In some applications, particularly touch-screen kiosk apps and casual games, it is desirable to be able to play a sound immediately upon a user action. For example, you may want to play a "click" sound when they press a key on an on-screen keyboard, or play a series of laser sounds when their on-screen spaceship fires its weapons.

Please note that this article and the attached sample code was written using the Silverlight 5 Beta, available at MIX11 in April 2011 and updated for the Silverlight 5 RC.

In previous versions of Silverlight, developers used a variety of tricks, including pre-loading sounds into a round-robin buffer of MediaElements in order to provide as low latency as possible. Windows Phone 7 introduced the XNA SoundEffect class to Silverlight developers. Silverlight 5 now includes that class as well.

Project Setup

Create a regular Silverlight 5 application. Most of the Xna libraries are in the core Silverlight runtime (some additional ones will be in the samples for the beta, and eventually in the SDK for release), so you don't need to add any additional references.

Add some wav files to the project (see notes below about format). I have a couple included in the source code with this post.

In MainPage.xaml, add a button and a click event handler. I called the button "ClickMe"

Loading and Playing a Sound Effect

Once you have a wav file in your project (as content), you can load it using the GetResourceStream method of the Application object. You then pass the stream to the FromStream method of the SoundEffect class and you're all set to play. Assuming you have a wav file in the root of your project, with its build action set to content and its name set to "laser_shot.wav", this is all you need to play sound. Put this code in the click event handler for the button.

var laserStream =

    Application.GetResourceStream(

        new Uri("laser_shot.wav", UriKind.RelativeOrAbsolute));



var effect = SoundEffect.FromStream(laserStream.Stream);

effect.Play();

While that was really easy to do, with SoundEffect, the devil's in the details. SoundEffect is notoriously picky about what kind of wav files you provide it. Make sure you are using PCM encoded files, 8 or 16 bit mono or stereo (no 24 bit floating point samples) and either 22.5, 44.1 or 48khz sample rates. The SoundEffect class will fail to load other formats. This is consistent with the implementation on XNA desktop and XNA/Silverlight on the phone.

Controlling Volume, Pitch and Pan

The Play method shown above has an overload which accepts three float values for volume, pitch, and pan.

These parameters are also available as properties on the SoundEffectInstance class as we'll see in the next examples.

Creating Multiple Instances of Sound Effects and Looping

What if you want to use the same sound effect at multiple places in your application? One thing you can do is load it once using the methods shown above, and then obtain a SoundEffectInstance using the CreateInstance method of the SoundEffect class.

Each sound effect instance has its own volume, pitch, and pan settings, as well as the ability to loop the sample. For example, here's how to create a sound effect instance for a looping low backgound engine sound played at 3/4 volume.

var engineStream =

    Application.GetResourceStream(

        new Uri("engine_rumble4.wav", UriKind.RelativeOrAbsolute));



_engineEffect = SoundEffect.FromStream(engineStream.Stream);



SoundEffectInstance engineInstance = _engineEffect.CreateInstance();



engineInstance.IsLooped = true;

engineInstance.Pitch = -1.0f;   // low sound

engineInstance.Volume = 0.75f;



engineInstance.Play();

In the next example, I use the same source engine sound to create two overlapping sounds with different pitch and volume settings. To delay the start of the second one by one second, I use a one-shot timer.

var engineStream =

    Application.GetResourceStream(

         new Uri("engine_rumble4.wav", UriKind.RelativeOrAbsolute));



_engineEffect = SoundEffect.FromStream(engineStream.Stream);



SoundEffectInstance engineInstance = _engineEffect.CreateInstance();

engineInstance.IsLooped = true;

engineInstance.Pitch = -1.0f;   // low sound

engineInstance.Volume = 0.75f;

engineInstance.Play();



// offset a second instance by 1 second, helps mask my bad loop point

DispatcherTimer timer = new DispatcherTimer();

timer.Interval = TimeSpan.FromSeconds(1);

timer.Tick += (s, ea) =>

    {

        timer.Stop();

        SoundEffectInstance engineInstance2 = _engineEffect.CreateInstance();

        engineInstance2.IsLooped = true;

        engineInstance2.Pitch = -.75f;   // slightly higher sound

        engineInstance2.Volume = 0.5f;

        engineInstance2.Play();

    };



timer.Start();

Now you can have great looping drones in the background with very low latency sound effects responding to user or application triggers. Sweet!

Source code for the Silverlight 5 Beta version of this application may be downloaded via the link below.

A video version of this tutorial will be on Silverlight.net shortly.