Web Audio APIで電子ピアノ

こちらのページのコードをベースにWeb Audio APIを使用した電子ピアノのページを用意しました。

サンプルコードに対し、i. 黒鍵の追加、ii. 関数を使った音の周波数の計算、iii. 音の名前をC, D, Eからドレミに、iv. スマートフォンのタッチ操作でも動作するように、という変更をしただけのコードになります。(スマートフォンのタッチ操作での動作は不安定です。)

Volume:
Current waveform:

このページで使用したコードを以下に記します。こちらのページのコードを少しだけ変更したコードになります。

1. cssのコード

<style type="text/css">
.container {
    overflow-x: scroll;
    overflow-y: hidden;
    width: 100%;
    height: 160px;
    white-space: nowrap;
    margin: 10px;
}

.keyboard {
    width: auto;
    padding: 0;
    margin: 0;
}

.key {
    cursor: pointer;
    font: 12px "Open Sans", "Lucida Grande", "Arial", sans-serif;
    border: 1px solid black;
    border-radius: 5px;
    width: 30px;
    height: 100px;
    text-align: center;
    box-shadow: 2px 2px darkgray;
    display: inline-block;
    position: relative;
    margin-right: 3px;
    user-select: none;
    -moz-user-select: none;
    -webkit-user-select: none;
    -ms-user-select: none;
}

.key.black-key {
    background-color: #000;
    color: #fff;
    height: 80px;
    vertical-align: top;
}

.key div {
    position: absolute;
    bottom: 0;
    text-align: center;
    width: 100%;
    pointer-events: none;
}

.key div sub {
    font-size: 10px;
    pointer-events: none;
}

.key:hover {
    background-color: #eef;
}

.key.black-key:hover {
    background-color: #778;
}

.key:active {
    background-color: #000;
    color: #fff;
}

.key.black-key:active {
    background-color: #fff;
    color: #000;
}

.octave {
    display: inline-block;
    padding: 0 6px 0 0;
}

.settingsBar {
    padding-top: 8px;
    font: 14px "Open Sans", "Lucida Grande", "Arial", sans-serif;
    position: relative;
    vertical-align: middle;
    width: 100%;
    height: 60px;
}

.left {
    width: 50%;
    position: absolute;
    left: 0;
    display: table-cell;
    vertical-align: middle;
}

.left span, .left input {
    vertical-align: middle;
}

.right {
    width: 50%;
    position: absolute;
    right: 0;
    display: table-cell;
    vertical-align: middle;
}

.right span {
    vertical-align: middle;
}

.right input {
    vertical-align: baseline;
}
</style>

2. HTMLのコード

<div class="container">
    <div class="keyboard"></div>
</div>

<div class="settingsBar">
    <div class="left">
        <span>Volume: </span>
        <input type="range" min="0.0" max="1.0" step="0.01" value="0.5" list="volumes" name="volume">
        <datalist id="volumes">
            <option value="0.0" label="Mute">
            <option value="1.0" label="100%">
        </datalist>
    </div>

    <div class="right">
        <span>Current waveform: </span>
        <select name="waveform">
            <option value="sine">Sine</option>
            <option value="square">Square</option>
            <option value="sawtooth">Sawtooth</option>
            <option value="triangle">Triangle</option>
            <option value="custom" selected>Custom</option>
        </select>
    </div>
</div>

3. JavaScriptのコード

<script>
const audioContext = new (window.AudioContext || window.webkitAudioContext)();
let oscList = [];
let mainGainNode = null;

const keyboard = document.querySelector(".keyboard");
const wavePicker = document.querySelector("select[name='waveform']");
const volumeControl = document.querySelector("input[name='volume']");

let noteFreq = null;
let customWaveform = null;
let sineTerms = null;
let cosineTerms = null;

const note_names =
[
    ["ラ", "", "A", ""],
    ["ラ#", "シ$\\flat$", "A#", "B$\\flat$"],
    ["シ", "","B", ""],
    ["ド", "","C", ""],
    ["ド#", "レ$\\flat$","C#", "D$\\flat$"],
    ["レ", "","D", ""],
    ["レ#", "ミ$\\flat$","D#", "E$\\flat$"],
    ["ミ", "","E", ""],
    ["ファ", "","F", ""],
    ["ファ#", "ソ$\\flat$","F#", "G$\\flat$"],
    ["ソ", "", "G", ""],
    ["ソ#", "ラ$\\flat$", "G#", "A$\\flat$"]
];

setup();

// -------------------------------------------------------
// functions
// -------------------------------------------------------

function createNoteTable() {

    let noteFreq = [];
    for (let octave = 0; octave < 9; octave++) {
        noteFreq[octave] = [];
    }

    for (let n = 0; n < 88; n++) {

        const frequency = getAudioFrequency(n);

        let octave = parseInt(n/12);
        if (n % 12 >= 3) {
            octave++;
        }

        const note_name_sharp_japanese = note_names[n % 12][0];
        noteFreq[octave][note_name_sharp_japanese] = frequency;
    }

    return noteFreq;
}

function getAudioFrequency(n) {
    return 27.5 * ( Math.pow( Math.pow(2, 1/12), n) );
}

function setup() {
    noteFreq = createNoteTable();

    volumeControl.addEventListener("change", changeVolume, false);

    mainGainNode = audioContext.createGain();
    mainGainNode.connect(audioContext.destination);
    mainGainNode.gain.value = volumeControl.value;

    noteFreq.forEach(function(keys, idx) {
        const keyList = Object.entries(keys);
        const octaveElem = document.createElement("div");
        octaveElem.className = "octave";

        keyList.forEach(function(key) {
            const key_name = key[0];
            if (key_name === 'ド' || key_name === 'レ' || key_name === 'ミ' || key_name === 'ファ' ||
                key_name === 'ソ' || key_name === 'ラ' || key_name === 'シ') {
                octaveElem.appendChild(createKey(key_name, idx, key[1], 'white-key'));
            } else {
                octaveElem.appendChild(createKey(key_name, idx, key[1], 'black-key'));
            }
        });

        keyboard.appendChild(octaveElem);
    });

    document.querySelector("div[data-note='ファ'][data-octave='5']").scrollIntoView(false);

    sineTerms = new Float32Array([0, 0, 1, 0, 1]);
    cosineTerms = new Float32Array(sineTerms.length);
    customWaveform = audioContext.createPeriodicWave(cosineTerms, sineTerms);

    for (i = 0; i < 9; i++) {
        oscList[i] = {};
    }
}

function createKey(note, octave, freq, keyColor) {
    const keyElement = document.createElement("div");
    const labelElement = document.createElement("div");

    if (keyColor === 'black-key') {
        keyElement.className = "key black-key";
    } else {
        keyElement.className = "key";
    }
    keyElement.dataset["octave"] = octave;
    keyElement.dataset["note"] = note;
    keyElement.dataset["frequency"] = freq;

    labelElement.innerHTML = note + "<sub>" + octave + "</sub>";
    keyElement.appendChild(labelElement);

    keyElement.addEventListener("mousedown", notePressed, false);
    keyElement.addEventListener("mouseup", noteReleased, false);
    keyElement.addEventListener("mouseleave", noteReleased, false);

    keyElement.addEventListener("touchstart", notePressed, false);
    keyElement.addEventListener("touchend", noteReleased, false);
    keyElement.addEventListener("touchmove", noteReleased, false);
    keyElement.addEventListener("touchcancel", noteReleased, false);

    return keyElement;
}

function playTone(freq) {
    const osc = audioContext.createOscillator();
    osc.connect(mainGainNode);

    const type = wavePicker.options[wavePicker.selectedIndex].value;

    if (type == "custom") {
        osc.setPeriodicWave(customWaveform);
    } else {
        osc.type = type;
    }

    osc.frequency.value = freq;
    osc.start();

    return osc;
}

function notePressed(event) {
    const dataset = event.target.dataset;

    if (!dataset["pressed"]) {
        const octave = +dataset["octave"];
        oscList[octave][dataset["note"]] = playTone(dataset["frequency"]);
        dataset["pressed"] = "yes";
    }
}

function noteReleased(event) {
    const dataset = event.target.dataset;

    if (dataset && dataset["pressed"]) {
        const octave = +dataset["octave"];
        oscList[octave][dataset["note"]].stop();
        delete oscList[octave][dataset["note"]];
        delete dataset["pressed"];
    }
}

function changeVolume(event) {
    mainGainNode.gain.value = volumeControl.value
}
</script>

Webで似たようなページを探したところ、出る音をピアノの音に近付けたページ、実際の鍵盤の位置のように白鍵と黒鍵を並べたページ、複数のOscillatorNodeを重ね合わせて音色を作成できるようにしたページ、マウスではなくパソコンのキーボードで音を出せるようにしたページ等もあり、時間のあるときに別バージョンを作って試してみたい気もしています。

おもしろい音が出るかはわかりませんが、時間があれば量子力学のシュレーディンガー方程式の解の波形をカスタム波形として試すことも少し考えています。

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