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App.xaml

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+<Application x:Class="BeatDetector.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:BeatDetector"
+             StartupUri="MainWindow.xaml">
+    <Application.Resources>
+         
+    </Application.Resources>
+</Application>

App.xaml.cs

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+using System;
+using System.Collections.Generic;
+using System.Configuration;
+using System.Data;
+using System.Linq;
+using System.Threading.Tasks;
+using System.Windows;
+
+namespace BeatDetector;
+/// <summary>
+/// Interaction logic for App.xaml
+/// </summary>
+public partial class App : Application
+{
+}

AssemblyInfo.cs

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+using System.Windows;
+
+[assembly: ThemeInfo(
+    ResourceDictionaryLocation.None, //where theme specific resource dictionaries are located
+                                     //(used if a resource is not found in the page,
+                                     // or application resource dictionaries)
+    ResourceDictionaryLocation.SourceAssembly //where the generic resource dictionary is located
+                                              //(used if a resource is not found in the page,
+                                              // app, or any theme specific resource dictionaries)
+)]

AudioProcessing/AudioBeatDetector.cs

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+using NAudio.Dsp;
+using NAudio.Wave;
+
+using System;
+using System.Linq;
+
+namespace BeatDetector.AudioProcessing;
+
+internal class AudioBeatDetector
+{
+    public event EventHandler<BeatDetectorEventArgs>? OnBeat;
+
+    public event EventHandler<BeatDetectorEventArgs>? OnNoBeat;
+
+    private readonly IWaveIn waveIn;
+    private readonly SampleAggregator sampleAggregator;
+    private readonly TimeSpan beatDetectionDelay;
+    private readonly int fftLength;
+
+    private readonly int chunkCount;
+    private readonly BeatChunk[] beatChunks;
+
+    public AudioBeatDetector(TimeSpan beatDetectionDelay, int fftLength, int chunkCount)
+    {
+        this.beatDetectionDelay = beatDetectionDelay;
+        this.chunkCount = chunkCount;
+        this.fftLength = fftLength;
+
+        beatChunks = new BeatChunk[chunkCount];
+        sampleAggregator = new SampleAggregator(fftLength);
+
+        for (int i = 0; i < chunkCount; i++)
+        {
+            beatChunks[i] = new BeatChunk();
+            beatChunks[i].StopWatch.Start();
+        }
+
+        sampleAggregator.FftCalculated += new EventHandler<FftEventArgs>(FftCalculated);
+        sampleAggregator.PerformFFT = true;
+
+        waveIn = new WasapiLoopbackCapture();
+        waveIn.DataAvailable += OnDataAvailable;
+
+        waveIn.StartRecording();
+    }
+
+    private void OnDataAvailable(object? sender, WaveInEventArgs e)
+    {
+        byte[] buffer = e.Buffer;
+        int bytesRecorded = e.BytesRecorded;
+        int bufferIncrement = waveIn.WaveFormat.BlockAlign;
+
+        for (int index = 0; index < bytesRecorded; index += bufferIncrement)
+        {
+            float sample32 = BitConverter.ToSingle(buffer, index);
+            sampleAggregator.Add(sample32);
+        }
+    }
+
+    private void FftCalculated(object? sender, FftEventArgs e)
+    {
+        Complex[][] chunks = e.Result.Chunk(fftLength / chunkCount).ToArray();
+
+        for (int i = 0; i < chunkCount; i++)
+        {
+            CalculateBeat(chunks[i], beatChunks[i], i);
+        }
+    }
+
+    private void CalculateBeat(Complex[] values, BeatChunk beatChunk, int chunkIndex)
+    {
+        double energyLevel = 0;
+        foreach (Complex value in values)
+        {
+            energyLevel += Math.Pow(Math.Abs(value.Y), 2);
+        }
+
+        double averageEnergyLevel = beatChunk.EnergyHistory.Count > 0 ? beatChunk.EnergyHistory.Average() : double.MaxValue;
+
+        if (beatChunk.StopWatch.Elapsed >= beatDetectionDelay)
+        {
+            double difference = energyLevel - averageEnergyLevel;
+
+            if (difference > beatChunk.AverageDifference / 2)
+            {
+                beatChunk.AverageDifference = (difference + beatChunk.AverageDifference) / 2d;
+                OnBeat?.Invoke(this, new BeatDetectorEventArgs(chunkIndex, difference));
+            }
+            else
+            {
+                OnNoBeat?.Invoke(this, new BeatDetectorEventArgs(chunkIndex, 0));
+            }
+            beatChunk.StopWatch.Restart();
+        }
+
+        beatChunk.EnergyHistory.Add(energyLevel);
+        if (beatChunk.EnergyHistory.Count > 43)
+        {
+            beatChunk.EnergyHistory.RemoveAt(0);
+        }
+    }
+}
+
+public class BeatDetectorEventArgs : EventArgs
+{
+    public int ChunkIndex { get; }
+    public double DetectedValue { get; }
+
+    public BeatDetectorEventArgs(int chunkIndex, double detectedValue)
+    {
+        ChunkIndex = chunkIndex;
+        DetectedValue = detectedValue;
+    }
+}

AudioProcessing/BeatChunk.cs

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+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace BeatDetector.AudioProcessing;
+
+internal class BeatChunk
+{
+    public Stopwatch StopWatch { get; } = new Stopwatch();
+    public List<double> EnergyHistory { get; } = new List<double>();
+    public double AverageDifference { get; set; }
+}

AudioProcessing/SampleAggregator.cs

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+using NAudio.Dsp;
+
+using System;
+
+namespace BeatDetector.AudioProcessing;
+
+internal class SampleAggregator
+{
+    // FFT
+    public event EventHandler<FftEventArgs>? FftCalculated;
+
+    public bool PerformFFT { get; set; }
+    private readonly Complex[] fftBuffer;
+    private readonly FftEventArgs fftArgs;
+    private int fftPos;
+    private readonly int fftLength;
+    private readonly int m;
+
+    public SampleAggregator(int fftLength)
+    {
+        if (!IsPowerOfTwo(fftLength))
+        {
+            throw new ArgumentException("FFT Length must be a power of two");
+        }
+        m = (int)Math.Log(fftLength, 2.0);
+        this.fftLength = fftLength;
+        fftBuffer = new Complex[fftLength];
+        fftArgs = new FftEventArgs(fftBuffer);
+    }
+
+    private bool IsPowerOfTwo(int x)
+    {
+        return (x & (x - 1)) == 0;
+    }
+
+    public void Add(float value)
+    {
+        if (PerformFFT && FftCalculated is not null)
+        {
+            fftBuffer[fftPos].X = (float)(value * FastFourierTransform.HammingWindow(fftPos, fftLength));
+            fftBuffer[fftPos].Y = 0; // This is always zero with audio.
+            fftPos++;
+            if (fftPos >= fftLength)
+            {
+                fftPos = 0;
+                FastFourierTransform.FFT(true, m, fftBuffer);
+                FftCalculated(this, fftArgs);
+            }
+        }
+    }
+}
+
+public class FftEventArgs : EventArgs
+{
+    public FftEventArgs(Complex[] result)
+    {
+        Result = result;
+    }
+
+    public Complex[] Result { get; private set; }
+}

BeatDetector.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net6.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <UseWPF>true</UseWPF>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="NAudio" Version="2.0.1" />
+  </ItemGroup>
+
+</Project>

LICENSE

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+MIT License
+
+Copyright (c) 2022 Stone_Red
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

MainWindow.xaml

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+<Window x:Class="BeatDetector.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:local="clr-namespace:BeatDetector" d:DataContext="{d:DesignInstance Type=local:MainWindow}"
+        mc:Ignorable="d"
+        Title="MainWindow" Height="450" Width="800">
+    <Grid Name="MainGrid">
+        <ItemsControl ItemsSource="{Binding BeatLights}" Background="Green">
+            <ItemsControl.ItemTemplate>
+                <DataTemplate>
+                    <Grid Background="{Binding Color}" Margin="10" Width="100" Height="100"></Grid>
+                </DataTemplate>
+            </ItemsControl.ItemTemplate>
+            <ItemsControl.ItemsPanel>
+                <ItemsPanelTemplate>
+                    <WrapPanel/>
+                </ItemsPanelTemplate>
+            </ItemsControl.ItemsPanel>
+        </ItemsControl>
+    </Grid>
+</Window>

MainWindow.xaml.cs

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+using BeatDetector.AudioProcessing;
+
+using System;
+using System.Collections.ObjectModel;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+using System.Windows;
+using System.Windows.Media;
+using System.Windows.Threading;
+
+namespace BeatDetector;
+
+/// <summary>
+/// Interaction logic for MainWindow.xaml
+/// </summary>
+public partial class MainWindow : Window
+{
+    public ObservableCollection<BeatLight> BeatLights { get; } = new ObservableCollection<BeatLight>();
+
+    public MainWindow()
+    {
+        DataContext = this;
+        InitializeComponent();
+
+        for (int i = 0; i < 4; i++)
+        {
+            BeatLights.Add(new BeatLight());
+        }
+
+        AudioBeatDetector audioBeatDetector = new AudioBeatDetector(new TimeSpan(0, 0, 0, 0, 100), 1024 * 2, BeatLights.Count);
+        audioBeatDetector.OnBeat += AudioBeatDetector_OnBeat;
+        audioBeatDetector.OnNoBeat += AudioBeatDetector_OnNoBeat;
+    }
+
+    private void AudioBeatDetector_OnBeat(object? sender, BeatDetectorEventArgs e)
+    {
+        Dispatcher.Invoke(() => BeatLights[e.ChunkIndex].Color = Brushes.Red);
+    }
+
+    private void AudioBeatDetector_OnNoBeat(object? sender, BeatDetectorEventArgs e)
+    {
+        Dispatcher.Invoke(() => BeatLights[e.ChunkIndex].Color = Brushes.White);
+    }
+}
+
+public class BeatLight : INotifyPropertyChanged
+{
+    public event PropertyChangedEventHandler? PropertyChanged;
+
+    private Brush color = Brushes.White;
+
+    public Brush Color
+    {
+        get => color;
+        set
+        {
+            if (value != color)
+            {
+                color = value;
+                NotifyPropertyChanged();
+            }
+        }
+    }
+
+    private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
+    {
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+    }
+}

README.md

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+# BeatDetector
+ Tries to detect beats in songs