hum with 1400 Hz and split up

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hum with 1400 Hz and split up

Permanent link to this post Posted by dev » Sun Feb 04, 2018 7:17 am

Hi,

the de-hum from here
https://forum.audacityteam.org/viewtopi ... 03#p341803
took care of most noises but there is one recording with a different spectrum where there is a superimposed hum with bands at 1400, 2800, 4200 ... Hz, each time split up into several bands that are close to 100 Hz wide.
I've tried to modify the de-hum plugin by entering 1400 instead of 50.68 and only 6 odd harmonics to stay within range and it removed something accordingly, so I can play a bit with the plugin, but I can't think of a way to take into account the range of bands. Is there a reasonable way to do this? Collateral damage doesn't matter as long as the voices are understandable. Maybe it would be more reasonable to remove a larger notch from say 1000 to 1700. I've tried to do this with Equalizer with limited success.

I'd just appreciate some help if this is easy. It's just one recording that has this. If this would take a lot of time to figure out please don't do it.

thank you

using Audacity 2.1.2 on mbp running Mac OS 10.12.6 Sierra
Attachments
Screen Shot 2018-02-04 at 07.40.45.png
left part is with 50.68 Hz 150 odd harmonics removed, right part is as-is.
Screen Shot 2018-02-04 at 07.40.45.png (548.1 KiB) Viewed 125 times
2018-01-25pm_1300Hz-q.wav
5 secs noise, 3 secs voices
(1.7 MiB) Downloaded 2 times
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Re: hum with 1400 Hz and split up

Permanent link to this post Posted by Trebor » Sun Feb 04, 2018 6:00 pm

dev wrote: 2018-01-25pm_1300Hz-q.wav 5 secs noise, 3 secs voices (1.7 MiB)

That's got a mixture of analog-main-hum and digital-whine.
The noise is greater than the sum of its analog & digital parts.

Fortunately the constant-noise is in-phase on the stereo tracks. So if you invert one of the tracks and mix to mono, the constant noise disappears, but the resultant voice has a lot of bubbly computery noises, (digital artifacts), see ...

2018-01-25pm_1300Hz-q , before-after , invert one channel.flac
trading one type of noise for another
(971.41 KiB) Downloaded 4 times

dev wrote: I've tried to do this with Equalizer with limited success.

Audacity has a tool which is more precise than the equalizer : spectral edit tool.
You could use spectral-edit-tool to manually take out the worst offenders, e.g. ...

Image
https://manual.audacityteam.org/man/spectral_selection.html#example
Last edited by Trebor on Mon Feb 05, 2018 10:45 am, edited 1 time in total.
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Re: hum with 1400 Hz and split up

Permanent link to this post Posted by dev » Mon Feb 05, 2018 1:56 am

okay, intermodulation I won't understand by tomorrow but that's what this is and how these bands split up further. Many thanks for the sound sample, as you say the bubbly noises don't sound so nice, so I'll leave this out though I've tried inverting and mixing myself and it's good to know one can do this. But the spectral edit tool works really great. Thank you for everything!
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