OpenAL

OpenAL ( Open has udio L ibrary) is a software Bibliothèque Multiplate-form providing a Application program interface (API) audio 3D suitable mainly for the video games but also of other audio applications. It was mainly developed by Loki Entertainment and Creative Labs. Other similar libraries exist like DirectSound3D of Microsoft, EAX of Creative Labs and A3D of Aureal, but OpenAL has the role to provide API the more standard whatever the platforms, following the example OpenGL. It is distributed according to the terms of LGPL for the majority of the platforms, but certain drivers are owners, inter alia those of the Xbox, Xbox 360, or those specific to the charts its Creative Labs under Windows.

Principal use

In 2005, the library exists and functions under Mac OS 8 and Mac OS 9 (Sound Manager), Mac OS X (Core Audio), Linux (OSI, ALSA), BSD, Solaris, Irix, Windows (ms, DirectSound, DirectSound3D…), Xbox, Xbox 360. The developers specify that it functions on other platforms (as BeOS) but in versions which are not published because under development.

Driving of play known use OpenAL like that of Id Software ( Doom 3 , Jedi Knight 2 , Jedi Knight: Jedi Academy , Quake 4 ) or the Unreal engine ( Unreal 2 , Unreal Tournament 2003 , Unreal Tournament 2004 , Postal 2 , America' S Army: Operations , Hitman 2 ); or of other like Freedom Fighters or Psychonauts . These professional uses make it possible to say that its use is largely accepted by the developers of video games.

Principle

The library makes it possible to model a whole of sound sources moving in a space in 3D, and a listener in this same space. Modifications on the sources can be added like echo or others sound effects. The library can then calculate made final, while drawing left accelerations from the recent audio charts.

The specifications are separate into two, on the one hand the core of the interface (API core) consisted of the functions accessible from OpenAL, on the other hand the API ALC (for Audio Library contexts ) which provides low functions level. The ALC thus makes it possible to separate the functions the API one from the device which realizes made final, that is an electronic chart, a demon, a driver, or even a service. It facilitates the use of various devices coexisting on the same system, by enumerating them and by allotting them, allows to know the extensions present on the system, as well as a means of reaching the microphonous entry if it exists.

Part of the sources is maintained by the manufacturer Creative Labs, but the library is designed to accommodate clean specificities of each one of the other different manufacturers and their audio charts, by the means of extensions to the API one. After a certain time, these functions can even become standard functions the API one. Between the two extensions can be promoted ARB (Architecture Review Board) which makes it possible to know that they will be maintained in the future versions of the library.

Technical comparison

Version 1.0 of OpenAL published by Loki Entertainment in June 2000 applies the major part of the functionality of DirectSound3D (attenuation of distance, Doppler effect), but deviates in some details (no TRANSFERS or CLAMP MAX_DISTANCE , a distance from reference to the place of MIN_DISTANCE , the Doppler effect is calculated by indicating the speed of reference and an initial factor of acceleration). The reverberation and other extensions like occlusion and the sound obstruction defined in I3DL2 ( Interactive Audio 3D Level 2 ) and applied for example in EAX do not form part of the specifications yet, but are supposed being supported for the next versions. The treatments of the signal based on geometrical forms as A3D proposes it are not included, and are not currently envisaged.

Version 1.1 published in June 2005 gum the differences quoted, which existed with DirectSound3D.

External bonds

Official site
Interview of Carlo Vogelsang in June 2003, one of the persons in charge of the maintenance of OpenAL

Random links: