dsp-collection/filter/SpecFilt.js

A collection of JavaScript modules for digital signal processing (written in TypeScript)

import ComplexArray from "../math/ComplexArray.js";
import * as Fft from "../signal/Fft.js";
function smoothingFunction(x) {
    return (Math.sin(x * Math.PI / 2) + 1) / 2;
}
export function getFilterCurveFunction(filterType, filterFreq1, filterFreq2, smoothingWidth) {
    switch (filterType) {
        case "LP": {
            return (freq) => {
                if (freq < filterFreq1 - smoothingWidth) {
                    return 1;
                }
                else if (freq < filterFreq1 + smoothingWidth) {
                    return smoothingFunction((filterFreq1 - freq) / smoothingWidth);
                }
                else {
                    return 0;
                }
            };
        }
        case "HP": {
            return (freq) => {
                if (freq < filterFreq1 - smoothingWidth) {
                    return 0;
                }
                else if (freq < filterFreq1 + smoothingWidth) {
                    return smoothingFunction((freq - filterFreq1) / smoothingWidth);
                }
                else {
                    return 1;
                }
            };
        }
        case "BP": {
            return (freq) => {
                if (freq < filterFreq1 - smoothingWidth) {
                    return 0;
                }
                else if (freq < filterFreq1 + smoothingWidth) {
                    return smoothingFunction((freq - filterFreq1) / smoothingWidth);
                }
                else if (freq < filterFreq2 - smoothingWidth) {
                    return 1;
                }
                else if (freq < filterFreq2 + smoothingWidth) {
                    return smoothingFunction((filterFreq2 - freq) / smoothingWidth);
                }
                else {
                    return 0;
                }
            };
        }
        case "BS": {
            return (freq) => {
                if (freq < filterFreq1 - smoothingWidth) {
                    return 1;
                }
                else if (freq < filterFreq1 + smoothingWidth) {
                    return smoothingFunction((filterFreq1 - freq) / smoothingWidth);
                }
                else if (freq < filterFreq2 - smoothingWidth) {
                    return 0;
                }
                else if (freq < filterFreq2 + smoothingWidth) {
                    return smoothingFunction((freq - filterFreq2) / smoothingWidth);
                }
                else {
                    return 1;
                }
            };
        }
        default: {
            throw new Error("Unsupported filter type.");
        }
    }
}
export function applyFilterCurveFunction(inAmplitudes, scalingFactor, filterCurveFunction) {
    const n = inAmplitudes.length;
    const outAmplitudes = new Float64Array(n);
    for (let p = 0; p < n; p++) {
        const frequency = p / scalingFactor;
        const filterFactor = filterCurveFunction(frequency);
        outAmplitudes[p] = filterFactor * inAmplitudes[p];
    }
    return outAmplitudes;
}
export function filterSignal(inSamples, sampleRate, filterType, filterFreq1, filterFreq2, smoothingWidth) {
    const n = inSamples.length;
    const inSpectrum = Fft.fftRealSpectrum(inSamples);
    const inAmplitudes = inSpectrum.getAbsArray();
    const inPhases = inSpectrum.getArgArray();
    const filterCurveFunction = getFilterCurveFunction(filterType, filterFreq1, filterFreq2, smoothingWidth);
    const outAmplitudes = applyFilterCurveFunction(inAmplitudes, n / sampleRate, filterCurveFunction);
    const outPhases = inPhases;
    const outSpectrum = ComplexArray.fromPolar(outAmplitudes, outPhases);
    const outSignal = Fft.iFftRealHalf(outSpectrum, n);
    return outSignal;
}
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