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Topic: Is there a better way to get rid of the CRT line in audio files? (Read 1245 times) previous topic - next topic
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Is there a better way to get rid of the CRT line in audio files?

I have been out of it for a long time, and recently started up again, noticed some rips have this annoying ~16kHz line. Some even have a harmonic(?) line at ~19kHz (luckily I can't hear that one anymore)
Found this topic/post and used the attached fillter in the convolver... but it removes more than that line. Is there a better way to get rid of that is more narrow, damps that exact frequency?
Problem is I don't know if it's a PAL or NTSC tube that caused it so need two different methods, one for 15.625kHz for PAL and one for 15.734kHz for NTSC

before and after:

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #1
A parametric EQ centered around 15kHz with a sharp Q should help filter it out, but it's hard not to affect neighboring frequencies unless you use a very sharp EQ.

The question may be whether or not you can hear that 15kHz/16Khz hum/whine, since it's usually pretty low in the mix (if you can hear it at all after a certain age).

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #2
Quote
his annoying ~16kHz line. Some even have a harmonic(?) line at ~19kHz (luckily I can't hear that one anymore)
It wasn't "annoying" when the recording was originally produced & released because almost nobody had a spectrum analyzer and nobody knew it was there.  ;)

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #3
I once had an FM tuner that applied a 19 kHz sine counter-phase to the incoming pilot tone. AFAIR they used an oscillator PLL locked to the pilot.
Maybe such a thing can be simulated by some DSP?

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #4
There is no good AND universal or easy way. And in some, rather frequent, cases there is not even a good way at all, for example when the frequency is not constant for any reason.
Unless something new was developed in the last 7 years or so. Which is unlikely given that most people cannot or do not want to hear* it or care about it (but I did, for some time - wasted some of it by using complicated methods to "carefully" tear it out).
Even in the simplest case, a super sharp EQ sounds like an easy solution, but look what happens any time when the energy at that exact frequency is quickly changing.
For example when the unwanted tone suddenly stops, the sharp EQ will briefly "add it back" before gradually recovering.

* with typical record/listening levels
a fan of AutoEq + Meier Crossfeed

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #5
One of the relatively simple routines I tried at some point, is roughly this:

A = SomeEQ(Original)
B = A - Original
C = SomeLimiter(B)
Result = Original + C

This is supposed to limit the amplitude difference that EQ will introduce, I probably f..ked up the formulas but I hope this still conveys the idea. Somewhat similar to turning the EQ off during the segments where it would do more harm than good, that is when the measured energy at the unwanted frequency goes above "normal" level, for example when some high pitched percussion hits followed by the "ripple" that a high-Q EQ inherently adds.

But you have to be super careful with choosing parameters for 2 DSPs which also interfere with each other (I mean you can't just assume you can "optimize" one of them and then the other and then you're done)
and with unlucky parameters the result can be worse than the simple EQ.
a fan of AutoEq + Meier Crossfeed

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #6
You can use notch filter in Audacity.
Justify My Love by Madonna is very bad when it comes to this.
In this case it is best to separate channels and fix them individually.
You can see quick demonstration in pictures below at lowest settings.
To get good results you will have to experiment little bit.



gold plated toslink fan

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #7
Being a Cool Edit / Audition affectionado, I would find the part if the audio with the least amount of audio material (meaning a part with nothing but noise) and profile that section to apply as the noise reduction with the needed parameters to deal the least amount of harm to the entire program. The best part of this method is the profile can be adjusted depending on which program material is being addressed. Perhaps Audacity has a similar function.
"Something bothering you, Mister Spock?"

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #8
It's all preference. I do all this stuff in Reaper. I'd notch filter with ReEQ (it's a kind of Fabfilter clone based on JSFX). Here it's not relevant but I remember there was some annoying noise in Aphex Twin - Tha I filtered out.

EDIT: Yeah it has that perma noise at 15.5k

X

In Autechre Piezo there is also some >15k perma and clean sine wave coming in after some beats, obviously intended, but I can't hear that one any more at my age of 50+

 

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #9
affectionado
Look it up.  I only mention it because pronunciation misunderstandings are becoming rife (eg should've) and then baked in by people writing what they think they hear ("should of").

Aficionado.
It's your privilege to disagree, but that doesn't make you right and me wrong.

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #10
Thanks all.

As @Julien already mentioned, most times I don't hear it if it's there, but in rare cases where the original audio level in the higher frequencies is in the low ends I just notice it's there. Especially when using headphones and just enough to be irritating as all heck.

Audacity's Notch Filter proved to be very effective for this particular track. Turns out there were actually two frequencies, one pulse tone at ~15625 and a constant tone at ~15425.
Thank you @Markuza97 and @Destroid for pointing me to that one. I am not that familiar with Audacity so didn't know this filter could do that.

left is before, right is after

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #11
@fooball It’s just a joke some ppl don't understand, such as unpronoucing certain words. (That was another joke just meow... again, a third time! Fun stuff.)

Edit: The point is I was still understood correctly despite the deliberate grammatical delivery.
"Something bothering you, Mister Spock?"

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #12
Quote
his annoying ~16kHz line. Some even have a harmonic(?) line at ~19kHz (luckily I can't hear that one anymore)
It wasn't "annoying" when the recording was originally produced & released because almost nobody had a spectrum analyzer and nobody knew it was there.  ;)
I still can hear that 16 khz line. Propably not on this recording but i have plenty where thats the case.
And so, with digital, computer was put into place, and all the IT that came with it.

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #13
The point is I was still understood correctly despite the deliberate grammatical delivery.
I admit I didn't spot it was deliberate poetic licence, but my point still stands: other readers might think it was the actual word and then it propagates.  No need to get het up about it, by following up with the correct spelling I have helped to prevent that.
It's your privilege to disagree, but that doesn't make you right and me wrong.

Re: Is there a better way to get rid of the CRT line in audio files?

Reply #14
Quote
his annoying ~16kHz line. Some even have a harmonic(?) line at ~19kHz (luckily I can't hear that one anymore)
It wasn't "annoying" when the recording was originally produced & released because almost nobody had a spectrum analyzer and nobody knew it was there.  ;)
I still can hear that 16 khz line. Propably not on this recording but i have plenty where thats the case.
It's a collection box, so not sure if you can still get it someplace "Enya - Only Time: The Collection", consist of 4 discs of which the 4th is an enhanced one with a video track. If you have the set, disc one is the one with the problem, tracks 3, 4, 5, 6, 10 and 12 are the worst. These came from the album "The Celts" and were likely not remixed/remastered. On that album almost every track has the same line(s) one pronounced around 15.625kHz and one less pronounced, for me inaudible, just under 19 kHz. Only 3 tracks are clean.