This demonstration shows how to use the audio authoring tool to generate an .xap project file that stores references for your wave files and their playback properties.
Later on, you will reference this project file in your XNA project to regulate the play- back of the wave files within your game. Whether you are building a 2D or a 3D game, the steps taken here to build your XACT audio project are the same. If you are building a 2D game for Windows or the Xbox 360, then parts B and C of this exam- ple are relevant for you. If you are building a 3D game, then all sections are relevant.
The audio portion of this example begins with an introduction. When the intro- duction finishes, two spacecraft engines start playing in a loop. For no particular rea- son other than to create an interesting soundscape and to demonstrate XNA audio features, each spacecraft also emits a telemetric beep. These telemetric beeps start af- ter the introduction. Ship0 travels with the camera and ship1 moves back and forth along the Z plane in the distance. You can left-click the mouse or pull the right trigger to play a laser firing sound. When you move or strafe, the pitch and volume of your craft (ship0) changes according to your acceleration level.
This project uses six WAV files: an introduction, two engines, two beeps, and a la- ser fire noise. The audio files for this project can be found in the Audio folder on this book’s website. The audio files for this demonstration are from the XNA Spacewar project that ships with Game Studio.
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Launching the XACT Authoring Tool
The XACT authoring tool can be found in the Start menu folder with Game Studio.
There you will see Tools | Microsoft Cross-Platform Audio Creation Tool (XACT).
Selecting Microsoft Cross-Platform Audio Creation Tool (XACT) launches this authoring tool. The authoring tool will appear as shown in Figure 27-1.
Creating a Wave Bank
To load a wave file, click the Wave Banks menu and then choose New Wave Bank.
You can now add wave files to your wave bank. Start by adding the intro.wav file. To do this, click the Wave Banks menu and choose Insert Wave File(s). When the Open dialog launches, select the intro.wav file. Your wave file now appears in the Wave Bank panel.
Adding a Sound Bank
Next, you need a sound bank so you can customize properties that determine how the wave file will be played. The sound bank consists of two parts—a sound bank name and a cue name. To add a sound bank, select the Sound Banks menu and then click New Sound Bank.
You then need to create a cue that your code will use to trigger playback. This can be done by left-clicking the wave file in the Wave Bank panel and dragging it down, with the left mouse button pressed, into the lower panel of the Sound Bank panel.
Your wave file instance should now appear in both the upper and lower sections of the Sound Bank panel (see Figure 27-2).
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XACT authoring tool
Referencing the Spaceship Engines, Firing Sound, and Beeping Sounds
For this part of the example, you repeat the steps you just completed for the intro.wav file for the beep0.wav, beep1.wav, engine0.wav, engine1.wav, and fire.wav files. When you are finished, these files will appear in wave bank, sound bank, and sound bank cue panels, as shown in Figure 27-3.
Setting the Category Property for Beep0
Sometimes you will want to group your sound banks by category. Having sounds that fulfill a similar role under the same category simplifies your ability to control how the sounds are played back in your code. Some code instructions can be applied once to an entire category rather than individually for each sound in the category.
For this example, you need a different category for beep0. This will enable the beep- ing noise to be paused and resumed separately in your code. The intro, engine0, engine1, beep1, and fire sound banks have been assigned by default to the Default cate- gory. If you were to set the volume to the Default category, the intro, beep1, engine0, engine1, and fire sounds would all be affected. The beep0 sound bank will be assigned to the Beep0 category so we can pause and resume it midstream. To create a Beep0 cat- egory, right-click the Category node in the XAP project and select New Category.
When prompted, name the category asBeep0. Then, click on thebeep0instance in the Sound Bank panel under the Category column. In the left panel, select the Beep0 cate- gory setting in the lower-left property panel (see Figure 27-4).
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XACT authoring tool with a wave file referenced on the wave bank panel at the top and the sound bank panel on the bottom
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Creating an Infinite Loop
The beep0 file is meant to play in an infinite loop, so the playback repeats every time the track finishes. To enable the loop, select the beep0 sound bank and highlight Play Wave in the tree view in the top-right panel of the XACT authoring tool.
Once you have highlighted Play Wave for beep0’s sound bank, you can set theloop propertyat the bottom of the left panel in the XACT authoring tool. Checking Infi- nite under looping enables the infinite loop for the beep0 sound (see Figure 27-4).
Both engine0 and engine1 sound banks also have to play in an infinite loop so they can be heard continuously throughout the game. You will need to set theInfinite property for these objects just as you did for beep0. However, when you do this, just use the Default category.
Adding a Finite Loop
For the second telemetric beep sound, beep1, the corresponding wave file only stores one beep. This example requires the beep1 sound to play twice so the sound is heard F I G U R E 2 7 - 3
Wave bank, sound bank, and cues after the wave files have been added
as “beep, beep.” A loop that repeats a specific number of times is called afinite loop.
You can add the “beep, beep” sound by creating a finite loop with one repeat. To set the finite loop, select the beep1 wave file in the sound bank and then highlight Play Wave in the tree view.
Highlighting the Play Wave property button in the tree view at the top-right of the XNA authoring tool will display the Play Wave Properties panel at the bottom left. In the Play Wave Properties panel, expand the LoopEvent attribute. Select Finite in the LoopEvent drop-down. You can then expand the LoopEvent drop-down where you can enter 1 for the LoopCount property.
Testing Your Audio
Now that you have created the sound banks and you have assigned properties, you can test their playback with the XACT Auditioning Utility. This tool allows you to hear how they will sound when played in your game. Launch the XACT Auditioning Utility by navigating from the Start menu to Programs | Microsoft XNA Game Studio Express | Tools. A command-prompt window will appear with the message “Waiting for the XACT authoring tool to connect.…” When you want to test a sound bank, se- lect it, right-click Play Wave in the right panel, and choose Play Sound.
Cue Instance Variables
Say you want to increase the ship’s engine volume and pitch whenever the player in- creases speed. You are going to need some way to tie pitch and volume values in your XNA code to the player’s move and strafe events. The authoring tool allows you to
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The Beep0 category is set for the beep0 file. The sound is also set for infinite looping.
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create cue instance variables for this purpose. You then define ranges of values for the variable and corresponding properties with an RPC preset object in the XACT tool.
You can then attach your sound files to these RPC preset objects. In your code you can reference your cue instance variables to set their values at run time.
To create a cue instance variable, right-click the Cue Instance node in the left panel and choose New Cue Instance. Your cursor will be placed at the bottom of the vari- able settings dialog in the Name column. Here you can assign your cue instance vari- able a name. For this example, assign your new cue instance variable the name Engine0Variable. Next, set the variableMinandMaxproperties to 0 and 1 re- spectively. These values will map nicely to values obtained from the move and strafe keys and the left thumbstick whose absolute values range between 0 and 1 (refer to Figure 27-5).
In your code, you can use theCueobject’sSetVariable()method to set these values:
Cue cue.SetVariable("Engine0Variable", float value);
Creating a New RPC Preset
For our example, a Ship0RPC preset is created to specify how different sound prop- erties are affected over the range of values of a cue instance variable. You can start by right-clicking the RPC Presets node, and in the dialog that appears, select your cue in- stance variable. From there, you can choose your new cue instance variable, Engine0Variable. Choose the Sound value for the Object and use the Volume se- lection as the Parameter. You are then presented with a curve, which you can shape to specify how your volume changes between 0 and 1. Two control points define the graph initially.
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Cue instance variable
To add a control point to shape your graph, right-click the rows of data under the Points heading and choose Insert Point in the drop-down that appears. You can then left-click these control points and drag them into position while your left mouse but- ton is pressed. This finished curve defines volume for different values of your cue in- stance variable. Changes in volume are shown by the top curve in Figure 27-6.
The process used to define the range of values for Pitch is similar to the steps taken to define the volume. First, you have to add another instance of the Engine0Variablevalue under the Variable heading. Then, you must pick Sound as an Object and Pitch as a Parameter. The bottom curve in Figure 27-6 shows the pitch values over the range whereEngine0Variableranges between 0 and 1.
For this example, name your RPC preset to Ship0RPC. Then right-click it to choose Add/Detach Sounds where you can select engine0. After you do this, you will see the reference to the sound (refer to Figure 27-7).
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RPC preset for controlling engine0’s volume and pitch between values of 0 and 1
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Later, you will be able to control the pitch and volume of your engine0 with this instruction:
Cue cue.SetVariable("Engine0Variable", float value);
Enabling Volume Attenuation
Audio attenuationrefers to how the volume changes as the sound source travels to- ward and away from the listener. First, you must adjust the maximum distance value for the cue. To do this, in the left panel of the XACT project, expand Cue Instance and click Distance to select it. While Distance is selected, in the Properties panel that appears, change the MaximumValue property to50(see the earlier Figure 27-5).
Next, to enable volume attenuation, you have to attach the sound to a Runtime Parameter Control (RPC) preset. To create an RPC preset, right-click RPC Presets in the left panel and choose New RPC Preset. Under the Parameter column choose Sound: Volume. Under the Variable column, choose Distance. The line that appears shows how the sound fades as it travels away from the listener. When you are fin- ished, the distance curve should be similar to the one in Figure 27-8. This volume level simulates how sound volume fades over distance.
To associate this attenuation with engine1, right-click your new RPC preset that appears in the left panel and choose Attach/Detach Sounds. When prompted, choose Sound Bank engine1 and click Attach. Click OK when you are finished.
The engine1 will now be listed as one of the attached sounds in the properties dis- play for theAttachedSoundsproperty under the RPC preset. Engine1’s sound vol- ume will now adjust according to the increase or decrease in distance between it and the listener. Figure 27-9 shows the new RPC preset, named Ship1 RPC, with the engine1 sound attached.
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RPC preset for references engine0
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Runtime Parameter Control settings to adjust volume with distance
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RPC preset with engine1 sound attached
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Saving Your Audio Project
Now your wave banks and sound banks are prepared to play sounds as required for this example. The next step requires that you save your XACT project. The .xap pro- ject file that is generated is used by your XNA game project to set the playback prop- erties for your wave files. To generate the .xap project file, on the XACT authoring tool’s File menu, select Save Project As. In the Save Project As dialog, browse to the directory where you want to export your project.
For the code portion of the example that follows, the .xap project file needs to be saved to the folder where the wave files are located; this ensures that the project file’s directory has the same relative path as the wave files. Enter the nameaudioProjectin the File Name text box and click the Save button. This action generates an audioProject.xap file that stores your project and includes your wave bank, sound bank, and sound bank cue settings. Also, be sure to keep this .xap file in case you want to edit your XACT authoring tool project later.