How to fix microphone hum

Monday, February 18th, 2013 | by

Does your podcasting or voiceover microphone hum? Do you hear a constant, low-pitched rumble, whine, or buzz in your audio tracks?

The problem might not be the microphone. The hum might exist in your room. The mic is just making it obvious.

I recently had a bad hum problem with a particular USB mic. I tried everything I could think of to make the noise go away:

  • changed USB cables
  • added a ferrite choke to the USB cable
  • changed USB ports on the computer
  • changed from desktop to laptop
  • turned off all the fluorescent lights in the house
  • unplugged and reset every connection in the audio chain
  • turned off the HVAC and every other appliance that might be causing line noise

None of these made any difference at all.

I tried a different USB mic. The hum was still there! It was less audible, but my spectrum analyzer showed a pronounced spike at 100Hz. Then I tried an analog mic through an external ADC. The 100Hz spike was still there. Clearly the hum was real — not a defective mic, not a bad cable, not some sort of weird USB crosstalk within the computer.

The problem was obvious, once I found it. For every test, I had mounted the mic to a boom arm attached to my desktop. (See my shootout and review of podcast/broadcast microphone boom arms.) Sitting on the same surface, three feet away, was a Seagate external USB disk drive, which runs 24×7 as a dedicated backup drive (running the OSX “Time Machine” utility). The vibrations from the spinning disk traveled across the desk, up the boom arm, and into the microphone. The mics without shockmounts, whether external or internal, captured more of the 100Hz hum.

I ran three tests at a fixed input gain level, using the USB mic most sensitive to hum. First up is the worst-case scenario, with the mic on its hard mount — essentially making it mechanically coupled to the disk drive’s motor. The 100Hz hum peaks at -44dB. (Click any of these images to zoom in.)

I replaced the mic’s hard mount with an elastic shockmount. The shockmount bought me 20dB of isolation; the hum dropped to -64dB.

Then I un-mounted the external Seagate drive from the desktop, and let its motor spin down. Predictably, the hum disappeared into the noise floor of the mic’s USB circuitry, around -100dB.

How to fix podcasting microphone hum

The lesson is that if your mic is picking up unwanted noise, the problem might not be some sort of esoteric EMI or RFI, or a bad mic or cable, but actual mechanical noise in your environment. Try this: take the mic off its desktop stand (USB mics nearly always come with desktop stands) and hold it it your hand. If that kills the hum, then there’s something on your desk that’s making the noise your mic is hearing. The culprit is probably the computer itself, or a disk drive, or a stereo component with a fan.

If you can’t get the noise source off the desk, you could try isolating it with Sorbothane feet or some other decoupling solution. I tested this idea by laying the Seagate external disk drive sideways on three Sorbothane feet; the 100Hz noise heard by the mic dropped by 30dB, well below the threshold of audibility. In other words, decoupling the disk drive from the desktop worked better at suppressing hum than putting the mic into a shockmount.

Another option is to mount the mic on a heavy floor stand. And I always recommend using a shockmount for the mic as well.

Bonus tip – freeware RTA

By the way, the RTA screenshots above are from BlueCat Software’s freeware FreqAnalyst spectrum analyzer plug-in. It is a great tool, and the price is right.

Posted in Acoustics, Microphones, Podcasting | 20 Comments »

20 Responses to “How to fix microphone hum”

  1. Joe Geoffrey

    February 18th, 2013 at 12:11 pm

    Great insight! It took me weeks to finally isolate an issue I was having. The culprit was my UPS (uninterruptible power supply). I moved all the audio gear to another leg of the fuse box and just kept the computer on the UPS. Problem solved.

  2. Mesa

    February 19th, 2013 at 11:58 am

    Moving the mic should be one of the first steps in troubleshooting the problem, maybe even the very first step. EMI can also be found by moving the mic, since its effect is proximal.

  3. Bill Poul

    July 21st, 2013 at 3:49 am

    Dude just thanks I tried everything also.
    I finally changed possition and guess what, its done!

  4. Dan Ortego

    August 14th, 2013 at 4:46 pm

    As usual, Matt finds a simple solution to a mysterious problem. Fortunately, that isn’t an issue I’ve encountered, or at least so far. My workstation is divided across three desk tables with anything that rumbles on the far end section.

    One thing I can add to the mix, is to be mindful of backup power supplies and cheap surge protectors. In fact, I only use high-grade surge protection and no battery backup box. Components that have external power supplies can also be a source of noise even if you can’t hear them.

  5. Ernest

    August 22nd, 2013 at 1:01 pm

    Doh! yes great insight and nice little right up – very helpful!

  6. Susannah

    October 12th, 2013 at 10:54 am

    THANK YOU so much. I had tried everything as well. Now, finally, I have silent silence.

  7. Rodrigo

    February 18th, 2014 at 9:37 am

    It happened to me as well. Fortunately, I have an old laptop and the vibrations were extremely obvious. Plus, it wasn’t a microphone but rather a portable Zoom H-1 recorder on a small tripod, so it was very obvious that the placement was the problem.

  8. BJ Mora

    April 4th, 2015 at 12:05 pm

    Another place I isolated hum was HDMI cabling (to computer/TV monitor). Switching “back” to VGA eliminated the hum.

  9. Maureen Murphy

    April 12th, 2015 at 6:57 am

    Tried all these things but I still have a a slight digital static sound in my VOs – its so frustrating – any recommendations are greatly welcome. I have wasted so much time

  10. MikeCJ

    October 19th, 2015 at 7:46 pm

    I have a TLM 103 and 102. Just got a TLM 193. When I plug in the universal audio pre-amp and then motu interface, it hums. Hums even worse if you touch the wire mesh. The 102 and 103 are completely silent. I also checked a Shure SM58, quiet.

    The only place it seemed to lose the hum was if it was within an inch of the interface. Again, the other mics, no hum anywhere. Any ideas?

  11. Garland Coulson

    November 16th, 2015 at 1:20 pm

    For me, I was getting a crackle and finally tracked it down to my wireless business phone.

    I unplugged the base station and the problem disappeared so now I just unplug it whenever I record with my USB microphone.

  12. Sunny

    March 9th, 2016 at 3:39 am

    Finally I got the solution. I m staying on 7th floor and my mic stand is heavy steel based. I made my room as much sound proof as possible, but couldn’t get off the 100hz peak. Finally I took the mic in my hand and sat on bed. Voila the hum is gone. Seems the him was originating from ceiling fan of the 6th floor flat or probably from the vibrations of the whole apartment.

  13. Michael Yanni

    July 3rd, 2016 at 10:05 am

    After reading your article, I figured out an incredibly simple fix for my bass hum issue. You know all those extra pairs of black socks you never wear? Well, I took 3 pairs and laid them into a square, crosshatch pattern. Then, I put my mic stand on top of it. Absolutely perfect vibration absorption. Thank you for helping me out! 🙂

  14. Joan Sanaker

    August 2nd, 2016 at 10:55 am

    I have an audio technica ATR2500-USB microphone for doing voice over auditions. I just bought a portable sound booth with wonderful padding and a head cover for background noise. I have a hum in my recordings. I have turned off everything in the house, including the AC, except the refrigerator which is a couple of rooms away. I am stuck. What could be making the hum?

  15. Peter Day

    October 11th, 2016 at 8:08 pm

    I was tearing out my hair (the little left on my bad head) when I found your article on microphone hum. I tried the remedies and that did the trick. No more hum! Thanks!

  16. Thomas Johnson

    November 4th, 2016 at 2:11 pm

    I had a problem with both a periodic whining sound and thumping using a good quality microphone. After weeks or reading and trying numerous things, my solution was to wrap the microphone cord in lamp cord (silver and copper wires). This is the same cord used to wire speakers, back in the day. I did not have to wrap it tightly, just a gradual candy cane wrapping, secured with electrical tape to prevent unraveling. The key was that the headphones and mic cord pairing, that came boxed with my voice to text program, did not have the above disturbance when I used it to make a voice recording. I was never able to determine the source of the disturbance. But, now it does not matter. I truly hope this helps everyone dealing with the frustration I went through.

  17. terrence

    March 16th, 2020 at 3:18 pm

    So had 100Hz hum. Disconnected mics from camera (hand held) and no more tone. Getting rubber rubber shock mounts, to test out.

  18. Tom

    November 30th, 2020 at 9:09 pm

    This post was very helpful. Sometimes we all need someone to point out the obvious. For years, I was plagued by a hum in an EarthWorks stereo pair and blamed the mics. Tonight I took your advice and experimented with possible external causes. It turned out to be proximity, first to the fluorescent piano lamp, second to an overhead light fixture. The mics are so sensitive, they pick up the vibration of the lightbulb filaments! Either that, or the oscillating electric field of the light bulbs generates interference in the mics via induction. Anyway, now I know what I need to address. Thanks!

  19. james knowles

    December 11th, 2021 at 9:25 pm

    I had a hiss floor with my SE V7 similar to other dynamic mics,
    but with a high-pitched scratchy sound in it.
    After trying many things, I ended up killing it off by
    loosen/tightening the external threads a turn or two with a tiny bit of
    WD40 on them and screwing them in tight.
    That killed the scratchiness, and some corrosion/machining gunk
    came out(as wiped off). The worst offender was the single
    screw that holds the XLR tail in.
    I love the SE V7. I think that the grit was acting like a ‘semi-conductor’.
    This was an electrical effect, but one I never read about before.
    Elon Musk said once that 9/10ths of the rocket failures were things they
    hadn’t even identified as failure modes. Hunting down noise is a picky business!

  20. Anthony

    October 27th, 2022 at 5:32 am

    I had exactly the same issue and found this page. You totally solved it for me! thank you!

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