小4丼の通知音(2018-09-04)

pdp-select.js

/* プラウザのJSコンソールに貼り付けて実行させると音が鳴る */
(function() {
    const n2hz = note => 440 * Math.pow(2, (note - 57) / 12);

    const ctx = new AudioContext();
    const notes = [65, 72, 77];
    const noteStep = 0.078;

    for (let delay = 0; delay < 2; delay++) {
        const stime = ctx.currentTime + 0.08 + delay * 0.29;
        const gainVal = 0.024 * Math.pow(3.9, -delay);
        for (let i = 0; i < notes.length; i++) {
            const oc = ctx.createOscillator();
            oc.type = 'square';
            oc.frequency.value = n2hz(notes[i]);

            const gain = ctx.createGain();
            gain.gain.value = gainVal;

            oc.connect(gain);
            gain.connect(ctx.destination);

            const ocstime = stime + i * noteStep;
            oc.start(ocstime);
            gain.gain.setTargetAtTime(0, ocstime, 0.09);
            if (i !== notes.length - 1) {
                oc.stop(ocstime + noteStep);
            } else {
                oc.stop(stime + 2);
            }
        }
    }

    setTimeout(1200, () => {
        ctx.close();
    });
})()