What does virtual reality sound like?

This article is part of a collaboration with iQ by Intel.

Much of the focus around virtual reality has targeted the visual experiences, but audio is critical for pulling people into stories that unfold through digital worlds. In the opening minute of Lost, the first VR short film by Oculus Story Studio, a compelling soundscape that brings the viewer into the scene before leading them deeper into the narrative. Saschka Unseld, creative director at Oculus Story Studio, knows that sound is critical to hooking people and heightening their experiences.

3D audio is an integral part of virtual reality.

“The first thing you see is the firefly,” said Unseld, describing the opening scene. “Our thought was to have something tiny, the opposite of overwhelming, and let her be our guide into the world of VR.” The story continues with a singing bird that flies by, drawing the user into the forest.

“We used spatialized audio, so you know it’s coming from the right. That’s when the story for Lost finally begins, because you have settled in and we have your attention.” 3D audio is an integral part of virtual reality. It’s different from what people typically think of as “surround sound.”

When a person is watching a home movie connected to a surround sound system, the sounds come from the speakers in front, to the side and behind the viewer. If the viewer moves, the sound doesn’t change direction.

In virtual reality, all the sounds come from stereo headphones, which are part of the VR headset, but sounds seem to emerge from every direction because the audio is processed in a way that mimics how a person actually hears. Instead of coming from multiple speakers, 3D audio seems to come from infinite spots around the wearer. It isn’t a soundtrack. It’s a spatial reality all around the user.

The sound of cricket chirping near a VR headset wearer’s feet will get louder as the person kneels down. When the wearer turns her head toward the sound, she will see the insect in front of her. It isn’t a soundtrack. It’s a spatial reality all around the user, according to Unseld.

Music can also be a vital component of the virtual reality word. ZeroTransform, the developer of Pulsar Arena, is currently working on a VR music video called NUREN.

“The chief difference is immersion and positionality,” explained Jake Kaufman, the music wizard at ZeroTransform. “You are actually there. That involves reverb, occlusions and geometry. The challenge is making a place.” Part of this realism comes down to HRTF, which stands for head-related transfer function. This is the name for how a sound is different coming in one ear than the other, which lets your brain determine where the sound originates.

It is also about how a sound changes when it vibrates through the bones and flesh of your head. Listen to this video with headphones to hear how HRTF sounds compared to a film soundtrack.

If the sound doesn’t perfectly match with the 3D visuals, you might be taken right out of immersion.

HRTF sounds are recorded with a pair of microphones placed like ears inside a container that mimics a human head. In addition to ensuring the sound works just right, implementing 3D audio can prove challenging in other ways. If the sound doesn’t perfectly match with the 3D visuals, you might be taken right out of immersion.

“Let’s say you are in a field, and you hear the wind blowing, and then you move your head and everything changes,” said Tom Smurdon, audio content lead at Oculus, explaining how bad audio can break the suspended belief that a person has while immersed in a VR experience.

“In videogames, you make a stereo loop, and you just place that in an area. The problem is, in VR, this sound would be glued to your head. That’s not what you want at all.”

With VR games, sounds are tied to specific objects or points in space, too. In the example of the field, Smurdon would place four different wind sounds in the cardinal directions of the scene. There may even be eight sound effects so that when the player turns around, the sound would change so that the wearer would instinctively know which way was north the entire time.

This careful placement of noises in a 3D space—placing both high and low, near and far—creates a spatial soundscape useful for realism and immersion as well as for direction and narrative. All of this serves the ultimate goal of any VR journey: making the user experience a particular set of feelings.

“You have a covenant of trust with somebody when you put a visor on their head,” said Kaufman. “You are replacing their mental soundtrack with your reality. It’s not called virtual reality for nothing. If anything, that emotional connection is doubly important in VR.”