A Java3D application running on a particular machine could have one of several options available to it for playing the audio image created by the sound renderer. Perhaps the machine Java3D is executing on has more than one sound card (e.g., one that is a Wave Table Synthesis card and the other with accelerated sound spatialization hardware). Furthermore, suppose there are Java3D audio device drivers that execute Java3D audio methods on each of these specific cards. In such a case the application would have at least two audio device drivers through which the audio could be produced. For such a case the Java3D application must choose the audio device driver with which sound rendering is to be performed. Once this audio device is chosen, the application can additionally select the type of audio playback type the rendered sound image is to be output on. The playback device (headphones or speaker(s)) is physically connected to the port the selected device driver outputs to.

AudioDevice Interface

The selection of this device driver is done through methods in the PhysicalEnvironment object - see PhysicalEnvironment class. The application would query how many audio devices are available. For each device, the user can get the AudioDevice object that describes it and query its characteristics. Once a decision is made about which of the available audio devices to use for a PhysicalEnvironment, the particular device is set into this PhysicalEnvironment's fields. Each PhysicalEnvironment object may use only a single audio device.

The AudioDevice object interface specifies an abstract input device that creators of Java3D class libraries would implement for a particular device. Java3D's uses several methods to interact with specific devices. Since all audio devices implement this consistent interface, the user could have a portable means of initialize, set particular audio device elements and query generic characteristics for any audio device.

Initialization

Each audio device driver must be initialized. The chosen device driver should be initialized before any Java3D Sound methods are executed because the implementation of the Sound methods, in general, are potentially device driver dependent.

Audio Playback Type

These methods set and retrieve the audio playback type used to output the analog audio from rendering Java3D Sound nodes. The audio playback type specifies that playback will be through: stereo headphones, a monaural speaker, or a pair of speakers. For the stereo speakers, it is assumed that the two output speakers are equally distant from the listener, both at same angle from the head axis (thus oriented symmetrically about the listener), and at the same elevation. The type of playback chosen affects the sound image generated. Cross-talk cancellation is applied to the audio image if playback over stereo speakers is selected.

Distance to Speaker

These methods set and retrieve the distance in meters from the center ear (the midpoint between the left and right ears) and one of the speakers in the listener's environment. For monaural speaker playback, a typical distance from the listener to the speaker in a workstation cabinet is 0.76 meters. For stereo speakers placed at the sides of the display, this might be 0.82 meters.

Angular Offset of Speakers

These methods set and retrieve the angle in radians between the vectors from the center ear to each of the speaker transducers and the vectors from the center ear parallel to the head coordinate's Z axis. Speakers placed at the sides of the computer display typically range between 0.28 to 0.35 radians (between 10 and 20 degrees).

Device Driver Specific Data

While the sound image created for final output to the playback system is either only mono or stereo (for this version of Java3D) most device driver implementations will mix the left and right image signals generated for each rendered sound source before outputting the final playback image. Each sound source will use N input channels of this internal mixer. Each implemented Java3D audio device driver will have its own limitations and driver-specific characteristics. These include channel availability and usage (during rendering). Methods for querying these device-driver specific characteristics are provided.

Instantiating and Registering a New Device

A browser or applications developer must instantiate whatever system- specific audio devices that he or she needs and that exist on the system. This device information typically exists in a site configuration file. The browser or application will instantiate the physical environment as requested by the end-user.

The API for instantiating devices is site-specific, but it consists of a device object with a constructor and at least all of the methods specified in the AudioDevice interface.

Once instantiated, the browser or application must register the device with the Java3D sound scheduler by associating this device with a PhysicalEnvironment. The setAudioDevice method introduces new devices to the Java3D environment and the allAudioDevices method produces an enumeration that allows examining all available devices within a Java3D environment. See PhysicalEnvironment class for more details.

General Rules for calling AudioDevice methods: It is illegal for an application to call any non-query AudioDevice method if the AudioDevice is created then explicitly assigned to a PhysicalEnvironment using PhysicalEnvironment.setAudioDevice(); When either PhysicalEnvironment.setAudioDevice() is called - including when implicitly called by SimpleUniverse.getViewer().createAudioDevice() - the Core creates a SoundScheduler thread which makes calls to the AudioDevice.

If an application creates it's own instance of an AudioDevice and initializes it directly, rather than using PhysicalEnvironment. setAudioDevice(), that application may make any AudioDevice3D methods calls without fear of the Java 3D Core also trying to control the AudioDevice. Under this condition it is safe to call AudioDevice non-query methods.