3D audio effect
3D audio effects are a group of sound effects that attempt to widen the stereo image produced by two loudspeakers or stereo headphones, or to create the illusion of sound sources placed anywhere in 3 dimensional space, including behind, above or below the listener.
There are several types of 3D audio effects:
 Those that only widen the stereo image by modifying phase information.
Those that can place sounds outside the stereo basis.
Those that include a complete 3D simulation.
Stereo widening
Widening of the stereo image can be achieved by manipulating the relationship of the side signal S and the center signal C:
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A positive part of the side signal S is now fed into the left channel and a part with its phase inverted to the right channel. Some boomboxes feature such a process.
Another way of looking at this same effect, without extrapolating a center and side signal from the left and right signals, is to simply add the left signal, slightly attenuated and phase inverted, into the right channel and vice-versa. Taking this a step further, a small delay (20-100ms) can be added to the inverted signal before mixing it back in to the original for output, adding a slight reverberation to the effect.
Placement of sounds outside the stereo basis
By manipulating parts of the sound according to psychoacoustic findings in phase and sound, it is possible to create sounds beyond the stereo basis. Effects from QSound Labs have been used on albums from Sting and Madonna in the beginning of the 1990s. Similarly, the pioneering work of researchers (Sibbald et al) at EMI Central Research Labs in England in the 1980s, and later with Sensaura, produced "3D Audio" CDs.
Complete 3D positional audio
The 3D simulation is the most advanced group of 3D audio effects. Using head-related transfer functions and reverberation, the changes of sound on its way from the source (including reflections from walls and floors) to the listener's ear can be simulated. These effects include localization of sound sources behind, above and below the listener.
Some 3D technologies also convert binaural recordings to stereo recordings.
3D Positional Audio effects emerged in the 1990s in PC and Game Consoles. As a medium, interactive games would benefit perhaps more than any other. However, although some technologies do seem to work better than others, 3D sound in games is still quite unconvincing, especially over speakers. Because of this most games make more use of Dolby Digital to create immersive audio.
3D audio techniques have also been incorporated in music and video-game style music video arts. The Audioscape research project, provides musicians with a real-time 3D audiovisual content authoring and rendering environment, suitable for live performance applications.
A site with animations and theory of a system using HRTF's to create 3D Audio: ISVR Virtual Acoustics.
Truly representation of the elevation level for 3D loudspeaker reproduction become possible by the Ambisonics and Wave field synthesis Principle.
Some products
A&G Soluzioni Digitali markets the X-spat boX processor, a tool for complete 3D positional audio based on a patent pending algorithm.
Behringer markets the Edison EX1 processor, a tool for widening the stereo image.
Duy produces the DUY Wide software plug-ins, a stereo enhancer effect, allowing you to place the sound outside physically-possible positions according to the placement of your monitors. Available for TDM, RTAS, VST, MAS and AU.
GenAudio  markets a 3D sound source placement technology, which does in fact count time as the 4th dimension even though sound can not exist out side of this dimension and so all '3D' audio effect could be considered as 4D.
Holistiks markets the AMPHIOTIK range of Virtual Auditory Environment processing software.
Maven 3D.com market several versions of their 3D rendering software, including Maven3D professional.
Prosoniq markets the Ambisone VST plugin.
QSound Labs markets QTools/AX, a product that lets the user place sounds outside the stereo basis.
Roland corporation marketed the RSS-10 that cost over 500 DM in 1995. It currently markets the RSS-303.
Sensaura , technology had been widely used on sound cards and by games to interactively position sounds in 3D.
Sonaptic www.sonaptic.com specialise in Hi-Fi 3D Audio for mobile devices such as cellphones and mobile games consoles.
SRS Labs markets both professional products and the WOW Thing, a stereo image enhancer with a built-in exciter and a bass processor.
VRSonic markets VibeStudio Designer, a spatial audio design suite for audio post production, immersive theater and training simulation.
Waves Ltd markets the S1 Stereo Imager, also for widening the stereo image.
Yamaha Corporation markets the YMU786 (MA-7), an audio chip for mobile phones which installs a 3D simulator.
Arkamys has begun a project aiming to create personalised 3D audio content for mobile devices such as mobile phones and mp3 players.
3-D audio presentations
Some amusement parks have created attractions based around the principles of 3-D audio. One example is Sounds Dangerous! at the Disney's Hollywood Studios at the Walt Disney World Resort in Florida. Guests wear special earphones as they watch a short film starring comedian Drew Carey. At a point in the film, the screen goes dark while a 3-D audio sound-track immerses the guests in the ongoing story. To ensure that the effect are heard properly, the earphone covers are color-coded to indicate how they should be worn. It should be noted that this is not a generated effect but a binaural recording.
See also
Surround sound
Binaural recording
Dummy head recording
Ambisonics
Wave field synthesis
External links
Example of 3D sound played back in normal stereo headphones. Requires the Adobe Flash Player
Virtual Barbershop Works best with headphones (noise-cancelling or earphones preferably)
Through My Ears - Binaural audio blog
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