With all of the attention and time that’s spent on shooting great footage, recording quality sound is often overlooked. A questionable visual shot here or there in your finished project will likely be unnoticed and just merge into the flow of the story- IF you have an excellent soundtrack that holds the edit together and makes great shots and average shots all flow together into a flawless final masterpiece. That is the great big Hollywood secret to moviemaking.
But a section, or even a single shot with bad sound will shock your enraptured viewers out of their reverie and immediately destroy the continuity of the edit, and thereby the illusion of moviemaking.
Great location sound is the biggest secret to great looking footage. And since capturing quality sound is in some ways more challenging than capturing quality visuals, we’re going to give you a few secrets and tips on recording location audio.
Sound principles > Direct vs. Reflected Sound
Sound that reaches your ears directly from the sound source is called direct sound. Sound that bounces off another surface before it reaches your ears is called reflected sound.
In the context of capturing great location sound, repeat this mantra over and over:
Direct sound… good!
Reflected sound… bad!
(It’s funnier if you imitate a caveman voice for this mantra.)
Imagine you and a friend are in an empty gymnasium. She speaks to you, standing one foot away. The sound of her voice radiates in all directions, but because she is so close, the sound coming directly from her mouth to your ear is heard much louder than the sound reflecting off the surfaces of the gym.
Then, she runs all the way across the gym, and again speaks. This time, her voice again radiates in all directions, but what little sound reaches your ear directly from her mouth is overwhelmed by all the reflected sound waves reaching your ear after bouncing one, two, three or sixteen times off the hard surfaces of the gym walls, ceiling and floor. Since each consonant and vowel is arriving at your ear at a multitude of times ranging over several seconds, you have no idea what she said. The sound is “blurred”-like rubbing a word freshly written in ink across the page until it is illegible.
Bottom line: Get the mic close to your subject. Even more important in rooms with hard surfaces like glass and hardwood floors.
Mic technology > What is a mic?
A mic is a transducer- it senses acoustic energy and coverts it into electrical energy. In a DV camcorder, the electrical energy is digitized into ones and zeros and recorded onto tape or disc along with the picture and other information.
Dynamic mics are usually lower cost, rugged, handle very loud sounds, don’t need power, and have mediocre high frequency pickup. Dynamic mics are often handheld.
Condenser (and electret condensor) mics are more expensive, more delicate, need power, are very sensitive to sound (a very loud sound close to the mic can actually damage it), and have excellent high frequency response. The best quality shotguns, lavalier mics and voiceover mics are condensers.
Mic technology > Impedance
Inexpensive mics and consumer stereo and television gear use high impedance connections. High impedance (high-Z) cables have one conductor and a shield. This is called an unbalanced connection. With very short cable runs of a few feet, such as between your DVD player and TV, high-Z connections work fine.
But when you need to run a cable 10, 20 or 30 feet, a high-Z cable will pick up all kinds of unwanted noise-60 cycle AC hum, stray RFI (radio frequency interference), electrical disturbances from a hair dryer or blender resulting in a buzz, and just plain noise, as well as losing high frequencies in longer cable runs.
As we learned earlier, it’s best to keep your mic close to your subject-but the camera will not always be close to the subject. What to do?
Enter low impedance (low-Z) connections to the rescue. Low-Z cables have two conductors and a shield. One conductor is run out of phase so that any noise or interference picked up during the length of the cable run neatly cancels itself out when the signals are combined at the receiving end. Wow! Neat trick! This is called a balanced connection.
Bottom Line: Always use balanced, low-Z mics and connections when the mic is more than 5 feet from the camera. You can run a balanced mic cable 50-100 feet and it will still sound great!
Warning: Do not run your audio cables right alongside electrical cables (like your light cables). Keep your mic cables on one side and your light cables on the other.
Typically, balanced mic cables have XLR connectors.
Mic technology > XLR adapters
Wait just a minute! Professional, balanced, low-Z mics have XLR connectors, but the mic input on my camcorder is a 1/8″ stereo mini jack? How do I plug it in?
The answer is that the balanced low-Z signal must be converted to an unbalanced high-Z signal before entering your camcorder (if your camcorder does not have XLR inputs). Many manufacturers offer XLR adapters for this purpose, as well as third parties, so you are all set- and the unbalanced cable run from the adapter to your camera is usually around 6 inches and so does not pick up any noise or interference.
You can watch a movie on XLR adaptershere.
Do not use a simple cable adapter-use a real impedance adapter with a high quality transformer to convert the impedance for the best quality.
If you are only using one channel with one mic, as would normally be the case, make sure and switch your XLR adapter to mono so the single mic feeds both channels of your camcorder. This will prevent all kinds of problems. Later, while editing, you can delete one of the (duplicate) tracks if you wish, but you’ll end up with cleaner, higher quality sound.
Warning: Please don’t get cheapo adapters that will hang off your camcorder and put strain on your camcorder input jack and break it. Get a professional adapter that mounts onto or underneath your camcorder or somewhere where there is no danger of damaging your input jack.
Phantom Power (thanks to Marty Atias)
Condensor microphones require power to operate, yet cameras with miniplug inputs DO NOT supply phantom power. The best strategy is to get an XLR adapter that also suppies phantom power- right through the XLR cable! (like the Beachtek DXA-6 on this page)
There are a few condensor mics that can be powered from an internal battery, but some of these, like the Audio Technicas, are notorious for putting out anemic levels, and a thin, noisy sound when powered by AA batteries, whereas they sound great when powered by true 48V phantom power.
Here’s a universal rule for location sound: Always wear headphones.
Comfortable, closed ear headphones with a decent sound level are an absolute must for evaluating your location audio as you shoot. Background noises that you don’t notice in the room can really jump out on a recorded track. Listen to your audio through headphones, and you’re hearing what the microphone hears. Watch out for rustling lav mics, wind noise, hum or buzz, and distortion. You cannot remove these sounds later.
Murphy says: The moment you feel you can safely remove your headphones is the moment someone will trip over a cord, a battery will fail, someone will use a blender upstairs, or some other calamity resulting in unusable audio.
If you have a soundperson who will be standing away from the camera, you’ll need a long headphone cable extension.
Some audio problems you just can’t fix
You can perform a variety of audio post-production tasks with modern digital audio tools. You can add reverb to make a dry studio recording sound like you recorded it in an airplane hangar. You can change the speed of a recording without changing the pitch, or vice versa. You can slice and dice your audio down to the millisecond, but there are many audio problems that you just can’t “fix in the mix”– so avoid them during production.
After shooting for the first minute in a new location, it’s an excellent idea to take a short break, tell everyone to be quiet and play back the recorded audio, listening intently on your headphones. This is the time to try and get better sound– you won’t have another chance!
Common production audio killers
Here are some common location audio problems and some possible solutions:
Problem: Any unwanted background sound. You cannot “lift” someone’s voice out of the noisy background like you can cut a figure out of the background in Photoshop. Particularly troublesome is music-if you want to add your own later.
Solution: Kill the unwanted sound (unless it’s a dog, then just sedate it). I mean unplug the fridge, air conditioner, etc. or shoot somewhere else.
Problem: Speech unintelligible due to too high a reflected/direct sound ratio.
Solution: Get the mic close to the talent.
Problem: Recording too low– bad signal/noise ratio.
Solution: Use a higher manual record level or switch to AGC. (Auto Gain Control)
Problem: Recording distorted.
Solution: Use a lower manual level or switch to AGC.
Problem: Wind noise.
Solution: Use a heavy-duty windscreen.
Problem: Radio mike dropouts.
Solution: Use a UHF, true diversity wireless or a hardwired mic.
Problem: Buzz or hum in the signal.
Solution: If you’re using a reference monitor, unplug your camcorder from AC and use batteries (could be a ground loop). If that doesn’t fix it unplug the S-Video cable from your monitor, you may need to shoot with your flipout once you’ve got your shot set up. Troubleshoot–it’s a bad cable, bad mic, bad connection, or you’ve run your audio cables alongside AC cables.
One tip to getting good audio in a difficult or impossible location: Don’t
One thing I always try to do when I encounter a problem is think of a way to easily and quickly bypass the problem in an elegant, outside-the-box way that results in a higher quality project-without having to actually face the problem head-on and grapple with it.
One day you’ll land the prestigious Gloppita Gloppita, Inc. account, and one of your first projects will be a training video on the GlopMaster 2008 Pro. Anticipating that the machine will be loud, you bring your main 3 chip camera and a small extra 1 chip cam, as well as your high quality voiceover mic and pop filter.
When shooting the factory foreman, even a good lavalier mic is overwhelmed by the bone-crunching din of the GlopMaster. So you instruct the foreman to simply perform the actions without speaking. After shooting, you go to his quiet office in another building, pop the tape in your little extra 1 chip cam, and have him watch the action on the flipout screen while commentating his actions while speaking on the voiceover mic, recording into your main camcorder.
Result? Much higher quality audio, better content because the foreman can concentrate on his actions when demonstrating the dangerous machine, and concentrate on what he’s saying in his quiet office, and a much better final project.
Extra credit: Set up an interview-type shot and get quality talking head footage– you can use this for an intro and outro, as well as cut back to it to provide visual variety to the project.
The Final Word:
Trust your ears on the set- if it sounds good through your headphones, clean and intelligible with low background sound, noise, buzz or hum, it is good!