gistfile1.cs

using System;
using System.IO;
using System.Windows;
using FragLabs.Audio.Engines;
using FragLabs.Audio.Engines.OpenAL;

namespace VoiceRecognition
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public static event EventHandler<FFTEventArgs> FftRan;

        protected virtual void OnFftRan(FFTEventArgs e)
        {
            var handler = FftRan;
            if (handler != null) handler(this, e);
        }

        public static Stream InputStream = null;
        public static CaptureDevice InputDevice = null;
        public static int SampleRate = 44100;
        public static int BitDepth = 16;
        public static int Channels = 1;
        public static byte[] ReadBuffer;
        public static int SampleSizeMs = 100;
        public static LiveAudioInfo LiveAudioInfo = null;
        public static FFT Fft = new FFT();
        public static uint FftSize;

        public MainWindow()
        {
            InitializeComponent();
            Loaded += OnLoaded;
            Unloaded += OnUnloaded;
        }

        private void OnUnloaded(object sender, RoutedEventArgs routedEventArgs)
        {
            InputStream.Close();
            InputStream.Dispose();
            InputStream = null;

            LiveAudioInfo.Close();
            LiveAudioInfo = null;
        }

        private void OnLoaded(object sender, RoutedEventArgs routedEventArgs)
        {
            var bufferSize = ((SampleRate/1000)*((BitDepth/8)*Channels))*SampleSizeMs;
            ReadBuffer = new byte[bufferSize];
            var sampleCount = (uint) (bufferSize/((BitDepth/8)*Channels));
            var logN = LogN(sampleCount);
            FftSize = (uint)1 << (int)logN;
            Fft.init(logN);

            InputDevice = OpenALHelper.CaptureDevices[0];
            InputStream = InputDevice.OpenStream(SampleRate, OpenALAudioFormat.Mono16Bit, SampleSizeMs); //  read 10ms of audio data each "read" operation
            InputStream.BeginRead(ReadBuffer, 0, ReadBuffer.Length, OnReadComplete, null);

            LiveAudioInfo = new LiveAudioInfo();
            LiveAudioInfo.Show();
        }

        private void OnReadComplete(IAsyncResult ar)
        {
            if (InputStream == null)
                return;
            var readBytes = InputStream.EndRead(ar);
            var samples = Convert16BitToDouble(ReadBuffer);
            var real = new double[samples.Length];
            var imaginary = new double[samples.Length];
            Buffer.BlockCopy(samples, 0, real, 0, samples.Length);
            Fft.run(real, imaginary);
            OnFftRan(new FFTEventArgs() {Real = real, Imaginary = imaginary, FftSize = FftSize, Samples = samples, SampleRate = SampleRate});
            InputStream.BeginRead(ReadBuffer, 0, ReadBuffer.Length, OnReadComplete, null);
        }

        private uint LogN(uint input)
        {
            return (uint) (Math.Log(input)/Math.Log(2));
        }

        public double[] Convert16BitToDouble(byte[] input)
        {
            var inputSamples = input.Length / (BitDepth / 8);
            var output = new double[inputSamples];
            var outputIndex = 0;
            for (var n = 0; n < inputSamples; n++)
            {
                short sample = BitConverter.ToInt16(input, n * 2);
                output[outputIndex++] = sample / 32768f;
            }
            return output;
        }
    }

    public class FFTEventArgs : EventArgs
    {
        public int SampleRate { get; set; }
        public double[] Samples { get; set; }
        public double[] Real { get; set; }
        public double[] Imaginary { get; set; }
        public uint FftSize { get; set; }
    }
}

gistfile2.cs

using System;
using System.Windows;

namespace VoiceRecognition
{
    /// <summary>
    /// Interaction logic for LiveAudioInfo.xaml
    /// </summary>
    public partial class LiveAudioInfo : Window
    {
        private double _dbScale = (double)20 / System.Math.Log(10);

        public LiveAudioInfo()
        {
            InitializeComponent();
            MainWindow.FftRan += MainWindowOnFftRan;
        }

        private void MainWindowOnFftRan(object sender, FFTEventArgs fftEventArgs)
        {
            var magnitude = new double[fftEventArgs.FftSize/2];
            double db = 0;
            var frequencies = new double[fftEventArgs.FftSize / 2];
            for (var i = 0; i < fftEventArgs.FftSize / 2; i++)
            {
                frequencies[i] = i*(fftEventArgs.SampleRate/fftEventArgs.FftSize);

                double re = fftEventArgs.Real[i]; // get the Real FFT Number at position i
                double im = fftEventArgs.Imaginary[i]; // get the Imaginary FFT Number at position i

                magnitude[i] = Math.Sqrt(re * re + im * im); // Convert magnitude to decibels

                magnitude[i] = _dbScale * Math.Log(magnitude[i] + double.Epsilon);
                if (magnitude[i] > db)
                    db = magnitude[i];
            }
            Dispatcher.BeginInvoke((Action)delegate
                {
                    var freqs = "";
                    for(var i = 0; i < fftEventArgs.FftSize / 2; i++)
                    {
                        freqs += String.Format("{0} Hz {1}{2}", frequencies[i], magnitude[i], Environment.NewLine);
                    }
                    lblDb.Content = String.Format("{0} dB", db);
                    lblFreqs.Content = freqs;
                });
        }
    }
}