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remove a generator rumble

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Nat Rovit
remove a generator rumble
on Jan 11, 2009 at 2:25:25 am

Hey everybody, I'm currently editing a project in Avid Media Composer and I could use some help. One sequence has a very loud generator rumble or buzz running through it and I was hoping that maybe somebody would know a way to cut the frequency at least so the dialogue isn't as overpowered (the dialogue is pretty well recorded). I would accept any solution from Final Cut Pro, Avid, Audacity, or even Garageband. Please try to be as specific as possible, I'm not very knowledgable when it comes to audio.
Thanks.


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Ty Ford
Re: remove a generator rumble
on Jan 11, 2009 at 2:22:20 pm

Hello Nat and welcome to the Cow Audio Forum.

Generators (internal combustion machines) usually make more than one frequency of noise while running. As a result, reducing just one frequency doesn't work very well. Soundtrack Pro has a noise reduction plugin. It should be in your FCP suite.

Rx from Izotope works as a stand alone or as a plugin. I've had pretty good results with that.

Regards,

Ty Ford






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Brian Reynolds
Re: remove a generator rumble
on Jan 12, 2009 at 10:07:58 pm

I have previously used a different technique.....
Do a copy of the faulty track as a seperate track, and adjust the equalizer of the copied track to boost or make the fault as bad as you can.
Then reverse phase this boosted track and add it to the original.
I use Adobie Audition... in the effects section it is called "invert"
If they are in exact align the fault then cancels out, leaving a clean signal for editing into the program.
I have used this on many things from aeroplane, helicopter, race car and even radar noise with good results.


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Ty Ford
Re: remove a generator rumble
on Jan 12, 2009 at 11:20:43 pm

Hello Brian,

Yes your approach will create cancellation. If they are in exact alignment and you flop the polarity, the voice (or anything else on the track) will also cancel, no?

How do you keep the voice from canceling?

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Brian Reynolds
Re: remove a generator rumble
on Jan 13, 2009 at 1:13:57 am

Yes Ty.. this is why you boost the bad sound and not what you want to keep. The offending problem may be reduced sometimes 20db + this way, depends if it is in the voice frequencies or not.

This technique also works with studio consoles for getting rid of studio / room rumble.
On a parametric EQ boost the gain to +15db or max then sweep the FREQ & Q point to create the maxium problem.... then reduce the the EQ gain for your needs.
I have found this way to be far quicker and with far better results than cutting first and then trying to find the FREQ & Q point.



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Ty Ford
Re: remove a generator rumble
on Jan 13, 2009 at 4:07:43 am

Brian,

I get it. Worth a try, but generators usually spew a pretty wide spectrum of noise. 40 Hz to, I don't know, up to 1 kHz or more, machinery depending. Anything over 100Hz can get into the voice frequencies.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Nat Rovit
Re: remove a generator rumble
on Jan 13, 2009 at 10:56:34 pm

Ty, Soundtrack worked pretty well, I was able to cancel out a lot of the generator noise with the High Pass Filter and the Denoiser, however, the dialogue is a little too quiet now, any other suggestions, what do you think of Brian's invertion option?
Nat



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Ty Ford
Re: remove a generator rumble
on Jan 14, 2009 at 4:16:04 am

Hello Nat,

What happens when you normalize your denoised track in Soundtrac? That'll tell you how well your noise reduction efforts were. :) I've been down that road. Apply enough noise reduction and everything gets quiet. When you gain it up, the noise reduction isn't as much as you thought.

You may have gotten it right. I'm just sharing my past experiences.

Brian's thinking process is very ingenious and we're lucky to have him on this board. As I mentioned, the wider the spectrum of the noise and the more it occupies the same frequencies as the voice frequencies, the less effective I expect this approach to be.

Roland used to make a simple outboard denoiser hardware box that worked pretty darn well. The new iZotope hardware and software work pretty well, but I'm unsure how much better they may be than the software tools you already have.

Last thing to try would be to find someone with a CEDAR system and have them do a pass though...oh, right, then there's the reshoot filter.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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Mike Lattimore
Re: remove a generator rumble
on Jan 30, 2009 at 8:02:44 pm

The solution is to fix it as well as you can with the tools and expertise available. Then when the director or others complain about it, tell them that the production crew screwed up by NOT parking the generator a decent distance away and someone is going to have to cough up the money and time for some preventable ADR.

I've had this happen before on a campfire scene where everyone was in such a rush that they didn't give a flying-bojangle (Flanders style word substitution).

This is a classic example of 'let's just fix it in post.' I wonder what the cost is for a few extra yards power cable versus a full blown ADR session with multiple actors?



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Jeff Friah
Re: remove a generator rumble
on Feb 3, 2009 at 10:13:32 pm

"Hear Hear" Mike!!!

I was actually on set once as a guest and was watching a scene with a similar-and very fixable-noise source that was actually mentioned by an actor. And I actually heard "the sound guys will fix that...don't worry." I wish I'd had the boom in my hands for that quote to play back during the mix.

Recent favourite: a scene shooting exterior on gravel/small rocks, a typical 'walk n talk'. The shot was all from the waist up. Was a carpet or anything put down? Nope. What did I hear in the final mix? "Can you turn down the foley feet?" Nope. There were none.

I digress---- YES---Izotope Rx and CEDAR are your friends!!! And if you can FIND friends who have them in their arsenal, pull favours. I believe Izotope Rx has a demo as well?

But yes, the danger--of course--is fixing it with tools ("lessening it" with tools---sorry!!!) and then people think you can do it again, easily. Not if you've called in favours.

Good luck!



"Sounds good!....I think?"


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