javascript - 为什么 getFloatFrequencyData 返回的值为负数？

Question

我想从麦克风获取输入并将其传递到分析器节点以提取频率数据。我探索了Web Audio Api和GetUserMedia一段时间，但无法弄清楚为什么控制台中的所有值都是负数。难道不应该有积极的值(value)观吗？这些负值有什么意义？

navigator.mediaDevices.getUserMedia({audio: true, video:false}).then(function(stream){               
              aContext = new AudioContext();
              analyser = aContext.createAnalyser();
              microphone = aContext.createMediaStreamSource(stream);
              microphone.connect(analyser);
              analyser.connect(aContext.destination);
              LoopFunc();
          });                    

     var LoopFunc = function (){
          setInterval(function(){
              frequencyData = new Float32Array(analyser.frequencyBinCount);
              analyser.getFloatFrequencyData(frequencyData);
              console.log(frequencyData);                  
          },100);
      }

Answer 1

来自 the spec

getFloatFrequencyData

Copies the current frequency data into the passed floating-point array. If the array has fewer elements than the frequencyBinCount, the excess elements will be dropped. If the array has more elements than the frequencyBinCount, the excess elements will be ignored.

The frequency data are in dB units.

这就引出了一个问题:What does negative numbers on the decibel scale mean?