Antisound

What do you get when you cross sound with more sound? Surprisingly, the answer can sometimes be silence...as long as you used antisound technology. The basic idea appeared in the 1957 Arthur C Clarke science fiction story Silence Please, where it was called a 'Fenton silencer'. It works by canceling out soundwaves. Sound is a pressure wave in the air - when we speak, for example, the vibrations from our mouths either increase or decrease the air pressure. These puffs then travel through the atmosphere to the ears of others, who are able to detect the changes in pressure. The brain decodes them back into speech. It's the same with any sound; it's just a pressure wave in the air. With antisound we want to make this noise vanish!

Nothing to hear here

To create antisound is simple. You record the sound that's being produced then quickly play it back, but sneakily you invert it: the loud bits get soft and the soft bits get loud. The sound and the antisound pressure waves mix, and where the original sound wave had a high-pressure area, there is a corresponding antisound low-pressure area. When combined, the two produce an area of normal pressure. Normal air pressure is, well, it's just air. Nothing to hear here. Move along please. So by generating an antisound wave that is the exact opposite of the original, the sound can vanish.

Antisound is good if you want to keep secrets but also good if you have a very noisy factory, say, or the throaty roar of your sports car is stopping you hearing the quiet music track you are listening too. Want to quiet the engine down a bit? Just play its antisound at the same time and hey presto - silence.

Sounds like a good idea

Sound can be horrible, pleasant or even secret. Today we are able to use digital technologies to capture sound waves and manipulate them in real time. This gives us new ways to change the soundscape around us and create new ways to listen (or not, as the case may be). Through understanding how to manipulate one of our basic senses, hearing, researchers can change our world. Remember, you heard it here first.