Virtual Audio – What Are the Possibilities and Why Is It Not Implemented in Everyday Life?
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Virtual audio
What are the possibilities and why is it not implemented in everyday life?
Bart Runia
Class:
Aeds709
Ass. nr.:
RA 202.5
Sub. Date:
06-09-2010
Word count:
1. Introduction
Technology is thriving as never before, thus virtual has become more and more an everyday addition.
Making friends on virtual communities or even dating through means of virtual worlds.(e.g. Second life). Slowly more and more aspects of daily life are becoming virtual, virtual business as well as virtual economy, virtual desktop, virtual memory and so on. And of course there is also virtual audio.
The definition of virtual audio by Christopher Currell:
Sound that is specially processed to contain significant psycho-acoustic information to alter human perception into believing that the sound is actually occurring in the physical reality of three-dimensional space.(Christopher Currell 2009: 1)
There are a lot of kinds of virtual audio, e.g. virtual surround or virtual acoustics to name a few. This essay explores these uses of virtual audio and how much these technologies are being researched at the moment. And how much virtual audio is being used by the consumer. The idea of virtual audio is not new at all since almost all of the virtual audio is based on psycho-acoustics. People have been experimenting with psycho-acoustics since the 1930s. So why is it taking so long for virtual audio to fully integrate in our yet technological advanced world? Which already includes some forms of virtual reality for example flight-simulators and all kinds of other training simulators.
One realization that quickly becomes apparent for those first venturing into virtual audio and
multimedia is that the development of sound within human interfaces has not been developed to
anywhere near the level that visual interfaces have. For instance, high-resolution color graphic
hardware and software have been around longer on personal computers than the audio equivalent,
CD-quality two-channel digital sound.
(Durand R. Begault 2000: 9)
What can we expect from this relative new technology? Will we ever get virtual audio realistic enough so it can replace normal audio in everyday life?
2. Head related transfer functions
Before one can the trick the brain into believing a sound is coming from a source which does not exist in reality, one must know how the brain localizes sound. This is done through head related transfer functions. The brain uses these three functions to localize a sound source anywhere in the three-dimensional reality.
Head related transfer functions are explained by the duplex theory, which is a model for determining a sound source location by two binaural cues: ITD(Interaural time differences) and IID(Interaural intensity differences). Interaural time difference is based on the principle that if a wavefront comes from the right side of the head, it will reach the right ear earlier than the left ear. Thus creating a cue for the brain as to where the sound is coming from.
When a sound source is on the right side of a person, the head will work as a barrier reducing the amplitude received at the left ear. This is known as Interaural intensity difference. These two cues are very important for the perception of sounds, if the sound source is on the horizontal plane. Which separates the top and bottom halves of the head.
So a sound source is perceived closer to the side of the head where the first wavefront arrives. The larger the time difference, the more the sound source is located on one side of the head. (see fig. 1)
A larger ITD translates to a larger lateral displacement. In other words, for pure sinusoids, the perceived lateral displacement is proportional to the phase difference of the received sound at the two ears. However, at approximately 1500 Hz, the wavelength of a sinusoid becomes comparable to the diameter of the head, and ITD cues for azimuth become ambiguous.(Corey I cheng 2001: 1)
ITD and IID are only cues for the horizontal plane, since they cant give any vertical information of a sound source. Therefore the human hearing system uses spectral cues which utilizes the head, the torso and shape of the pinnae, to introduce phase to the sound which your brain can translate into a vertical position.
So head related transfer functions is based on adding phase to a sound, since these phase changes are the same on eighty percent of the humans. These phase changes can be added to a signal, the ears will pick up the signal with the phase changes and the brain will believe the signal comes from someplace else other than the sound source.
3. Applications of virtual audio
The applications of virtual audio are virtually endless, of course we already know virtual instruments(which are not based on head related transfer functions, but are nevertheless virtual)Which are already a standard for everyone producing music on the computer, especially with todays computing power, and the price of these instruments has made it very attractive to replace the hardware with software synthesizers. Also virtual surround sound has been a while on the market. Things that we can expect in the future, or is being researched at the moment are augmented audio, audio for virtual reality, virtual acoustics.
3.1. Virtual Surround Sound
A regular surround system is quite a hassle for people without knowledge, it involves a lot of cables speakers and adjusting. That is where virtual surround comes in, it