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Old February 22nd, 2009, 01:08 PM   #1
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Removing Audio Hum

I'm using Vegas 8.0c. I've recorded some SD video, with a consistent background hum. Could have been gain level. What built in noise removal in Vegas might I try? Other options?

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Old February 22nd, 2009, 03:24 PM   #2
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I'm using Vegas 8.0c. I've recorded some SD video, with a consistent background hum. Could have been gain level. What built in noise removal in Vegas might I try? Other options?
Jeff
A NoiseReduction package would help, though often, they are heavy handed and produce watery artifacts on their own.

If you can isolate the frequencies of your hum, try the parametric equalizer. The easiest is to export the audio and use a spectrum analyzer with a lot of bins (65000+). Find a section of room noise, or even just some silence in your conversation. Then, dial in the settings with a very high Q and at least -20dB of reduction. Another tedious and less accurate way is to use a parametric equalizer to find the hum. Set it's Q to 2 (low) which provides a wide response. Set the gain to at least +20 dB. Then, while monitoring,sweep the frequency around until you hear the hum get loud. Hone in on the frequency by progressively narrowing the Q . Usually, there will be more than one hum.

Auto Gain control is bad in that it typically distorts the start of every loud sound after a period of amplified room hum. If you really want, add it in Post.
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Old February 23rd, 2009, 09:30 AM   #3
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I was hoping for something much simpler. In Camtasia for example, you choose a few seconds of the isolated noise, it analyzes it, and removes it from the entire timeline. So there are no noise reduction add-ins in Vegas that could do similar?
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Old February 23rd, 2009, 09:42 AM   #4
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I was hoping for something much simpler. In Camtasia for example, you choose a few seconds of the isolated noise, it analyzes it, and removes it from the entire timeline. So there are no noise reduction add-ins in Vegas that could do similar?
Yes there are ADDINS. But you specifically said "Built it".

The Sony Noise Reduction plugin does exactly what you said. However, it's a separate product. I believe it may come included with the current versions of Sound Forge, though.

There are other addins that will do this. Do a search for izotope to see another option.
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Old February 23rd, 2009, 09:57 AM   #5
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Jeff, grab Audacity as it has a Noise Removal tool built into it.
It's not up to the quality of Sound Forge or Izotope but it is free.
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Old February 23rd, 2009, 01:52 PM   #6
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I was hoping for something much simpler. In Camtasia for example, you choose a few seconds of the isolated noise, it analyzes it, and removes it from the entire timeline. So there are no noise reduction add-ins in Vegas that could do similar?
I see the Sony noise reduction plug-in in the Audio plug-in list. I don't know if this is a standard feature since I've been a long-time Vegas user and have taken the incremental upgrade path. It works just as you describe, though the twist is that after you check the "Capture Noise Profile" checkbox, you have to play the audio on the timeline.

Honestsly, I don't like the noise reduction for simple hums. The main problem is that a hum attenuation of -20 dB isn't enough to completely remove major hums and the coloration of the rest of the sound is quite audible. Yes, -20dB is an appreciable reduction, but I think that is just a parameter and not the actual reduction.

Even though I have the noise reduction available, I much prefer the EQ method I described above. I removed a nice 120Hz hum from a recording last night that way. The noise reduction package is better for slowly changing hums with multiple frequencies.
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Old February 23rd, 2009, 02:29 PM   #7
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Sony's noise reduction plugin does not come with Vegas. As I mentioned, I believe is it now included with Sound Forge.
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Old February 23rd, 2009, 10:48 PM   #8
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Honestsly, I don't like the noise reduction for simple hums. The main problem is that a hum attenuation of -20 dB isn't enough to completely remove major hums and the coloration of the rest of the sound is quite audible. Yes, -20dB is an appreciable reduction, but I think that is just a parameter and not the actual reduction.
The Sony Noise Reduction plug-in is really very good. Several things which might help reduce (or eliminate) the artifacts are 1) set it to "Mode 3" always and 2) experiment with the FFT size, lower sizes are generally better for dealing with lower frequency noise, 1024 or 2048 should work well. 3) on the "Noiseprint" tab, set the "fit size" to the maximum. Also, even though the Sony Noise Reduction plugin can be used in Vegas, it is much easier to use it in an audio program like Sound Forge.

The absolute best "forensic audio" program is Izotope RX. It has a number of truly excellent audio restoration tools. More often than not, the results from this program are nothing short of a miracle.

iZotope RX - Complete Audio Restoration: Declipping, Declicker, Hum Removal, Denoiser, Spectral Repair, Restore, Remaster, Download
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Old February 24th, 2009, 04:34 AM   #9
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) experiment with the FFT size, lower sizes are generally better for dealing with lower frequency noise, 1024 or 2048 should work well.
Thanks, I never really experimented with the Fit parameter. You probably meant to write that larger FFTs are better for low frequency hums as the spectral resolution = sampling frequency/FFT size. I didn't mean to write that the Sony noise reduction doesn't work well. It does remove noise well, but I don't like the way it removes much more than the hums I seek to nix. I don't see a way to tell it to remove lower frequency hums only. When longer FFT sizes are used for higher spectral band resolution, you get pre-echoes that smear transients due to temporal aliasing. Sometimes, you just want a plug-in to search for the most significant hum.
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Old February 25th, 2009, 01:10 AM   #10
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Sometimes, you just want a plug-in to search for the most significant hum.
Do yourself a massive favour - download a Demo of Izotope RX. Bloody marvellous!

ALL GUIs should be this easy, AND they have this truly voodoo like approach to N.Redux.

You can actually SEE the noise you want to remove.

Grazie
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Old February 25th, 2009, 04:10 PM   #11
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Do yourself a massive favour - download a Demo of Izotope RX. Bloody marvellous!
Grazie
Thanks, Graham. The Izotope interface is beautiful. Still, the hum remover module could still use more advancement. For example, it's difficult to find hums with high-Q notch filters. The Izotope Free Mode doesn't allow for Q less than 30, but at least the frequency sliders are logarithmic. The software should be able to find them for you. The implementation is essentially identical to the Hum Remover audio plug-in I wrote for Final Cut Pro ten years ago: a few notch filters that are adjusted with a common base frequency. Both Izotope and FCP provide a good method of high-Q notch filters to remove hums with harmonics. However, they don't work well on finding and removing hums that are made of 3-4 unrelated frequencies. You can do this in two steps (visual frequency analysis) and adjusting a few notch filters, but I'd like to see this automated.
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Old February 26th, 2009, 02:33 AM   #12
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Thanks, Graham. The Izotope interface is beautiful. Still, the hum remover module could still use more advancement. . . . . . they don't work well on finding and removing hums that are made of 3-4 unrelated frequencies. You can do this in two steps (visual frequency analysis) and adjusting a few notch filters, but I'd like to see this automated.
O . . K . . . I think Izo would love to hear from you. And maybe you might get some consultancy work to improve it along the lines you have suggested. Hell's teeth, I've carved my way forward out of doing change management & idea creation "work" over the past 12 years by inviting others to "think" outside of the box ( . . or whatever the "This Century" equivalent is of that saying is!) - Maybe you could do the same? Get over to Izo and invite them to consider your ideas. Then we would ALL benefit!!

Grazie
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Old March 10th, 2009, 01:31 PM   #13
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Both Izotope and FCP provide a good method of high-Q notch filters to remove hums with harmonics. However, they don't work well on finding and removing hums that are made of 3-4 unrelated frequencies. You can do this in two steps (visual frequency analysis) and adjusting a few notch filters, but I'd like to see this automated.
I recommend trying the Denoiser module of RX for hum removal. It will automatically capture the hum profile (i.e. adjust to unrelated frequencies) and the processing quality may be better than with the Hum Removal module (at least if you have time to render Algorithm C). Plus, you have the choice to only suppress peaks of hum and not broadband noise, if you want to.
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