Microphone picking up neighbor's AC

Hello all,

I’m very new to audiobook production, but I landed my first gig. With the increased amount of time spent recording, I’ve noticed that whenever my upstairs neighbor’s AC kicks in, my microphone is certainly picking up a steady humming.

I record in a small closet, with every other conceivable noise in my apartment dealt with. I only have issues when this AC kicks in.

This may be the biggest red flag in my situation, but I’m using a Blue Snowball microphone. I’ve read the Blue Yeti is acceptable in many situations for audiobook production, but the Snowball is definitely a lower-quality mic. I’m wondering if I may need a dynamic microphone, based on some additional quick research.

Should I consider a dynamic microphone? Are there any other pointers you can provide me to help minimize or remove this sound?

I’m going to include an audio sample that clearly depicts when the AC is kicking in - from my “normal” silence, straight in to the humming itself.

You will need to be wearing headphones and turn your volume up; it starts at about 14.5 seconds.

Am I overthinking this? Should I be concerned, or does this need to be dealt with before I can hope to take audiobook recording seriously, and if so, what do you recommend?

Thanks, and bear with me and my lack of knowledge on technical terms and so forth :slight_smile:

I should also state I am, at the moment, limited to using USB microphones.

If you are recording on a laptop computer, try running it on batteries (disconnected from the mains) and see if that eliminates the hum problem when recording.

This sample was recorded on battery power only, as it happens.

Could this maybe be solved by putting the mic in a box of some kind?

Probably not. It can be filtered out quite effectively, but better if we can find a way to prevent the interference getting into the recording.

AC = Air Conditioning?

Just as a test, if you move to a different location in your apartment, while the AC is running, does the amount of hum change?

AC = air conditioner, yes.

I haven’t tried recording in other areas, but I can personally attest to the humming being much more noticeable in my living room, for example. The closet I’m using is the best place overall for recording, and the humming is indeed faintest back there.

As a test, try burying the mic in a big pile of coats / towels / heavy blankets or similar, and check if the hum is more / less or the same.
The idea of this is to see if the interference is sound, or electrical.

I’ll give it a shot tonight when I’m home. Thanks for your help, it means a lot to me. Recording audiobooks is kind of a dream job for me, so I feel like I need to get this right. I was pasting room silence over the humming in the sample I sent to the rights holder on ACX, and they don’t seem to notice anything “off”, but I do (the humming is faintly there in my spoken parts, and going from “normal” silence to speaking with a faint hum is jarring) and I am certain any job worth a decent per finished hour rate will have a much higher standard. And on top of that it’s vexingly time consuming, so yeah I really gotta figure this out. I’ll let you know what happens later.

If you can’t hear it In Real Life, then it may be coming up through the floor/desk. My little air conditioner used to shake the house. Are you using the standard Snowball desk mount?

Try adding the Book/Towel option.

Make sure the USB cable is a little sloppy and not tight. Noise can come up that way, too.

Please also note the furniture moving blanket on the desk. That’s not an accident.

The Snowball switch should be in cardioid position. 1, I think. And you should be talking into the blue name.


That’s right down there in the noise, isn’t it? I think your worst problem may be the effect going on and off.

Try the book and towel thing and then post a forum voice test.



Hi there, thanks for your input. My partner and I can definitely hear this humming ourselves. I’ll double check the Snowball when I’m home and get back to you - I’ve also been trying to sus out a means of further soundproofing the closet with moving blankets. The sound is coming from directly above and my space is pretty cramped.

Don’t fall into that “if only I had a better microphone” thing. Each microphone has it’s strengths and weaknesses and each interface has a personality. Let’s get one thing working first.

And when you do get something working Do No Change Anything during a book reading. ACX wants all the segments and chapters to match.


further soundproofing the closet

Low pitch hum is hard.

I published a kitchen table studio if that’s of any use to you.

That kind of thing may be enough. It doesn’t produce a NASA Sound Chamber, but it does cut down on environment noises and it kills room echoes.

I would really like that voice test. We are warned not to solve problems in a vacuum.


There is one other thing. I had a hum problem in my ‘studio’ and before I found where it was coming from, I moved the microphone around the room and found the one place where it was almost gone. I pushed several sound tests through that configuration. You can listen to the computer in monitor mode and move the microphone around in real time as you listen on headphones. It doesn’t matter if there’s an echo in your headphones. This isn’t Pulitzer readings.


Oh, the hum? My music bass cabinet didn’t turn off when I switched it off. I pulled the power cord.



The main hum frequencies are:

60 Hz (strongest)
120 Hz
240 Hz

There’s also a rising amount of sub-bass rumble, peaking at around 8 Hz. This can be mostly taken out with “Low rolloff for speech” Eq setting (https://manual.audacityteam.org/man/equalization.html)

I bet you’re wondering why we’re obsessing about this problem. You’re right. Nobody can hear 8Hz. We in California call those earthquakes, but the audiobook mastering tools work on whatever sound shows up, whether or not you can hear it. Having earthquake tones is a good way to throw off the volume balance of your audiobook submission.

60Hz is barely audible to most people and most sound systems can’t handle it, but 120 and 240 are perfectly audible. There is no removing 120/240 noise without removing those tones from your voice. That’s vocal tone damage.

When you cut your forum sound test, do it with the air conditioner running. Your last test was clear about what’s happening and what to listen for.


Of course, I’m home and the AC shut off just before I could record. But, here’s a clean sample, with what I consider my ideal room noise.

…and here we have our classic “humming, coming from above”. This is my upstairs neighbor’s central AC.

Apart from sub-bass rumble, that is very quiet. I’d say the level of that rumble is low enough to not be a problem. As I wrote previously, that can be greatly reduce with “Low rolloff for speech”.

Here’s the hum sample after applying “Low rolloff for speech” and Notch filters at 59 Hz, 120 Hz, 240 Hz, and then applying a little “soft Limit” (Limiter - Audacity Manual). Audio books are usually mono, so I’ve exported as mono MP3. Last time I asked, ACX said that they will accept stereo, provided that the entire book is stereo, but they prefer mono.

Note that I have used no “Noise Reduction”, though I probably would apply just a little for an actual submission.

We still don’t know if the hum is being picked up acoustically or through electro magnetic interference.