This is something very special when creating sounddesign: creating sounds using only contactmics.
It’s not that difficult. There are a few things to consider. First you’ll have to keep in mind that you’re recording vibrations instead of airwaves moving about. Second of all, you need the proper gear for making good recordings. Let’s have a look at the piezo element itself.
A quick search across the internet learns that there are more than one contactmics available. And also, in many different pricecategories. You have to keep in mind that none of them are made to make some real serious sounddesigntorture that we have in mind. All these piezopickups are made for acoustic instruments like acoustic guitar, violin, cello and so on.
To deliver a product for everyone there are different setups and kits available. A few only deliver the actual contact element, a round disc, soldered to a cable with a plug (30 to 80 euros). Like for example the Dean Martin Artist Transducer Acoustic Pickup.
Then there are the ones who deliver a complete system. Like the Barcus Berry 4000 XL with separate preamp and a special kind of pickup (350 euros). And there are Fishman products (like the Fishman GII), they do look a little less professional, although the new series is somewhat more ‘confident’-looking. There a 2 or 3 different manufacturers to complete your search, all with their own special capabilities and ways to set them up on your instrument.
Then, there is always the DIY community; why not build one yourselves? The piezo pickups are cheap, easy to get your hands on and really easy to solder a cable onto. But that is where the tricky part comes in.
The tricky part with these kind of piezopickups is that they tend to be VERY sensitive to humming, crackles and such, if not protected correctly with electromagnetic shieldwrapping and such. I tend to lean to a quick but reliable solution for your first steps into contactmicworld.
Your soundcard and its impedance
Take a look at Barcus Berry; nice gear and expensive; but what would be in that little black box? That little magic box is actually a preamp with a high imedance input; using contactmics is all about impedance. You have to make sure your Hi-Z input on your preamp (or Guitar or instrument input) has a impedance bigger than 1 Mohm. In most cases your average prosumer soundcard is equipped with average impedance preamps. Typically for normal average mics. But a piezo is not your average mic. In fact, it is NOT a mic, it is a piezo element. The impedance of the element and your input of your soundcard need to match as closely as possible.
Without this high impedance your piezopickup will sound like singing with your nose pinched. The low impedance of you regular mic input wil cause the electric ciruit to act as a highpass filter. With the high impedance you’ll be right in the ballgame, you’ll have lowend and highend from your contactmic.
The Barcus Berry preamp and the Fishman preamp make sure your mic will sound just right by delivering a preamp that will provide you with a high impedance input to connect to the line in of your soundcard. To avoid buying extra gear (and thus spending extra money) I suggest you start digging up the manual of your AD converter and have a look at the values for the Hi-Z input.
There are also a few circuit designs available for the true DIY guys, google for Alex Rice Preamp for example. I’ll put up a link sometime later.
Now in my humble studio I do have some pretty solid outboard preamps. One of it is a Focusrite ISA428. The manual states that the instrument input has a impedance of… 1 Mohm! In many cases with cheaper outboard gear these values are hard to find or not even mentioned at all.
In this case the preamp has been provided for. So now what is left to do is to buy a transducer which is strong enough to clamp on something and already has a proper jack connected. In this case the Dean Martin Artist Transducer would be a great choice.
It comes in a small box, just big enough to house the cable and the transducer. No manual, no pictures on how to place it, just the plain pickup. Not a word can be found anywhere on the box about the impedance. So, let’s take it for a spin, what does it sound like?
The piezo pickup is rather standard gear, if I might say so. Sure, there are different shapes and sizes, but in general they all transduce vibrations into a electric component. There’s not much magic about that. We do know we need a high impedance preamp, so we got our hands on that also. So where is the magic happening then? It’s all about placement of the pickup.
I got my capo-dastro and fixed the pickup on a kitchenhelper. Adjusted the preamp input, which was on instrument setting. Put Cubase on record… Wauw. The sound was just awesome. That much lowend! Ofcourse, the more clamping you use to connect the pickup to the ‘instrument’ the better contact you’ll have. But this first test was amazing.
Then I took out my ridecymbal, put it on a stand and starting trying. First with my fingernails, then with my ring rolling around. Then I saw a box with screws! The sounds being recorded are rather outside of this world. Get ready for some new experiences in sounddesign!
Now there’s so much to explore, how does a running motor of the dishwasher sound? Or the big steel stairwell?
You can listen to the first recordings on my soundcloud.
For now: I do regret not having a second one, but that one will be here in a few days, so I can start recording stereo stuff to do some heavylifting sounddesign. 🙂
If you have any questions, please let me know!