Low level hum in background of recordings

Hi there,

I am running Audacity 2.4.2 on an MacOs Catalina version 10.15.7. I have a Samson G-Track Pro microphone and am getting a low level hum that is noticeable in my recordings. At first, I thought it may be a problem with my headphones because when I unplugged them, it seemed to go away at first. But, in reality, it didn’t go away. There is no fan running, or any obvious ambient noise in my recording area. I have attached a quick recording that you can hear it in. The recording is unedited/treated, other than the recommended Audacity mastering steps for RMS.

Thanks for your help,


That’s not wall power hum. That’s 90Hz. I would have called computer fan.

You know those pictures you see of people swinging metal detectors back and forth at the beach?

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You can do that with your microphone. Aim it back and forth over your studio. You can set Audacity to listen in real time while you do this. Wear your headphones. The side grill above the company name is the “front” of the microphone.

This is how I found a bad speaker in my music room. Constant super-low volume hum coming from somewhere.

I think you missed a step. Post another test and this time don’t do anything to it.


As it’s exactly 1.5x mains frequency, my money is on Intermodulation between 60Hz mains and 30Hz subharmonic, (or maybe 30Hz artefact from the A/D converter).

Ok, here is a naked recording. I had my headphones on and plugged into the mic.

And, actually I don’t hear it in this one. This is the problem. It’s intermittent.

And another, where I can hear it. No editing.

my money is on Intermodulation between 60Hz mains and 30Hz subharmonic

In which case the metal-detector, sweeping the microphone across the room won’t do anything. Tests with negative results still tell you stuff.

It could be lights, too. Nobody actually dims LED lights. They finagle time-sharing and pulse width management (because it’s cheap and inexpensive) That could certainly give you intermodulation products. I have an air cleaner which “appears” to have a yellow light on the front. If I flip my fingers in front of it, it’s actually switching very rapidly between red and green lights.

The easy way to test that is turn all the room lights off.

I don’t actually believe this one, but it’s easy to test. Make a test recording and leave your phone in another room.

Are you reading from a tablet like normal people? Those can have a 90Hz display. Temporarily put that in another room.


You got it! There is no 90Hz hum in that sound file.

I applied Audiobook Mastering and the file passes ACX Audiobook testing (but not by much).

Screen Shot 2021-01-05 at 09.11.48.png
You still need to find that noise. There’s nothing more crazy-making than sound damage that comes and goes.

I drag-selected some clean background noise and Analyse > Plot Spectrum at those settings. I pulled the display sideways to make it easier to see. This is the first example, with the noise.

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See that big purple spike?


I’m using the ACX Audiobook testing and mastering because, in general, if you can pass that, you can submit anywhere else. Their standards pass broadcast proof of performance.

You are warned to use all three Audiobook Mastering tools. Don’t add any and don’t leave any out. They clean up after each other.


It’s intermittent.

Isn’t that just the very best? Nobody wrote you can’t have two or more problems, either.

The first ACX Mastering tool, Filter Curve, is a rumble filter. It’s job is to get rid of everything lower pitch than about 100Hz. Many home microphones produce rumble, thunder, and low pitch trash (because they’re home microphones) and basic wall power hum is 60Hz. All gone. That’s what saved the sound file I analyzed. It had a lot of low pitch stuff going on, but much of it is more or less normal and it all vanished in the Filter Curve correction.

90Hz is right on the edge. Some of that gets quieter, but a lot of it survives the mastering corrections. There was no 90Hz trash in the second sound file I checked. That’s why it worked so well.

I would so start waving the microphone around the room and see if you can figure out where this is all coming from. At least the 90Hz tone. That one is not normal and may represent something broken.

How are you reading the work? Not paper, right? You’re reading from something electronic?

I use a paper script, record on a stand-alone sound recorder, and leave my phone in the garage. I don’t have any of these problems.


Nowhere in the messages do you tell us why you’re doing this. Are you producing training exercises for a school?

Stand-alone training classes or is the goal to submit for audiobooks?

Fair warning that there are two relatively new restrictions for new audiobook readers. I have to be able to buy your book in paper or eBook on Amazon. No fair trying to submit both at once. One forum poster tried that. It wasn’t pretty.

There is a list of book types they’re not interested in.

Scroll down.


The fuzzy rule is your book should have plot, characters, and setting. There was a forum poster who was going to try to read her cookbook. Probably not.


Ok, so I’ll turn off the lights, record. Take my phone out, record. I don’t have anything else electronic in the room. What else should I try? It is totally crazy-making. Especially when I record a big long thing and then it’s ruined. Could it be the mic itself? It’s only a year old, I wouldn’t think so but…

I record curriculum for an online education company. I do typically read text off my phone to record, so that could most definitely be it. I’ll try taking it out and see.

Could you explain a little more how to do the wave around test? What am I looking for in the playback that indicates a problem? I don’t have access to my space right now, but will double check my mastering set up. I set it up on a shortcut and don’t actually remember how to see the steps!

Thanks for all your help. This extra work has been really important this year and I’d like to make sure my quality doesn’t go in the toilet!


Ok, so I’ll turn off the lights, record.

I know you’re waiting for me to trot out a magic formula for solving this, but sometimes step-by-step scut work is the answer.

If you’re making actual recordings, slate them. “I turned the lights off,” “I’m turning my phone off,” “Turning my tablet off.” Hold your breath for a second or two after you do that so we don’t have to compete with your lungs for the analysis.

Could it be the mic itself?

I don’t think so, either. I really liked the G-Track before this one.

I told the owner if he wasn’t paying strict attention after this photo shoot, I was going to take it home with me.


I need to step away for a bit.


The G-Track can be set for Cardioid (directional) and it probably should be. That means the sensitive spot is the side grill just up from the company name. You can pick up the microphone and aim it to different parts of the room and it will “prefer” that direction over others. I expect if you aimed it to the room heater or air-conditioner, the wind or rumble noises will increase.

This is how I found my bad sound cabinet. I aimed my microphone to the cabinet (which was supposed to be off), and it said, “mmmmmmmmmmm.” So I got closer and it said, “MMMMMMMMMMM.”

So I pulled the power plug and it said, “______________”

A bit ago I was recording a simple voice track on a messy desk and I laid the microphone on top of the mixer power cables.


You can do all this live by plugging your headphones into the G-Track, set Monitor On (on the rear) and listen as you go. It’s perfectly “legal” to jam the microphone close to the source of noise just to make sure of what’s happening. You can also yell into a microphone. That’s OK, but never blow into one. That can reduce some microphones to expensive trash.

Let us know how it goes.


Ok, I will try that. I also played around with some different conditions – I think I hear more hum in the file with my bluetooth on and the lights off than the one with my phone put away and the lights off. I expected the opposite.

Also, here are the mastering specs I use.
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It counts if you can make it worse. That won’t do you any immediate good, but it will tell us more about the problem.

Nobody wrote it can’t be a monitoring problem. Are you on wireless headphones or earphones? Wireless means you can’t live monitor yourself for real time quality control. Wireless also greatly increases the possibility of listening damage.

Can you post the actual Macro text? I’ve been avoiding publication because of the wonky way Loudness Normalization behaves.