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Fixing audio buzz?

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April
Fixing audio buzz?
on Oct 11, 2005 at 4:13:16 pm

Someone shot interview footage with a camera plugged into an outlet, as opposed to running on a battery, and the result is a fluctuating buzz throught the 2 hour interview, sometimes really high, sometimes not that noticeable.

Is this fixable at all, maybe in FCP? Not sure what audio filters to use?

Thanks! I'm desperate for advice!
April


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Matte
Re: Fixing audio buzz?
on Oct 11, 2005 at 4:31:50 pm

Continuous hum is one of the kinds of noise that can be addressed.

This is the kind of "continuous" noise that a program like Bias "SoundSoap" can help remove.

http://www.kenstone.net/fcp_homepage/review_soundsoap.html

Bias has recently released "SoundSoap 2"

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

SoundSoap was retailing for about $50 (up to $80 just before the new "2" release).
SoundSoap 2 is priced at about $100.


You export the audio, process it through SoundSoap 2 and re-import it to FCP.

OTOH, If you have FCP 5 Studio, Soundtrack Pro has "sampling" noise-reducer that does the same operation as SoundSoap.

Lastly, if you don't have either program, you can try using the standard FCP "Hum Remover" filter, but it usually ends up eliminating most of the WANTED audio as well.


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Ty Ford
Re: Fixing audio buzz?
on Oct 13, 2005 at 2:09:46 am

and next time, listen, listen and then, um, listen.

Ty Ford



Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. Find out more at http://www.tyford.com


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April
Re: Fixing audio buzz?
on Oct 13, 2005 at 4:15:43 am

Thanks helpful post Ty.

I wasn't the one shooting.


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Redflag
Re: Fixing audio buzz?
on Oct 13, 2005 at 8:52:40 am

Why can being powered from the mains cause hum like this? sorry off the point but I,ve never heard of this.

Thanks



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Matte
Re: Fixing audio buzz?
on Oct 13, 2005 at 11:41:12 am

[Redflag] "Why can being powered from the mains cause hum like this? sorry off the point but I,ve never heard of this."


Well, under "normal" conditions, it should not cause this.
Most indoor and many outdoor shoots have the camcorder connected to the AC supply and there is no reason that this should be the direct CAUSE of a hum.

But...

There is a condition called a "ground-loop" ("earth-loop") that manifests when one component of a an electrical combo is grounded (earthed) to one potential of electricity-supply and another component in the same combo is grounded to another "level" of power potential.

In short, this will cause a "rogue" current that runs through the ground-earth-shield of the cables connecting the components together.
This current can be from AC lines or RF (radio frequency) induced by proximity to a generating source. That's why there can be hum present under battery-operated conditions as well.

Once flowing, the current's frequency (commonly a tone that we call a "hum") can be amplified by the audio circuits and recorded to tape.

Rearranging how the mic cables are laid-out, adding in-line "hum-buckers" (transformers that isolate the shield of one end of a cable from the other), or "Ground (earth)-lifts" (they simply disconnect one end of the cable's shield) the "loop" (current flow) can be eliminated and stop the hum.

Another source of hum can come from using "unbalanced" mic cables (one inner conductor surrounded by a shield). With unbalanced, the shield is fully connected to the audio section and is involved in carrying the actual audio signal.
If there's any extraneous hum-generated through (or NEAR) the cable, the shield is not very effective in isolating it.

By using "balanced" mic cables (2 inner conductors surrounded by a shield). The audio signal is only carried by the 2 conductors and the shield has much more ability to reduce outside interference.
In "phantom-powered" microphones, the shield also is used as the "neutral" of the current to power the mic's built-in amplifier. The "hot" power for the phantom is carefully sent EQUALLY down BOTH of the inner 2 conductors. If you are not using a phantom-powered mic, its best to turn OFF the phantom supply sent from the mixer or camcorder.

Still more hum can come from using an AC power supply that is improperly built (or has been damaged) so that it has inadequate AC-rectification. That means that the natural hum of the AC power is not "smoothed" enough inside the supply and the remaining fluctuation makes its way into the camcorder and its' audio section.


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Redflag
Re: Fixing audio buzz?
on Oct 13, 2005 at 12:24:08 pm

Thanks for the answer,a bit high tech for me to be honest,but I think I get the picture.

Thanks



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Matte
Re: Fixing audio buzz?
on Oct 13, 2005 at 1:19:11 pm

[Redflag] "a bit high tech for me to be honest,but I think I get the picture."


Sorry if it was a bit "involved", but I've found that if I just give a "the buzz is from the cables" kind of answer, many times a forum "troll" will respond with a "you don't know enough to answer this" kind of response.



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Ty Ford
Re: Fixing audio buzz?
on Oct 13, 2005 at 12:50:45 pm

Hi April,

Interesting that you presume the shooter does the listening. Over here where I am, the shooter shoots and usually would rather not have to concentrate on both picture and sound. Shooter and sound person work together as a team. There's more than enough detail to keep each person busy. On some shoots, the director has his/her own feed as well.

Of the many audio problem posts I answer, the most frequent problem is that no one was listening continually. People don't shoot without looking through the viewfinder. Typically one blows a gig because of bad audio and learns from it to never neglect the audio in the future. Hopefully, this will be your/their reality check.

BTW, the second most often asked question is what one mic can one buy to do everything. The answer is you can't expecct one mic to do everything.

The third most often asked question is which shotgun to buy for interior shots. The answer is -- trick questions!!-- NO shotgun should be used inside unless you are inside on a shooting stage. A hypercardioid is a much better choice.

Regards,

Ty Ford

Ty Ford's "Audio Bootcamp Field Guide" was written for video people who want better audio. Find out more at http://www.tyford.com


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April
Re: Fixing audio buzz?
on Oct 13, 2005 at 2:06:47 pm

Ty -

I wasn't involved in production at all. In fact, didn't even know this person when she shot it. I was brought in to edit months later.

Regardless, you're quick to jump to conclusions and tone is pretty off-putting -- disappointing, usually very impressed with the help I get on here.


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Ty Ford
Re: Fixing audio buzz?
on Oct 13, 2005 at 2:23:51 pm

Pretty easy to jump to the conclusion that no one was listening.

As to the removing, the tools available today to reduce buzz, more often than not, make the audio unusable in the end.

I can understand why you're disappointed. There's no magic fix. Killing the messenger doesn't usually make things any better, though. :)

Ty Ford





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Jon Smyth
Re: Fixing audio buzz?
on Feb 18, 2010 at 7:53:51 am

Where exactly is "over here" where you are, Ty? England? If you were in Canada you would have said, 'up here,' eh? Clearly you have a command of the English language, so I'm just curious where "over here" is?


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