Frequency Shifter for https://www.elementary.audio/

frequencyShifter.js

//Inspired by https://larzeitlin.github.io/RMFS/
//IIR Coefficients from http://yehar.com/blog/?p=368
function hilbert(part, input) {
    function allpassIIR(coefficient, input) {
        return el.biquad(
            coefficient ** 2, 0, -1,
            0, -1 * coefficient ** 2,
            input
        );        
    }

    switch(part) {
        case "real":
            return el.z(allpassIIR(0.9987488452737, allpassIIR(0.9882295226860, allpassIIR(0.9360654322959, allpassIIR(0.6923878, input)))));
        case "imaginary":
            return allpassIIR(0.9952884791278, allpassIIR(0.9722909545651, allpassIIR(0.8561710882420, allpassIIR(0.4021921162426, input))));
    }
}

function frequencyShift(frequency, input) {
    let phasor = el.phasor(frequency);
    let sine = el.sin(el.mul(2.0 * Math.PI, phasor));
    let cosine = el.cos(el.mul(2.0 * Math.PI, phasor));

    return el.sub(
        el.mul(hilbert("real", input), sine),
        el.mul(hilbert("imaginary", input), cosine)
    );
}