hum removal

[shinnen]

Hi,
I have a hum on a short voice (wav file) recording, that I've had for years.
I don't know how it got there, but I would like to remove it.
Any suggestions are appreciated.
..... john

[kozikowski]

Not in Audacity 1.2. The noise removal tools in 1.3.7 are very much better at this and you can put both 1.2 and 1.3 on your machine as long as you only use one at a time. Audacity 1.3 projects will not open up in 1.2.

Select a segment with only hum. Effect > Noise Removal > Get Profile.

Select the whole piece (or a representative sample) and Effect > Noise Removal. I would start with gentle settings of 18dB, 200Hz, and 00 delay. That should help. More and more noise goes away as you increase the dB number, but you can go too far. The Hz number controls how much hum gets left behind within words and phrases. Too low and people gargle and too high the hum starts pumping with the show.

Adjust your brains out. Edit > Undo if you don't like it. Use a representative sample so you're not there all night waiting for the noise reduction to apply itself on an hour show. When you're happy with the sample, then apply it to the whole show.

Koz

[allencmcbride]

What I've used for hum is a "notch filter" or "parametric EQ" (I think they're the same thing). I use an Apple thingy that you won't have, but I see there's a "Mag's Notch Filter" in the set of LADSPA plug-ins (http://audacityteam.org/download/plugins) that would probably do the same thing. I've used "Plot Spectrum" under "Analyze" to find peak frequencies that might be the one I need to get rid of, then, in a separate file, I use "Tone" under "Generate" to see if that is actually the frequency I'm hearing. Then I remove that frequency with the notch filter. Sometimes I have to remove overtones, too, but these are easy to find because they're exact multiples of the base frequency.

There are probably other ways to do this, like using Noise Removal, but this has worked for me. Also it looks like a Google search turns up other info on this: http://www.google.com/search?q=audacity+remove+hum.

--Allen

[allencmcbride]

Oops; I posted before seeing Koz's response. Anyway, Koz: I can't run both 1.2 and 1.3 at once? What bad happens? If I've been doing that, do I need to purge some preferences file somewhere? --Allen

[shinnen]

Hi Koz,
I tried various settings up to 48 db and 1000hz. Didn't seem to make much difference. Other than a slight muffling of the voice, the hum seemed to stay the same. Is there a way of determining what freqency the hum is?
..... john
PS. Hi Allen. Thanks for your suggestions. I'm going to see if noise removal works before I go to another method.

[kozikowski]

<<<Didn't seem to make much difference.>>>

Then you did something wrong. Settings like that should have destroyed your show.

Noise Removal is a slave to the profile step. You must select as much Hum as you can on the timeline without getting any performance in the selection. Play your selection before getting profile and it should be pure hum (and long enough to hear it) The tool will try to remove the sound in this selection from the rest of the show.

After you get the profile the tool will close. Select the whole show and open the tool again and apply it.

There's another thing that could be wrong since you're on a Windows machine. How sure are you you have a WAV file? Do you have Windows adjusted to show you file extensions? Did you do the File Properties thing? If you have a "foreign" file type, all sorts of nasty things happen.


<<<I can't run both 1.2 and 1.3 at once? What bad happens?>>>

They will usually refuse to both run. They will actively step on each others preferences and tool settings and create unstable work.

Koz

[kozikowski]

Profile step. It's sometimes necessary to edit a bit to get enough hum for the profile to chew on. Edit out some words so only the hum between words remains. Use that edit to get the profile and then either close the clip without saving or UNDO your way back to the original show.

Koz

[shinnen]

Hi Koz,
Properties says that it's a pcm file.
... john

[kozikowski]

Let's try it this way. Download piano2.wav from here...

http://www.kozco.com/tech/soundtests.html

...and put it on a timeline by itself. It's a six second piano solo. Some of my best work (my only work). Drag select one of the piano notes, doesn't matter which one, open Noise Removal and Get Profile.

Select the whole performance, open up Noise Removal again (use my original posted settings) and when you apply it, most of the performance should vanish or dip very significantly. This has nothing to do with removing hum. This is to make sure the tools work correctly and you know how to use them.

If that doesn't work, then we need to get really particular about your installation and tools.

Koz

[kozikowski]

One other note. When you change the settings in Noise Removal, use the sliders and not the text entry windows.

Koz