The internet has rediscovered audio illusions, thanks to the ongoing argument over Laurel and Yanny. Audio illusions, though, have been around for a long, long time, and they’re a lot easier to create, especially now, than you might think. Fooling the ear is harder than fooling the eye, but it can be done if you’re willing to download some free software and spend a little time.
Let’s start with an explanation of how we hear sound. All sounds designed for us to hear them range from 20 Hz (deep, deep bass) to 20,000 Hz (shrill treble). There are people who can hear sounds at a lower or higher pitch, depending on the person, their age, and their hearing, but as a rule of thumb, we can hear pretty much anything between those ranges. This is how Laurel/Yanny works: Yanny is in the higher frequencies, and Laurel in the lower:
The final piece is our speakers and headphones. Some of them reproduce sound at a lower pitch, others at a higher pitch, so depending on whether you’ve got the bass or treble turned up, you’re more likely to hear one over the other. Unless your hearing in a particular range of tones is completely wiped out, it’ll change depending on how the sound is reproduced.
We live around audio illusions all the time. Stereo mixing sounds like three-dimensional space, but it’s just careful tweaking of audio in both your ears. “Noise-canceling” headphones seem to make unwanted audio disappear, but in fact they’re playing even more noise in your ears, just the exact opposite of the noise you don’t want to hear so it cancels each other out. But if you want to make your own illusions, you can do it in a handful of steps:
- Download and install Audacity: Audacity is powerful audio editing software that works on pretty much any desktop and is completely free. If you can work an iPod, trust us, you won’t have any problem using Audacity.
- The “say yes” illusion: This one is dead easy: Just record yourself saying the phrase “say yes.” Then highlight it, go under effects, click Reverse, and give it a listen. Sounds just the same, right? “Say yes” is a phonetic palindrome: Whether you say it forwards or backwards, it sounds the same. Try “easy,” “dry yard,” “selfless” or “Sorry, Ross” (adding “WE WERE ON A BREAK!” after that last one is optional.)
- Use constantly repeating phrases and words: Record yourself saying a phrase, and cut away the dead air (Anything that’s just a straight line. Just drag your mouse across it and click the scissors). Then hold shift and click Play. Give it a little time and it will start to sound like you’re singing it; the repetition makes you phase out the content and you listen to the structure of what you say, while the loop gives it a form of a beat. The Monkees used this illusion to create the song Zilch. Even simpler, say one word like “rest” and loop it; you’ll begin hearing “phantom words” like “say” and “stress.”
- Make syllables you cut out magically reappear: This is another easy, and absolutely freaky, one. Richard Warren, who studies sound at the University of Milwaukee, created an audio clip where he yanks out a syllable from the middle of a word and replaces it with a cough. You can easily do this in Audacity, just pick out a bit and replace it with a cough. But then have people try to figure out which syllable you replaced; they likely can’t do it. Their brain fills in the rest of the word.
- Discover binaural beats: Another simple illusion is to use Audacity’s tone generator to create a tone of, say 520 Hz in one channel, and a tone of 530 Hz in the other. Just two drones in your ears, right? Nope. The tones are just far enough apart to create a beat where a beat doesn’t exist. It’s popular among the meditation set.
There are plenty of other audio illusions, especially if you’re musically inclined. But these are enough to show you that messing with our ears is easier than you think.