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Topic: strange 16kHz "line" in flac spectrogram (Read 15310 times) previous topic - next topic
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strange 16kHz "line" in flac spectrogram

Hi,

I have a flac file (obtained by ripping an original CD and encoding) and noticed that there is some kind of 16 kHz "line"
in the spectrogram.  Does someone have an idea what this is?  [a href='index.php?showtopic=77742']spectrogram[/a]

thnx,
Steven

strange 16kHz "line" in flac spectrogram

Reply #1 –
CRT TV in the studio. That's the line whistle - the sound coming from the back of the CRT TV tube at the line frequency of the video signal. 15.625kHz for PAL; 15.734kHz for NTSC.

It's quite common in recordings. Occasionally it can be horribly loud, and people with good high frequency hearing can be annoyed by it. It doesn't "look" that loud in this case though.

Cheers,
David.

strange 16kHz "line" in flac spectrogram

Reply #2 –
I sometimes see this spectrum line on “original”, uncompressed material. And even on a CD “test” disc (!) I see a heavy spectrum dip at a band of this central frequency in an electronic music sample, as a result of sound engineers’ attempt to “kill” this line! All this says that there sometimes defects even in studio equipment causing such a contaminating signal. I don’t know what it is exactly.

strange 16kHz "line" in flac spectrogram

Reply #3 –
That's the horizontal sweep frequency of a TV. The recording equipment was not properly shielded from a nearby television.

strange 16kHz "line" in flac spectrogram

Reply #4 –
Quote from: pdq on
That's the horizontal sweep frequency of a TV.

Yes, many people said in forums that it was. I didn’t want to believe it because what must be the level of equipment servicing personnel in professional recording studios, neglecting their duties to a degree to let such contaminating signals spoil commercial products! A thing that is easily seen by any “customer”!
An obvious degradation? But why?

But now I trend to believe it…

strange 16kHz "line" in flac spectrogram

Reply #5 –
I doubt you can even hear that line - It's barely visible. I have tons of other popular music with this, not only highly visible, but terribly annoying as well, since I can easily hear this frequency.

Maybe most older persons can't hear this, but that such failure often just slides through the entire music production system, surprises me.

Coincidently I actually made an impulse file today to get rid of it - Not worth much, if you can't hear the frequency anyway, but here you have it. Use with foobar2000 and the foo_convolve component. It's made with Audition notch filter at 15675hz with 70dB attenuation using "Very Narrow" Notch Width. To me it applies perfectly on the tracks I have with this problem. If anyone could suggest better settings, please post

[attachment=5622:Unitpuls...16khzfix.wav]
Can't wait for a HD-AAC encoder :P

strange 16kHz "line" in flac spectrogram

Reply #6 –
I got such a ~16kHz tone just recently. I recorded it myself using a really old and cheap Sony F-V05T mic connected to my onboard mic-in. I recorded the whole night (wanted to know if I'm beginning to snore...  I don't, btw).

It was there constant, the whole night. And of course, there was no TV running the whole night in my house.

PS: It's even there when there's no mic connected to the mic-in... 

strange 16kHz "line" in flac spectrogram

Reply #7 –
Quote from: Fandango on
I got such a ~16kHz tone just recently. I recorded it myself using a really old and cheap Sony F-V05T mic connected to my onboard mic-in. I recorded the whole night (wanted to know if I'm beginning to snore...  I don't, btw).

It was there constant, the whole night. And of course, there was no TV running the whole night in my house.

PS: It's even there when there's no mic connected to the mic-in... 


Do you have a graphics card with TV output?

strange 16kHz "line" in flac spectrogram

Reply #8 –
This may be a scanline generator on your graphics card.

strange 16kHz "line" in flac spectrogram

Reply #9 –
I don't know actually. It has an HDMI output, but I don't know if it still has S-Video/Composite output.

edit: Damn. Yes, it has an S-Video out (which I ironically won't need at all.) Line-In recodings have even worse background noise, not only the scanline.

strange 16kHz "line" in flac spectrogram

Reply #10 –
Quote from: Fedot L on
I didn’t want to believe it because what must be the level of equipment servicing personnel in professional recording studios, neglecting their duties to a degree to let such contaminating signals spoil commercial products! A thing that is easily seen by any “customer”!
An obvious degradation? But why?

Sorry to shatter your belief in so-called "professionals", but there's a war going on for some years now.
It's only audiophile if it's inconvenient.

strange 16kHz "line" in flac spectrogram

Reply #11 –
Quote from: Fedot L on
Quote from: pdq on
That's the horizontal sweep frequency of a TV.

Yes, many people said in forums that it was. I didn’t want to believe it because what must be the level of equipment servicing personnel in professional recording studios, neglecting their duties to a degree to let such contaminating signals spoil commercial products! A thing that is easily seen by any “customer”!


Well thats's true of, any customer who has access to good spectral analysis tools. Today pretty fair spectral analysis tools are even freeware, but back in the day we paid the big bucks to have them. I'm talking thousands of dollars.

Quote
An obvious degradation? But why?


The alleged degradation is generally not audible at all. Typically they are more than 40 dB down.  Between masking and the elevated threshold of audibility at high frequencies, nobody hears nuttin'.

When people hear 16 KHz tones from NTSC  TV CRT horizontal output transformers, its usually at a reliatively high acoustic level, even though the means of generation and transmission are not obvious.

Sometimes the source of spurious high frequency tones is in the production equipment itself. For example some of the early professional consoles with digital mixdown controls had a TV monitor CRT right in the console. It was used to program and control the console's automated mixdown computer. I have encountered a number of recordings with this trivial flaw in them.

Today, most technical sources of high frequency interference are either well-shielded and/or operate at such a high frequency that their interference is at such a high frequency that they don't show up in recordings.  For example the displays we use today have far higher sweep frequencies, and any switchmode power supplies are either well-filtered and filtered; and/or have their operational frequencies so high that they leave no tracks on any consumer media.

Finally, if a production engineer does find a spurious tone in a recording that he wants to make go away, he can just notch it out with his handy-dandy digital notch filter. Situations like this generally can't happen in the digital domain, so once the production shifts to the digital world, it can be made to appear as clean as desired, even if it started out a little dirty.


strange 16kHz "line" in flac spectrogram

Reply #12 –
I noticed the problem first when I heard a high-pitch sound in a commercial CD. I started investigating with spectral analysis tools, and found it on more CDs, though in most cases it wasn't audible. I saw it on CDs of many genres, on recordings older and newer. Had a discussion about it on another forum. The interesting thing was that the frequency was typically slightly (but clearly) off the frequency expected from TV (NTSC or PAL) contamination...
Ceterum censeo, there should be an "%is_stop_after_current%".

strange 16kHz "line" in flac spectrogram

Reply #13 –
I'm thinking that this problem might re-emerge due to the professionalisation of home recording and the general use of consumer PCs in audio production. Because like in my case a graphics card with a scanline generator could introduce this tone once again.

strange 16kHz "line" in flac spectrogram

Reply #14 –
Doubt it. People doing proper recording install sound cards that don't record such interference from within the PC! It's often said you should mount your sound card as far away from you graphics adapter as possible - or use an external sound card.

Typical PC monitors are fine - much higher scan rates.

Cheers,
David.

strange 16kHz "line" in flac spectrogram

Reply #15 –
Quote from: Fandango on
I'm thinking that this problem might re-emerge due to the professionalisation of home recording and the general use of consumer PCs in audio production. Because like in my case a graphics card with a scanline generator could introduce this tone once again.


In your case it was tied to having a TV out signal.  For computer monitors the sweep frequencies are much higher.  Mine is running about 65 khz. (864 lines x 75 hz refresh rate)