C#获取声音信号并通过FFT得到声音频谱

最近研究了下用C#通过麦克风获取声音信号，再通过快速傅里叶变换，得到声音的频谱。

想应用到实际的led灯上，放歌曲，led灯展示频谱，现在用C#先模拟实现下，如下图。

上面的表展示的是声音的电压信号，下图是频谱信息

一、获取声音信号

通过麦克风获取声音用的是NAudio这个库，可以通过NuGet获取

具体使用方式是：

        private NAudio.Wave.WaveIn sourceStream = null;
        private NAudio.Wave.DirectSoundOut waveOut = null;

获取麦克风列表

List<NAudio.Wave.WaveInCapabilities> sources = new List<NAudio.Wave.WaveInCapabilities>();
for (int i = 0; i < NAudio.Wave.WaveIn.DeviceCount; i++)
{
    sources.Add(NAudio.Wave.WaveIn.GetCapabilities(i));
}
sourceListView.Items.Clear();
foreach (var source in sources)
{
    ListViewItem item = new ListViewItem(source.ProductName);
    item.SubItems.Add(new ListViewItem.ListViewSubItem(item, source.Channels.ToString()));
    sourceListView.Items.Add(item);
}

初始化麦克风

 if (sourceListView.SelectedItems.Count == 0) return;
 int deviceNumber = sourceListView.SelectedItems[0].Index;
 sourceStream = new NAudio.Wave.WaveIn();
 sourceStream.DeviceNumber = deviceNumber;

 int a=WaveIn.GetCapabilities(0).Channels;
 sourceStream.WaveFormat = new NAudio.Wave.WaveFormat(9600, 16, 1);
 sourceStream.DataAvailable += new EventHandler<NAudio.Wave.WaveInEventArgs>(sourceStream_DataAvailable);
 sourceStream.BufferMilliseconds = 20;
 sourceStream.StartRecording();

回调函数，lastBuffer就存储的是声音信号

private void sourceStream_DataAvailable(object sender, WaveInEventArgs e)
{    
    int samplesRecord = e.BytesRecorded / 2;
    if (lastBuffer is null||lastBuffer.Length!=samplesRecord)
        lastBuffer = new double[samplesRecord];
    for (int i = 0; i < samplesRecord; i++)
        lastBuffer[i] = BitConverter.ToInt16(e.Buffer, i * 2);
        
}

二、FFT变换

FFT变换原理之前文章我用C++写过

C++实现二维快速傅里叶变换（FFT）_c++ fft-CSDN博客

这里我用C#再实现下，复数可以直接using System.Numerics里面的Complex，而不用自己定义了。

FFT源码如下：

int ReverseBin(int a, int n)
{
    int ret = 0;
    for (int i = 0; i < n; i++)
    {
        if ((a & (1 << i)) != 0) ret |= (1 << (n - 1 - i));
    }
    return ret;
}

public void FFT(ref Complex[] a, int log2_N, int opt)
{
    int index;
    int length = 1 << log2_N;
    Complex[] tempA = new Complex[length];
    for (int i = 0; i < length; i++)
    {
        index = ReverseBin(i, log2_N);
        tempA[i] = a[index];
    }

    //生成WN表，减少重复计算
    Complex[] WN = new Complex[length / 2];
    for (int i = 0; i < length / 2; i++)
    {
        WN[i] = new Complex(Math.Cos(2 * Math.PI * i  / length), opt * -1 * Math.Sin(2 * Math.PI*i / length));
    }

    //蝶形运算
    int Index0, Index1;
    Complex temp;
    for (int steplenght = 2; steplenght <= length; steplenght *= 2)
    {
        for (int step = 0; step < length / steplenght; step++)
        {
            for (int i = 0; i < steplenght / 2; i++)
            {
                Index0 = steplenght * step + i;
                Index1 = steplenght * step + i + steplenght / 2;

                temp = tempA[Index1] * WN[length / steplenght * i];
                tempA[Index1] = tempA[Index0] - temp;
                tempA[Index0] = tempA[Index0] + temp;
            }
        }
    }

    for (int i = 0; i < length; i++)
    {
        if (opt == -1)
        {
            a[i] = tempA[i] / length;
        }
        else
        {
            a[i] = tempA[i];
        }
    }

}

三、总结

这样可以实时得到了一段声音信号，可以加个汉明窗处理下，再FFT下，就得到声音的频谱信息了。后续计划，可以通过这种方式，控制led灯，展示音乐的频谱跳动。