What is this noise? (image)


what is this noise called, and is there a way to remove it? This is spoken word. using Audacity 2.1.2 on macbook pro running 10.12 Sierra.

If you have an idea what could cause this, info is appreciated as well. I have no access to the setup. My guess is, there is a mixer, some fairly ok mics plugged in, a zoom H2n recorder or similar, a set of speakers, and not very stable electricity with frequent power outages where all those things don’t happen and some Limiter2 amplification gives very listenable recordings.


I have no access to the setup.

So you can’t get a sound clip? 10 seconds stereo, 20 seconds mono.

I don’t know we can do anything with the pictures. We need the sound signature and spectral distribution analysis, etc. etc. etc.


sorry, I wasn’t aware. 10 secs of just the noise and 5 secs with some voice. Thanks for looking at this.

It’s a real-bad case of mains-hum, where the fundamental frequency is 50.68Hz, (it’s usually closer to 50Hz),
and you only have the odd-numbered harmonics of 50.68Hz.

Notch-filters can remove the buzz , but there is collateral-damage …

Wow that would be really cool. That kind of collateral damage is much better.

Are you using an extra plugin? Notch Filter doesn’t do the same when entering 50.68 Hz and going down to 0.1 with Q. (I don’t understand what I’m doing, I understand Hz but not Q and don’t know the frequencies of harmonics)

For some other time, Is there something easy to not pick this up while recording? I get about a third of what wikipedia says about mains hum but not the main points.
thank you

150 notches are required: the odd multiples of 50.68 Hz , i.e. 50.68 Hz, 152.04 Hz , 253.4 Hz, etc

Below is a hacked version of Steve’s plugin which will make all of those notches …
de-hum 50point68Hz.NY (2.19 KB)
Install the plugin, then apply it to the affected audio without adjusting any of the settings.

this is so cool. a private plugin. thank you so much, Trebor! : ) the recording location is rural India with power outages and such and minimal portable equipment, so not much hope of troubleshooting anything from the recording side. There are a few recordings that have had this on and off and it didn’t correlate with anything happening on them (except for the joking remark on the uploaded recording). this is much easier and perfect sound quality for what it is needed for. thank you!

Typically mains-hum is exactly 50Hz or 60Hz, and only a few harmonics, so only a handful of notches are required.
But in your example a standard 50Hz de-hum filter misses the target, and the full 150 odd harmonics are necessary …
Audacity spectrogram, Before-after notches .png

ah! now I see them. the horizontal lines in spectrogram view with spectrogram settings window size to 8192. and they’re gone as soon as I apply your de-hum. nice, thanks!