irf.js

const chev_filter_presets = [
    [
        0.01,
        0.0008663387, 0,
        0.001732678, 1.919129,
        0.0008663387, -0.9225943
    ],
    [
        0.025,
        0.005112374,
        0.00001504626,
        0.01022475,
        1.797154,
        0.005112374,
        -0.8176033
    ],
    [
        0.05,
        0.01868823,
        0.0002141509,
        0.03737647,
        1.593937,
        0.01868823,
        -0.6686903
    ],
    [
        0.075,
        0.0386943,
        0.0009726342,
        0.0773886,
        1.392667,
        0.0386943,
        -0.5474446
    ],
    [
        0.1,
        0.06372802,
        0.002780755,
        0.127456,
        1.194365,
        0.06372802,
        -0.4492774
    ],
    [
        0.15, 0.1254285,
        0.01180009, 0.250857,
        0.8070778, 0.1254285,
        -0.3087918
    ],
    [
        0.2, 0.1997396,
        0.03224554, 0.3994792,
        0.4291048, 0.1997396,
        -0.2280633
    ],
    [
        0.25, 0.285811,
        0.07015301, 0.5716221,
        0.05423258, 0.285811,
        -0.1974768
    ],
    [
        0.3, 0.3849163,
        0.1335566, 0.7698326,
        -0.3249116, 0.3849163,
        -0.2147536
    ],
    [
        0.35, 0.5001024,
        0.2340973, 1.000205,
        -0.7158993, 0.5001024,
        -0.2845103
    ],
    [
        0.4, 0.6362308,
        0.3896966, 1.272462,
        -1.125379, 0.6362308,
        -0.4195441
    ],
    [
        0.45, 0.8001101,
        0.6291693, 1.60022,
        -1.556269, 0.8001101,
        -0.6441713
    ]
];
function ct2hz(cents) {
    return 8.176 * Math.pow(2.0, cents / 1200.0);
}
export default function get_iirf(ctx, freq, sr) {
    const fc = ct2hz(freq);// / sr;
    console.log(ct2hz(freq), freq, sr, fc);

    for (const [fcc, b0, a0, b1, a1, b2, a2] of chev_filter_presets) {
        console.log(fc, 'vs', fcc);
        if (fcc > fc / 48000) {
            return new IIRFilterNode(ctx, {
                feedback: [b0, b1, b2],
                feedforward: [a0, a1, a2],
            });
        }
    }
    return null;
}