How does 3D sound work? The Evolution of Sound

How does 3D sound work?


3D audio effects take the traditional sound produced by stereo speakers, surround sound speakers or headphones, and shape them in such a way as to ensure that sound sources are virtually placed above, below or behind the listener.


The 3D means that the sound sources are virtually placed anywhere in the 3D space.


Similar to some soundbars, it tricks the brain into placing different sounds in different locations, even though the sound is coming from say 2 speakers.


So in layman’s terms 3D sound refers to a system that can position sound anywhere around a listener.


So in 3D audio it is the perception of the sound that is created by the listener that gives the effect of sound coning from different directions in space.


A conventional stereo system cannot artificially place sounds above or below a listener.


You would have to get a sophisticated surround sound system for that. 3D sound/ audio attempts to correct this problem.


Now the following explanation can get a little scientific so brace yourself, but this will give you a great indication of how 3D sound works.


Lets consider how humans center/contain sounds using 2 ears. When a sound is created, it creates a sound wave that comes to the ears of a listener.


A sound coming from the right of a listener reaches the right ear before the left ear.


The left ear signal is thus delayed with respect to the left ear signal. Additionally the left ear signal will be reduced in force due to being “shadowed” by the head.


The signal that you hear is also influenced by the pinna (external ear). The various folds of the pinna reinforce some frequencies and weaken others.


We unconsciously use the time delay, amplitude difference, and tonal information at each ear to determine the location of the sound. All of these indicators are termed sound localization cues.


Lets talk about hear related transfer functions (HRTF’s). These measure the transformation of sound from a pint in space to the ear canal.


They are measured by inserting small microphones into the ear canal or on the ear of a manikin.


A measurement signal is played by a loud speaker and recorded by the microphone.


The recorded signal are processed by a PC in order to derive a pair of HRTF corresponding to the sound source location.


A 3D audio system works by imitating the process of natural hearing. This is done by reproducing sound localisation cues at the ears of the listener.


This is most easily done by using a pair of measured HRTFs as a specification for a pair of digital audio  (equalizers).


When a sound signal is processed by the digital filters and listened to over headphones, the sound localization cues for each ear are reproduced, and the listener should perceive the sound at the location specified by the HRTFs.


This process is called binaural synthesis (binaural signals are defined as the signals at the ears of a listener).



How does 3 D audio differ from other audio formats


The most popular audio format is 2 channel or stereo sound. Stereo systems record 2 signals.  1 left and 1 right.


You as the listener plays them back through a left and right loudspeakers or headphones.


Surround sound systems add a front center speaker, rear speakers and a subwoofer for added base.


In fact some headphones even struggle to appropriately reproduce stereo.


With speakers, your left ear will pick up sound from your left, but your right ear will do the same if only with a small delay and with slightly lesser force.


With Headphones, however the right channel reaches only your left ear and vice versa for the right channel.


The experience is artificial, and it causes some odd perceptions.


For example, when a voice speaks equally loudly in the left and the right channels of headphones, it will seem to be emanating from inside your head, not from some position in front of you.


That’s why musical experiences can sometimes seem somewhat odd when heard through headphones.


3 D sound/audio as discussed in the previous paragraphs, ensures that sound is heard far more effectively where it is coming form and to be more realistic.



Dynamic 3D Audio


3 D audio is essentially virtual reality for your ears. You now get to hear sound as if you were actually in the environment.


In a typical basketball video game, the sound would be uniform. Now however you can hear coaches yelling from the court and players trash talking and the audience screaming and booing.


In a combat game, you will hear bullets whizzing past your ears. When you turn your head, the sound comes stronger from the direction in which you turned.


3D sound
3D sound

Advantages of 3D sound


Ideally, it should be possible for users to selectively attend to audio information from locations within 3D space.


This supports the everyday filtering that people use to attend to a single speaker in a crowded room.


It should be possible to be aware of various channels of information from audio sources in different positions


This essentially mimics the daily experience of listening to different conversations at the same time without attending to all of them.



Disadvantages of 3D sound


Some products do claim to be 3D technology products but upon closer analysis there can be great disparities in the technology used.


So when it comes to new technologies beware of exaggerated marketing claims. Always conduct thorough analysis and listen to a multitude of reviews.


Sometimes stereo enhancement systems/widening systems can be accidentally confused with (or deliberately marketed as) 3D sound.


Such systems expand the sound field of a stereo recording, by widening or extending the sound images that would ordinarily extend to the location of the left and right speakers, to beyond the speakers.


Such systems do not place individual sounds around, behind, above or below a listener.


Even the best 3D technologies have inherent limits that limit the amount o sound you can here all around you.


How does 3D sound differ from surround sound?


3D sound is the upgrade to surround sound. With surround sound the sound comes from all directions around you.


Therefore, if someone in a movie is approaching you from the back then the sound will tend to com from the back speakers.


3D sound ups the ante by making sure that sound comes from above and below you.


For more detail on surround sound please refer to the following article


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