Noise Reduction

I know this has been discussed a fair amount but I still havent found a clear understanding of it..Im using the newest version of audacity 2.1.2 and recording some basic music tracks…usually one or two guitars and vocal…4 tracks maximum…Shure SM-57 microphone and guitar plugged into an Alesis 3 channel USB mixer into an Asus laptop computer with Windows 7…overall it sounds pretty good but Im trying to get the best results I can. In noise reduction Ive experimented with different settings.the default 12 6 3 seems to work ok…or 0 for frequency smoothing…usually about 5 seconds for noise profile…sometimes Ill run the whole process twice with the same settings...different settings dont seem make that much difference…I understand its subjective but if anyone can give me some tips for best results Id be greatful…thanks

What kind of noise do you have? Microphone or preamp noise is ffffffffff, rain-in-the-trees sound. That takes careful selection of equipment when you buy it. Computer fan noises, air conditioning noises should be solved before you record. Those are preventable. Traffic noises, street noises, jet going over noises as a rule can’t be helped in post production. Stop recording while the jet goes over. This is a specific suggestion from ACX AudioBook.

What do you have? Is your work posted anywhere so we can hear it?


these are MP3s of silence then a short guitar track…I dont know how to send you a picture of the wave form...if you could explain that to me it would be helpful..basically there is hum on my recordings that Im almost positive are internal…I turn off everything in the room when recording including the cooling pad under the computer

the 1st example is with no noise reduction

the second example is with one time noise reduction set at 18 9 1 which is generally more reduction than I usually apply…its more or less acceptable on my end however Im only hearing it thru somewhat inexpensive headphones and/or speakers…when I post MP3s online I can usually hear some background hum…its not unacceptable but Id like to get rid of as much of it as possible

I`m reading a significant amount of background on the meter when I record and seeing a constant low level pattern on the waveform when everything else is silent…it pretty much goes away when I apply reduction but it sounds a little off during playback


We can get everything from the raw, unfiltered work. Don’t help.


Try running this code in the Nyquist Prompt effect ( before applying any noise reduction.

      (notch2 *track* 4000 50)
      3000 40)
    2000 30)
  1000 20)

It is a series of notch filters at 1000, 2000, 3000 and 4000 Hz.
Then apply the least amount of Noise Reduction that you can get away with.

That better? That’s Steve’s code and my Noise Reduction 12, 6, 3. I got the profile from the first two seconds of the clip.

You should not be doing production in MP3. MP3 creates compression sound distortion and it gets worse every time you use it. Use WAV (Microsoft) for everything until you have to produce a small version for posting or your personal sound recorder.


I wouldn’t mind listening to that for a while. Are you going to overdub other instruments?


You answered that earlier.

This version has a bit more hiss than koz’s version, but greater clarity of the guitar sound. I’ve also added a little Reverb effect (Vocal 2 setting with the “wet” turned down a bit)

I think the equipment is probably letting you down a bit. SM-57s are good reliable mics, but not the most sensitive, so I guess you’ve got the gain turned up high on the mixer?

Thanks…that seems to have helped a lot…one question I`ve had the from the beginning is how much time should I use for the noise profile…the manual gives the minimum but not the optimum…I always keep 10 seconds of space at the beginning and end of my recordings…I read somewhere 7 seconds is good…does it hurt to grab too large a profile?

I`m not sure what was done in the last example…was it the same as previous but you just added the reverb?

I dont have the gain turned up very much on the mixer...maybe a third at most...Im not sure whats going on...I was making some recordings with the laptop mic that seemed to have had less noise but sounded terrible..overall Im pretty happy with things the way they are as long as I can get rid of some of the noise but I`m always trying to get it better.

Also Ive been converting to WAV for CDs etc but they dont seem to upload online…I understand MP3s are lossy but Im not sure how else to post anything..I didnt really understand what you said about that…I`m not a tech guy just a greasy guitar player.

Yes I`m going to add lead guitar…probably some bass and percussion.

One last question…what is the point to saving compressed files? I generally just save my Audacity files to an external drive in case something happens and sometimes make a CD in case I lose everthing.


It only hurts if the profile is not just the constant noise that you want to remove. For example, in the audio sample that you posted, there were some clicks with the “silence” at the beginning. The noise profile should not include those clicks.

The old version of “Noise Removal” (as it was then called) required a longer noise sample than the current version. One or two seconds should be plenty for the new version. The exact length is not critical.

I used a little less noise reduction than koz (if I recall correctly, the first slider was set to 10). I then applied a little bit of Eq with the “Equalization” effect to reduce the bass and give it a bit of boost at around 4000 Hz (4 kHz). The original sounded a bit boomy through my headphones which is why I reduced the bass, and after noise reduction it sounded a bit dull, which is why I added a little boost to the high frequencies.

I then trimmed the start, and applied a very short fade-out at the end so that it ended at absolute silence, then added a bit of extra silence to the end so there was space for the reverb. Finally added a bit of reverb and amplified the whole thing to a “reasonable” level.

Neither am I. There’s a lot more hiss than I would have expected from your setup. Did you amplify the recording before you sent it to us?

Do all your production in WAV (Microsoft). Convert to MP3 only when you have to. MP3 is an end-product delivery format—that’s what it was designed to do. Post on-line or make a copy for your portable music player. Never open an MP3 because you want to do production or some other job. Each time you do that, the MP3 sound distortion gets worse.

The sound inside Audacity is WAV quality and the sound on a Music CD is WAV quality. So stay WAV the whole way. Producing an MP3 in the middle is just adding distortion you don’t have to.

does it hurt to grab too large a profile?

Darn good question. I don’t think I’ve never used longer than two or three seconds. It doesn’t come up often. Most people are trying to grab the silence between spoken words. There just has to be enough noise for Noise Reduction to chew on.

what is the point to saving compressed files?

I don’t think there is one. It’s a mistake. The archives should be uncompressed. WAV (Microsoft) works well. The only reason you’d need to save Audacity Projects is if you wanted to save the individual tracks in a mix.

Projects do not save UNDO.

That and as you get further and further away from the Audacity version that made a Project, the chances of it not opening goes up. Projects will not open anywhere else.

If you ever do collaboration with other people, you may want to find a file posting service so you can ship large files around. It’s nice to think you can do a live collaboration on Skype, but that rarely works well and recording it can be a challenge. This piece looks like a live Skype session, but it’s really just shipping files around and clever editing.


I did think of a reason not to use too long a profile. You’re more likely to capture sounds by accident that aren’t noise. In your clip we can hear quiet rhythmic drumming on the body of the guitar as you count down to the first note. DO NOT include those in the profile. That will cause music distortion.


just a greasy guitar player.

Works for me. Are you published anywhere?


I have a website but its very basic..the music on it sucks and atm its pretty much just a learning experience…I hope to get it up to a reasonable quality within a few months.

I am somewhat disappointed with the noise levels Im picking up..Im using a pretty basic setup but Im not taking an el cheapo approach...I think its just this computer on the way out…its crashed on me a few times and the operating system is getting unstable..the strange thing is I was doing this before basically just plugging straight into the computer to see if I could do it and I wasnt getting much background noise…although it sounded like AM radio at best.

Ill definitely be posting again to try to get this right..will be an ongoing thing..Ill try not to get on your nerves too bad.

the whistling/humming noise could be coming from the computer, but I doubt that the hiss is, unless your computer makes a very audible hissing sound (some do make “shhh” noises from their fans). While recording, place yourself as far from the computer as you can to reduce the amount of fan noise in the mic. Also, look through the manual for your mixer at how to set levels. There are multiple places where the levels are set, and they all need to be set correctly for best results.

Plugging into the computer direct or using the laptop microphone can give you Skype or conference voice quality because of Windows processing. It hates music.

You can do your own noise search. Plug headphones into the computer headphone socket and make Audacity show you the signal.

Audacity > Edit > Preferences > Recording > [X] Playthrough (select) > OK.
Right-click the top sound meters (recording) > Start Monitoring.

That will feed show sound live into your headphones. You can move things around and change settings and hear in almost real time what you’re doing. That’s how I found that my bass cabinet was humming. I set it up, put my headphones on and kept waving the microphone around until it pointed to the sucky cabinet. Hmmmmmmmmm.

My opinion is the mosquito whine is coming from your USB system (Steve’s code) and the hiss is coming from your mixer (my noise reduction). You can help the hiss with careful volume settings, but I think you’re stuck with the USB whine.

I gotta leave for a while.


Alesis 3 channel USB mixer

There doesn’t seem to be a 3 channel Alesis mixer. Can we get a model number? You have to be careful what you tell us because we can get hitches like that and have to wait for a whole posting cycle to solve. We have no idea what you have and can only go with what you tell us. I know exactly what an SM57 is. I used to own one.

This is my mixer.

The three circled controls do different things, but there is a generic rule where they should be set. Start with all the controls at 2/3 or 3/4 up. That’s the two knobs at about 3:00 o’clock and the master slider at 0.

Where are the mixer volume flasher lights when you play? Do you see them at all or are they so high they’re flashing red? If they’re close but too low, advance the gain control (upper left) until the sound meters are happy. My mixer starts to act funny all the way up, so I never go that far. If that’s not enough, start advancing the level control. If you’re listening to all this live, you will hear both the music and the hiss level go up and down.

The three controls affect volume, but they each have production jobs, too. The idea is for them not to be too far apart from each other—at least at the start of the session.

Note we’re just making the mixer happy. We haven’t touched Audacity yet.


Thanks…Im still working on this..its actually marketed as a 4 channel mixer Alesis Multimix 4 USB is the name but channels 3 and 4 are really the same with one gain control and a balance for left and right…it seems to work ok but the distortion is coming from there…when I unplug the unit it goes away…when I plug it in it appears…on the waveform its just a narrow band that exist around the 0 line…I dont know how to describe it but Im sure you know what Im talking about..a jagged line that stays there when I record..I havent really experimented with the settings but just unplugged everything and it`s always there.

I suppose the only fix is to upgrade to a better mixer which isn`t going to happen anytime soon but I will eventually…I like it actually despite the noise.

It’s not distortion. It’s noise. Once we got rid of most of it, the guitar sounds fine.

I need to come back in a bit.