在Actionscript computeSpectrum和节拍检测方面苦苦挣扎

Question

我试图理解从computeSpectrum方法中返回给我的值。我想用较低的频率挑选出曲目的低音鼓。我从字节数组中得到的数字毫无意义。例如，当明显有声音播放时，它说值为 0。我在这里错过了什么...我确实知道节拍检测并不容易，并且已经查看了有关该主题的大多数帖子......只是返回给我的数字毫无意义，有人可以向我解释一下吗？提前谢谢。

我的代码：

import flash.display.Graphics;
import flash.events.Event;
import flash.media.Sound;
import flash.media.SoundChannel;
import flash.media.SoundMixer;
import flash.net.URLRequest;
import flash.display.MovieClip;
var snd: Sound = new Sound();
var req: URLRequest = new URLRequest("mySong.mp3");
snd.load(req);
var channel: SoundChannel;
channel = snd.play();
addEventListener(Event.ENTER_FRAME, onEnterFrame);
snd.addEventListener(Event.SOUND_COMPLETE, onPlaybackComplete);
const CHANNEL_LENGTH: int = 256;
const BUFFER_LENGTH: int = 512;
var bytes:ByteArray = new ByteArray();
function onEnterFrame(event: Event): void 
{
  SoundMixer.computeSpectrum(bytes, true, 0);

  for (var i:int = 0; i < CHANNEL_LENGTH; i++) // channel_length = 256
  {

      var sampleValue:Number = bytes.readFloat() * 200;
      var byteArrayIndex = bytes.position;
      trace(byteArrayIndex, sampleValue);
  }
}
function onPlaybackComplete(e:Event):void
{
    removeEventListener(Event.ENTER_FRAME, onEnterFrame);
}

Answer 1

很高兴再次见到你，我想这次我更理解你的心思了。

如果您要检查歌曲的特定时间是否存在"节拍";我可能会建议这种方法供参考：

import flash.events.Event;
var snd: Sound = new Sound();
var req: URLRequest = new URLRequest("mySong.mp3");
snd.load(req);
var channel: SoundChannel;
channel = snd.play();
addEventListener(Event.ENTER_FRAME, onEnterFrame);
snd.addEventListener(Event.SOUND_COMPLETE, onPlaybackComplete);

// I want to specify which region of byteData is passing to my check function.
// this two value help me to extract the sample I need.
var checkLength:int = 20; 
var checkStart:int = 0; 
var theshold:Number = 0.5; // How big the value should I determine it is the 'beat'.
const CHANNEL_LENGTH: int = 256;
const BUFFER_LENGTH: int = 512;
var myArray:Array;
var bytes:ByteArray = new ByteArray();
function onEnterFrame(event: Event): void 
{
    SoundMixer.computeSpectrum(bytes, true, 0);
    myArray = [];
   for (var i:int = checkStart; i < checkLength; i+=8) // extract the sample
   {
     var sampleValue:Number = bytes.readFloat();
       myArray.push(sampleValue);
   }
   if( CheckBeat( myArray ))
   {
       trace("here maybe a beat!!", getTimer());
   }
}
function CheckBeat(valueArray:Array):Boolean  // check the whether 'beat' exist
{
    var meanValue:Number = valueArray[0];
    for(var i:int = 1; i < valueArray.length; i++)
    {
        meanValue = (meanValue + valueArray[i])/2;
    }
    return meanValue > theshold;
}
function onPlaybackComplete(e:Event):void
{
    removeEventListener(Event.ENTER_FRAME, onEnterFrame);
}

但这种方法只是一个估计，根本不足够准确。