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Entries in Cold (2)

Monday
Feb042013

Field Recording in Cold Conditions

A cold wind is blasting your face. Your hands are shaking and your teeth are chattering. Your legs are caked in white powder from trudging through the high snow drifts. And you have not even set up the gear yet... It's going to be a long day.

On a field recording assignment there are a million things to think about, both technical and creative. Sometimes you also have to worry about the environment in which you are recording as well, specifically the temperature you can expect to be working in. Both hot and cold extremes call for special preparations if you want to have a successful session. Extreme heat might come with the humidity which can wreak havoc on electronic gear and the inner workings of microphones. Heat can also lead to human error as a result of dehydration or even heat stroke. Today I am going to focus on what I think is the more difficult weather extreme, and the effects freezing cold can have on a field recording session. Plummeting temperatures can create obstacles that are difficult to overcome.

Living in a area of the planet that gets pretty cold for a good part of the year, I have had to prepare to record in cold conditions many times. The first thing you will notice in frigid temperatures is that you'll get dramatically reduced lasting-power from from any battery-operated gear. The power-producing chemical reaction that happens in a battery depends on extremely fast moving ions - and cold temperatures prevent this process from being efficient. The cold effect on batteries is no joke, the difference is drastic. So cold temperature sessions require first of all a comprehensive battery strategy if you don't have access to plug-in power on the shoot. You'll need more batteries than usual and you will also have to keep your extra/back-up batteries warm until they are put to use. If they're already cold when you need them, then their performance will be even worse. This can be tricky to overcome if you don't have a heated place to store them until they are needed. Using your own body heat by keeping batteries inside your jacket is usually the best way to keep your spares warm until they are pressed into service. And make sure all your batteries are fully charged before you head out into the cold. A half-charged battery in normal temperatures is a dead battery in chilly conditions. I find that “AA” batteries are affected quite significantly by cold temperatures and will drain much faster than the lithium-ion batteries used in some recorders (for ex: the Sound Devices 7 series.) So think ahead and stock up on extra batteries and organize and charge them up the day before. 

So your spare batteries are being kept nice and warm in your inside pockets, but you want to keep the batteries that are in use as warm as you can too. This can be done by having blankets to wrap your gear in. The blankets help in two ways, shielding the gear from wind and falling snow as much as possible. If there's snow on the ground I find it's extremely helpful to bring along a smallish sled. The sled can be used to help you transport everything to your location through the snow. It can also be used as a dry work surface for your equipment set-up.

You will have to keep yourself warm as well. The answer here is layers. When you're running around setting up all your gear you will find things a lot warmer than when you are sitting still waiting for things to happen. Having the ability to drop and add warm layers will allow you to adjust as the day goes forward. Lined boots, gloves and a warm knit hat, or a toque as they are called here in Canada, are extremely important. Gloves can make operating gear difficult though. They can make clumsy work out of simple scroll dials and button pushes. I find that gloves with with exposed fingers and a mitten flap are great to use on a recording trip. These gloves keep you warm when you have the flap over your fingers but allow you to easily push small buttons and accomplish fiddly tasks with the flaps back and your fingers exposed.

Although these gloves are good for using gear with small buttons and dials, if you are used to using any touch screen devices on a shoot you are better to leave those gadgets at home. In general they do not perform exceptionally well in the cold, and your small motor skills deteriorate as the temperature drops too. It's hard to work an iPhone's keyboard if your hand is shaking in the cold. 'Smart' gloves, which have electro-conductive thread woven into them, are becoming popular, allowing you to use touch screens with your gloved hands, but I still think that in cold weather using a paper and pen for notes is much better than a tablet, since you won’t have to worry about the batteries failing with a pad of paper (although it is possible for the ink in the pen to freeze!) and if your notebook falls into a slushy puddle or a snowbank you can just wipe it off instead of crying all the way to the Apple store at the end of the day.

Human ears were not designed well for cold conditions. They stick out, basically defenseless against the elements. Your ears are among the first parts of the body likely be affected by frostbite (along with fingers and toes.) You have to keep them covered in sub-zero temperatures. Yet on a recording field trip your ears are the most important tool you have. How can you get the most out of your hearing if there is a dense layer of fabric between your ears and the sounds you are trying to record? There is no simple solution here. If the temperatures are very low and you are planning to be out in the cold for a long time you have to cover your ears to stay comfortable (no recording is worth messing with the functionality of your ears!) I find that in short stints you can get away with using your headphones as earmuffs. That will only work for so long though, since headphones are optimized for sound reproduction, not heat insulation. The best way to tackle this issue is to wear a warm hat with the headphones over top. This will affect the sound from the headphones but not so much that you don’t have a decent idea of what you are recording. Every couple minutes you can pop the hat off your ear and listen for a moment to make sure all is still good. With experience you will find that the hat is not much of an issue.

Another thing to think about when shooting in snowy conditions is the noise interference you yourself are going to create. Every move you make will be noisy. Synthetic jackets create a lot of cloth movement noise with every little body shift. The simple act of taking a photo on the fly will ruin a take as you fumble around through your gloves and big winter jacket, generating a blizzard of nylon swiffling noises. Nope, you must stay as still as possible... not fun (or easy) when freezing your butt off.

You will also find that in the snow, every step you take can be really loud. Snow is an amazingly complex-sounding substance. Sometimes it's crunchy, other times mucky, while still other times it can be fluffy or even glassy. The temperature of the air will affect what the snow sounds like: the colder it is the more dry crunchiness you will hear, but there are lots of other factors at play too: 

How deep is the snow? 

What surface is under the snow? 

Has it been compacted down in tire tracks or footsteps? 

Has any ice formed in the snow from a fast drop in temperature? 

Is there any slush as a result of a fast rise in temperature? 

Has the area been salted? (rock salt is spread on pavement to melt ice)

Depending on these variables, and many others, you get remarkably different sounding snow under your feet. Yet they are all loud and distracting unless "footsteps in snow" is what you are actually setting out to record. So for this reason too, you will be forced to stay still once you are rolling.

Another thing to plan for is acclimatizing your gear to the cold before you start rolling. This applies mostly to the microphone. Most shotgun microphones work very well in the cold (DPA tests their mics to -25°C or -13°F) but issues can crop up as the microphone itself cools down to the ambient temperature. So ideally you want to have the mic out in the cold for an hour or so before you start rolling. I have not always been able to follow this rule and have actually not noticed any problems, but if you have the time it is a good idea to plan for enough time to cool down the mic in advance. The main thing you want to do is keep the microphone as dry as possible. Since water expands when it freezes you really don’t want any moisture in the mic that will cause a problem. Humidity in a mic can also interfere with the electric activity in a condenser mic. This really comes into play if you have multiple transitions between warm and cold environments. Condensation can develop when you bring a mic in from the cold, and if moisture has collected in and on the mic you won’t want to bring it right back out to freezing conditions. To avoid this, try to find a place to put the mic for a bit that is somewhere between freezing and normal room temperature. Then bring it all the way in to normal temperature after a while. Normally the car ride back to the city is perfect for this. The car will slowly warm up over the drive home, making for a good transition. Any condensation that has formed will have a chance to evaporate.

Another tip I can offer is to avoid recording near your vehicle unless you have lots of time to set up. If you drive to your location in a car or even a snowmobile you will be shocked how long it takes for the vehicle to become silent. As the engine cools it will sizzle, ping, and pop for a lot longer then you'd think. The hood will give little metal flexes as it cools, water will drip down and melt the snow below the exhaust. Lots of other little noises will continue on well after the ignition is shut off. If you are there to record a chainsaw, then this will not be an issue. But if you are looking to record blustery winds or the delicate ambience of a winter wilderness you'll end up with an editing nightmare when you go to master the file back at your studio.

Winter conditions make for a fantastic recording environment if you have planned properly and come prepared. Specifically recording in nature. The blanket of snow covering everything acts as massive sound insulation system, dampening distant echoes. As a result the sound of deep winter is very different. And also eerily silent. The leaves are all off the trees, so the wind makes very little noise in the woods. The vast majority of the birds have flown south taking their daily chatter with them. When the wind is calm, standing in a northern forest can be as silent as the most expensive acoustician-designed floating recording booth. It can actually be a little disorienting when you find yourself surrounded by such an enveloping quiet - it's not something we city folk are used to. Yet these conditions can be perfect for a field recordist looking to record clean takes of explosions, firearms, or anything else that needs a wide open quiet space. 

Just remember to stay warm, keep your wits about you and bring a lot of batteries.

Finally, just be glad you are not recording on the ground in this picture, which I took while flying over Greenland.  I have no idea how cold it would have been down there but I am sure most of us are dealing with much more hospitable conditions!

Monday
Apr252011

Underneath the Ice

In the dead of winter I was up up north staying at a family cottage and on the second day I was there it was extremely warm.  Well, extremely warm for northern Ontario in January, the temperature popped up above zero and the sun was out in full force.  The river was frozen solid but the full day of warmth melted a layer off the ice leaving about an inch of water on top.  Then when night fell the temperature changed quickly and severely as a cold front entered the area, plummeting everything back far below zero in what seemed like just a few minutes.  In these situations the ice makes crazy sounds as it freezes and shifts.  I was hoping to get out on the lake and get some stereo recording of these sounds but the wind was just too unforgiving and even with my blimp the wind noise was too loud to get any usable recordings of the ice.  But luckily I had brought my Hydrophone, underwater microphone.

After everyone else had gone to bed, I headed out on to the frozen river looking for a crack I could drop the hydrophone into, hoping that maybe I could get some of the huge ice shifting sounds from underneath and avoid the wind altogether.  The ice was very thick, more then 6 inches, so it took lots of roaming around in the pitch black night, before I found a good crack with a small hole just barely big enough to get the hydrophone through and immediately found I could hear some crazy sounds. 

This is a picture of the crack in the ice with the hole and the hydrophone's cable coming up out of the ice.

 

I was hoping to get big, low end booms of the ice cracking but what I ended up getting was the opposite, tiny sounds of the water in the immediate area of the microphone cracking and popping as it froze.  I left the hydrophone in the ice for about 45 minutes and got a whole lot of silence but here is a clip of about 8 different sections where the ice came to life with crackles and pops.

I also took some time to grab some blocks of ice near the shore and smash them on the ice surface above the where I was recording.  It was so cold and I had been out on the river for such a long time by this point that I was having trouble fidgeting with record levels on the gear because my fingers were starting numb up a bit.  This did not really work out as I had hoped as the sounds are not that interesting, but something that is kind of cool is simply the sounds of my footsteps walking around above the mic.  They could be useful someday.  Here is a clip of a bunch of impacts followed by footsteps at the end.

 

Ice Impacts Recorded from Below Surface by azimuthaudio