create microphone demo

[swharden]

It is not obvious this project contains a realtime microphone FFT demo application in the /src folder.

Add an animated screenshot of this to the main page so users know it exists.

[swharden]

Actually, a microphone demo may not exist after all. Create one!

Mimic https://github.com/swharden/Csharp-Data-Visualization/tree/master/examples/2019-06-08-audio-fft

[swharden]

Done! Looks good, fewer than 100 lines.

FftSharp/src/FftSharp.Demo/FormMicrophone.cs

Lines 1 to 81 in 7751885

	using System;
	using System.Collections.Generic;
	using System.ComponentModel;
	using System.Data;
	using System.Drawing;
	using System.Linq;
	using System.Runtime.InteropServices;
	using System.Text;
	using System.Threading.Tasks;
	using System.Windows.Forms;
	namespace FftSharp.Demo
	{
	public partial class FormMicrophone : Form
	{
	private const int SAMPLE_RATE = 48000;
	private NAudio.Wave.WaveInEvent wvin;
	public FormMicrophone()
	{
	InitializeComponent();
	formsPlot1.Configure(middleClickMarginX: 0);
	cbDevices.Items.Clear();
	for (int i = 0; i < NAudio.Wave.WaveIn.DeviceCount; i++)
	cbDevices.Items.Add(NAudio.Wave.WaveIn.GetCapabilities(i).ProductName);
	if (cbDevices.Items.Count > 0)
	cbDevices.SelectedIndex = 0;
	else
	MessageBox.Show("ERROR: no recording devices available");
	}
	private void cbDevices_SelectedIndexChanged(object sender, EventArgs e)
	{
	wvin?.Dispose();
	wvin = new NAudio.Wave.WaveInEvent();
	wvin.DeviceNumber = cbDevices.SelectedIndex;
	wvin.WaveFormat = new NAudio.Wave.WaveFormat(rate: SAMPLE_RATE, bits: 16, channels: 1);
	wvin.DataAvailable += OnDataAvailable;
	wvin.BufferMilliseconds = 20;
	wvin.StartRecording();
	}
	double[] lastBuffer;
	private void OnDataAvailable(object sender, NAudio.Wave.WaveInEventArgs args)
	{
	int bytesPerSample = wvin.WaveFormat.BitsPerSample / 8;
	int samplesRecorded = args.BytesRecorded / bytesPerSample;
	if (lastBuffer is null || lastBuffer.Length != samplesRecorded)
	lastBuffer = new double[samplesRecorded];
	for (int i = 0; i < samplesRecorded; i++)
	lastBuffer[i] = BitConverter.ToInt16(args.Buffer, i * bytesPerSample);
	}
	ScottPlot.PlottableSignal signalPlot;
	private void timer1_Tick(object sender, EventArgs e)
	{
	if (lastBuffer is null)
	return;
	double[] window = FftSharp.Window.Hanning(lastBuffer.Length);
	double[] windowed = FftSharp.Window.Apply(window, lastBuffer);
	double[] zeroPadded = FftSharp.Pad.ZeroPad(windowed);
	double[] fftPower = cbDecibel.Checked ?
	FftSharp.Transform.FFTpower(zeroPadded) :
	FftSharp.Transform.FFTmagnitude(zeroPadded);
	formsPlot1.plt.XLabel("Frequency Hz");
	// make the plot for the first time, otherwise update the existing plot
	if (formsPlot1.plt.GetPlottables().Count == 0)
	signalPlot = formsPlot1.plt.PlotSignal(fftPower, 2.0 * fftPower.Length / SAMPLE_RATE);
	else
	signalPlot.ys = fftPower;
	if (cbAutoAxis.Checked)
	formsPlot1.plt.AxisAuto(horizontalMargin: 0);
	formsPlot1.Render();
	}
	}
	}