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Old January 27th, 2005, 10:58 AM   #1
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removing AC hum

I have some audio that I am working with that has a nasty Air Conditioner hum underneath it. It is very low pitched and is ruining the audio and my usual tricks aren't helping much. I was wondering what tricks you guys use for situations like this?
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Old January 27th, 2005, 12:57 PM   #2
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Have you tried using SoundSoap? It does a pretty good job at getting some of this junk out. You just need to filter out that frequency. You can try it in FCP but Bias Peak would be better (and it came with FCP). I would look at SoundSoap or SoundSoap Pro. It can be found here.

http://www.bias-inc.com/products/soundsoap/

I have SoundSoap and it's pretty easy to use and works quite well. Basically you can find a section of the audio where only the hum is present and sample it. Then SoundSoap will remove that sound from the entire clip. Its really fast too.

EDIT: oops sorry, I copied the link incorrectly. It has been fixed now.
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Old January 27th, 2005, 04:13 PM   #3
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Rhett,

I tried that link and got a 'forbidden access' message. However, I was going to add that I use a freeware open source program called Audacity that does the same thing. Although I am using it on WinXP, there are versions available for Linux and Mac OS.

Audacity is the only software I have found that lets you zoom all the way to individual sample points and move them. Great for removing stubborn clicks and pops that automated routines don't get rid of. It also supports VST plug-ins but not with their graphicical interface like other hosts do.

I am afraid if Kevin's ac noise is 'noise' rather than 'hum', he's in for a tough fight. I had some wedding audio ruined last summer by the sound of the AC units in the church and I couldn't remove it with any of the tricks I had. It simply covers too broad a frequency range and I couldn't notch it, phase cancel it, or anything. I was actually editing that video on FCP with a borrowed dual G4, but tried processing the audio with my arsenal of pc sound editors.

Good luck Kevin,

=gb=
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Old January 27th, 2005, 09:26 PM   #4
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Thanks Greg, I fixed the link. I have seen Audacity before. It is similar to the "Peak" program I was referring to that comes with FCP.
SoundSoap is pretty amazing from a simplicity standpoint and it runs inside FCP, Peak, Deck and as a stand alone application. They have some sample audio files on their web site if you want to hear some. It won't save the world, and obviously filtering any freq is going to effect the audio, but it does do some pretty amazing stuff in a short sweet interface.
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Old January 28th, 2005, 07:51 AM   #5
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Thanx guys. Unfortunately I am on a really tight budget so buying more software is out of the question. i am going to give peak a try. I was wondering exactly what frequencies I should try to eliminate, what filters to play with and so forth... Also just to give you some more info the "hum" is a very low pitched sound... a lot of bass. And to make things worse the video is a bunch of interviews with kids so the audio is really weak and has to be cranked in order to understand what some are saying. The ones who spoke up are ok b/c I don't have to crank the gain so I can just use the parametric eq in FCP, but the ones that I had to crank you can hear a distinct difference. So any specific techniques you use to eliminate such noise would be greatly appreciated. Thanx!
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Old January 28th, 2005, 10:21 AM   #6
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Have you tried capturing audio of the background noise and inverting it and putting it down, cancelling out the hum? Make sure there's no dialogue...

There's more steps to this, but I've never done it, just a friend. I'll email him for the steps.

heath
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Old January 28th, 2005, 11:45 AM   #7
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I am defiinitely interested! Thanx
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Old January 28th, 2005, 04:54 PM   #8
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1- Use a parametric EQ to cutoff all but the voice frequencies. The voice frequences is roughly 100hz - 6000hz. Go overboard with the EQ until you hear the voice get messed up, then back off.

Unfortunately, the next thing to do requires a noise reduction plug-in of some sort. Soundsoap is a cheap way to pickup such software.

see http://www.digitalpostproduction.com...e.jsp?id=25455

You can play around with using a noise gate instead, but a NR plug-in is so much better. With a noise gate, the basic idea is to go overboard with it then back off. Listen for the beginning and ends of words to get them to sound right. Hiss/hum/noise while someone is speaking can't really be dealt with.

If there are noises other than white noise, then there may be other specific tricks you can use to remove that noise. White noise is the hardest kind of noise to remove.

2- Noise reduction can be better though of as noise hiding/masking. If the problem is too great then the noise cannot really be dealt with.
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