Suggestions on cutting background noise?

entilza72 wrote on 11/13/2009, 4:33 AM
Hi gang,

I'm editing a large amount of "problem" material and would love some suggestions.

Basically, the audio for several scenes has a constant drone of a 10Kva generator under it. It's distant, but its still distinct.

I've found 2 frequency bands, one at around 90Hz and the other at around 300Hz. Cutting both of these removed perhaps 60% of the noise (as well as some of the actor's voices, sadly), but there's still this 40% that doesn't seem to sit at any particular frequency.

I could almost live with this "40% background noise", but the noise changes depending on where the boom was pointing, and how much load was on the genny. This really draws attention to the editing.

Using Noise Gate isn't much help, as it only draws attention to how noisy it is whilst the dialogue is running. :-D

Are there any suggestions for cancelling out this noise? I believe that for most shots, I should be able to generate a "room noise" sample that matches each shot. But, is there anything that can be done?



drbam wrote on 11/13/2009, 6:13 AM
This seems like the perfect situation for Noise Reduction 2.0 (included in Sound Forge and may be available separately?). Continuous noises such as drones, AC units and so on are quite easy to fix as long as the frequency range is not primarily the same as the source content you wish to keep/salvage. Risking an oversimplification, in NR2.0 you capture a "noise print" of the material you wish to remove and allow the application to do its work. The learning curve isn't difficult and there are lots of posts on this in the Sound Forge forum - do a search.

There are many noise reduction/restoration applications available - some are quite expensive but you may be able to find something for free if you check around. Personally I don't see how anyone could use Vegas without an editor like Sound Forge and most editors include some type of noise reduction feature. Even Audacity (a freebie) includes a basic, albeit primitive, noise reduction plugin. Again, the situation you describe is not a difficult fix for these programs.
Mike M. wrote on 11/13/2009, 11:31 PM
Couple of suggestions:

1. There are a lot of VST plugins for noise reduction, some free and some not that you might try.

2. If you can isolate some of the noise by itself, copy it, put it on another track and reverse the phase........the idea being that the two would phase cancel each other like a comb filter. This way you can also control the gain...etc of the effect.

Just an idea.

The problem as you've and others have already noted, is if the "wanted" audio is close in frequencies to the "unwanted" audio, you wind up losing some of the good audio.

entilza72 wrote on 1/22/2010, 10:55 PM
Hi team,

Just for the record, I ended up doing the following to achieve a good result:

1. Cleaned the audio with Noise Reduction 2.0. This unfortunately ate into some of the vocal dynamic range

2. Filtered out some more frequencies in Vegas itself. Also ate into vocal frequencies.

3. Rode the vocal levels up and down a lot harder than I usually would (not using a compressor though - just envelopes to ensure BG noise wasn't unnecessarily being included

4. Added an overall compressor after the envelopes, but subtly.

5. Carefully cross faded edits between shots with different BG generator hum levels - I'd often crossfade them for over 1 second, 2 seconds if there was room.

6. Added a heavy room tone - an airconditioner hum.

After all of those, the genny can still be heard, but you'd never pick it. It just sounds like a noisy room.

Mission accomplished!