Tech: Removing noise with Audacity

Subject: Tech: Removing noise with Audacity
From: Genie
Date: 13 Apr 12 - 10:04 PM

Sometimes when I record audio or video with my laptop I get some machine noise (a low volume, sort of high pitch hum) in the audio.   GarageBand can do a lot to tweak audio (iMovie can't do much except normalize the clip volume and adjust overall volume), but Audacity is supposed to have a noise removal function.

Problem is, when I'm working with an audio file in Audacity and I click "Noise Removal" (under "Effects"), it tells me to select a few sec. of just the noise -- so they can analyze it - and then to click "Get Noise Profile." That's Step 1.   

OK, so I figured out how to select a short segment with just the machine noise. I did that and even copied it, in case I needed it.   Then I clicked "Get Noise Profile" and the program seemed to be doing something ("Creating Nose Profile"), but I couldn't see the noise profile or any info on its variables.

Step 2 says "Select all of the audio you want filtered, choose how much noise you want filtered out, and then click "OK" to remove noise."

It then asks me to decide the following (insert numbers or leave the default ones):

Noise reduction (db) -
Sensitivity (db) -
Frequency smoothing (Hz)
Attack/decay time (secs)

The program does not seem to tell me what levels should be punched in, but even if I go with the preset levels, when I check the previews on noise removal, nothing seems to have changed.   In fact, I can't seem to find anything that reduces, much less removes, the machine noise.

Does anyone have experience with using Audacity to remove noise?   The "Help" instructions are quite unhelpful. They don't tell you any more than what the pop-ups tell you when you use the drop down menus and click on things like "Noise Removal."

I'd really appreciate any information or suggestions if you know how to do this.

Thanks,

Genie

Subject: RE: Tech: Removing noise with Audacity
From: GUEST,Hookey Wole
Date: 13 Apr 12 - 10:15 PM

I'm no expert but I had a quick test experiment with same thing your'e trying.

I connected a valve amp with power soak & speaker emulation to line in of USB audio interface.

Telecaster single coil pickup, hi gain, and CRT monitor - so predictable nasty loud hum..

All I did was select Audacity Noise Reduction pre-set

and it automaticlly eradicated the hum, to the extent that it was nearly inaudible.

Interesting side effect, was that it is not a transparent process.

The recorded guitar rhythm lead track also had significantly less bass and lower mid frequencies.

Which was actually an unforseen benefit, as it sounded almost like
the guitar had been recorded using a vintage Rangemaster treble booster.

Subject: RE: Tech: Removing noise with Audacity
From: GUEST,Hookey Wole
Date: 13 Apr 12 - 10:22 PM

May be worth checking your connections for earth loop hum.
Plenty tutorials on google
and cheap plugin inline hum filters for laptops* on ebay/amazon

[* Some say they are very effective, some audiophiles say they adversley affect audio quality]

Subject: RE: Tech: Removing noise with Audacity
From: Genie
Date: 14 Apr 12 - 01:09 AM

Thanks, Hookey.

I think I did try Audacity's preset Noise-Reduction -- at least the levels that popped up automatically -- but when I tried (twice) to apply them to the audio file, I couldn't detect any noise reduction.


I'm not sure why my built-in webcam on my MacBook is getting this sort of hum now. It didn't seem to do that in previous years, but the original one did break down a while back (sometimes recording no audio, sometimes producing noisy static), so I replaced it.   The replacement part may be slightly defective too.
But I think maybe if I set the sound input level for less than the maximum, it might reduce the hum.
Alternatively, maybe if I use an external mic input, that will avoid this problem, but that's not always feasible.   Many of my videos are recorded when the music is unamplified and there may be multiple performers, so a single mic wouldn't work unless it was a condenser mic, and even that won't work too well with a spread-out group of performers.

As for the plug-in line hum filters, do they prevent the hum when the mic is built into the laptop?

Subject: RE: Tech: Removing noise with Audacity
From: Genie
Date: 14 Apr 12 - 01:16 AM

BTW, in case I didn't make it clear, I'm not using any sort of line-in.   The noise is from the MacBook's built-in mic, which works as the default in iMovie, if you don't use and specify any external mic or camera.

Subject: RE: Tech: Removing noise with Audacity
From: Mick Pearce (MCP)
Date: 14 Apr 12 - 02:45 AM

Genie

Did you remember to unselect the portion you used to get the noise profile - otherwise all you'll do is reduce the noise in the selection (I usually come out of noise reduction (when I click Get Profile), press the double-left-arrow to move the cursor to the start and then do Noise Removal again to remove the noise (Or select repeat Noise Removal - I think that does the removal without changing any parameters).

I use it all the time when listening to old blues recording when I'm looking for lyrics. The setting I've got are: noise removal 12; Sensitivity 0.0; Smoothing frequency 150; Attack/decay 0.15. And they're usually fine for what I want. Occasionally I up the noise removal to 30 or 40 on really bad recordings.

(I'm currently running 1.3.13-beta under Ubuntu; but I don't think the NR parameters have changed in the last several versions).

Mick

Subject: RE: Tech: Removing noise with Audacity
From: GUEST,BobL
Date: 14 Apr 12 - 03:01 AM

With the built-in mic, is it possible that you're picking up mechanical noise from the hard drive?

Subject: RE: Tech: Removing noise with Audacity
From: treewind
Date: 14 Apr 12 - 04:45 AM

Noise removal tools are a band-aid for rescuing recordings over which you have no control. They always affect the wanted sound, and not usually in a beneficial way. If you are getting machine noise because of recording with an internal mic in a laptop that makes mechanical noises (hard drive or cooling fans usually) you should find a way of recording so you don't get that noise in the first place. Then you don't have to mess your sound up with noise removal tools. You'll have a far better recording for several other reasons too, such as (almost certainly) a better mic, and the freedom to position that mic where it will get the best sound.

Subject: RE: Tech: Removing noise with Audacity
From: Nick
Date: 14 Apr 12 - 05:55 AM

Apart from recording somewhere quieter...

I tend to use Reaper rather than Audacity if I record things just because I find it better. One of the many things on that when recording is to put a noise gate on the track when you are recording which stops some of the low level hum and background rubbish appearing so that you don't have to try and remove it afterwards which, as said above, tends to affect the whole track.

It does at least mean that in the quietest bits or in in 'silence' that you can cut the background sound out - which is where you tend to most notice it.

Audacity have one too - Noise Gate - so it might be worth doing some experimentation with it. You need to get the right balance so that things sound smooth but it may help. If it doesn't get there in the first place you don't have to remove it!

Subject: RE: Tech: Removing noise with Audacity
From: s&r
Date: 14 Apr 12 - 06:49 AM

For sessions and such I've had good success with boundary microphones


Stu

Subject: RE: Tech: Removing noise with Audacity
From: Bonzo3legs
Date: 14 Apr 12 - 08:10 AM

Better to find a cracked version of Adobe Audition - preferably CS5 where you have control of many aspects of the noise reduction.

Subject: RE: Tech: Removing noise with Audacity
From: Charley Noble
Date: 14 Apr 12 - 08:31 AM

I'll ask Judy about how she does it. She also uses Audacity but on a PC platform. She edits out occasional static and fingerboard squeaks on a regular basic.

Sometimes she uses the automatic fixes. But other times we see a colored screen profile of the sound wave and she's able to highlight and delete various deviations from what would be a normal sound signature.

Charley Noble

Subject: RE: Tech: Removing noise with Audacity
From: GUEST,Tony
Date: 14 Apr 12 - 01:46 PM

I've gotten rid of noise with Audacity, but I use an older version, 1.2.6, which doesn't give all those options. Step 2 is just a slider between Less and More, and a Preview button to help you pick where to set the slider. It works pretty nicely if the noise is consistent and if I can find a patch of pure noise with no music or talk. After reading your post, I'm going to try the new version. It sounds like it's much improved.

I've also used Acoustica 2.25a, which gives you the option to create your own noise profile, or alter a profile obtained by analyzing a sample. But I haven't figured out how to use that to get better results than with Audacity.

Subject: RE: Tech: Removing noise with Audacity
From: Genie
Date: 14 Apr 12 - 02:36 PM

Bobi, it's obvious that the hum I'm getting is noise from the hard drive.   What's not clear to me is why this wasn't an issue when the laptop was newer - with my original built-in mic/cam before it started acting up (possibly as a result of a cat knocking the laptop off a chair onto the floor);    The hard drive makes noise sometimes and doesn't at other times.

There are really two questions about that, but they're not really the issue in this thread. Yes, I'd like to know how to use the built-in mic without getting the machine noise (e.g., if I reduce the volume on the sound input, would that help?).   And if I use an external mic, what's the best one (or type) to use in an acoustic, unamplified setting where there may be multiple performers and I may not be able to have the mic closer to the performers than about 6 to 8 feet?

Mick (MCP), I think I did unselect the short noise clip first, but it's not clear how to do that. Do I copy the clip first?    If I select the brief noise clip and then unselect it, how does Audacity know that's the clip I want used?    I can't do any selecting or unselecting while I'm in the Effects menu (e.g., on "Noise Removal").    I tried this and that sequence but it never seemed to do anything, so obviously I'm not doing it right. Thanks for those setting suggestions. I'll try that.


BTW, it seems GarageBand can do some of this, but I'm still experimenting to figure out how. They have an "Au Filter" setting that lets you reduce the volume on parts of the auditory spectrum and if I reduce the very high treble it does cut out a lot of the hum, but it also can make the voices and instruments sound mushy if I remove most of the hum.   They also have a couple of preset filters that you can play around with to see which ones may help with this.

Subject: RE: Tech: Removing noise with Audacity
From: Mick Pearce (MCP)
Date: 14 Apr 12 - 03:07 PM

Genie

You need to select a short clip which is mostly noise (no need to copy it - just select it in your file; it doesn't need to be very long), open Noise Removal, press Get Noise Profile. On my version when I do this Noise Removal closes automatically, but if not, close it. (This step creates the noise profile that will be used the next time you select Noise Removal and press OK).

Now unselect your noise selection (I normally press the rewind to start double left arrow on the transport bar); if you don't unselect it now, the Noise Removal will only be applied to the short selection you used to generate the profile; it will do a great job on that!

Then do Noise Removal again, alter any parameters you want, and press OK to apply the removal using the noise profile you created last and the parameter settings you chose. (At this point you can use Preview to hear what it's like, but often this isn't useful: very often the selection I use to generate the noise profile is at the start of the file and since Preview only plays a few seconds from the start you mainly hear silence where it does a great job on the part of the file used to create the profile. So mostly I just press OK and listen to the file afterwards. Noise Removal is pretty quick, so it doesn't waste much time).

I've assumed here that you're applying Noise Removal to the whole file. If you want to apply it to only part of the file, then make the selection of the part of the file you want to clean after generating the profile and before you reopen Noise Removal and press OK.


Many similar systems allow you to save your noise profile and allow you to pick a saved profile, but Audacity requires you to create one just before you use it; hence the two step process with the Noise Removal effect.

Hope this helps. If not post here or PM me if you want - I'll be around most of the evening.

Mick

Subject: RE: Tech: Removing noise with Audacity
From: Charley Noble
Date: 14 Apr 12 - 08:56 PM

It's actually Adobe Audition that we have been using.

Charley Noble

Subject: RE: Tech: Removing noise with Audacity
From: Barbara Shaw
Date: 15 Apr 12 - 09:25 AM

I tried removing a low hum with Cool Edit (now called Audition) and the process took out much of the guitar sound, as mentioned above. Not acceptable. Interested to find a solution since some of those earlier recordings are not replaceable, some done by a departed friend.

BTW, my noise was the result of using a PA interface that wasn't good. After switching to a Dual Pre (preamp meant for this process) to which I connected a condenser mic, and plugging the Dual into the computer's USB port, I eliminated this problem. (Not to say that I haven't found new problems, like latency issues on the multiple tracks...)

Subject: RE: Tech: Removing noise with Audacity
From: Arkie
Date: 15 Apr 12 - 10:04 AM

Have you tried playback on another device to see if the noise was still there?

Subject: RE: Tech: Removing noise with Audacity
From: GUEST,Hookey Wole
Date: 15 Apr 12 - 10:54 AM

Cleaning hum from already recorded tracks will always be a balancing act compromise.

All kinds of noise reduction and multi band compression are available
at price points hobbyist & semi pro recordists can reasonably afford.

At most basic you can manually edit unwanted noise from the silent gaps on each recorded track
but will still have to put up with it underlying the music performance,
certainly if it's not at a low enough level to be masked by all the other instruments..

At worst it can sound unnatural if the edits are too apparent.
Sometimes it's best to leave in a certain level of the noise
to maintain a consistent sense of performance environment in the 'silent' gaps.

That's why it's best to try to eliminate distracting extraneous noise
from the equipment chain before pressing 'record'.

Good quality leads and connectors, properly matched impedance pre-amps & DI boxes,
modern building wiring to defeat earth hum loops, or adapter boards with line cleaning filters.
Foot pedal nopise reduction/suppressors - whatever it takes to ensure as clean a recording chain as possible.

But we know and must accept that real world clubs and venues are not great for on the spur of the moment recordings..

A healthy diet of listening to vintage classic live bootleg recordings
can help put 'noise issues' into perspective.

Subject: RE: Tech: Removing noise with Audacity
From: GUEST,Hookey Wole
Date: 15 Apr 12 - 11:13 AM

... almost forgot to mention another important factor...

make sure gain levels are carefully matched for all items of equipment
in recording chain
to keep noise floor at most optimum..

A simple illustration, my mum is 80 and phoned up distressed that her telly had developed a horrible hum
and she could no longer hear the dialogue in Coronation Street.

I got a train to visit her asap expecting at worse the price of a new TV.

Long time examining her TV and arial setup later,
I discovered the cause of the problem...

She'd set the volume level on her Freeview box at minimum
and was compensating by turning her TV volume to maximum.
Thus amplifying all the circuit & interference hum from the freeview box to intolerable levels.

I explained that she needs to set the freeview box to max
and only control volume levels with the TV remote control for best noise free listening...

She still gets it mixed up and I have to sort it out every time I see her.
But at least I know what the problem is.

Subject: RE: Tech: Removing noise with Audacity
From: Tootler
Date: 15 Apr 12 - 01:30 PM

Instructions for using the Audacity Noise removal effect in the Audacity online manual here. The instructions are straightforward and clearly written.

Note what it says about selecting a region to get a noise profile, then selecting the region you want to remove the noise from. If it's the whole track, then do as Mick Pearce says. I usually press the "home" key on my laptop which does the same thing.

Note what it says about mains hum and using a notch filter first. It is quite possible the noise the noise from the hard drive the OP describes is at mains frequency (50 or 60 Hz, depending where you are) or possibly, a multiple of mains frequency.

It's also worth testing the effect of the input volume. On my Linux system in the sound settings there is a slider for input volume and I find that if that's set too high, the noise starts to dominate and trying to remove it has too much of an adverse effect on the signal. I find I need to keep the input level down quite a lot. It may reduce the signal level on your recording but the effect on the noise seems to be much greater. I suspect there is an internal preamp and that adds noise to the mic signal.