This post is from my MUSIC OF SOUND blog, November 11, 2011 – ten years ago!
“My new HISSandaROAR library is officially released now and as it consists solely of contact mic recordings I thought I’d share some of the most important aspects of recording with a contact mic that I’ve discovered the hard way – through experience….
The first rule of using a CONTACT MIC is not actually about the mic itself, its this:
1. WHAT IS IT PLUGGED INTO?
At a guess I’d say I own over a dozen piezo/contact mics of various forms, bought over the last dozen years, but only three of them deliver seriously useable results. And just one of those three ‘good’ contact mics cost ten times more than all the others combined, simply because the people who created them understood rule number one. Its not ‘just’ a contact mic, because the mic is only as good as what it is plugged into, and the only way to insure you get great results is to also match the preamp, and the only way to do that is to sell both as a package. I’m sure the reasoning behind this is very basic for anyone who has studied electronics but THIS ARTICLE spells it out…
“The problem with piezo guitar pickups and contact mics is that they are not well matched to typical audio inputs. By their nature they can generate a lot of signal, but they cannot drive a 50 kilohm typical line input. The pickup needs to work into a much higher impedance, typically 1 megohm or so.
The reason why these devices often sound tinny is because the piezo sensor presents its signal through a series capacitance which is small, typically 15nF or less. When wired to a normal 50 kilohm line input this forms a 200Hz high-pass filter, which eliminates the bass.
If wired to a consumer plug-in-power microphone input of about 7 kilohms impedance, the result is a 1kHz high-pass filter. Hence the reputation for poor bass performance…..”
YES, Its all about IMPEDANCE
I have seen people suddenly ‘discover’ contact mics. And by ‘discover’ I suspect it tends to mean ‘discover the work of someone else who has used one’ who then heads off to an electronics shop, discover piezo mics cost less than $5, buys one, plugs it in, gets a signal but then wonders why they don’t get the same results…. Well now you know, its all about the IMPEDANCE!!! Re-read that quote from the article above:
“When wired to a normal 50 kilohm line input this forms a 200Hz high-pass filter…”
How many times have I seen a piezo element wired up to a 1/4″ jack plug? Many, many times… And now that you know the above tech to be true, what will the results be? Unintentional high pass filter (aka small speaker syndrome) Take anything you’ve ever recorded or listened to, put a HPF on it set to 200HZ and have a second listen…. It suddenly sounds like its coming from a transistor radio from 1973. Great if that is your intention, but otherwise…..
The second rule of using a contact mic is more practical. The results are often surprising – sometimes I’ve found a prop (this happened last weekend) and thought: “THIS will sound AMAZING with a contact mic” and then hooked it up & been thoroughly underwhelmed. What seems resonant & complex through the air may well be singular & far less interesting with a contact mic. But it’s when the reverse is true that things get exciting.
My old studio at Ropa Lane in Maupuia was originally owned by a metal company (literally, not the music genre) and when I took the lease they left some huge long I-beams in one of my warehouse spaces. When you lightly tap these 5m long beams they rang like bells, I loved them & couldn’t wait to get my contact mics out. But when I did they were WAY less interesting than through the air. I’m sure I’ll work out the pattern at some stage, but in many ways the mystery is actually a pleasant side effect. Not knowing the outcome means when you do stumble across a beautifully resonant body, time slows down… Recording this library for HISSandaROAR I’ve had many moments where through experimenting I’ve stumbled across a sound, and hours have past before I really became conscious again – I had a sore back for three days because of it. The situation generates what calls someone with a complex name I can’t remember calls ‘flow’ and the only other device that does that for me these days is my modular synth, but thats a different kettle of fish – I now know every time I switch it on, three to five hours will pass!
So if there is a rule 2 to CONTACT MIC club it is this:
2. YOU KNOW NOTHING
Keep an open mind & explore. A contact mic makes you look at the world in a different way, and for that alone you should be thankful. The flip side to those I-Beams I mentioned, was another prop I bought for practically nothing and hadn’t found a use for, at all – it was a slightly scodey stainless steel shower tray. The trick with it was suspending it so it was free to resonate, and one listen with a contact mic attached would make you wonder WHAT was creating the beautiful musical tones! It sure wasn’t what the literal description makes you think of, thats for sure!
No doubt I’ll think of more rules at some stage & continue this post, but also when creating the CONTACT MIC library I slowly developed a method for both creating and naming the sounds I was recording. Heres the analogy: when someone plays violin, you could happily define the sound created as consisting of four parts:
1. the human performer
2. the resonant body (the violin)
3. the activator (the bow)
4. the acoustic space
Any HISSandaROAR library you know is me, so I ignored part 1 but one aspect of using a contact mic that bears discussion is rule 3:
3. THERE IS NO ACOUSTIC
Check this video to see what I mean:
Until the drill bit meets the metal surface that the contact mics are attached to, there is no sound. You could hold a contact mic up & scream at it & record nothing! As with the drill that can work to your advantage. You don’t have to worry about extraneous noise – you could be listening to loud music and recording with a contact mic with zero leakage! But it is also a key factor in the use of the sounds – because there is no acoustic to help cue the listener what produced the sound, they appear almost more abstract. But due to their great resonance they work brilliantly as hidden components of complex composite sounds!
Also referring back to that list above, I became fascinated with parts 2 and 3. So maybe rule 4 is this:
4. SEPERATELY CONSIDER THE RESONANT BODY AND THE ACTIVATOR
With experience I collected up various activators (see photo below) and of course, only some activators would work with some resonant bodies… But it gave me a language & a mental model to use when attempting to identify likely candidates, and equally that is invaluable for the imagination.
Most of the resonant bodies and activators I used in the HISSandaROAR library are shown, briefly, in this video:
As far as low end goes, you can hear in that video some of whats possible. Heres some recordings of that big yellow half deflated balloon – the low frequencies created are beautifully expressive:
Rule number 5 isn’t really a rule but requires thought:
5. HOW DO YOU ATTACH A CONTACT MIC?
I use two methods, depending on the resonant body. First I always carry a roll of thin double sided sticky tape which works well if the surface is clean & flat. Its fiddly to apply and can be frustrating if the surface is dirty, because as soona s you move it you have to replace the tape, but when the surface is clean its my preferred method…. The other method I use sometimes is a product called BluTak – its intended for attaching posters to the wall, but it works well when the surface is more irregular or dirty…. It pays to always have both with you when recording, along with the always essential gaffer tape. In some extreme cases I’ve used Blutak between the contact mic and the surface and then wrapped the whole thing in gaffer tape. But you have to be careful as too much tape can deaden the very resonance you are trying to record…
When attaching a contact mic to tensioned long wires, I’ve been using large paper clips which are light but strong. For heavier cables eg transmission tower guy wires, I have used heavier spring clamps.
Rule number 6 is
6. PLEASE DON’T EMAIL ME ASKING WHAT MODEL OF CONTACT MIC I USE
I’ll list the models below, just so I can forward this article any such emails in the future!
Most of the recordings in the new library were done with two Barcus Berry Planar Wave contact mics combined with & two of their 4000XL preamp. Here is a link to the Barcus Berry product page. I like the 4000 preamps they come with due to them being phantom powered and having a 12dB switchable pad. I could not have cleanly recorded some of the metal shrieks & creaks in the library without that pad!
The other contact mic I own is a Trance Audio Inducer, which appears has been discontinued (incorrect – see update below) but here is a link to the Trance Audio site. Their preamp runs on two 9volt batteries which I like less than phantom power but I prefer Trance Audios actual contact mic capsule. Here is a photo comparing the two:
There are many other types of contact mics out there, the first I ever heard of was the C-Ducer but the contact mic element seems a bit big & awkward for my applications… Feel free to comment with any others you have experience with?
Lastly rule number 7 is
7. LEARN THROUGH EXPERIENCE
A contact mic is like any microphone, you have to learn to use it… and (hopefully) you never stop learning! So in the meantime here’s a preview of the new library:
check out SD008 CONTACT MIC Library
check out SD018 CONTACT MIC TWO Library
UPDATED Nov 12: I got an email from Trance Audio “We still custom make the mono Inducer System, and we also do a custom modification of our stereo Amulet System to make it more useful for SFX work. We don’t list these on our website as they are not stock items, but are happy to enquiries”