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Filmmaking | How To's | Technology

Almost Everything a DSLR Moviemaker (or Anyone Else) Needs To Know About Sound

30 Jun , 2010  

Written by Peter Bohush | Posted by:

When DSLR cameras exploded onto the market over the past year, they offered an awe-inspiring improvement in picture quality over video camcorders. But they have one glaring weakness: poor audio recording capabilities. Here's a thorough report on audio recording so that you can spare yourself some unfortunate mistakes.

Since the dawn of the talking pictures, the film cameras captured the images and an audio recorder captured the sound. Video camcorders changed that, offering image and sound recording all in one. Then DSLRs came along and messed everything up!
When DSLR cameras exploded onto the market over the past year, they offered an awe-inspiring improvement in picture quality over video camcorders. But they have one glaring weakness: poor audio recording capabilities.

Don’t fault the cameras; they weren’t originally designed with shooting high-quality audio in mind. Even the video was an afterthought. But their popularity has skyrocketed due to the awesome picture capabilities and control.

The audio on DSLRs is considered by many to be only “scratch track” quality. The tiny onboard microphones pick up a lot of internal camera noises along with every touch onto the camera by the operator. Plugging in an external microphone is better, but still some camcorders have automatic gain control (AGC) built in, or lack input volume controls, both of which will hinder the recording of clean, controlled audio.

What’s old is new

The solution is as old as talkies themselves. Record the audio separately using a high quality recorder, and sync up the picture and sound in post production. This technique is called double-system sound. It’s obvious when you see someone holding the clapper board in front of the camera, calling out the shot name, then slapping down the clapper stick.

The purpose of the clapper is to record the loud clap, which will be visible on the audio waveform file as well as seen in the video. Matching these two files up at that clear point should result in audio that is in sync with the picture. Out of sync looks like a kung fu movie when the mouths don’t move in sync with the words.

Film shoots have done double-system sound for nearly a hundred years. However, there are at least three crew positions required for this — a sound recordist, a boom operator, and a sync specialist — that videographers haven’t needed or have gone without in recent years.

The process of syncing the audio to the film can be tedious and expensive, even using modern timecode technologies. But for moviemakers who want their images to look “like film,” as DSLRs are sometimes described, they’ll likely have to adopt the old ways of double-system sound recording.

This isn’t as hard as it might seem. And syncing audio to picture is at least somewhat easier in computer non-linear editing programs, such as Final Cut Pro or Avid, than doing it in a post production lab. See companion story on PluralEyes audio syncing software.

Recording the sound

Big budget Hollywood motion picture productions are designed to get the picture first, and sacrifice location audio recording if necessary. Dialogue and sounds can be redone later by having the actors dub their lines and sound effects artists add in the background sounds.

Lower budget and indie productions can do this, but it’s much better to try to record good audio, especially dialogue, on set. It eliminates the expensive process of dubbing dialogue later, plus it is difficult for many actors to deliver their lines in a dubbing session with the same emotions they did when acting for the camera, let alone in perfect sync.

A good sound recordist on set is crucial. Some productions may have two people, one who runs the recording deck and another who holds the boom and points the microphone. On smaller productions, one person can sometimes operate the boom and mic while also recording the audio into a portable deck, usually hung from a shoulder strap.

It’s impossible to hold the boom with two hands and make adjustments to the audio input levels at the same time (sound guys with three arms are few and far between and in high demand!) So there may be situations where the sound peaks too high or isn’t loud enough, and the boom/sound person won’t be able to tweak that during recording.
(A trick when recording is to record two mono tracks from the one mic input, and set one of the tracks input level lower than the other. That way if a loud noise or actor blows out the audio on the main track, the second track can be used.)

Audio recorders

The gold standard of production sound recorders are made by Nagra and Aaton, with prices from $10,000 to $14,000 for a portable digital recorder.

On the lower end, brands such as Tascam and Zoom offer decent recording capabilities in hand-held digital recorders that can accept external microphones for around $300 to $500.

In the middle, Sony, Fostex, Marantz and others offer digital recorders from $500 to $5,000 and up. The higher end ones will include timecode syncing features to lock to cameras with different frame rates, EDL exports and many other pro features. The Marantz PD661 records 2-track audio at various user-controlled quality settings. It doesn’t feature timecode lock to high-end cameras, but at around $700 is more rugged than the cheaper models and is well-suited to indie production sound needs.
Some people want to record the sound directly into the camera. This single-system sound, easier to do in video camcorders, is complicated in DSLRs by their unsophisticated audio limitations.

There are products that interface between the microphone and the camera to help improve the quality and levels of the audio signal. BeachTek products have been around for many years, and primarily interface between a balanced, powered mic and the unbalanced input on the camera or camcorder.

A new company called Juicedlink offers a similar product but with a low-powered pre-amplifier on it that can power the microphone, override the camera’s automatic gain control (which otherwise messes with sound levels) and clean up the audio signal going into the camera.

Shotguns and cardiods

There could be an endless discussion about microphones. Everyone has their favorites. Most experts would at least agree on the type of mics to use in various situations.
Shotgun mics are preferred for most on-location and soundstage recording situations. Shotgun mics pick up sound from a narrow pattern in front of the mic. The width and distance of this pattern varies among mics.

Cardioid mics include handheld models that singers and speakers use, as well as studio mics you might see in a radio station or music recording studio. They have a wider pickup pattern that is not suitable for outside uses, since they would record all the noises around the subject as well.

Mics come in other flavors, too, from balanced or unbalanced to powered or phantom powered.

Powered mics use their own battery to operate and send the signal to the recording device. Phantom powered mics rely on power being sent up the cable to them from the recording device (or mixer or amp.)

The power source isn’t usually as critical as whether the mic is balanced or unbalanced. Generally, balanced is better. It is less susceptible to picking up interference and can run longer cable lengths. Balanced mics and instruments are typically noted by their XLR, or three pin, connectors.

Boom poles

Boom poles are made of aluminum or carbon fiber and extend from 6 to 14 feet to allow the operator to get the mic in over the talent without himself being seen on camera. There are do-it-yourself videos online that show boom poles made from PVC piping and mop handles. They will work to a point, even if they won’t win any beauty contests.
Professional, hand-held boom poles are usually wired internally, so the operator plugs the mic into one end and the cable to the recorder in the other for a quick and easy set up. There’s also a practical reason for this. Mic cable wrapped along the outside of the boom pole can twist or bump, resulting in vibration noise on the audio track.

There are plenty of things conspiring to ruin audio takes already; ruining your own take by bumping the mic or boom pole shouldn’t be one of them. Boom poles range in price from around $200 to $800 and up.

On large productions and on TV shows, the boom is sometimes hydraulically operated by a sound man seated at the controls.

On the end of the boom pole, the microphone is mounted onto a shock mount, often a type of bracket that suspends the mic on rubber bands. To suppress wind noise, a foam windscreen or fuzzy “softie” can be placed over the mic. In really windy conditions, the mic is mounted inside a mesh canister called a blimp or zeppelin. And then the blimp is wrapped in a fuzzy cover sometimes referred to as a “dead cat.”

Pointing the mics

Too many inexperienced directors and sound people don’t understand some of the basics of how mics work. The result is audio that is noisy, muddy or riddled with echos or tinny sounds. The problems are often the result of simply not placing and aiming the shotgun mic properly.

Shotgun mics are sometimes attached to the top of the camcorder, pointed level at the talent. This is not good because it conflicts with the design of the mic. While the shotgun’s narrow pickup pattern will record the dialogue in front of it, it’s the wrong way to do it. A shotgun mic will pick up pretty much everything in front of it within its narrow pattern. And like a beam of light, the pattern widens the farther away it is from the mic.
So a shotgun pointed level will record the talent in front plus everything behind the talent for some distance. It also records some of the audio directly behind the mic, so a level-aimed mic will record noises from behind the cameraman and add this to the talent and the background noise. The result is not clean.

The best way to use a shotgun mic is to position it just out of frame above and slightly in front of the talent, pointing downward. Get as close as possible. (But not too close — we’ve all seen that boom mic drop into the top of the frame in movies before. That’s the boom operator doing his best to get as close as possible, though.)

Pointing downward at the talent, the mic will pick up the dialogue, plus what’s past it and what’s behind the mic. Well, the ground is past the talent in front, and it doesn’t usually make too much noise except in earthquakes. And the sky would be behind the mic, and that doesn’t make noise except when planes fly over.

In windy conditions or when there is noise above or below the talent, the next best position for the shotgun mic would be below the talent pointing slightly up from level, where the talent’s body would block the sounds from behind it.

A good boom operator, together with the sound recordist, will quickly test different positions before each shot to ensure positioning that will give the cleanest sound with the least amount of ambient noise.

Wired or wireless

Wireless mics can have balanced or unbalanced connectors. While balanced is generally considered better, it’s the wireless part where the problems occur. As the signals go through the air, interference can occur. It can be static or buzzing sounds from conflicting electrical equipment, or even radio signals from cell phones, radios, microwave towers, etc.

Cheap wireless camcorder mic systems will likely be affected by interference at some point, more so than more expensive systems with better electronics. But you’ll never be able to predict interference situations. They just happen.

However, wired systems can have their own set of audio problems. Plugging the recording system (including a camcorder) can pick up interference, low-frequency ground hums and other static through the AC power lines. Sometimes the power cords act as a sort of antenna to bring in all sorts of weirdness. I have even experienced hearing short-wave radio broadcasts from Europe bleeding into the system through the AC cords.

So many sound recordists and camera operators prefer to run their systems on battery power, off the grid from the location’s electrical system, to avoid interference and potentially damaging power spikes.
In prepping for a production, always make sure you have plenty of batteries.

It’s picture and sound

Film shooters don’t have a problem comprehending a camera that doesn’t record sound. That’s how film cameras have been since the beginning. Video shooters have found the DSLRs frustrating, since video camcorders for the most part all record audio, and some do it quite well.

But whether you shoot film or video, most of the important attributes of sound recording still apply. Quality, balanced microphones. Avoid introducing interference to the audio. Get the dialogue tracks recorded on set whenever possible. Get the mic in as close as possible. The issue or choice of recording double-system or in-camera isn’t that big of a deal if all the other steps are taken to record good, usable audio.