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-   -   AC noise reduction? (https://www.dvinfo.net/forum/all-things-audio/89540-ac-noise-reduction.html)

Alfred Okocha March 21st, 2007 07:17 PM

AC noise reduction?

I shot a dialouge on the street the other day in the vincinity of an AC (exhaust?)

Although the audio is OK I'd like to improve it as much as possible. Does soundforge or any other program (My editor is using Avid express) have a tool that could take out the noise (well, reduce it at least) and leave the dialouge intact?

My editor doesn't have any experience with this so any tip would be appreciated.

(We can't re-do it.)

THanks a lot!

Seth Bloombaum March 21st, 2007 08:44 PM

Sony Noise Reduction 2.0 is a great product I've used, it is available as a direct-x plugin that would work with sound forge, vegas, or another editor that uses direct-x. http://www.sonymediasoftware.com.

Audacity is a freeware/open source sound editor that comes with a basic noise reduction tool - the price is right, it's worth a try. http://audacity.sourceforge.net

I've not used it, but others have sung the praises of soundsoap. http://www.bias-inc.com/products/soundsoap/

Jon Fairhurst March 21st, 2007 09:34 PM

You can also try Goldwave. It's $50 and offers a free trial. I generally use it by copying a segment with noise only, then apply it at about 70%. If you go with 100% it removes more noise, but affects the dialog a bit too much.

Alfred Okocha March 22nd, 2007 04:18 AM

Thank you!

Michael Liebergot March 22nd, 2007 10:17 AM

You also may want to try using the "Graphic EQ" and play with the low end frequecies to eliminate the low ac air rumble.

Jon Fairhurst March 22nd, 2007 10:47 AM


Originally Posted by Michael Liebergot (Post 646148)
You also may want to try using the "Graphic EQ" and play with the low end frequecies to eliminate the low ac air rumble.

If the frequencies are below, say, 200 Hz, this can really help. Anything you can do to reduce noise that doesn't harm the dialog is worthwhile. Then, when you apply the NR, you can dial it way down and step on your audio much more lightly.

In a recent video of ours an unbalanced cable must have been right next to the power cord. The hum was literally as loud as the signal. And the actors had to go back to their colleges after winter break. We couldn't reshoot. What's worse is that almost everything we do has music under it - except this scene!

Fortunately, the 60Hz hum and buzz (lots of high harmonics) were cyclic. We were able to sample the hum, loop it, invert it and mix it in. The cancellation was almost perfect - except where the auto-gain/limiter kicked in. There we had to modulate the cancellation signal to the best of our abilities.

It still wasn't perfect, so then we applied some *very* light NR. The recording wasn't as good as a clean one would have been, but it was usable for our purposes.

BTW, just applying NR without these tricks sounded like crapola. The buzz was just too wideband.

Anyway, you can hear the results here:
http://colonelcrush.com/movie/index/00030401 The exposed section starts about 1:10. You can hear some moments when we didn't match up the levels well during auto-gain.

It ain't perfect, but we saved Colonel Crush's butt!

Bill Busby March 22nd, 2007 06:05 PM

I use Adobe Audition for situations like this with great results by creating a noise profile, roughly 1/2 a second without dialog is all you need of the surrounding noise you want to reduce/eliminate.


Mark OConnell March 22nd, 2007 07:07 PM

If you have any musician friends with Digital Performer the included Masterworks EQ will let you actually see where the noise is, making it very easy to dial out (usually...).

Michael Nistler March 23rd, 2007 12:09 AM

AC noise
Hi Alfred,

If you're lucky enough that your AC noise is defined in a very narrow frequency spectrum, the above mentioned software tools should do a good job of letting you isolate the frequency and removing it (such as a hum). But if the AC noise won't be so well defined (involving displaced air mixing with fan vibrations, etc), they you may need to use parametric equalization. Using a high-pass filter will probably be your last resort.

Good luck, Michael

Brett Sherman March 23rd, 2007 07:50 AM

Voxengo's Redunoise (VST PC only) is the best value in broadband noise reduction. It's a little difficult to figure out at first but quite powerful with a lot of tweaking available. I've used Sony's and Waves X-Noise, and SoundSoap Pro. It blows all of those out of the water. And it's only $100.

I think Waves considerably improved their noise reduction with Z-Noise, but I've never used it. Of course it's like $1000.

Alfred Okocha March 24th, 2007 05:50 AM

Thanks for all your suggestions. I just realised that AC (airconditioner) could be mixed up with AC-power..
My bad! I was talking about an airconditioner(exhaust) although I think all the suggestions are valid anyway.

I've tried the Audacity solution and I found the voices get a bit ehh.. "tinny" even when I use the absolut less option. (Maybe mixing down the original track and using the processed one maybe makes for a good result? Anyway, I'll try some of your other suggestions too until I find something!

Jon Fairhurst March 24th, 2007 11:22 AM

Try http://GoldWave.com The demo version is free. Sample the noise by copying it into the clipboard, then apply. The problem with fan noise is that it's wideband. Try removing as little noise as you can get away with.

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