08 Tim Preble – Contact Mics
If you know how to use them, contact mics can get you some great recordings. We were not getting great recordings. Around sunset, we were standing by the side of the road at the top of a hill yelling and clapping at a street sign. It was our 5th or 6th stop of the day and we’d gotten a little desperate. We’d already tried a trash can, the car door, a creaking tree, and a metal railing in a skate park. None had yielded results of much interest.
Before we’d set out with our newly acquired contact microphones, we had spent the morning reviewing our basic physical understanding of sound, which we then spent most of the car ride discussing. Here’s how we understood it: something in the world vibrates. That vibration creates pressure waves (aka sound waves) in whatever medium is around it—water, air, etc. If the vibration is strong enough or we are close enough, the waves reach our ears and vibrate our eardrums, which our brain can then interpret as sound.
Put simply: sound is vibration. (The first person who ever said that succinctly to us was Hoby Wedler, a sensory consultant who has been blind since birth and who we interviewed for a public radio story. More on that in a later newsletter.)
This brings us to how microphones work, which we had also just brushed up on. The typical microphone is a diaphragm microphone, which, like our ears, has a surface, or diaphragm, that can register soundwaves that reach it through the air. A contact microphone however picks up vibrations in solid objects. That means you can put them on a piece of metal or wood or whatever, and even if it is not producing soundwaves in the air, if the material itself is vibrating, the contact microphones will pick it up.
In principle, this allows you to tap into whole other realms of sound. There are so many vibrations that are acting primarily in a medium besides air: the rumble of a train track, hum of a wire fence, cracks deep inside a block of ice, the digestion of a sourdough starter inside a jar. Recording vibrations in a material can allow you to capture subtle sounds like the footsteps of an ant or internal clicks of a clock which may not generate enough pressure variation in the air for our ear to pick them up.
Because contact mics don’t record vibrations in the air, they are also helpful to get recordings from an object that has a lot of ambient noise around it. Two idiots could be standing on a hill next to a road screaming at a street sign, but the contact microphones on the sign won’t pick that up. The screams are vibrating the air. The contact microphones are picking up the vibrations in the sign itself. This is why contact microphones are helpful for amplifying instruments like a guitar, bass, violin, or piano. They pick up the vibration straight from the body of the instrument itself and don’t capture any bustling, coughing, yelling, involuntary vocalizations, etc., in the air.
People use contact microphones to record wonderful and surprising sounds, like the ones we played this week. These are a sample compilation released by New Zealand-based sound recordist Tim Prebble. Tim is a big part of the reason we decided to purchase contact microphones. Unlike us, he knows more than just the basic physics of how sound and diaphragm microphones work.
Tim runs a sound studio called HISSandaROAR. Like a Foley artist, Tim creates sounds by manipulating objects and recording the noises they make. But what Tim and others in their profession do is not quite Foley. They aren’t watching a film and creating sounds to bring it to life. They are in the business of making sound libraries that can then be used in media like movies, music, video games; or just listened to on their own for pure enjoyment.
If you were to catch someone like Tim at work, it might seem like you had stumbled on a person who had completely lost their mind. For example, Tim has a sound library called Sofa Smash, which was made with two old leather couches. To gather the sounds he dragged the couches out onto the sidewalk and spent hours destroying them: ripping, whacking, dragging, and dropping the couches until they were an unrecognizable heap of materials. There is a whole period of the process where he just hits the couches with a large variety of sticks and mallets and listens for a great sound. This is an art that it seems like Tim really, really enjoys.
I’ve listened to Tim’s collection of contact microphone recordings about a dozen times. At first, I found myself trying to identify the source of the sound and the process. Is this the water jug or piece of plexiglass? Is he slicing a utility knife into cardboard? Is that a marble swirling around on metal? What is he using to pluck the bicycle spokes? As I listened more times to the clips, I began to let go of that drive to identify, and started listening to the textures of the sound themselves. I began noticing patterns—similar timbers, movement, and dynamics. I realized that what I was hearing was Tim’s sensibilities and craft: the way he interacted with objects to generate sounds; the way he placed his microphones; what he found arresting, amusing, or beautiful.
A collection of short clips not only reveals a recordist’s artistry but also their habits and ruts. Do they always place the microphones in a similar position; gravitate only toward certain sounds; hit, shake, rub and otherwise manipulate objects in an identical way? The same can be said about listening to a series of short mixes by a sound designer or engineer. Do the sounds always build in a particular way, have the same rhythms and timber, spacing and pauses? Chris and I often worry about that, as it would suggest you really don’t have much to say. You’re just iterating the same patterns with different sounds. Which is why you should mix it up, and do things like impulse acquire a pair of contact microphones.
If you are thinking of doing so, or like us have already done so and then were at a loss, Tim is a great resource. Not only can you listen to his work, he has videos of his process, and has written about his approach.
About a decade ago, Tim published this post all about his experience with contact microphones. There is a lot to learn technically, but at the core his advice is to experiment—stick contact microphones on stuff and listen to what you get. Unlike with a diaphragm microphone, your ear isn’t your guide, your fingers are. If you feel something, put the mic there and record. Sound is vibration.
What we played this week is just a sampling of Tim’s work with contact mics. He has many other libraries built from many other kinds of materials: rolls of wire, sheets of metal, and bicycle spokes that he bangs, scratches, scrapes, and drops into his wonderful sound libraries.
Tim does one simple thing that really makes his recordings dynamic. He uses two contact microphones. His rationale is straightforward: humans have two ears, so he uses two mics. One contact mic acts as the left ear of the listener, the other as the right ear. This allows Tim to create a recording that is spatialized when you play it back on headphones. When a vibration moves toward the left contact mic, you hear it in your left ear and vice versa. It is as if your head is inside the object that is producing the vibrations.
We are far, far from Tim’s mastery of contact mics, but it’s something to aspire to. Just listening to Tim’s work and playing around with contact mics has opened our ears to the possibility of sounds inside the objects around us. Maybe there’s a whole sonic world hidden in a pedestrian-seeming light pole, piece of wire, or street sign by the side of the road at the top of a hill where two guys are yelling and clapping like fools.