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Old November 29th, 2005, 10:04 AM   #1
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Bad electronic hum! Help!

I need help. I shot about 40% of my first short film on AC power. I didn't realize that this was going to cause a ground loop and a nasty electronic hum over all my audio. I did tests with my Rode VideoMic and the GS400's gain controls but I guess all my testing was done under battery. During the shoot I was near AC and figured I'd use it. Bad idea.

I've tried to clean up the sound with Audicity and SoundSoap but I'm not having any luck. Audicity did get rid of the hum but it also removes some of the dialog. Makes my audio sound like a 60kps MP3 or something.

SoundSoap's 60Hz hum removale did nothing at all. I can't seem to get the learn noise to work well either. I don't know what I'm doing wrong because I see tons of great reviews on SoundSoap.

Can anyone help me out? Will Final Cut Express's noise reduction be able to remove the hum yet keep the human voices? Or do I need FCP or a high-end audio app?
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Old November 29th, 2005, 11:23 AM   #2
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Brian,

I think you've probably reached the limits of what a filter is going to do for you. It might be time to start looking at the time/cost of doing ADR as opposed to trying to somehow filter what you have.
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Old November 29th, 2005, 01:55 PM   #3
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Have you looked at a spectrum analyser to make certain that it is actually a 60hz problem? There could be other potential problem frequencies, as well as DC offset problems or some other broad-band noise issues at work here.
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Old November 29th, 2005, 02:04 PM   #4
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I am all for doing ADR. I think it is a waste of time to try to get useable audio on the set. All that it does is cause delays when a bunch of crew are sitting around. ADR is almost always the best way to go. Reverb and background noise can always be added later after doing a dry ADR. Background noise and room reverb can never really be removed. Everyone doing movies needs to learn ADR and now is your opportunity. It may be inconvenient for the actors to come back in, but it only takes a little while and it is in a much easier setting than on the set.
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Old November 29th, 2005, 02:38 PM   #5
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But how do you get the same performance from the actor? Do you just have them watch & listen back to the original and do their best to match? Seems like ADR should be a last resort.

I have beautiful audio when I used battery power. When I went with AC I have the terrible hum. I've got to think that this can be removed with software. (I hope).
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Old November 29th, 2005, 02:42 PM   #6
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Brian,
The hum can't be removed without altering the dialogue in some fashion. That's a fact.

You don't get 'the same' performance from your actors... you can get better ones. Charlton Heston in his autobiography, talks about how much he enjoyed ADR as a chance to polish his performance.

Yes, you put the actors in a sound booth with headphones on. They watch the screen are re-record their lines. It's not that hard. How many times have YOU delivered the lines from a famous scene verbatim in a movie as it's playing back?
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Old November 29th, 2005, 03:14 PM   #7
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I might add that some of the better audio programs make ADR pretty straighforward. Steinberg's Nuendo, for example, has a loop record mode where you mark the loop in and out points and within it the punch in and punch out record points. When you play it it shows picture and plays back sound repeatedly over the loop. When it hits the punch in point it switches into record automatically yet if your sound card is full duplex, playback of the original through the talent's headphones can continue even while it's recording on the new track. Each time through the loop causes a new take to be laid over the top of the previous one, preserving all of them so you can select the best take or even slice them up and pick the best portions of each take to combine into the final track after the recording session.
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