Nov 16, 2020
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3D audio or spatial audio is emerging as the next evolutionary stage in sound, but like many other new, unfamiliar media technologies, the terminology and descriptions may seem confusing and hard to grasp at first. We had a chance to sit down with Waves Audio’s Senior Director of Business Development & Marketing Adam Levenson and ask eight important questions. Hopefully what we learned will give our readers a deeper appreciation for the immersive qualities of spatial audio.
OnQ Team: For starters Adam, what exactly is spatial audio?
Adam Levenson: Spatial audio describes a variety of sound playback technologies that make it possible to perceive sound all around you without the need for any specific multiple speaker setup.
OnQ: Can you go over the difference between stereo, surround sound, and spatial audio?
AL: Both stereo and surround sound formats such as 5.1 and 7.1 are tied to fixed speaker setups. Throughout the years, masterful works have been produced using stereo and surround including some of the most beloved music and movies. But if real-world sound is the ideal, then these formats only provide windows into that ideal experience. Spatial audio allows listeners to step out of a windowed vantage point and into an immersive, emulation of real-world sound.
OnQ: Are there different kinds of spatial audio?
AL: There are several different spatial audio products available to consumers. There are "object-based" formats in which the location of a sound is baked into the position of the thing that emits the sound such as a car passing by in a movie, or violin playing stage left. Then there's "Ambisonics" that provides a sphere of sound centered around the listener. There are spatial virtualizers, technologies that project sound into a virtual acoustic space. Waves Nx is a virtualizer capable of spatializing any stereo or surround content.
OnQ: How is it possible to hear spatial audio on earbuds or headphones?
AL: Human hearing has evolved over millennia to allow us to precisely and rapidly identify the location of sounds. Our brains interpret location cues according to how sound interacts with our hearing anatomy including the shape of our ears and heads. Over earbuds or headphones, spatial audio technologies emulate that acoustic interaction to stimulate the mind into perceiving sound in 3D. That emulation is achieved through sound filters called Human Related Transfer Function or HRTF. The process of playing spatial audio through two earbud or headphone speakers is called binaural rendering, with binaural meaning "through two ears."
OnQ: What is personalized spatial audio?
AL: Human anatomy is unique to each individual, so some spatial audio technologies use personalized HRTF filters. These HRTFs are generated from an analysis of a photograph of your ear(s), or from measurements of your head and the distance between your ears.
OnQ: What is head-tracking and why is it an important part of the spatial audio experience?
AL: On conventional earbuds or headphones, turning your head means the sound turns with you. The sound is between your ears, so where your head goes, the sound goes, even if you are listening to spatial audio. But with headtracking, a turn of the head accurately changes your listening angle: as you look around, the sound field remains anchored in place, just like it does in the real world. Center stays in the center, left stays left, right stays right, rear stays in the rear. In addition to HRTFs, headtracking is another experience vector that produces a convincing, believable 3D experience.
OnQ: Is it possible to experience spatial audio over speakers?
AL: The acoustic principles that make perceiving spatial audio possible over a pair of earbuds also apply to technologies that produce spatial audio from two or more speakers. Earbuds and headphones have a built-in advantage in that each speaker is acoustically isolated by the proximity to your ear and by the obstacle of your head. Over speakers, this acoustic isolation is achieved through a process called cross-talk cancellation.
OnQ: Does spatial audio only work with special content?
AL: Some popular spatial audio formats require the content to be produced using proprietary authoring tools and require the user to have playback hardware, such as a home theater receiver, equipped with special decoding technologies. Other solutions use virtualization techniques that are capable of spatializing any content in stereo, surround, or spatial formats.