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Entries in Learning (1)

Thursday
Jun212012

Learning to Record Vehicle SFX

In my years of field recording I have been lucky enough to capture some pretty awesome sounds, but one thing I've never really attempted to record is vehicles.  I have not been avoiding them entirely though; I have recorded automobile passes and exteriors (some of which can be found as a part of the Sound Collectors Club "Car Passes" collection). Yet I have never tried to do full coverage of a vehicle, using multiple mics to gather various aural perspectives simultaneously.  I've been meaning to tackle a vehicle recording session for a while but I guess I've never seen and had access to a particular vehicle that really caught my interest. That has all changed.  I have been in contact with the owner of an Argo, a 6-wheeled all-terrain amphibious vehicle, and I have been given permission to do a full recording of this strange machine.  

Here is a shot of the Argo I will be recording, with its owner John Beumer and his grandson Simon.

One look at the photo above and you will begin to get an idea of how peculiar this vehicle is.   First of all it has 6 wheels - not something you see every day.  The Argo provides continuous torque to all three axles, allowing the vehicle to be propelled forward even if only one set of wheels is touching the ground at any given moment - as is often the case in rugged terrain.  Secondly, it's amphibious, meaning you can drive it right off the shore into water; it will float and keep going on its way.  Once in the water it moves painfully slowly though, unless the Argo is outfitted with the kind of outboard motor a normal boat would have.  A third distinctive feature is the steering mechanism.  Instead of a steering wheel it has something called "skid steering".   The steering is operated by two hand levers that can activate brakes to stop the wheels on either side of the vehicle, causing it to pivot.  This means if you have all the wheels on the right side of the Argo turning forwards while simultaneously having all the wheels on the left side on full brake the whole machine can spin on the spot.

Needless to say I am really looking forward recording this thing.

Since I really don't know what I am doing with regards to vehicle recordings I figured I should do a couple of practice runs ahead of time, just to get a feel for the process and see if I can get some of the learning curve out of the way before I am under the pressure and time constraint of the Argo recording session.  The vehicle I currently have full access to is obviously my own car, a 2006 Toyota Matrix.

My plan for the real recording day will be to rent a Sound Devices 788T, so I can have several mics recording back into the same device, but for this exercise I used my Sound Devices 702, which has 2 record channels, so only 2 mics this time around.

This is where I have to 'fess up to a sad truth.  I know absolutely nothing about cars, even though I have had a license for nearly 20 years.  I never owned a car until I bought the Matrix, used, in 2011, and it's been running in perfect condition since, so I have never needed to do any real maintenance on it.  I live in a big city, right near a subway station, and parking downtown is always a pain in the butt.  Having a car in the city has never seemed to me to be worth the hassle.  As a result I never learned anything more than the basics of how a car works (foot on gas = go, foot on brake = stop).  Because of this ignorance I was especially nervous about wiring up expensive mics under the hood of my car, for fear of getting cables caught up in the mysterious workings of the engine, overheating a mic, or any other potential mistake I could make.  I have a matched pair of DPA 4060s which I hope to use on engines once I know what I am doing but I decided that for this first attempt it would definitely be a bad idea to put such prized/expensive mics to use.  Instead I opted for a Naiant X-S Miniature Omnidirectional Condenser mic I picked up a while ago.  These are quite inexpensive microphones and sound amazing given their price point.  Unlike the DPAs, if one of these got destroyed in some unexpected bungle I would not spend the rest of the month kicking myself.....  only a couple of hours...... tops.

So on a lazy weekend at the cabin I started to mic up my Matrix.  I chose to put to put mic #1 under the hood and #2 at the back of the car to record the tail-pipe. I popped the hood and considered the engine...  Then I hemmed and hawed over where would be good place to fasten a mic.  Again I had no idea really what part of an engine really made good noises.  I was alone, without even any internet access, so I could not ask for help or look anything up. I decided to be ultra-conservative and I taped the mic to the windshield-washer fluid access.  This looked good because it wasn't too close to any moving parts, and was near a seam where I could feed the cable directly out from under the hood. I was worried about getting cabling caught up in a mechanism of some sort, so this seemed like a good spot.  I popped a wind foam on the mic, secured it with some gaffer tape and then taped the mic cable with more gaffer tape up the side of the car into the passenger-side window.

The mic can be seen on the left side of the photo taped to the white plastic of the windshield-washer fluid intake.

This photo gives you an idea of the microphone's aural point of view looking at the engine. Here you can see the cabling leading from under the hood into the vehicle where the recorder was stationed.

The second channel of audio I planned to record was of the tail pipe in the rear of the Matrix.  This would make for a much easier cabling job as I could simply go right into the interior of the car through the hatchback door and straight up to the passenger seat.  I was not too worried about the mic being damaged except that I was planning to drive on a gravel road.  It would be possible for a rock to get kicked up at the mic.  Since I had no plans for these recordings I figured why put the DPAs at any risk until I was really counting on the results - so I put another Naiant X-S Miniature on the job.

I guessed that wind would be my main problem with this microphone perspective, as the mic would be out in the open as the car moved at high speeds.  To combat the wind I got a little bit DIY, covering the mic in some foam padding and then putting a chunk of fun-fur over the the foam (see my full wind protection kit blog post for more info). I was hopeful this would do the trick, so I positioned the mic just above the tailpipe and got ready to take the car out on the road.

The tailpipe mic perspective shown here covered in foam, wrapped in fun-fur and taped to the vehicle exterior.

Since I was the only person around I had to simultaneously act as the stunt driver and the location mixer on this outing.  If you have never done this, I would highly recommend it... but also warn against it.  It's awesome because it makes driving your boring car suddenly feel a lot like a video game.  With the headphones on, monitoring the exterior microphones, every time you change gears, or step on the gas  it sounds hyper-realistic, just like a great racing game.  Suddenly, driving my beat-up old car was exciting and adventurous. It was a bizarre experience.  I would say it's also more than a little dangerous because I was not 100% focused on the driving, as I was keeping tabs on levels on the recorder next to me in the passenger seat.  Luckily I was in a pretty quiet and remote area, and never came across another person on the back roads where I was doing this. I would not have attempted this otherwise.  I do not in any way endorse driving with headphones on in a populated area!  That could be a disaster waiting to happen.

So what did I learn?  The tailpipe mic sounded fantastic at lower speeds.  My foam and fun-fur trick worked marvellously against the wind until the car hit about 80km per hour. At that point some wind and tire noise started entering the recording.  I had the car all the way up to 100 kilometers per hour (62 mph), so the air-flow over the body of the car would have been significant.  Since the Argo can not reach any where near those speeds I am not worried about this issue for when it comes time for that recording session.  The  Naiant X-S sounded pretty great back there.  It was able to pick up the tail-pipe growl really well considering it's a fairly inexpensive mic and it was wrapped up in multiple layers of foam and cloth.  In the end I was happy with this mic perspective and plan to follow a similar mic technique when I get my chance at the Argo.  Take a listen:

The engine microphone perspective was a different story.  Turns out my safe approach to mic placement under the hood was not a great choice.  I got a lot of sound from the engine but not much definition at all.  Basically, dirty white noise.  Also, I was not nearly prepared for the amount of wind that came through the front grille of the Matrix.  At slower speeds this was not a problem but once I got the car going faster, wind became a big issue.  Here is a sample of the engine recording:

All in all I would say that my under-the-hood mic was not a success.  But I did learn a lot from the process.  Now I know I need to think about wind protection even under the hood, and that I will have to do some more testing to find a better spot to place the microphone.  

Here is a mixdown of both mics playing togther:

I also learned a lot simply going through the process.  I still have a ton to learn on vehicle recording techniques but by getting my feet wet with this little practice exercise I am a lot more confident going forward with the Argo recording session in a few weeks.

Keep checking back over the next while as I post a few other articles on research and tests I will be doing to further prepare for my first full-out vehicle record on the 6 wheeled amphibious Argo.