javascript - WebAudio 在开始和结束时播放声音

Question

每当我使用如下代码播放声音时

// binaryData = a wave file from a websocket
let ctx = new AudioContext();
ctx.decodeAudioData(binaryData, function(audioData){
   let source = ctx.createBufferSource();
   source.buffer = audioData;
   source.connect(ctx.destination);
   source.start(0);
});

播放的每个剪辑之间都有非常明显的咔哒声或爆裂声。忘记我正在尝试使用该系统播放实时音频这一事实；为什么在播放的每个声音片段的开头和结尾都有杂音？我不明白这是 2017 年音频播放设备可接受的行为......有什么办法可以减轻或消除这种情况吗？

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回答

下面的答案后面是一组很好的 #s，可用于将点击次数减少到基本为零。我并不是说这对音调非常有用，但它对声音来说是完美无缺的。

// start of clip
// clipPlayTime may be 0 or your scheduled play time
gain.setValueAtTime(0.01, clipPlayTime);
gain.exponentialRampToValueAtTime(1, clipPlayTime + 0.001);
// end of clip
gain.setValueAtTime(1, clipPlayTime + clipLength - 0.001);
gain.exponentialRampToValueAtTime(0.01, clipPlayTime + clipLength);

这会产生上升和下降。

Answer 1

使用 exponentialRampToValueAtTime()消除(或至少减少)咔嗒声。

这是一个很好的解释:Web Audio, the ugly click and the human ear

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完整示例

基本示例取自:https://developer.mozilla.org/en-US/docs/Web/API/BaseAudioContext/decodeAudioData

<button class="play">Play</button>
<button class="stop">Stop</button>

<script type="text/javascript">
var audioCtx = new(window.AudioContext || window.webkitAudioContext)();
var source;
var play = document.querySelector('.play');
var stop = document.querySelector('.stop');
var gainNode = audioCtx.createGain();


function getData() {
    source = audioCtx.createBufferSource();
    var request = new XMLHttpRequest();
    request.open('GET', './sample.wav', true);
    request.responseType = 'arraybuffer';
    request.onload = function() {
        var audioData = request.response;

        audioCtx.decodeAudioData(audioData, function(buffer) {
                source.buffer = buffer;
                source.connect(gainNode);
                gainNode.connect(audioCtx.destination);
                gainNode.gain.setValueAtTime(1, audioCtx.currentTime);
            },

            function(e) {
                console.log("Error with decoding audio data" + e.err);
            });
    }
    request.send();
}


play.onclick = function() {
    getData();
    source.start(0);
    play.setAttribute('disabled', 'disabled');
}

stop.onclick = function() {
    gainNode.gain.setValueAtTime(gainNode.gain.value, audioCtx.currentTime);
    gainNode.gain.exponentialRampToValueAtTime(0.0001, audioCtx.currentTime + 1);
    setTimeout(function() {
        source.stop();
    }, 1000)
    play.removeAttribute('disabled');
}
</script>