Initial commit

Measurer.cs

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+using NAudio.Dsp;
+using NAudio.Wave;
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace SoundThermo
+{
+	/// <summary>
+	/// Generates sine sample in the form
+	/// amp * sin(x / freq)
+	/// </summary>
+	class ThermoSampleProvider : ISampleProvider
+	{
+		public const int SAMPLE_RATE = 44100;
+		WaveFormat format;
+		float freq;
+		float amp;
+		int alreadyGeneratedSamples;
+
+		public ThermoSampleProvider(float freq, float amp)
+		{
+			format = WaveFormat.CreateIeeeFloatWaveFormat(SAMPLE_RATE, 1);
+			this.freq = freq;
+			this.amp = amp;
+			alreadyGeneratedSamples = 0;
+		}
+
+		public WaveFormat WaveFormat
+		{
+			get
+			{
+				return format;
+			}
+		}
+
+		public int Read(float[] buffer, int offset, int count)
+		{
+			for (int i = 0; i < count; i++)
+			{
+				int sample = alreadyGeneratedSamples++;
+				buffer[offset + i] = amp * MathF.Sin(2 * MathF.PI * sample * freq / SAMPLE_RATE);
+			}
+			return count;
+		}
+	}
+
+	/// <summary>
+	/// Returns ratio of output signal to input signal
+	/// </summary>
+	class Measurer
+	{
+		public enum MeasureChannel
+		{
+			Left,
+			Right
+		}
+
+		const int THERMO_FREQ = 6000;
+		const float THERMO_AMP = 0.1f;
+
+		WaveInEvent inputDevice;
+		WaveOutEvent outputDevice;
+		MeasureChannel channel;
+
+		public Measurer(WaveInEvent inputDevice, WaveOutEvent outputDevice, MeasureChannel ch)
+		{
+			this.inputDevice = inputDevice;
+			this.outputDevice = outputDevice;
+			this.channel = ch;
+		}
+
+		public async Task<float> Measure(float duration)
+		{
+			var recorder = new Recorder(inputDevice);
+			var provider = new ThermoSampleProvider(THERMO_FREQ, THERMO_AMP);
+			outputDevice.Init(provider.ToStereo(channel == MeasureChannel.Left ? 1 : 0, channel == MeasureChannel.Right ? 1 : 0));
+			outputDevice.Play();
+			await recorder.Record(duration);
+			outputDevice.Stop();
+			var newSamples = new List<float>();
+			int leftPos = 0;
+			while (leftPos < recorder.samples.Count && MathF.Abs(recorder.samples[leftPos]) < 1e-4) leftPos++;
+			int rightPos = recorder.samples.Count - 1;
+			while (rightPos > 0 && MathF.Abs(recorder.samples[rightPos]) < 1e-4) rightPos--;
+			for (int i = leftPos; i <= rightPos; i++) newSamples.Add(recorder.samples[i]);
+			int pow = 1;
+			int m = 0;
+			while (2 * pow <= newSamples.Count)
+			{
+				pow *= 2;
+				m++;
+			}
+			var data = new Complex[pow];
+			for (int i = 0; i < data.Length; i++)
+			{
+				data[i].X = newSamples[i];
+				data[i].Y = 0;
+			}
+			FastFourierTransform.FFT(true, m, data);
+			float max = -1;
+			int argmax = 0;
+			for (int i = 0; i < data.Length; i++)
+			{
+				var amp = MathF.Sqrt(data[i].X * data[i].X + data[i].Y * data[i].Y);
+				if (amp > max)
+				{
+					max = amp;
+					argmax = i;
+				}	
+			}
+			float desired = THERMO_FREQ * pow / ThermoSampleProvider.SAMPLE_RATE;
+			if (MathF.Abs(desired - argmax) < 1e-3)
+			{
+				// max - amplitude on desired frequency
+				return max / THERMO_AMP;
+			}
+			return float.NaN;
+			
+		}
+	}
+}