创建AudioAnalyser对象, 使用[link:https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode AnalyserNode]
			去分析音频数据.
			使用了 [link:https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API Web Audio API].
		
			[example:webaudio_sandbox webaudio / sandbox ]
			[example:webaudio_visualizer webaudio / visualizer ]
		
		// create an AudioListener and add it to the camera
		var listener = new THREE.AudioListener();
		camera.add( listener );
		// create an Audio source
		var sound = new THREE.Audio( listener );
		// load a sound and set it as the Audio object's buffer
		var audioLoader = new THREE.AudioLoader();
		audioLoader.load( 'sounds/ambient.ogg', function( buffer ) {
			sound.setBuffer( buffer );
			sound.setLoop(true);
			sound.setVolume(0.5);
			sound.play();
		});
		// create an AudioAnalyser, passing in the sound and desired fftSize
		var analyser = new THREE.AudioAnalyser( sound, 32 );
		// get the average frequency of the sound
		var data = analyser.getAverageFrequency();
		
		创建[page:AudioAnalyser AudioAnalyser].
[link:https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode AnalyserNode]用来分析音频数据.
2的幂次方最高为2048, 用来表示确定频域的FFT (傅立叶变换)大小. 这个[link:https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode/fftSize page]有详细信息.
用来分析数据的Uint8Array的大小由[link:https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode/frequencyBinCount analyser.frequencyBinCount] 确定.
使用网络音频的[link:https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode/getByteFrequencyData getByteFrequencyData] 方法. 看这个页面.
通过方法[page:AudioAnalyser.getFrequencyData getFrequencyData]获取平均频率.
[link:https://github.com/mrdoob/three.js/blob/master/src/[path].js src/[path].js]