It's the most anticipated movie of the year. The room goes dark and you hear scratching sounds coming from the speakers to your right. The scratching slowly makes its way behind you, to the left, and as it moves towards the front, a large cat leaps onto the screen, startling the audience.

The advent of surround sound technology has changed how we experience media including movies, television, video games, and music. But where did this amazing technology come from?

Before surround sound, all sound recording and reproduction was done in a monophonic ("mono") manner—in one channel. Basically, think of it as having the same sound transmitted through every speaker. It doesn't sound unbelievable, does it? That's because most of us don't notice the subtle differences being pumped out of each speaker or earphone.

Did you know? Disney's Fantasia (1941) was the first film to feature surround sound.

Then, in the 1940's, surround sound emerged and stereophonic ("stereo") sound, sound in more than one channel, started to become mainstream. It became such a hit that by the 1970's music records were no longer made in mono. 

Did you know? Although stereophonic refers to anything with multiple sound channels, most people will refer to two channels as "stereo" sound.

The first step in sound reproduction is recording: Mono recordings are done with one microphone, stereo recordings with two microphones, and surround recording with many microphones. Surprisingly, the majority of sound in the media today is recorded in mono because it's easier to record and edit one channel of sound rather than multiple channels.Then a foley artist or another person will mix in some artificial sounds and place them in the appropriate channel to make you hear it a certain way in surround. That means most surround sound is artificial!

For instance, in the scenario mentioned at the beginning of this article,the sound editor placed the scratching sound in the right channel, made it fade out while making it fade into the back channel. Then it faded out from the back channel, and faded into the left channel, producing the effect of moving sound. This is a popular effect known as sound panning.

That explains the technology, but what's the biology behind surround sound? The best known explanation of how we locate sounds is known as the binaural delay—the delay between your ears from which the brain can figure out when sound reaches them. Some of these differences are much less than a millisecond! That covers left and right localization, but what about front and back?

Here's where it gets a bit complicated. The best explanation scientists have right now is based on the fact that the shape of your ear is different at the front than it is at the back. However some believe there's more to it than that.

To illustrate this principle, listen to music on your headphones and try to locate where the majority of the sound is coming from: Most of the time you won't be able to tell because your brain is telling you it's coming from inside your head! This happens because you don't have the shape of your ear to distort the sound.

People a century ago probably never imagined audio to be as complicated as it is today, yet we've only scratched the surface. There's still much we can do to improve the fidelity and realism of what we listen to, as well as finding new ways to trick the mind into believing it's hearing surround sound. As we unlock the human mind and develop new technologies, it'll be interesting to hear how tomorrow sounds.

Learn More!

Whitfield I.C., Mechanisms of Sound Localization. Nature 1971;233:5315.

Surround Sound

Surround Sound Formats

Die Hard Photo Credit: Game Guru

Al Thai is a fourth year human biology and zoology student at the University of Toronto, where he conducts research and teaches in human anatomy. He loves listening to various types of music and playing the occasional video game (after homework of course!)

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