| The AudioDevice Class defines and encapsulates the
audio device's basic information and characteristics.
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.
|