Generate audio tone to sound card in C++ or C#

Question

I am trying to generate a tone to the sound card (Frequency: 1950 hz, duration: 40 ms, level: -30 db, right-channel, on steam 1). Any recommendations on how to accomplish this using C++ or C#. Are there any libraries (C++ or C#) for generating such precise tone?

Answer 1

David, playing audio to the speakers was built right into .NET (i think in the .NET 2.0 Framework). Using the System.Media.SoundPlayer you can play a sound from a memory stream that you build (in WAV format). Here is a function i coded that plays a simple frequency for a certain duration. Regarding the decibels and sending it to the sound card, i don't really understand what specifics you are referring to. For instance i fail to understand how audio as measured in decibels is sent to the sound card. My understanding is that decibels are simply a measure of how loud a sound is, thus after it's been reproduced by the speakers. Thus the volume control on the speakers affects what decibel your sounds will produce, and sending a certain decibel to the sound card thus makes no sense to me. Maybe you need something more detailed and maybe this doesn't work for you. But maybe you can run with this and get it to work for what you need. And maybe it is almost exactly what you are asking.

The process i use in this code allows one to build any audio you want, and plays it. So you can create 2 sine waves or many, many more, or triangle waves, or even speech synthesis with this method if you want. This method takes sound samples which are calculated and then plays those, so you need to code what each audio sample needs to be at the given moment in time. WAV allows stereo sound too, but this code sample only uses non-stereo sound. If you want stereo sound then it just needs modified to generate the bytes for a stereo WAV format instead. I expect it would not be too difficult.

Happy coding!

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Windows.Forms;

public static void PlayBeep(UInt16 frequency, int msDuration, UInt16 volume = 16383)
{
    var mStrm = new MemoryStream();
    BinaryWriter writer = new BinaryWriter(mStrm);

    const double TAU = 2 * Math.PI;
    int formatChunkSize = 16;
    int headerSize = 8;
    short formatType = 1;
    short tracks = 1;
    int samplesPerSecond = 44100;
    short bitsPerSample = 16;
    short frameSize = (short)(tracks * ((bitsPerSample + 7) / 8));
    int bytesPerSecond = samplesPerSecond * frameSize;
    int waveSize = 4;
    int samples = (int)((decimal)samplesPerSecond * msDuration / 1000);
    int dataChunkSize = samples * frameSize;
    int fileSize = waveSize + headerSize + formatChunkSize + headerSize + dataChunkSize;
    // var encoding = new System.Text.UTF8Encoding();
    writer.Write(0x46464952); // = encoding.GetBytes("RIFF")
    writer.Write(fileSize);
    writer.Write(0x45564157); // = encoding.GetBytes("WAVE")
    writer.Write(0x20746D66); // = encoding.GetBytes("fmt ")
    writer.Write(formatChunkSize);
    writer.Write(formatType);
    writer.Write(tracks);
    writer.Write(samplesPerSecond);
    writer.Write(bytesPerSecond);
    writer.Write(frameSize);
    writer.Write(bitsPerSample);
    writer.Write(0x61746164); // = encoding.GetBytes("data")
    writer.Write(dataChunkSize);
    {
        double theta = frequency * TAU / (double)samplesPerSecond;
        // 'volume' is UInt16 with range 0 thru Uint16.MaxValue ( = 65 535)
        // we need 'amp' to have the range of 0 thru Int16.MaxValue ( = 32 767)
        double amp = volume >> 2; // so we simply set amp = volume / 2
        for (int step = 0; step < samples; step++)
        {
            short s = (short)(amp * Math.Sin(theta * (double)step));
            writer.Write(s);
        }
    }

    mStrm.Seek(0, SeekOrigin.Begin);
    new System.Media.SoundPlayer(mStrm).Play();
    writer.Close();
    mStrm.Close();
} // public static void PlayBeep(UInt16 frequency, int msDuration, UInt16 volume = 16383)

Answer 2

NAudio provides a robust audio library for .NET.

NAudio is an open source .NET audio and MIDI library, containing dozens of useful audio related classes intended to speed development of audio related utilities in .NET. It has been in development since 2002 and has grown to include a wide variety of features. While some parts of the library are relatively new and incomplete, the more mature features have undergone extensive testing and can be quickly used to add audio capabilities to an existing .NET application. NAudio can be quickly added to your .NET application using NuGet.

Here's an article that walks step-by-step through using NAudio to create a sine wave. You can create the sine wave with any desired frequency, for any desired duration:

http://msdn.microsoft.com/en-us/magazine/ee309883.aspx