], points[i + 1]);
    }
    return medians;
}
export function medianOf5(a, b, c, d, e) {
    // These swapping computation should be faster than separately using the minimum and maximum
    // functions but maybe less readable.
    // Ensure b is greater or equal to a (swap if needed)
    if (b < a) {
        [a, b] = [b, a];
    }
    // Ensure d is greater or equal to c (swap if needed)
    if (d < c) {
        [c, d] = [d, c];
    }
    // What this part does is compute the two middle medians of the first 4 elements
    // given to the function (a, b, c, d), but it doesn't actually determine their relative order:
    const firstMedianOfABCD = Math.max(a, c); // First median of a, b, c, d
    const secondMedianOfABCD = Math.min(b, d); // Second median of a, b, c, d
    // Now in relation to all five numbers, the median can only be either
    // the first median of ABCD, the second median of ABCD, or E:
    return medianOf3(firstMedianOfABCD, secondMedianOfABCD, e);
}
export function medianOf3(a, b, c) {
    // This function uses a decision tree to find the median of three numbers.
    //
    // I tried to ensure that the comparison preserved the natural altering of
    // a, b and c such that in case that they are given already in order,
    // then all the initial branches would be directly taken.
    // Possible orderings:
    //
    // a, b, c
    // a, c, b
    // b, a, c
    // b, c, a
    // c, a, b
    // c, b, a
    if (a <= b) {
        if (b <= c) {
            return b; // a, b, c
        }
        else if (a <= c) {
            return c; // a, c, b
        }
        else {
            return a; // c, a, b
        }
    }
    else {
        if (a <= c) {
            return a; // b, a, c
        }
        else if (b <= c) {
            return c; // b, c, a
        }
        else {
            return b; // c, b, a
        }
    }
}
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