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。