Advertising’s come a long way from the television jingles and old-fashioned radio spots of decades past. In the age of social media and targeted algorithms, the ads you see and hear online are very often tailored to your particular user profile. Of course, that’s just when you’re online. But what if it wasn’t? What if, while you’re out shopping or walking down a crowded street, you heard an ad aimed specifically at you, an ad that nobody around you could hear?It might sound like something out of a particularly surreal science-fiction movie, but directional audio technology’s already being used in everything from billboard ads and street kiosks to grocery stores and museum exhibits. Some of the most surprising audio breakthroughs over the past few years have involved sound perception, the art of controlling just who hears a particular sound and where that sound seems to be coming from. For sonic branding, directional audio can mean the difference between just hearing an ad as a listener and engaging with it on a more personal level.One of the very first uses of directional audio in advertising was back in 2007, and it gave pedestrians in New York quite a start. It was a billboard for the spooky reality TV show Paranormal State, and people who walked directly in front of the billboard would hear ghostly voices whispering in their ears. Anyone else who wasn’t in just the right spot, no matter how close by they might be standing, couldn’t hear anything. The directional audio portion of the campaign only lasted a week, but that week made headlines.Just a month later the same technology was featured in the Brooklyn Historical Society’s exhibit “In Our Own Words: Portraits of Brooklyn’s Vietnam Veterans,” allowing visitors to hear a recording of each veteran’s personal story by standing directly in front of their portraits, without anyone else being able to hear them. It ran for a year, and since then directional audio’s been used for other museum exhibits, convention booths, and even to sell bananas in New Zealand supermarkets, where sales increased by over 130%.If you’d like to see a short video of such a display in action, and the dramatic difference that standing just a few inches off to the side can make, just check out the link on my blog:https://www.youtube.com/watch?v=sXxIApwIiqMAs for just how directional sound technology works, it’s a fascinating subject: you could almost call it a sonic laser beam. Ultrasound beams are created and aimed at the precise spot where the sound should be heard, and they’re so intense that they distort the air itself as they move through it, creating lower frequency sound waves that our ears can detect. Like a laser, the effect only works along the beam’s path, so only the people who are meant to hear the sound will notice it. For everyone else, it’s just silence.Ultrasound isn't the only way to trick the brain into hearing sounds that seem to come from nowhere. Another startling form of directional sound delivery is binaural audio, a technology that's more than a century old but has only come into its own over the past decade. Unlike surround sound, which relies on the listener setting up an array of speakers, binaural audio uses a simple pair of headphones to simulate a three-dimensional soundscape that seems to surround the listener. Sounds can come from in front of them, behind them and all around them in ways that might seem impossible.For a spooky demonstration of binaural audio’s ability to immerse the listener, you can find a link here to a short audio journey through a haunted hospital. There’s nothing too scary or graphic to worry about, but you’ll want to wear headphones to truly appreciate the 3D audio effect. And you may want to keep an eye on the volume: some of the sound effects can get pretty loud:https://www.youtube.com/watch?v=MytAOmbnLpgBinaural audio is created by using two microphones covered by a...