Prerequisites: Install NAudio, an open-source .NET library written by Mark Heath. After that, see this tutorial, figure it out and implement the code. Our code will be based on that.
Now you have a WinForm app where you can record audio to a WAV file. Now we want to add a feature to allow us to test the mic before we start recording. We’ll add a real-time volume level meter to our app.
First let’s define a isRecording flag right after the closing flag.
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bool closing = false;
bool isRecording = false;
Now let’s add a Test mic button, and a progress bar which serves as our volume meter, right after the existing buttons.
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var buttonTest = new Button() { Text = "Test mic", Top = buttonStop.Bottom };
var volume = new ProgressBar(){ Top = buttonTest.Bottom, Size = new Size(800,20) };
Then we’ll modify some event handlers. When we click Test mic button, we want the recording starts but we don’t want the audio to be saved. After we click Record button, we set isRecording to be true.
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buttonTest.Click += (s, a) => { waveIn.StartRecording();};
buttonRecord.Click += (s, a) =>
{
writer = new WaveFileWriter(outputFilePath, waveIn.WaveFormat);
isRecording = true;
buttonRecord.Enabled = false;
buttonStop.Enabled = true;
};
The recorded audio samples are represented as a byte array. Each sample is 16bit integer, so we need to convert every two array items into a sample. We calculate a max value in every buffer to represent the volume value in that period of time.
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waveIn.DataAvailable += (s, a) =>
{
if (isRecording)
{
writer.Write(a.Buffer, 0, a.BytesRecorded);
// Limit the length to 30s.
if (writer.Position > waveIn.WaveFormat.AverageBytesPerSecond * 30)
{
waveIn.StopRecording();
}
}
float max = 0;
for (int index = 0; index < a.BytesRecorded; index += 2)
{
short sample = (short)((a.Buffer[index + 1] << 8) | a.Buffer[index + 0]);
// to floating point
var sample32 = sample / 32768f;
// absolute value
if (sample32 < 0) sample32 = -sample32;
// is this the max value?
if (sample32 > max) max = sample32;
}
volume.Value = (int) (100*max);
};
This is what our simple app looks like:
The full program code:
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using System;
using System.Drawing;
using System.IO;
using System.Windows.Forms;
using NAudio.Wave;
namespace Recorder
{
static class Program
{
static void Main()
{
// Set output path. Save recording to desktop/recorded.wav
var outputFolder = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "NAudio");
Directory.CreateDirectory(outputFolder);
var outputFilePath = Path.Combine(outputFolder, "recorded.mp3");
var waveIn = new WaveInEvent();
WaveFileWriter writer = null;
bool closing = false;
bool isRecording = false;
var f = new Form();
var buttonRecord = new Button(){Text = "Record"};
var buttonStop = new Button(){Text = "Stop", Left = buttonRecord.Right, Enabled = false};
var volume = new ProgressBar(){ Top = buttonStop.Bottom, Size = new Size(800,20) };
var buttonTest = new Button() { Text = "Test mic", Top = volume.Bottom };
f.Controls.AddRange(new Control[]{buttonRecord, buttonStop, volume, buttonTest});
buttonRecord.Click += (s, a) =>
{
writer = new WaveFileWriter(outputFilePath, waveIn.WaveFormat);
isRecording = true;
buttonRecord.Enabled = false;
buttonStop.Enabled = true;
};
buttonTest.Click += (s, a) =>
{
waveIn.StartRecording();
};
buttonStop.Click += (s, a) => waveIn.StopRecording();
waveIn.DataAvailable += (s, a) =>
{
if (isRecording)
{
writer.Write(a.Buffer, 0, a.BytesRecorded);
// Limit the length to 30s.
if (writer.Position > waveIn.WaveFormat.AverageBytesPerSecond * 30)
{
waveIn.StopRecording();
}
}
float max = 0;
for (int index = 0; index < a.BytesRecorded; index += 2)
{
short sample = (short)((a.Buffer[index + 1] << 8) | a.Buffer[index + 0]);
// to floating point
var sample32 = sample / 32768f;
// absolute value
if (sample32 < 0) sample32 = -sample32;
if (sample32 > max) max = sample32;
}
volume.Value = (int) (100*max);
};
// RecordingStopped event handler. Disposes writer
waveIn.RecordingStopped += (s, a) =>
{
writer?.Dispose();
writer = null;
buttonRecord.Enabled = true;
buttonStop.Enabled = false;
if (closing)
waveIn.Dispose();
};
// Stop recording when form is closed
f.FormClosing += (s, a) =>
{
closing = true;
waveIn.StopRecording();
};
f.ShowDialog();
}
}
}
