计算分贝 [英] Calculate decibels

问题描述

我使用XNA库（我不认为这真的是具体的技术，但它绝不会伤害）录制麦克风输入。每当我得到的样本，我想计算分贝。我已经做了很多的搜索在互联网上，并没有找到一个坚如磐石的例子...

I'm recording mic input using the XNA library (I don't think this is really technology specific, but it never hurts). Every time I get a sample I would like to calculate the decibels. I have done many searches on the internet and not found a rock solid example...

下面是我从样本计算分​​贝的尝试：

Here is my attempt at calculating decibels from a sample:

        double peak = 0;

        for (var i = 0; i < _buffer.Length; i = i + 2)
        {
            var sample = BitConverter.ToInt16(_buffer, i);
            if (sample > peak)
                peak = sample;
            else if (sample < -peak)
                peak = -sample;
        }

        var decibel = (20 * Math.Log10(peak/32768));

如果我输出的分贝值在屏幕上，我可以看到的价值观得到更高的，因为我得到响亮，下为我说话柔和。然而，它始终徘徊在-40时，我绝对安静......我会假设这将是-90。我必须有一个计算错误在上面的块？从我读过一些网站-40相当于软说话......然而，这是完全安静。

If I output the decibel value to the screen I can see the values get higher as I get louder and lower as I speak softer. However, it always hovers around -40 when I'm absolutely quiet...I would assume it would be -90. I must have a calculation wrong in the block above?? from what I have read on some sites -40 is equivalent to "soft talking"...however, it's totally quiet.

另外，如果我静音我的麦克风，它直接为-90。

Also, If I mute my mic it goes straight to -90.

难道我做错了？

推荐答案

在测量声音信号的电平，你应该从RMS值计算分贝。在您的样品你正在寻找的绝对峰值电平。单（峰值）采样值决定了你的分贝值，即使在其他所有样品中是完全0。

When measuring the level of a sound signal, you should calculate the dB from the RMS value. In your sample you are looking at the absolute peak level. A single (peak) sample value determines your dB value, even when all other samples are exactly 0.

试试这个：

double sum = 0;
for (var i = 0; i < _buffer.length; i = i + 2)
{
    double sample = BitConverter.ToInt16(_buffer, i) / 32768.0;
    sum += (sample * sample);
}
double rms = Math.Sqrt(sum / (_buffer.length / 2));
var decibel = 20 * Math.Log10(rms);

有关'瞬间'分贝水平，你通常会在20-50毫秒段计算RMS。
注意，计算出的dB值是相对于满刻度。对于声音的分贝值应该与20 UPA，你将需要校准信号，找到的数字值pressure值正确转换。

For 'instantaneous' dB levels you would normally calculate the RMS over a segment of 20-50 ms. Note that the calculated dB value is relative to full-scale. For sound the dB value should be related to 20 uPa, and you will need to calibrate your signal to find the proper conversion from digital values to pressure values.

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