分贝机器人 [英] Decibels in android

问题描述

我已经创建了一个让getMaxAmpitude一个应用程序，然后将其转换为分贝，但我只得到了一系列30分贝的。

请问Android手机只能有一个范围30分贝，或者是它在我的code的一个问题？

 公共类getMaxAmpitude扩展的AsyncTask＆LT;太虚，浮法，太虚＆GT; {
     列DB =;
     INT ampitude;
     浮动分贝;
     @覆盖
    公共无效doInBackground（虚空...... PARAMS）{
        而（REC ==真）{
            尝试{
                视频下载（250）;
            }赶上（InterruptedException异常E）{
                e.printStackTrace（）;
            }
            ampitude = recorder.getMaxAmplitude（）;
            DB =（浮点）（20 * Math.log10（ampitude / 700.0））;
            publishProgress（DB）;
        }
        返回null;
    }
    公共无效onProgressUpdate（浮...进度）{

        //database.addSoundData(dB）;
        分贝=（进展[0]的ToString（））;
 

解决方案

分贝标度总是相对的东西的措施 - 在数字音频的情况下，什么是习惯上的最大值，一个样品能够保持。这要么是 1.0 浮动样本点再presentations和 32767 有符号16位采样。计算分贝值为负，提供0dB是剪辑。

如果没有什么precisely什么记录是一个实例，我会以为这是Android的 MediaRecorder 知识 - 它采用16位有符号整数。

正确的公式在这种情况下，因此将是：

DB = 20.0 * LOG10（peakAmplitude / 32767.0）

您但是上面所使用的公式，仅仅是偏见的结果，因为它是eqivelant为：

DB = 20.0 * LOG10（peakAmplitude） - 20.0 * LOG10（700）

= 20.0 * LOG10（peakAmplitude） - 〜56.9

30分贝的动态范围的数字可能并不奇怪，如果你正在录制自带的话筒和自动增益控制已启用 - 因为这将是除非你已经采取了积极的步骤来禁用它。

I have created a application that get the getMaxAmpitude and then converts it to decibels but i only get a range of 30dB.

Does an android phone only have a range of 30dB or is it a problem in my code?

public class getMaxAmpitude extends AsyncTask<Void, Float, Void>{
     String dB = "";    
     int ampitude;
     float db;
     @Override
    public Void doInBackground(Void... params) {
        while(rec == true){
            try{
                Thread.sleep(250);
            }catch(InterruptedException e){
                e.printStackTrace();
            }
            ampitude = recorder.getMaxAmplitude();
            db =(float) (20 * Math.log10(ampitude/700.0));
            publishProgress(db);
        }
        return null;
    }
    public void onProgressUpdate(Float... progress){

        //database.addSoundData(dB);
        dB = (progress[0].toString());

解决方案

The decibel scale is always a measure relative to something - and in the case of digital audio, that something is customarily the largest value that a sample is capable of holding. This is either 1.0 for floating point representations of samples and 32767 for signed 16-bit samples. Calculated dB values are negative, with 0dB being clip.

Without knowledge of what precisely what recorder is an instance of, I will assume it's Android's MediaRecorder - which uses signed 16-bit ints.

The correct equation in this case would therefore be:

db = 20.0 * log10(peakAmplitude/32767.0)

The equation you've used above however, merely biases the results as it's eqivelant to:

db = 20.0 * log10(peakAmplitude) - 20.0 * log10(700)

=20.0*log10(peakAmplitude) - ~56.9

The dynamic range figure of 30dB might not be surprising if you're recording the onboard microphone and automatic gain control is enabled - as it will be unless you've taken active steps to disable it.

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