Greetings, In response to “I’m curious what the next ‘medium’ may be, and how surround sound will be shaped by paradigm shifts,” Dr. Lennox wrote:
“I’d bet that one day we’ll discern a difference between ‘surround sound’ and ‘3-D sound’, where the latter contains a great deal more depth of field - distance information is probably at least as important in spatial hearing as is direction perception...” (By the way, Peter, I look forward to reading Violentyev, Shimojo, and Shams (2005), Touch-induced visual illusion. NeuroReport, 16, 1107-1110. Thanks for ref.) I will now attempt to describe a “visual” (compared to “optical”) illusion and how it could apply to acoustical depth-of-field. Just a few days ago and while driving, I pointed to an object and said, “I wonder what type of blimp that is.” The object had (roughly) the shape of a blimp, to include a rudder. It was suspended in air, over the city, but no other foreground or background references to provide information as to its actual size. I was at a stop light, so motion didn’t provide a cue either. As I made a turn, I could see light reflecting from the fine wire that the “blimp” (actually a pigeon) was resting on. Light direction initially obscured or camouflaged the wire. Mildly embarrassing, but funny. Experience tells me small-ish objects can’t float, even when filled with helium (buoyancy force less than weight of fabric), so I assumed a large object. Blimps aren’t nearly as common as birds, but they’re not terribly uncommon in Phoenix. So in this situation, I had allowed experience to be the noise. Unlike some illusions (such as the moon and the Ebbinghaus illusions), I had no relative size references -- just the sky as background -- until I could see the wire (its expected size also based on experience). There were no optical aberrations aside from an "invisible" wire. Simply put, my brain (or bifurcated ganglion) relied on past experiences to (wrongly) determine what the object was as well as its size. How, then, does this fit into acoustics? Experience also gives us insight to a signal’s distance when there’s no relative noise. When there is noise, we expect nearby objects to have a a better SNR than distant objects and a large signal-to-reverb ratio (an important type of SNR). Without noise, we might expect the sound to “agree” with the size and material/composition of the sound source. Furthermore, Ecological Psychologists (e.g. Gaver) might describe the sound by how it’s produced (rolling, tearing, breaking, liquid dropping), and we would likely expect the sound of a drop of water to be close to us. Loud speech and yelling have tonal and prosodic characteristics that set them apart from normal speech, so we use relative level-to-vocal effort to determine the distance of talker. Because learning and experience is involved, acoustical field – distance information depends, to some extent, on a person’s knowledge of the sound being heard, not just the physical aspects of the wave. Not that I’m saying anything you don’t already know, but I thought I’d share an amusing, true-to-life anecdote: The Pigeon Blimp. Best, Eric C. -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20130411/803fe0da/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
