Recording Audio with the Microphone

The XNA Microphone class allows you to capture audio data from the phone’s microphone. Microphone resides in the Microsoft.Xna.Framework.Audio namespace.

To use the Microphone class you need to create a GameTimer to pump the XNA FrameworkDispatcher. XNA components usually rely on initialization of the XNA environment before they can be used, and the Microphone class is no exception. Creating a GameTimer to pump the XNA FrameworkDispatcher normally involves adding some code to your App class that creates a GameTimer and subscribes to its FrameAction event. For more information on initializing the XNA environment, see Chapter 7, “Employing Media and Web Elements.”

Microphone does not have a public constructor; an instance is retrieved using the static Microphone.Default property, as shown:

Microphone microphone = Microphone.Default;

Microphone uses an event driven approach to periodically deliver audio data while it is recording. The Microphone.BufferReady event is raised as soon as the Microphone instance’s buffer is full. The size of the buffer is specified using the Microphone.BufferDuration property, like so:

microphone.BufferDuration = TimeSpan.FromSeconds(1);

The Microphone.GetSampleSizeInBytes can be used to determine the space requirements for reading the sample data when the BufferReady event is raised.

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int sampleSizeInBytes
         = microphone.GetSampleSizeInBytes(microphone.BufferDuration);

This provides the opportunity to create a byte array for storing the sample bytes when the buffer has been filled:

byte[] buffer = new byte[sampleSizeInBytes];

The buffer can later be copied to a stream and saved in isolated storage, as shown:

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void HandleBufferReady(object sender, EventArgs e)
{
    microphone.GetData(buffer);
    stream.Write(buffer, 0, buffer.Length);
}

The next section looks at putting this together to create a page that allows the user to record and play back audio.