It's a Noisy World

Unless you’re sitting in the middle of a soundproof room, the sounds of distant traffic noise, construction and aircraft are everywhere.

It seems the days of peace and quiet are gone forever. When you’re shooting a video, you will likely have to deal with the everyday noises, along with other mechanical whirs and buzzes. Our audio and video equipment makes noise, too. Zoom motors, tape drives, computer fans, mixers and even microphones create mechanical and electrical noise that can drive an editor crazy in post. It would be nice to have a single plug-in that automatically zapped these offenders, but it’s just not that simple. This month, we’ll explore three different ways to minimize the noise in your videos and save your sanity.

Best Line of Defense

Trying not to nag here, but there’s one sure way to eliminate noise in your project: don’t record it in the first place. I know, it’s not that easy but, with some planning, you can simplify your editing tasks much earlier in the production process. If you know where you’ll shoot the project, start with a location scout. If possible, visit the location at the same time of day you’ve scheduled to shoot. Listen closely for both loud and subtle background sounds. Typical offenders are air conditioning systems, traffic noise and sounds from adjoining areas. Walk the area to see if it’s quieter in certain areas, and make a mental note. If you identify an area that is quieter than others, decide if you can relocate your shoot, and take a couple of still pictures for reference. You can usually disconnect or temporarily shut down electrical devices like refrigerators and air conditioners, but make sure you have permission first. Minimizing the noise could be as simple as closing a door.

Don’t forget to check your audio and video equipment prior to the shoot. Check for fresh batteries, good cables and clean connections. Any of these items can create extra noise in your audio, and some simple tests can eliminate the problem. Keep your power and audio cables separate and, if you have to cross them, do it at right angles. Better yet, run your audio and video equipment on batteries, if possible. Finally, make sure neither you, your subject nor anyone on the crew has a cell phone anywhere near the audio and video equipment. Cell phones – especially GSM models – emit some nasty radio frequencies that will permanently ruin your nice clean audio signals. A little time and attention before the shoot will increase the odds of a clean recording.

Filter It

Many noises are located at specific frequencies or in certain ranges. For these types of noise, a filter or two may be in order. When audio, video and power systems are combined, they often create ground loops between the various pieces of equipment. You’ll hear this as a low-frequency hum or buzz in the audio signal. Because U.S. electricity runs at 60Hz, that’s exactly where you’ll find the hum. Buzzes are often multiples of that frequency. If this is your noise problem, some audio filtering will either minimize or eliminate it. The first thing to try is a notch or band filter. Apply the filter to the audio track, and tune it to the offending frequency. If possible, make the notch as narrow as possible, to minimize its effect on surrounding frequencies. Play with the depth of the filter until your noise is gone or at least tolerable. If the noise contains buzz too, apply separate filters for those frequencies, but be careful. Too much filtering can make your audio sound a little strange. If you’re working on a dialog track and hum is the culprit, you can try a high-pass filter instead. High-pass filters allow audio above a set point to pass unaffected. As before, apply the filter to the track, and set the cutoff point to 90Hz as a starting point. Depending on your subject, you can move this point up as high as needed to minimize the noise, but don’t set it too high. You want to keep as much low frequency as possible to retain the natural quality of the voice.

Not all noise is hum or buzz – sometimes the problem is hiss. Whether from a noisy audio mixer, wireless pack or even the audio circuitry in your camera, hiss can be eliminated with a simple low-pass filter. These filters work the same as the high-pass version, except this time, the unaffected audio is below the cutoff point. For voice tracks, you can easily set this at 10kHz for starters. Anything below 8kHz will start to sound a bit dull, so listen carefully and find the best compromise that sounds the cleanest and clearest.

Digital Surgery

If everything else has failed, maybe a little digital noise reduction will work. Adobe Audition offers a nice noise-reduction option. There are also many other plug-ins like Sound Soap that work in a similar manner. Every program works differently, but the basics are the same. Start by identifying a section of the audio that contains only the noise. A full second would be nice, but you can work with less. Highlight the noise, and open the noise-reduction section. Audition has a button marked “Get noise from selection.” You simply click it and wait for the computer to analyze the noise. When it’s finished, you’ll see a graph of the noise. At this point, you have the option to choose how aggressive the noise reduction should work.

There are other settings that allow you to fine-tune the process, and it will always be a trial-and-error process. You’ll have to experiment to find the best ones for each type of noise. Finally, apply the noise reduction to the entire track, and listen to the results. If you used the aggressive settings, you’ll probably hear some serious artifacts in the sound. These show up as gurgling noises and strange, alien sounds that weren’t in your original track. You may also notice the strange addition of reverb to the ends of sounds. If you hear any of these artifacts, undo the noise reduction, and try different settings until you get something you can live with. You can also experiment with running the noise reduction two or more times with less-aggressive settings. The first pass may get rid of one type of noise but reveal another in the background. It takes some time to get it right, and the process isn’t perfect, but it’s better than leaving the noise in the track.


Blast That Noise

It really is a noisy world, but, using these techniques, you can gain control. The wonderful thing about reducing noise today is the Undo button. If your first try doesn’t work, all you have to do is undo it and try other options. You will find a combination of recording technique, filtering and digital noise reduction that can zap even the most offensive noises.

Contributing Editor Hal Robertson is a digital media producer and technology consultant.

Side Bar: If At First You Don’t Succeed…

Sometimes, it’s not possible or practical to eliminate all the noise in an audio track. In those cases, you either live with the noise or hide it using masking techniques. To mask with environmental noises, simply record a background noise track and fly it in at a reduced volume. Add some random environmental sound effects to spice it up and fully embrace the noise. Another common technique is masking with music. A simple bed of music under a dialog track can hide many undesirable noises.

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