javascript - 在树莓派上使用 node.js 进行和弦音频播放

Question

我一直在尝试在运行最新 raspbian 的树莓派 3 上使用 node.js 创建和弦 WAV 播放:

• shelling out to aplay/mpg123/some other program - 让我一次只能播放一个声音
• 我尝试了 https://github.com/sebpiq/node-web-audio-api 的组合和 https://github.com/TooTallNate/node-speaker (下面的示例代码)但音频质量很低，有很多失真

这里有什么我遗漏的吗？我知道我可以用另一种编程语言轻松地做到这一点(我能够用 SDL 编写 C++ 代码，用 pygame 编写 Python)，但问题是 node.js 是否可行:)

这是我当前的 web-audio-api + node-speaker 代码:

var AudioContext = require('web-audio-api').AudioContext;
var Speaker      = require('speaker');
var fs           = require('fs');

var track1       = './tracks/1.wav';
var track2       = './tracks/1.wav';

var context      = new AudioContext();

context.outStream = new Speaker({
  channels:   context.format.numberOfChannels,
  bitDepth:   context.format.bitDepth,
  sampleRate: context.format.sampleRate
});

function play(audioBuffer) {
  if (!audioBuffer) { return; }

  var bufferSource = context.createBufferSource();

  bufferSource.connect(context.destination);
  bufferSource.buffer = audioBuffer;
  bufferSource.loop   = false;
  bufferSource.start(0);
}

var audioData1 = fs.readFileSync(track1);
var audioData2 = fs.readFileSync(track2);

var audioBuffer1, audioBuffer2;

context.decodeAudioData(audioData1, function(audioBuffer) {
  audioBuffer1 = audioBuffer;
  if (audioBuffer1 && audioBuffer2) { playBoth(); }
});

context.decodeAudioData(audioData2, function(audioBuffer) {
  audioBuffer2 = audioBuffer;
  if (audioBuffer1 && audioBuffer2) { playBoth(); }
});

function playBoth() {
  console.log('playing...');

  play(audioBuffer1);
  play(audioBuffer2);
}

Answer 1

audio quality is very low, with a lot of distortions

根据 WebAudio 规范(https://webaudio.github.io/web-audio-api/#SummingJunction):

No clipping is applied at the inputs or outputs of the AudioNode to allow a maximum of dynamic range within the audio graph.

现在，如果您正在播放两个音频流，将它们相加可能会产生超出可接受范围的值，这听起来像是失真。

首先尝试通过 GainNode 管道降低每个音频流的音量这样:

function play(audioBuffer) {
  if (!audioBuffer) { return; }

  var bufferSource = context.createBufferSource();
  var gainNode = context.createGain();
  gainNode.gain.value = 0.5 // for instance, find a good value

  bufferSource.connect(gainNode);
  gainNode.connect(context.destination);
  bufferSource.buffer = audioBuffer;
  bufferSource.loop   = false;
  bufferSource.start(0);
}

或者，您可以使用 DynamicsCompressorNode ，但手动设置增益可以让您更好地控制输出。