XNA Game Studio 4.0 : Playing Sound Effects (part 2) - Microsoft Cross-Platform Audio Creations Tool

Microsoft Cross-Platform Audio Creations Tool (XACT)

The Microsoft Cross-Platform Audio Creations Tool (XACT) is a powerful graphical audio-authoring tool that enables you to manage large numbers of source wave files and to control their playback in the game. Using the XACT graphical interface, you can load existing wave files, group the files, and layer them with effects. The provided XNA Game Studio APIs can trigger their playback.

Although the XACT tool provides several features, we cover the basics of the graphical interface and the XACT APIs to enable you to get started using the tool.

Opening XACT

You can find the XACT tool under the Microsoft XNA Game Studio 4.0 program files menu under the Start menu. Select the Tools: folder, and then click the Microsoft Cross-Platform Audio Creation Tool (XACT) menu item. This launches the XACT tool, which looks like Figure 1.

Figure 1. XACT graphical interface

The XACT graphical interface contains many menus, icons, and options. We cover the different areas as they are needed in the following examples.

Creating a New XACT Project

In the XACT tool, select File, then New Project. The New Project Path dialog box displays. Because we use the XACT project in our game’s content pipeline, it is often easy to use the content folder of the game to store the XACT project file. Locate the content project folder for your game, and then enter a name for your XACT project and make sure it ends with the .xap extension. Click the Save button.

Adding a Wave File to the XACT Project

The starting elements of an XACT project are wave files that must be loaded from source recordings. In the following example, you load a single wave file and then play back the sound using the XACT APIs provided in XNA Game Studio.

First, you need a wave bank to load the source wave files into. A wave bank is a collection of wave files that are grouped together. To add a new wave bank, click the Wave Banks menu and select New Wave Bank. A new entry displays under Wave Banks in the XACT project tree with the default name “Wave Bank”. You can change the default name by clicking the wave bank in the tree or by right-clicking the wave bank and selecting Rename. A wave bank menu also displays in the right side of the XACT workspace. Your XACT workspace should look like Figure 2.

Figure 2. Wave Bank window in the XACT tool

Next, you need to add the first sound bank to the project. A sound bank is a collection of wave banks. To add a new sound bank, click the Sound Banks menu and select New Sound Bank. Just as with the wave bank, the new sound bank is added to the XACT project tree, but this time, the new item displays logically under the Sound Banks tree node. The new sound bank has a default name of Sound Bank, but you can change the name by clicking on the sound bank or by right-clicking the sound bank and selecting Rename. The sound bank window is also added to the XACT workspace to the right.

The workspace might be getting cluttered now, so the wave bank and sound bank windows might be overlapping. XACT provides a nice window-ordering option to organize your windows automatically. Click the Window menu option to display the windowing options. Select Tile Horizontally from the drop-down menu. The sound bank and wave bank windows should now organized as shown in Figure 3.

Figure 3. Sound and wave bank windows

You can now add the source wave files to the project. Right-click the Wave Bank in the XACT project tree and select Insert Wave File(s). In the open file dialog box, choose a wave file and click the Open button.

To hear the newly added wave file play, launch the XACT Auditioning Utility. This tool can be found in the same Tools folder under Microsoft XNA Game Studio 4.0 as the XACT tool is located. Launching the XACT Auditioning Utility should bring up a console window like the one in Figure 4.

Figure 4. XACT Auditioning Utility

To listen to the wave file you just added to the wave bank, right-click the entry and select Play.

Finally, you need to set up a cue. The developer uses the cue to play back a sound or a group of sounds. The cue is stored and accessed from the sound bank.

The quickest way to add a cue is by dragging a wave from the wave bank onto the cue section of the sound bank windows, which is in the lower left corner (see Figure 5).

Figure 5. XACT windows after dragging wave to the cue window

After you drag the wave file and create the cue, notice there are a number of new items that display in the sound bank window. Because a new sound has been created, by default, it is created with the same name as the wave. The sound is displayed in the top left of the sound bank window. After selecting the sound entry, there is a track listing to the right of the window. Each sound can contain a number of tracks. In this case, a single track is created that plays the wave from the wave bank. Below the sound bank is the cue window that you dragged the wave to. A new cue is created using the same name as the wave that was used to create it. As we discussed, the cue is used in the game code to control the playback of the sounds. So, a cue is required if you want to cause the sound to be played in your game. A cue is made up of multiple sounds from the sound bank entries in the window above it. Because the cue is created by using the dragging shortcut, the sound of the same name is added to the cue. By right-clicking the cue, you can select the Play menu option to hear the cue play.

Now you are ready to switch over to the code to show you how to play the cue you just created. Save your project and open XNA Game Studio.

Sound Playback Using Cue

It’s time to play the cue you just created in the XACT tool. You need to add the XACT project you created to the content project of your game. Just like adding other types of content, it is easy to add the XACT project. Right-click the content project and select Add, and then click Existing Item. Then, select the .xap XACT project file in the dialog box and click the Add button. Building the content project now should show that three files are built from the single .xap file. XACTProject.xgs is the audio engine file and is named after the project name that was used for your XACT project. The Wave Bank.xwb file contains the data from the wave bank of the same name. If you renamed the wave bank in your XACT project, this file uses the name you used for your wave bank. The Sound Bank.xsb file contains the data from the sound bank in your XACT project. Like the wave bank, the name of the file is the same as you used for the sound bank in the XACT project and is set to whatever you named your sound bank.

In your game, add the following member variables for the AudioEngine, SoundBank, WaveBank, and Cue:

AudioEngine audioEngine;
SoundBank soundBank;
WaveBank waveBank;
Cue cue;

The AudioEngine is used to perform necessary updates to the underlying audio system. The AudioEngine.Update method is required to be called once per frame to ensure the audio playback stays up to date and is not stalled. The other three variables for the SoundBank, WaveBank, and Cue are the code counterparts to the ones created in the XACT project.

To load the files that were built by processing the XACT project through the content pipeline, add the following lines of code to your games LoadContent method:

// Load file built from XACT project
audioEngine = new AudioEngine("Content\\XACTProject.xgs");
waveBank = new WaveBank(audioEngine, "Content\\Wave Bank.xwb");
soundBank = new SoundBank(audioEngine, "Content\\Sound Bank.xsb");
// Get an instance of the cue from the XACT project
cue = soundBank.GetCue("Explosion");

Finally in the games Update method, check to see whether the spacebar is pressed. If the spacebar is pressed, the cue plays:

// Play the cue if the space bar is pressed
if (currentKeyboardState.IsKeyDown(Keys.Space) &&
    lastKeyboardState.IsKeyUp(Keys.Space))
{
    cue.Play();
}

// Update the audio engine
audioEngine.Update();

After playing the sound, call the AudioEngine.Update method to ensure it is called each frame.

A Cue has similar playback methods as SoundEffectInstance, such as Play, Pause, Resume, and Stop. There is also an Apply3D method, which takes an AudioListener and AudioEmitter.

After Play is called on the Cue, it can’t be called again. You can call Pause and then Resume, but calling Play again will cause an InvalidOperationException. To play the sound more than once, create a new Cue instance by calling the SoundBank.GetCue method. Each Cue returned from GetCue is its own instance. This also means you should not call GetCue unless you need a new instance since it will allocate memory.

You can use the SoundBank.PlayCue method to just play a cue and have no other controls on the cue similar to how fire and forget sound effects work. You can use the following code to play a cue without creating an instance of a Cue:

// Play cue without cue instance
if (currentKeyboardState.IsKeyDown(Keys.P) &&
    lastKeyboardState.IsKeyUp(Keys.P))
{
    soundBank.PlayCue("Explosion");
}

Streaming

Some wave files are large, especially the wave files that are used to play back music in your game. By default, the wave files used in the XACT project are loaded into memory at runtime. This can cause problems if your file is quite large because the file might not fit into memory or it might take up more space than what you would like. Streaming is set at the wave bank level for all of the wave files contained within the wave bank.

Let’s add some streaming music to the previous XACT sample. Open the XACT project you created previously. Add a new wave bank and call it Music. Select the new wave bank in the XACT project tree. The properties of the wave bank display in the lower left window. In the Type section, select the Streaming button. It should be highlighted a green color (see Figure 6).

Figure 6. Setting wave bank to streaming

To add the music source files to the wave bank, right-click the wave bank and select Insert Wave File(s). Select your music file in the dialog window and click the Open button. Now that the source wave file is added to your streaming wave bank, you need a cue to use for playback. Like you did before, drag your music wave into the sound bank’s cue window to create the cue for your music wave.

Finally, you change the sound that was created for the music cue to mark it as background music. Setting a sound category to Music allows users on the Xbox 360 to play their own music library over your game’s music. This allows the user to hear the sound effects in your game but to override the music to what they are playing using the media playback provided on the Xbox 360.

To change the sound category, select the music sound entry that you just created in the sound bank. In the lower left, select the Category drop-down and select Music (see Figure 7). Next, select the Infinite checkbox under the Looping section to have the sound continually play until it is stopped. Save the XACT project, so you can add the music to your previous code sample.

Figure 7. Setting sound category to Music

You need two additional member variables to add streaming music to the previous example. Add the following two member variables:

WaveBank streamingWaveBank;
Cue musicCue;

Like before, you need to load the wave bank. After the other audio loading in the games LoadContent method, add the following lines of code:

// Load streaming wave bank
streamingWaveBank = new WaveBank(audioEngine, "Content\\Music.xwb", 0, 4);
// The audio engine must be updated before the streaming cue is ready
audioEngine.Update();
// Get sue for streaming music
musicCue = soundBank.GetCue("Music");
// Start the background music
musicCue.Play();

The overload of the WaveBank constructor takes an additional two arguments. The first is the offset into the wave to start. In most cases, you want to start at the beginning, so a value of 0 should be set. The last parameter is the packetsize, which determines the size of the streaming buffer used internally to store the file as it is loaded. It is in units of DVD sectors, which are 2,048 bytes each. The minimum value must be 2. The higher the number, the larger the memory buffer, which allows for smoother playback. You can test different values to determine the minimum value that smoothly streams the music in your game.

After creating a new streaming wave bank, you must call the AudioEngine.Update method to play a cue that contains the streamed data from the wave bank.

The last two steps are to get the Cue from the SoundBank and to call the Play method to start the background music. Now your game has streaming background music that can be overridden by the player.