Sound effects are created as part of the Content project, as has been the case with all the other resource data (textures and sprite fonts) that we used in previous chapters. They are added in just the same way: by right-clicking the main Content project node inside Solution Explorer and then selecting Add / Existing Item. The sound file can then be located and added to the project.

You will see after adding a sound file that the content item's Content Importer is set to WAV Audio File, and the Content Processor is set to Sound Effect, as shown in Figure 5-1.

Figure 5.1. The properties for a WAV file added to an XNA Content project

All sound effects must be created from WAV files. WAV (short for Waveform Audio File Format) files are one of the oldest sound formats used by Microsoft. They usually store sound in an uncompressed format, making them easy to read and write, but result in large file sizes.

On desktop PCs, WAV files have largely been replaced by formats offering higher levels of compression such as MP3, but XNA unfortunately cannot use MP3 files for sound effects (though it does use them for background music, as you will see later in this chapter). As a result, we find ourselves with no choice but to use WAV files for our sounds.

Once the file has been added, we are ready to load it into our game. Once again, this is handled in the same way as with other resources that we have loaded from the Content project: using the Content.Load method. Listing 5-1 shows a piece of code that declares a SoundEffect object and loads it from the Content project. Just as before, we provide the Load method with the type of object that is being loaded.

SoundEffect mySound;
        mySound = Content.Load<SoundEffect>("Piano");

With a sound effect loaded, we are now ready to play it by simply calling the Play method of the SoundEffect object.

Two overloads of this method are available. The first takes no parameters and simply plays the sound at full volume. The second overload provides some additional control, allowing us to provide values for the volume level, the pitch, and the stereo panning of the sample:

Play is asynchronous and returns to your game immediately, leaving the sound playing in the background. If you call Play again before an earlier call has completed, the new sound will play alongside the older sound. Options to stop the earlier sound are provided via the SoundEffectInstance object, which we'll discuss in a moment.

Just as we have added GameFramework support for textures and fonts, so we will add support for sound effects too. This support is implemented using another Dictionary within the GameHost class, this time named SoundEffects. The declaration of the dictionary is shown in Listing 5-2.

// A dictionary of loaded sound effects.
    public Dictionary<string, SoundEffect> SoundEffects { get; set; }

We can then use the dictionary to load sound effects in the same way as we do for textures and fonts, and can access the dictionary items anywhere within the game.

The SoundEffects example project that accompanies this chapter shows how sound effects can be loaded into the game engine and then played back. It loads four different samples (named EnergySound, Piano, MagicSpell, and Motorbike) and divides the screen into four regions to allow each to be played. Experiment with the project and with playing multiple sounds together.

The example project also sets the sound effect's panning based on the horizontal position of the screen tap. Tapping the left side of the screen will pan to the left; tapping the right will pan to the right.

Try experimenting with changing the source code to produce different volume levels and different pitches, too.

Calling the Play method on a SoundEffect object provides a very easy way to get a sound playing, and in many cases this will be sufficient. For gunfire, explosions, player achievement sounds and all sorts of other one-off effects, this is likely to be all that you need.

In other places, however, you might find that a greater level of control is needed over the sounds that you play. The ability to loop a sound, for example, can be very useful, but the functions provided by the SoundEffect class alone cannot offer this ability. The main reason is that we would have no way to stop the sound; we don't obtain a sound ID value or anything similar, so once several sounds were active we would be unable to tell the class which one it should stop.

This problem is resolved by the inclusion of the SoundEffectInstance class. Instances of this class are created by calling the CreateInstance method of a SoundEffect object.

SoundEffectInstance objects are very similar to SoundEffect objects, with the following key differences:

The SoundEffectInstances example project demonstrates the use of this class. It looks just the same as the SoundEffects example, but works in a different way. When you press and hold your finger on one of the sound panels, the sound will play and will loop endlessly. When you release your finger, the sound will pause. When the panel is touched again, playback resumes from where it left off (this is most noticeable with the Piano and Motorbike sounds). This behavior couldn't have been accomplished with just the SoundEffect class.

Additionally, if you slide your finger to the left and right as the sound is playing, the pitch of the sound will change in response. Once again, only the SoundEffectInstance allows this change to be made because the SoundEffect class only allows the pitch (as well as the volume and panning) to be set when the sound playback is first initiated.

The code that plays, repitches, and pauses the sounds, taken from the example project's Update method, is shown in Listing 5-3.

TouchCollection tc = TouchPanel.GetState();
        if (tc.Count > 0)
        {
            // Find the region of the screen that has been touched
            screenRegion = (int)(tc[0].Position.Y * 4 / Window.ClientBounds.Height);
            // Ensure we have a region between 0 and 3
            if (screenRegion >= 0 && screenRegion <= 3)
            {
                // What type of touch event do we have?
                switch (tc[0].State)
                {
                    case TouchLocationState.Pressed:
                        // Set the pitch based on the horizontal touch position
                        _soundInstances[screenRegion].Pitch =
                                (tc[0].Position.X / this.Window.ClientBounds.Width) * 2 - 1;
                        // Start the sound for this region
                        _soundInstances[screenRegion].Play();
                        break;
                    case TouchLocationState.Moved:
                        // Is the sound for this region currently playing?
                        if (_soundInstances[screenRegion].State == SoundState.Playing)
                        {
                            // Yes, so set the pitch based on the horizontal touch position
                            _soundInstances[screenRegion].Pitch =
                                (tc[0].Position.X / this.Window.ClientBounds.Width) * 2 - 1;
                        }
                                break;
                            case TouchLocationState.Released:
                                // Pause all of the sounds
                                for (int i = 0; i < _soundInstances.Length; i++)
                                {

_soundInstances[i].Pause();
                                }
                                break;
                        }
                    }
                }

Try changing the code when the touch point is released so that it calls the Stop method of the SoundEffectInstance objects rather than Pause. You will then see that each time the sound is played, it restarts from the beginning rather than resuming from where it was interrupted.

Among the other properties exposed by the SoundEffect class are two that we will briefly look at.

The first is the Duration property, which returns a TimeSpan indicating exactly how long the sample will take to play at its default pitch. This property can be useful for queueing up sounds to play one after another.

The second is the MasterVolume property, which is actually a static property called against the SoundEffect class rather than on an instance. It controls the overall volume of all sound effects, subsequently played or already playing, so it is a great way to fade up or down the sound from or to silence.

Just like the volume of individual sounds, MasterVolume is set in the range of 0 (silence) to 1 (full volume, based on the current device volume level). It defaults to 1.

Although you mightwant to create your own sound effects, there are many thousands available on the Internet that you can use in your game instead. It is generally much easier to get hold of quality sounds this way because you can search through the libraries playing each sound you find until you locate one that will fit into your game.

The main issue to be aware of with downloaded sounds is licensing. Just as with everything else in life, it is hard to find good things for free—particularly if you intend to sell your game. An organization called Creative Commons has made this particular area easier to deal with, however, and this is extremely helpful for getting good sound effects.

A number of different Creative Commons licenses are available, many of which permit the material that they cover to be used in free or commercial products, and some of which also allow modifications to be made to the licensed items. The only general requirement is that you include attribution for the source of the material in your game. Soif you include the details of the sound author and a link to the site from which it was downloaded, all such licensed sounds can be freely used within your games. Do check the license of each individual sound that you want to use, however, because some licenses forbid commercial use.

A couple of great sites for finding Creative Commons licensed sound effects are the following:

Both of these sites clearly describe the license applied to each sound and have search facilities and online previews of each sound in their database. Many other sound sites exist, too, and can be found via your search engine of choice.

Selecting a sound can be tricky, and it is essential to try out each sound that you like and see how it fits in with the game environment. Sometimes sounds that initially seem ideal just don't work well inside a game, so spend some time experimenting to get things sounding just right. Don't forget that altering the volume or pitch can help with getting your sounds to fit in, too.

To manipulate sounds that you have downloaded or to convert them between different formats, a sound editing application is essential. This application will let you cut out or exclude sections of a sound, fade its volume up or down, add echo and distortion, anddo dozens of other useful things.

Lots of commercial applications are available for this task, but if you are looking to keep your costs down, a free application called Audacity is well worth a look. It has a large range of sound processing effects, has flexible editing features, and supports saving to numerous file formats (including WAV and MP3). Visit audacity.sourceforge.net to download a copy.

Recall the Balloons project that we created in Chapter 4 to illustrate mapping input coordinates to objects on the screen. To bring a little more life to the example, an updated version of Balloons is included with this chapter with some sound effects added.

Three different popping sounds are included to make the sound a little more varied, and as each sound is played it is also given a slightly randomized pitch as well as being panned to match the balloon position on the screen. This makes for an entirely more satisfying balloon-popping experience!

The certification requirement complication for Windows Phone 7 games revolves around the fact that one of the other primary uses for the device is as a media player. The operating system has a flexible media library that allows music and other audio content to be played on the device, even when the media library has been moved to the background.

As a result, it is entirely possible that, when the user launches your game, music is already playing in the background. Microsoft has decided that this existing music should take priority over your game music and that you must not stop it from playing without either directly asking the user for permission (by displaying a dialog box, for example, asking if the user wants to play the game music instead of the current audio track) or by providing a configuration option that allows it to be configured on a more permanent basis (in which case the option must default to not interrupting the existing media playback). Without observing this requirement, your game will be rejected when you submit it to the Windows Phone Marketplace.

We will look at how to perform this check (and how to pause the background music if appropriate) in a moment, but for now please bear in mind the need to do this.

Note that this check applies only to playing music with the MediaPlayer class, which is the class that provides access to the music player functionality. Sound effect playback is permitted even if the device is already playing music, so no special checking needs to be performed for sound effects. The certification requirements state that sound effect objects should not be used for playing background music, however, so this isn't a way to bypass the requirement.

Music is also added to the Content project. Unlike sound effects, music is expected to be in either MP3 or WMA format. This is a good thing because such formats produce much smaller files than WAV files due to the way they are compressed. Because music is likely to be much longer in duration than a sound effect, having compression applied is essential for keeping the size of your finished game under control.

MP3 files have taken over the world during the last decade and must surely form one of the most widely known file formats in existence. Sound files encoded using MP3 are compressed using a lossy compression algorithm. Although this means that there is some degradation of the audio when it is played back (just as there is a loss of image quality with JPG images), in most cases the quality loss is virtually or completely unnoticeable.

MP3 can compress audio data to different degrees, and the higher the compression the greater the quality loss on playback. The compression level is set when the MP3 is created by specifying a bit rate, which controls how many kilobits of data can be used to store each second of compressed audio. Compressing files at a bit rate of 128 kilobits per second will typically reduce CD quality audio to about 9 percent of its original file size—a massive saving.

Windows Media Audio (WMA) files are similar in approach to MP3s, also using a proprietary Microsoft compress to provide lossy compression (although a lossless variation is available). Microsoft claims that WMA files can be created that have the same quality level as an MP3 while using only half the storage space, though there are those who dispute this claim. Nevertheless, it is still a capable format and certainly worth considering as a format for your game music.

When you add a music file to the content, the properties show the Content Processor as Song, as shown in Figure 5-2.

Figure 5.2. The properties for an MP3 file added to an XNA Content project

"Song" is in fact the term that XNA uses to refer to a piece of music, and its class names reflect this. To load a song, we use the Song class along with the usual Content.Load call. In the game framework, we store a collection of songs within the GameHost class inside a Dictionary named Songs. Listing 5-4 shows the instruction within a project's LoadContent function that loads a song into the framework.

// Load our song
        Songs.Add("2020", Content.Load<Song>("Breadcrumbs_2020"));

Playing a song is very easy: just call the static MediaPlayer.Play function, passing in the Song object that you have loaded. Only one song can play at a time; trying to play a second song will stop the first song from playing.

However, we have the tricky issue of whether we are allowed to play music or not because, if the device is already playing background music, we must leave it alone.

This is determined using the MediaPlayer.GameHasControl property. If it returns true, we have full access to playing music; if it returns false, there is music already playing; and unless the user has explicitly confirmed that they want for our game to take control, we must allow it to continue. Listing 5-5 shows some code from the LoadContent function of the BackgroundMusic example project that accompanies this chapter. If it detects that media are already playing, it doesn't even attempt to load the song; otherwise, the song is loaded and played.

// Load songs
        if (MediaPlayer.GameHasControl)
        {
            // Load our song
            Songs.Add("2020", Content.Load<Song>("Breadcrumbs_2020"));

            // Play the song, repeating
            MediaPlayer.IsRepeating = true;
            MediaPlayer.Play(Songs["2020"]);
        }

Assuming that we can play our music, there is a number of other methods and properties that we can access from the MediaPlayer class to affect the way in which the music plays:

Each loaded Song object also has a series of interesting-looking properties that might be interrogated. Unfortunately, it turns out that they aren't too useful after all. Properties are available to provide information on the song's Album, Artist, and Genre, among other things, but when songs are read from a game's Content project, none of them is populated even if the information is present inside the MP3 file. These properties are instead used to access data on songs contained within the device's media library.

One useful property that we can read from the Song is its Duration, which also returns a TimeSpan, this time containing the length of the song. We can use this alongside the MediaLibrary.PlayPosition for our playback time display. The BackgroundMusic example project displays such a timer and generates its text as shown in Listing 5-6. An example of the display it produces is shown in Figure 5-3.

// Are we playing a song?
        if (MediaPlayer.GameHasControl)
        {
            // Yes, so read the position and duraction
            currentPosition = MediaPlayer.PlayPosition;
            duration = Songs["2020"].Duration;
            // Display the details in our text object
            TextObject positionText = (TextObject)GameObjects[0];
            positionText.Text = "Song position: "
                        + new DateTime(currentPosition.Ticks).ToString("mm:ss") + "/"
                        + new DateTime(duration.Ticks).ToString("mm:ss");
        }

Figure 5.3. The display from the BackgroundMusic example project

This is nearly all you need to know about playing music, but there is one other thing that you should be aware of, and it is a rather annoying feature of XNA's media playback functionality. When you set a song to loop, there is a very slight pause between the song finishing and restarting. If your song fades to silence at the end, it will be unnoticeable, but if you try to loop the song so that it restarts seamlessly, this pause can be quite noticeable.

Although there is nothing you can do to eliminate the pause, you can make a minor adjustment to the song to slightly reduce its impact. The pause can be irritating on two levels: it enforces a brief moment of silence and it results in the music playback being thrown slightly off-beat. This second problem can be very distracting indeed.

To eliminate the timing problem, edit your music file and trim about one-tenth of a second from the end. Then save it and use this modified version in your game. The pause will then be offset by a corresponding gap in the music track, allowing the beat to continue uninterrupted.