Liminal Spaces

Published 2022-12-09
Liminal Spaces is the first piece to our knowledge to make use of a layered immersive spatial audio system, consisting of two high-density loudspeaker arrays (HDLAs) - a far-field 140-loudspeaker array and a nearfield 32-loudspeaker array (the Tesseract), coupled with bone conduction headphones. This configuration allows us to deliver sounds in the range from highly intimate sounds delivered via bone vibrations, all the way to acoustic infinity with the far-field speaker array. An interstitial array of eight loudspeakers allows us to explore the liminal spaces between the two main HDLAs.

As is seen in the documentary video, a four-member audience walks into the performance space with ambient immersive sound, they enter the Tesseract cage, assistants hand audience members a bone conduction headphone, and once the audience is comfortably seated, the lights go down and the Liminal Spaces experience begins.

From the outset, Liminal Spaces addressed an underlying challenge posed by our spatial experiences with HDLA systems, such as in the Cube. While we could create extraordinarily rich spatial experiences around and above the listener, we could not bring the sound close to listeners given their physical distance from the loudspeakers. A drone could bring the sound closer to the listener. But we found another way to accomplish audio proximity, using different technologies. The Tesseract, developed by ICAT media engineer Tanner Upthegrove, is a configurable scaffolding bearing up to 64 loudspeakers. Putting the Tesseract inside the Cube gave us a nearfield loudspeaker array in addition to the more distant Cube array. Adding a bone conduction headphone to the Cube and Tesseract allowed us to bring sound right up to the head of the listener without occluding the ears, so that all three layers of spatial sound could contribute to a musical experience without mutual interference. The two main HDLAs were mediated by eight loudspeakers arranged radially, in a configuration that we refer to as the “Starburst” array. Taken all together, this layered audio system is the canvas on which we painted Liminal Spaces.

The sound sources for Liminal Spaces are primarily of two kinds – spatially encoded four-channel field recordings made at our homes, and purely synthetic sounds. The third sound source was a poem written by Ben Knapp and read by Natasha Staley. With these ingredients, we were able to place Natasha’s voice inside the listener’s head with the bone conduction headphones, very nearby with the Tesseract, and increasingly distant with the Cube. Rainstorms were presented with nearfield delicacy just above the head of the listener, combined with menacing thunder in the distance. Our layered audio system allowed us to create a more naturalistic spatial sound experience than we had ever heard before in an electronic music context.

Unlike the recorded natural sounds, the synthetic sounds do not provide a spatial model that is intuitively understood by the listener. Therefore, we could create more abstract spatial patterning, such as a passage where a group of six chords are heard alternating among the headphones, the Tesseract, and the Cube, creating a palpable sense of audio perspective. In the final section, a melodic texture starts in the headphones, it then moves out to the Tesseract, and then up to the ceiling of the Cube. The final chord of this texture culminates in a massive reverberation trail. But rather than dying away naturally, the reverberation descends the walls of the Cube, then swirls around the audience, coming closer and closer, through the Starburst array, the Tesseract, and finally the reverberation arrives and dissipates in the bone conduction headphones – a private sound heard only inside one’s head.

Learn more: icat.vt.edu/