What is this noise? (image)

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dev
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What is this noise? (image)

Post by dev » Tue Jan 30, 2018 5:18 am

Hi,

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.

thanks!
zoomin.png
zoomin.png (148.16 KiB) Viewed 447 times
oneperiod.png
oneperiod.png (140.28 KiB) Viewed 447 times
zoomout.png
zoomout.png (154.87 KiB) Viewed 447 times

kozikowski
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Re: What is this noise? (image)

Post by kozikowski » Tue Jan 30, 2018 12:37 pm

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.

Koz

dev
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Re: What is this noise? (image)

Post by dev » Tue Jan 30, 2018 1:54 pm

sorry, I wasn't aware. 10 secs of just the noise and 5 secs with some voice. Thanks for looking at this.
Attachments
2018-01-26pm-10secAudacity.wav
(1.74 MiB) Downloaded 16 times
2018-01-26pm-voice.wav
(1.87 MiB) Downloaded 14 times

Trebor
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Re: What is this noise? (image)

Post by Trebor » Tue Jan 30, 2018 3:27 pm

dev wrote:what is this noise called, and is there a way to remove it? ... 2018-01-26pm-voice.wav (1.87 MiB)
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 ...

dev
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Re: What is this noise? (image)

Post by dev » Tue Jan 30, 2018 7:56 pm

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

Trebor
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Re: What is this noise? (image)

Post by Trebor » Tue Jan 30, 2018 10:58 pm

dev wrote: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)
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 KiB) Downloaded 17 times
Install the plugin, then apply it to the affected audio without adjusting any of the settings.

dev
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Re: What is this noise? (image)

Post by dev » Wed Jan 31, 2018 6:50 am

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!

Trebor
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Re: What is this noise? (image)

Post by Trebor » Wed Jan 31, 2018 7:56 am

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
Audacity spectrum window size 8192 , (default is 1024)
Audacity spectrogram, Before-after notches .png (338.38 KiB) Viewed 382 times

dev
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Re: What is this noise? (image)

Post by dev » Sun Feb 04, 2018 5:49 am

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!

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