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Removing audio buzz?

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Removing audio buzz?
on May 30, 2005 at 3:12:04 am

Transferring a bad audio VHS into FCP, the resulting footage is very low and mono. After raising the volume as high as it'll go and making it stereo, everything sounds good save for the high buzzing/hum sound. I see there's a "remove hum' audio filter, but doesn't seem to do anything when applied. Any ideas for removing audio buzz due to having to raise the volume so high?


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Re: Removing audio buzz?
on May 30, 2005 at 10:57:54 am

In FCP 4 and earlier, you will likely need a 3rd party filter to more completely perform hum and other constant noise removal.

SoundSoap from Bias is very popular and costs under $100.

If you don't want to buy more software, you can TRY the following:

The 3 Band EQ and turn down the 60Hz, 120Hz, and 240Hz frequencies (but this is what the "Hum Remover" filter also does.)

The Parametric EQ and find the "worst" noise frequencies and reduce them.

The Expander/Noise Gate audio filter and adjust it to make the louder sections (audio) louder and the softer sections (hum) softer... but this will also allow the noise to "fluctuate" in level along with the "good" audio.

The "buzz" you hear is made up of some noise in the higher frequency ranges as well as the lower-frequency hum components. If you try to reduce all of the buzz, you're likely going to reduce the actual program audio too much.

IMO, an "intelligent" filter like SoundSoap will be much more effective in reducing constant noise without destroying the "good and wanted" audio along with the hum.
(I read that FCP 5 now includes this kind of noise filter.)

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Re: Removing audio buzz?
on May 30, 2005 at 2:41:15 pm

I'll build on Matte's comments by suggesting that you "tune" your filter by adjusting the frequency control so it removes as much of the noise as possible. Sometimes the noise isn't exactly 60Hz.

Using the Hum Remove filter, adjust the Gain to a minus number to start removing some of the noise. Start with -15. Don't worry how this affects the overall sound of your track just now. You'll tweak later. Now slide the Freq control to get the most noise removal. Adjust the Gain control up or down to get the best sounding result. Don't spend too much time on this right now.

The other control parameter to adjust is Q. This tells the filter how wide a range of frequencies around the center frequency (the one you just found) to remove. The wider the Q, the more of the "good" signal you'll remove. Adjust the Q to be the narrowest it can be and still remove the noise.

At the bottom of the filter controls you'll see a bunch of Harmonic check boxes. Harmonics are multiples of an original or fundamental frequency. Most hums aren't just the fundamental. They are comprised of a number of harmonics added to the fundamental as well. The frequency you first chose by adjusting the Freq control is the fundamental. You want to choose as many Harmonic check boxes as make a difference in the noise removal. Choose at least the 2nd and 3rd harmonic.

After you've done this, tweak the Gain and Q to get the final result. Understand that it rare you will totally eliminate the noise and leave the original track unaffected. There's a lot of trial and error in noise removal. There are third party plugins like Soundsoap that can do a better job than the Hum Remove filter, but they have their own issues, too.

Hope this helps.


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Re: Removing audio buzz?
on May 30, 2005 at 3:58:49 pm

[JRF] "Sometimes the noise isn't exactly 60Hz."

You are exactly right, if this was an "unknown" hum (say, from an on-location noise-source other than AC-line noise).

But if this is an NTSC analog tape that has "sync buzz"(and other video-related hum) related to a too-low level of audio, it is 99.44% sure that it IS 60 Hz.
That's why I didn't explain "finding" the proper frequency.

The heads are rotating (and "switching") locked to (basically) 60Hz in the USA.
The "sync buzz" in a TV signal is (virtually) 60 Hz and harmonics thereof.

When trying to knock-down hum/buzz on a poorly-modulated analog video tape, 60 Hz (and the harmonics of 120 Hz and 240 Hz) are the center frequencies to adjust.

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