Old 09-13-2014, 10:08 AM   #1
kenz
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Default Remove Broadcast Tone (15750Hz) ?

Hey guys,

This has been annoying me for a while. On older recordings in my collection, they seem to have some annoying tone around 16khz, which upon researching I found it is from CRT monitors in the recording studio. These "broadcasting monitors" were very common I guess some years ago, hence why mostly on older recordings I guess.

I'm trying to do some audio restoration on them, but can't quite get how to get rid of that "Broadcast tone" from CRT monitors (the scanline sound, 15750Hz to be exact for US NTSC).

I know I can use a steep filter there, but how much should I attenuate? Obviously if I do -100db it will remove all the 15750Hz range of frequencies, even if they are music.

Any programs out there for the job or is there some tricks that restoration gurus use for this with filters?

And yes I can hear it by the way, and it's driving me kind of nuts.
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Old 09-13-2014, 10:33 AM   #2
msmucr
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Hi Kenz,
i've used to remove same line frequency (only PAL variant) from voiceovers.
Freeform linear phase filters worked best for me and i attenuated something around 60dB, i can't recall exactly, in very narrow range around center frequency.
You can use ReaFIR for this job.. It is bit cumbersome to set right points as there isn't zoom at frequency spectrum, but it can be done.
If you switch it to Points (flat) mode, you can enter exact position of each point via context menu item "Set...". Here i would add four points, so resultant filter will grab something like 10Hz range. Then i will experiment with FFT length to be as "invisible" as possible. But as frequencies are around 15k, it won't be necessary to go to longest FFT lengths.

Michal
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Old 09-13-2014, 01:28 PM   #3
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I have similar issues. I notch out the specific frequencies with ReaEQ, set to minimum bandwidth. Works great.
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Old 09-13-2014, 02:38 PM   #4
planetnine
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Likewise with a much lower frequency -a 700Hz whistle caused by the air intake of a fire/environmental monitoring system in a cathedral. Using an almost minimum width notch filter in ReaEQ and automating the gain from 0dB down to about -8dB during quiet sections in-between recital playing/choral.

The precise frequency is found using the spectrum analyser in ReaEQ and sweeping the a boost to find the centre of the tone by ear. That frequency is then used as a cut, but we don't use it during the music where it is masked, only during interludes and fade-outs by automating that band's attenuation. The exact frequency is checked for each recording as it varies slightly day-to-day.


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Old 09-13-2014, 03:20 PM   #5
kenz
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Thank you for the tip guys.

I thought there would be some kind of automated tool for this, but I suppose I was right from the start assuming I have to do it manually, and perhaps even use automation for parts of it (i.e in loud music parts with high frequencies, it is masked).

At least now I don't feel like I'm wasting time for something stupid, and yes Linear Phase filters is what I find ideal here too, they are also much more steep than analog filters or the like; the fewer it affects the rest of the material, the better.

I wanted to experiment with this ISSE much easier to spot: http://isse.sourceforge.net/

but it crashes everytime I try process something, I guess it's alpha meh.
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Old 09-13-2014, 05:39 PM   #6
RJHollins
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hmmm ... glad this has been brought up, as I thought my ears were giving me trouble or something.

I received a few tracks to master and I kept hearing this annoying hi pitch ...

I'll go back and slap an analyzer on it to see if I can spot it.

thanks
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Old 09-13-2014, 06:43 PM   #7
EpicSounds
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I can batch process with RX for you, but with spectral editing it's as easy as selecting vertically and hitting delete. Let me know if you need someone to do the job quick
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Old 09-13-2014, 07:30 PM   #8
Moogie
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Quote:
Originally Posted by EpicSounds View Post
I can batch process with RX for you, but with spectral editing it's as easy as selecting vertically and hitting delete. Let me know if you need someone to do the job quick
RX really is the best tool for something like this.
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Old 09-13-2014, 10:22 PM   #9
RJHollins
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Thanks for the RX tip ... it is an amazing app that gets lots of use for my restoration task.

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Old 09-14-2014, 01:01 PM   #10
suleiman
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I would humbly suggest ReaFIR for such surgical removal. Let the plugin have a taste of some of the hum / noise and then let it work its magic. Very quick and clean. Detailz are in the Reaper User Manual as well as ReaFX guide and wiki.
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Old 09-22-2014, 02:44 PM   #11
kenz
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Quote:
Originally Posted by TexasFury View Post
Is it one exact frequency? If so, why not use phase cancellation instead?
It is sort of one frequency, but the signal isn't pure for that to work, there's all sorts of noise since it's from recording it.

Sorry for the late reply, I am very busy lately, again thanks for the tips guys I will take note & use.
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