Avoiding hum/noise during recording... What to look out for

[Zissou]

Recently i shot a brief commercial at a commercial equipment (no pun intended) retailer, and we had a HELL of a time convincing the staff to shut off certain appliances so we could get a clean recording, and i figured this would be a great time to do a little write-up.

When i first started with video, i also purchased a pair of Rode NTG-2 mics, because i had one camera that supported XLR's and one that didnt, and the NTG-2's had great ratings and more importantly a low price relative to other models. I knew shotguns were very sensitive to handling noise, so i had bought a boom light stand, well insulated XLR cables, and a shock mount as well as a foam and windscreen. I figured i was set; just aim, adjust, and shoot. I knew there were a total of 4 different kelvin temperatures of fluorescent lights, all 60Hz, so i decided to shoot 1/60 and overwhelm the fluorescent lighting with halogens so i had a more even color temperature, i knew the angles (worked there for years), i knew the employees (most were my friends or former co-workers), and i knew all the locals that would be there during the shoot, so i figured i had it in the bag.

My first job was shooting an ad for my parents' restaurant for the local cable providers' advertisment channel, so it was obviously 90% interior work and all next to noisy appliances, fluorescent lighting, banging/clanging plates/dishes, and a million other little electrical nightmares i had never taken great notice of.

Naturally, i first realized the shotguns i had bought were creating a LOT of reverb, and that i should have gone with cardioid mics, so i ended up using a PETE based foam to cover most of the 'slits' on the shotgun barrels and dropped the mic (mounted on a boom light stand) away from the fluorescent transformers. next, i canned the stereo recording idea as it exacerbated the reverb effect, and recorded in mono. The building was mostly wooden interior in the dining room, with composite recycled paper ceiling panels, and pretty open, so i didnt have a problem with reverb in the main dining room, and i killed the compressors for the fridges and beverage machines, but the kitchen was another story.

Small, narrow, and FILLED with stainless steel, from the fridges to the walls and ceilings, EVERYTHING reverbed. Worse still, there was a hum. actually SEVERAL hums. at first i thought the preamp on the XH A1 was just very noisy or i had the audio gain up, and i spent half a day trying to figure out how to minimize the noise. In the end i re-recorded it with a single cardioid, shut down ALL the fridges, boomed away from the fluorescent transformers, and unplugged the microwaves, dishwasher, electric deepfryer, killed the stereo, and several other items.

Im a big believer in learning through experience, and this one taught me A LOT in a very short period of time, but i learned to do things with the right tools as well, and a lot about background noise and electrical noise.

Basically, watch out for the following when mic'ing. Its not just on-camera noise or someone coughing/moving etc behind the camera.
Fluorescent light ballasts
refrigerators
fans
refrigerator/freezer compressors
DC converters
dense or metal walls, especially near angles/corners
picture tube TV's
transformers (exterior or interior)

Any other ideas on what to watch out for in the field would be a great resource for all of us; i couldnt find a thread on what to watch out for, so i figure i start one. Maybe it could be added to and made into a sticky; i know i am missing a LOT to look out for; im a novice!

Heres a shot from the shoot...

 

[Steve House]

A hypercardioid would have definitely helped here ... directional to better reduce ambience but without the misbehaviour of a shotgun in a reflective environment.

Getting the mic close to the talent is crucial, the closer to the speaker the louder the voice will be compared to all the interfering room noises. You mentioned using a "boom light stand." A boom OPERATOR would have been a better investment, holding the mic just out of frame up close to the talent. The rule of thumb is the talent should be able to reach out and tap the end of the mic with their finger without having to stretch their arm all the way straight.

Try to shoot when the restaurant is closed so that as much equipment as possible can be shut off.

Stereo for dialog is pointless. Save stereo for music and ambience. A person has only one mouth to speak from so human speech is mono by its fundamental nature.

 

[dano]

You hit on a couple good points...a hypercardioid is most definitely going to work better for you on interior locations. Turn off as many offenders as possible, HVAC, fridges, etc (can always turn them back on for a period of time at a break if they are worried about spoiling, although should be fine as long as they keep the units closed). Hanging sound blankets to enclose the area a bit may help a bit. These noises, especially if you are shooting from different angles & perspectives, will make cutting the scenes together very difficult. Make sure to get as much room tone as possible on different set-ups, angles to give you a fighting chance in post.

Also - someone please correct me if I'm wrong, but I wouldn't suggest covering the "slits" on the shotgun. I don't believe this will achieve the effect you are looking for. Booming the shotgun with the noise offenders behind the mic to take advantage of the mic's off-axis rejection characteristics may be helpful. Have had a Sanken CS3e work well to help reject some of that in situations like this.

 

[Chadfish]

Dano the covering of the shotgun slits experiment didn't work. He used another mic, but the right tool for interior dialogue is a hypercardioid. My favorite mid level hyper is the AT4053b.

Zissou, I don't know what else to add about controlling your set. It's about turning off anything that hums, and with a directional mic like a hyper you minimize extraneous sounds. I keep a couple moving blankets from U-Haul handy for reflection suppression. I have found that often things sound more reverberant in my cans than they do when I get the audio up in my monitors at home, but that's good so you can really be aware of what's happening. Kitchens are the worst to shoot in! But as you also learned shotguns are designed for outdoors, and stereo use of shotguns is a useless thing to do outside of ambiance and music. On second thought, I would never use a shotgun for music, just stereo mics. Stereo only makes dialogue more diffuse and harder to hear.

I suppose I can add that if you shot in one of these hellish environments, and weren't able to control the set, you have an option of using iZotope RXII for restoration. It's a great plug-in/stand alone app that goes for 250.00 and is like magic sometimes. You can see every sound in the spectrum, select it, and delete it. I use it all the time. It's a necessity for field recordings.

Check out the demos: http://www.izotope.com/products/audio/rx/

 

[Richard Crowley]

Other options in a hostile ambient:
1) Lav or headset mic (to dramatically increase the direct vs. ambient ratio)
2) Avoid lip-sync dialog altogether. Do it with "B-roll" and voice-overs recorded in a proper acoustic environment.]
3) And, of course, there is always ADR.

But congratulations for properly monitoring the audio during production. At least you could minimize the problems on the spot.

 

[Zissou]

guys, thanks for the suggestions. i spent the first few hours (before the restaurant opened) figuring out the hum issues, the shot angles, practicing with all the gear, monitoring audio and video separately, etc. i did have all the appliances off after the first round, and i used a light boom because i didnt have anyone who could hold a boom properly present. the mic was never more than a foot from the speakers' head; when i got the noise offenders dialed out and used the correct mic, i got great audio. covering the slits helped cut down on some of the reverb; but using the correct mic would have eliminated the problem entirely; it was out of necessity that i did it.

i filmed when the restaurant was open, because i wanted the ad to show a bit of dynamism and liveliness (would you eat at a place that looked empty or boring?) and i followed an order being taken, made, and delivered during the ad so it needed 'filler' people, all the customers knew in advance and were basically there as 'props'. i lived and breathed that place for years, and my folks own and operate it so i could do whatever i needed. The moving blankets idea is a good one, and you guys gave me some great ideas, and that izotope software looks like it could be very useful.

Normally, i have one of my partners who does everything audio related, and he does a great job, that day was his sisters wedding, so he was not only busy but also had all his gear with him, so i was SOL. Thanks a lot guys, and keep up the suggestions!

Ill be looking into a wireless lav system that i can record direct into the XH A1 and a hypercardiod such as the aforementioned AT4053b. I'm spending all of next week working out my own audio gear and training my second cameraman with it; we'll probably pick up a lav system and hypercardioid. On a tight budget, are there any good lav recommendations? I looked into the new Rode lav, which connects to both wired XLR and sennheiser wireless systems, but no solid reviews yet. It does seem more versatile, and the price is only $249.

 

[Noiz2]

In theory covering the slits should convert the shotgun into a (very long) sort of Cardioid/ Hyper. It might also have some unwanted side effects. Sounds like a fun experiment...

If you could overwhelm the fluorescence then you probably could have killed them and that would have helped.

 

[sonidista]

instead of hanging blankets I suggest bringing carpets of all shapes and sizes you have lying around in your house or wherever. They tend to be less in the shot than stuff you put on the walls. Floor reflections are often quite underrated. Sometimes if you can afford it open a window. You'll be surprised how much less reverb you'll get. That is of course not practical in many locations due to unwanted sounds from outside. Having a lot of people standing in the room also makes a room less reverberant than when it's empty, so get those spectators in, as long as they're quiet! HMI lamps, used often on professional sets, can be noisy bastards all too often. You won't have any problems with tungsten lights.