Have you noticed that you can hear significantly fewer birds outside of your bedroom window than you could five years ago? What we consider silence has been rapidly changing right under our noses (or under our ears). I am fascinated by the distinction between the absence of speech versus the absence of noise. Humans are constantly taking in and filtering noise through the subconscious brain (hey, has your fan been that loud the whole time?) without realizing it. It’s a survival mechanism, but one that sound designers have learned to harness.

You are always hearing something, even if you may feel like you aren’t. The hum of electronics, wind, etc. create something called a “noise floor” which is the sum of all these quiet noises into one blanket for your mind to process. You are very likely ignore the noise floor unless something significant changes in it. When that happens, your brain tunes back in, scanning for danger. That increase in awareness and anxiety can be a very, very useful tool in storytelling, especially if you introduce something that our brains are hardwired to dislike, like dissonance. That particular technique is very popular in horror movies.

While the concept of “toying with the survival instincts of the subconscious mind through sound” seems a little high-falutin, it’s really more science than philosophy. As another example, getting goosebumps while listening to music is called “frisson,” which neurologists and musicologists have been studying for quite some time. It is generally agreed that frisson occurs when your expectations are subverted by--or there is a sudden change in--music. The most reliable indicator of frisson, according to musicologist David Huron, is a rapid increase in loudness, like the crescendo before a singer’s impressive high note. If you know what causes frisson, you can create it. It makes an audience more responsive to a song, or any other time you want to give them “the chills.” I, and many others, use this technique when mixing live sound. If you bump up the last chorus and the button of a song, you'll find that the audience will applaud louder and longer. Thanks, frisson!

Humans hear as we do because it was evolutionarily beneficial when listening for predators and other threats. While we have come a long way since being hunter-gatherers, our brains still retain the same instincts that kept us alive back then. This is the heart of modern sound design: using sound, music, silence, and more to engineer a specific response from the subconscious parts of your brain. And it works better than you might think.