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class="style5" Removing Line Hum

>Published : 24th April 2005

>Anyone have some tricks for removing line mic hum? It's in the upper mid-range, but basic EQ is killing the voice signal as well. (obviously)

>Editing a doc and have some second camera audio that wasn't supposed to be used, but turns out the main audio source got corrupted in one section, so I'm trying to make do. Have access to avid 9000 and final cut for cutting.

>Heard something about cancellation technique???

>I'm an editor with a basic grasp of audio, hoping to avoid sending the audio out. no budget, etc.

>Thanks,

>Paul Buhl


>Paul Buhl wrote:

class="Paragraph">>I'm an editor with a basic grasp of audio, hoping to avoid sending the >audio out. no budget, etc.

>The typical hum found in audio tracks as a result of poor grounding or as a result of motors, ballasts, or electronic equipment present in the recording environment contains a base frequency and a series of harmonics that are multiples of that base frequency. In the US, of course, that usually means 60 Hertz and harmonics such as 120, 240, 480... etc. Hertz are usually prominent. Less prominent harmonics may be found at 180, 300, 360, 420... etc. REALLY nasty hums that have that "snappy" quality are filled with tightly spaced upper harmonics.

>Removing these harmonics requires VERY, VERY steep (selective) notch filters. Typical parametric EQ's don't have a high Q and don't function well as notch filters; ie: they filter out broader ranges of frequencies rather than honing in on a specific frequency.

>My first recommendation would be to find someone with a Pro Tools workstation who owns one or all of these plugins: the Restoration Bundle from Waves, the NoNoise plugin by Digidesign, and/or DINR (Digital Intelligent Noise Reduction) by Digidesign. DINR is a bit long in the tooth by today’s standards, but an experienced user can get results with it. The Restoration Bundle is very automatic with less parameters to tweak, but it is very good. Digidesign's NoNoise plugin is a software "rewrite" licensed from Sonic Solutions and is based upon their original algorithms. NoNoise was the pioneer in high end software NR.

>If you own Peak, which comes bundled with many media applications, you can try a plug-in by the maker of Peak, Bias. The Bias plug-in is called SoundSoap. There's also a stand alone version.

There is also a SoundSoapPro :

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

>One is $99, the other is $599. I'm not familiar with either. A 14 day free trial version of SoundSoapPro is available. It's cross platform (Mac and PC). There are other products for the PC about which I know nothing.

>So...you can always try the Bias demo --that gives you 14 days to figure out how to use the software and see if you can fix it yourself. That said, noise reduction software can be tricky to use, _especially_ if you want to minimize artefacts. Like color correction or any other task that requires a patient and persistent "tweaker" mentality, noise reduction can benefit from an experienced hand. The $600 you may end up spending on software might well be spent putting the problem in front of a pro audio person.

>Best,

>John McDaniel
Audio Post Facility Owner
Sonic Arts Digital Audio Services, Inc.
Cincinnati, OH USA


class="Paragraph">>and/or DINR (Digital Intelligent Noise Reduction) by Digidesign. DINR >is a bit long in the tooth by today’s standards, but an experienced user >can get results with it.

>Did they ever put the hum removal feature back in DINR ? I seem to recall it was missing in the Audio Suite version, although it was in the original Sound Designer II plugin.

>Sam Wells


>John,

>Thanks. I really appreciate the info.

>I've used Pro Tools and wish I had it right now. I will try the Sound Soap demo.

>Paul Buhl