Noise Floor Woes/ Mastering for Audiobook Help!

Hoping I can get some serious help here because I am in dire need.
I am currently trying to produce an audiobook for ACX but no matter what I do my noise floor can’t get down low enough, so I am wondering if there are any steps I can take to pass the ACX requirements?

A bit of background: The way I learned to master each chapter was export the file as a WAV then run it through a free app called “Levelator” and then normalize in Audacity to -3db and things should be smooth sailing. For me though I feel like it just makes it sound worse, probably because my noise floor sticks at about -57 to -54.

Anyway, I have attached a raw file with nothing done to it, just my voice and I hope that by some miracle there is something I can do.

Thank you!!!

Turn off the cement mixer?

Thank you for the good sample.

I couldn’t do it, either.

I prepared a boosted sound clip of your noise. The little periodic sharp tick isn’t real. What in your house could be making that noise? It’s bad enough I don’t think anybody’s going to be able to get rid of it without affecting your voice quality.

It sounds like you’re waiting for clearance from the control tower to take off, doesn’t it? Let’s see. Single engine Cessna, I think.

If you need too much Noise Reduction, you start sounding like talking in a wine glass. ACX will not accept either one, the noise or the glass.

So where do you have a large pump or other large motor? Want to start from the beginning? Which microphone do you have and is it sitting on the table?


If you have trouble hearing that low pitch rumble (I’m serious, cement mixer), you may have the second common home studio problem. Bad earphones or speakers.

How are you listening?


Sometimes, you can have one “thing” making noises and it will produce interference with several tones an octave apart. Not yours. It sounds like mixing rocks.


Oh boy,

Unfortunately, I don’t know what is making the noise. When I am just sitting in my space it is incredibly quiet and the microphone reads at -57 which I know still isn’t great but I didn’t realize it was that terrible. If this helps, I am using a Mac with Audacity 2.2.1 with an ATT2020USB mic. I’m listening through both of the ear headphones and then ear buds most of the time when I edit.

I’m afraid the culprit must be something in the building?

Now, here is the twist. I downloaded the ACX check from this forum while waiting for a response, and oddly enough when I went through the Levelator and Normalize to -3db and had the entire clip selected…it passes for Noise floor??

It’s an ATT2020USB mic and it is on a corner desk that I have actually padded with blankets. Plus the entire corner I have padded and then I close myself off with moving blankets held up by a shower rod. If that helps anything…

it passes for Noise floor??

Not that surprising. The motor went off. That’s not the good news. That means you have an unstable studio.

By the way, that’s an AT2020USB, not what you said.


Sitting on the desk? How did you do it?


I went with large motor instead of cooling fan in the computer because computers typically don’t make that much powerful rumbly noise. They make EEEEEEEE screaming and insect noises.

I guess it could be the computer…

If somebody wanted me to bet money, I wouldn’t do it.


Hmm perhaps? Although I keep my computer away from the mic, it is outside of the moving blanket/curtains that I have drawn on another desk, so it is a few feet away from it.

Soooo am I basically screwed then?

Third time.

Do you have the microphone sitting on the table?


Oh, I answered that earlier. Yes, it is on the table on my desk that is padded with a blanket.

I answered that earlier.

Missed it. Sorry.

I don’t have any better ideas, so let’s go with the bath towel solution.

Fold up a bath towel and put a book on top of it. Park the microphone on top of the book.

That should eliminate any vibration from the desk or floor. Note it’s sitting on the table moving quilt.

The sound test is muffled, like it’s having a hard time getting into your cave. But not hard enough time.

I think the worst problem you have right now is not knowing when the motor comes on. Can you feel the heat or air conditioning come on? Do you have that kind of HVAC system? My old house Heater/AC had provision to just shut it down. OFF.


Ok I will definitely test that out.

Well, I am in an apartment complex and I think it might be the buildings water heater upon further inspection :neutral_face:
We control our own heater and I never have it on when recording.

Pack it up and try your equipment somewhere else far away. If the clicking goes away, you’ll know it’s something in your building. If not, it’s something to do with your equipment. If it turns out to be interference from your building, you’re in trouble. You may never find the source, and even if you do you may not be able to do anything about it. Your only option may be to change your equipment to something less vulnerable to interference.

As for the noise floor, try to find something like a studio to see if recording there will affect the noise floor. Try a closet full of fur coats or just draping a huge quilt over your head and shoulders. If the noise floor drops, you’ll know that the solution is to build a real booth in your apartment (not difficult, I did it for under $100). I’d also try recording to another computer just to see if that changes anything.

If the clicking goes away, you’ll know it’s something in your building.

It’s not clicking. It’s almost classic electric motor noises. Listen to the sample. And it’s complicated by not being there all the time. So even if you do move out temporarily, it’s rough to know if it worked or not.

There was a recent poster who had ‘sometimes noises’ which turned out to be their external hard drive spinning up. They had their laptop, drives and microphone close to each other on a table, so it was rough to hear what was going on in real life. But it was close enough for the microphone to pick it up.

a real booth in your apartment (not difficult, I did it for under $100)



a real booth in your apartment (not difficult, I did it for under $100)


Well I guess that depends on your definition of “real”. This is definitely an amateur job, but it works nicely for my purpose, which is not being able to hear screaming kids. I chose the quietest spot in my house, the attic, and built a closet out of 2 by 3s and noise insulation bats you get at the hardware store, and lined it inside and out with one inch sound absorbing board. This includes the door, which is more like a wall on hinges. For air, I fed a 3" duct from a hole in the ceiling to the input (the WRONG end) of a $12 bathroom fan. I added a fan “dimmer” and put it on lowest setting, which gives a low hum outside of the booth where the fan is, but is barely audible within the booth, and creates enough negative pressure to let air seep in through the cracks and keep me from suffocating. Because the booth is so small, the price of materials was low. I actually regret not having made it bigger, as it would be a nice study or rest area if it were more roomy.

This is definitely an amateur job,

Unless you’re going to give tours, it doesn’t have to be elegant. One poster did it with plumbing supplies. It’s pushed together. No glue.

I did it with furniture moving pads. Mine had to knock down for transport.

For air, I fed a 3" duct from a hole in the ceiling

That kills a lot of people putting studios in their coat closets. Ian in Hollywood has to some out periodically and gasp for air.

Did you have a chance to listen to that clip?


Notch filters in Audacity’s Nyquist prompt can reduce the “cement mixer” …

(setf *track* (notch2 *track* 120 10))
(setf *track* (notch2 *track* 147 15))
(setf *track* (notch2 *track* 152 15))
(highpass8 *track*  120)

notch code in Nyquist prompt.png
The “cement mixer” sounds more like a mains-hum to me, rather than acoustic like a motor,
as the loudest component is exactly 120Hz , (2nd harmonic of 60Hz mains)

I can hear a nasty hum that sounds like a machine, but that doesn’t mean it’s a machine at all. It doesn’t sound like mains hum to me ( except possibly the harmonics explanation, I wouldn’t know). Since it’s intermittent, then it’s not mains itself, but maybe some other source bleeding over into mains. If it’s a laptop computer, one could try unplugging it and running on battery. Power supplies can have intermittent problems. I would increase the gain and try moving around the apartment while listening, to see if the noise varies. That could either help pinpoint the source, or if there is no variation at all, it can indicate that the problem is with the recording equipment.

There are of course limits to what makeshift booths can do. I recorded this just now. The fiddle rang in at -48, still enough to totally wreck a recording.