Loud Hum in PA system

[GuyS]

The tribute video I just shot has a loud ground loop type hum to it. The PA system had it but my microphone system picked it up so bad the footage is just about useless.
I'm sure people have run across this before and the question has been asked before. But is there any thing that I can do to salvage the audio?
Are there any filters in 6.5? Any plug-ins etc. that might have reasonable effect?

[antonsvideo]

you can apply the parametric EQ filter and create a notch like this, then drag along the frequency range until the noise goes as much as possible

or use the graphic EQ and drag one slider down at a time and up again until you find the bad frequency

[rob stowell]

As Anton says... or another option that's worked for me was exporting the audio and using the 'noise removal' effect in audacity, which is a free audio programme. You might need to find a quick guide to using this function: you have to select a few seconds of just the noise you want removed, then select the whole track (if it's on the whole thing) and then play with a slider til, if you're lucky, you get a spot where the noise is gone and the audio you need sounds ok. Then export back to a wav file, and substitute that... It certainly doesn't work with everything, but a hum at a relatively fixed frequency it can work very well.

[Ron Evans]

Sony SpectralLayers will take detailed frequencies out rather than a noise match file if you want to spend the money. Works very well. http://www.sonycreativesoftware.com/spectralayerspro

Ron Evans

[Thor]

I feel your pain! I've had to deal with ground loop a/v interference, too.

Some advice to other event videographers: be proactive!

1) Set-up early, test all equipment with sample recordings to detect any issues. You should be able to hear the hum and/or see the horizontal interference bars in your video upon playback.

2) Use ground-loop isolator in-line filters for your wiring. Several manufacturers make isolators for just about every type of a/v connector, and most are inexpensive.

[plasma_video]

Hey Ron, what do you think about Spectral Layers? I've been intrigued by the few examples I've heard, and thinking seriously about it.

I also have tried Izotope RX, and it's godsend for some problems, especially heavily clipped audio. Been thinking about getting that.

Oh dear, I have a strong feeling my back pocket is about to be depleted again . . . .

[GrassValley_BH]

I'm curious too. There are tutorials and more info over at DIVIDE FRAME's site.

[THoff]

In addition to what Jon said, use a good pair of studio headphones to monitor the sound if possible. If you are solely relying on the meters on the LCD of your camera to look for activity in tune with the event you could wind up with an unpleasant surprise at the end of the day.

[dpalomaki]

The humm is likely at line (mains) frequency, with numerous harmonics of the lime frequency as well. A sharp notch filter at line frequency, and possibly first and second harmonic would probably help. The potentially better solution is to use the noise cancelling capability in most decent audio editing programs. I use Audition my self.

[Ron Evans]

I'm curious too. There are tutorials and more info over at DIVIDE FRAME's site.

I got it on a special price sent to me by Sony but still not low cost at $199 it works very well but there is a learning curve though. It is a more refined way of taking a noise print so works well in combination with noise reduction in Sound Forge. Since all my project are in the theatre I have almost no control of the audio most of the time. A/C fans, people coughing etc is the norm. I set up several mics ( depends on location ), recorders and find the best mix. So getting room sound before anyone comes in etc etc is a standard procedure for me. These days it often takes me more time to get the audio to my satisfaction than editing a 2 hour, 4 camera show !!!! A nice HD picture with poor sound doesn't cut it for me anymore. My aim is to get the feel of the sound that a viewer would get from the audience. For the dance shows I get the sound track but have found that it is too dry and people want to hear the audience reaction as they want to re live the experience not listen to the music !!! Same for the theatre really. So task is to remove noises that are not obvious to the audience but very clear when recorded ( fans, people coughing etc )

Ron Evans