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Old February 26th, 2008, 07:40 PM   #1
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Shooting indoors around HVAC

A few days ago I did my first shoot where I was responsible for audio, because we couldn't get anyone else (I am mostly an editor and camera guy but looking to expand my skill set). Although this is just hobby stuff, I really wanted to get it right, so I read everything I could about location audio. I went out and bought a Rode NTG-2 and a boom pole to use with my Canon XH-A1. A friend of mine with no audio experience was our boom holder. He seemed to do a good job as far as I could tell... he was able to keep the mic within about 2 feet of the actor's mouth while keeping it just barely out of the frame. I used manual audio levels with peaks at -12dB, and was monitoring everything with headphones.

Unfortunately, one thing that I did not foresee was that our chosen venue (a bar, which the owner was graciously letting us use for free) had a pretty noisy heating system which could not be turned completely off because it was shared by other establishments in the same building.

Since we had no choice but to go ahead with the heating system running, we did the best we could to have the actors speak extra loud and get the mic as close as possible to them. In my headphones the noise didn't sound so bad, and I thought it would be low enough and the voices would be strong enough that I could get around it with an expander/noise gate filter or a little noise filtering.

Unfortunately, when I got home and captured the footage, the air whooshing noise is much worse than it seemed in the headphones, and I have played around with some audio filters but can't make a significant improvement in the noise without adversely affecting the voices. It isn't unusable (you can clearly hear what they are saying), but it certainly doesn't sound professional either. Looking at the meters in FCP, the noise is at around -35dB and the voices range from -30dB to -12dB. I tried a noise gate and expander filter with various settings around -35dB to -45dB but I found the results too "choppy," and the noise filtering in STP sounded too artificial and electronic and also made the voices less clear.

Now, I realize that my only option will be the shootitagain filter, but, assuming I do shoot it again in the same venue, what can I do on set to minimize the noise? Would using a lav mic or a different kind of boom mic be better? Keep in mind we are on a very limited budget and since we are in Japan we can't just order things off of B&H or rent gear, we are stuck with what is available locally.

Any ideas? Thanks!
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Old February 26th, 2008, 08:11 PM   #2
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Man, bars can be amazingly noisy. There is no solution here that I can think of. The problem with HVAC noise is that you can't filter it, because it shares some frequencies with the human voice, and it's essentially everywhere so a more directional mic might not be much help. In an office setting, where the carpet and cubicles deaden a lot of sound, a cardiod can help with noise from the ceiling, since they have so much rear rejection, but bars are pretty reflective environments usually. Best bet are lavs on everybody I think. Have you tried adding ambient sound, like people talking and laughing (typical bar noises) to the mix to see if you can cover up a lot of the noise? That might help.

Last edited by Marco Leavitt; February 27th, 2008 at 12:01 PM.
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Old February 27th, 2008, 03:20 AM   #3
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adobe audition is about to become your friend. if you don't have it, DL the trial

basically go into spectral view, hilight some pure noise, sample it, then perform noise reduction on spectral selections. don't try to knock it all out in one pass, but try several lighter passes, them compare to the original. at some point you'll remove too much,so plan on saving out when you can.

I'd also say try some hard EQ to remove 80 to maybe 120/180ish hz with a low cut / high pass filter. that will help.

soundtrack can do some of this too, but the real tool is audition.
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Old February 27th, 2008, 04:26 AM   #4
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Are these machinery noises or air movement noises?

Not going to help with this, of course, but air movement noises from HVAC as well as from moving the mic itself to follow action are why wind shielding is required indoors as well as outdoors.. Just FYI.
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Old February 27th, 2008, 08:03 AM   #5
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To add on to what Steve Oakley has already said.

Here is a tutorial on how to remove unwanted noise using Adobe Audition. Using it I was able to remove A/C noise from my last interview taping where I could not control it.

http://maltaannon.com/

Scroll down the page and look for "Hiss and Rumble"

Hope it helps.
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Old February 27th, 2008, 12:37 PM   #6
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Three options:
* Noise Reduction
* The shoot it again filter
* ADR

Good luck with the noise reduction approach...
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Old February 27th, 2008, 12:52 PM   #7
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Quote:
Originally Posted by Marco Leavitt View Post
The problem with HVAC noise is that you can't filter it, because it shares some frequencies with the human voice
I have had reasonable success reducing (not eliminating, but reducing) HVAC noise with Soundtrack Pro's noise reduction filter.

- Martin
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Old February 27th, 2008, 01:17 PM   #8
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One new comer to this area is Izotope's RX. I used it recently when we shot an interview in a car scene and had to kill as much of the road noise and car engine noise as possible. It worked fairly well. I'm really hoping that they come out with a plug-in version soon. Right now you have to use it as a stand-alone product and it kills the BWAV header, so timecode is no longer available if you use that. Otherwise it seemed to do a better job than Soundsoap pro on my project.

Wayne
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Old February 27th, 2008, 01:39 PM   #9
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Has anyone had any luck removing this kind of noise using the phase reversal trick? I.e., second mic near the noise source with the phase reversal switch engaged?
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Old February 27th, 2008, 03:14 PM   #10
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Wouldn't you have to record the HVAC from the same position as the subject for them to be in phase?
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Old February 27th, 2008, 04:49 PM   #11
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Quote:
Originally Posted by Jason Livingston View Post
... what can I do on set to minimize the noise? Would using a lav mic or a different kind of boom mic be better?...
You want to do everything possible to isolate the sound from the room and shape the interior room acoustics to absorb excessive noise.

If the noise is coming through a vent....you need to safely block the vent with something that has mass (gypsum drywall) gaff taped over the source. Don't forget to remove it when your done.

To shape the interior room acoustics, you can use GOBOS, sound blankets, carpet, vertical baffles in the ceiling, glue acoustic foam on the under side of tables,...couches, etc...
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