15840 Hz

We use a camera and a monitor for our organist when the sight line to the conductor is blocked (which is frequent).  We also use TV monitors at the front row of the audience for some of the singers when their back is to the conductor.  Thus, even though we've never shot for TV, it is quite common to find that 15,625 signal in my recordings.  And it takes very little of it to show up in spectral view.

As far as the other instances go, I can only imagine what all has gone on in the studios.  It's reasonable to suppose that all manner of reference who-knows-what, as well as communications, could be in play here.

Can a TV camera create this as well?  A friend recorded a vocal album with one of the London orchestras about a decade ago, and his audio has "flyback whine" also.  I've no idea why a TV would have been present.

I've just spent half an hour ripping bits of tracks from commercial CDs, and the results are variable. There seems to be more of this on the left channel when it shows up, and it's usually around the -70dB mark. And you can see it on a frequency analysis, certainly. On some tracks it comes and goes, as well. I've not seen a really solid line of it, but a few that get pretty close.

I have no idea exactly what the production process was on all these random CDs, so for a comparison, I picked a commercial CD where I know exactly what the processing involved was - because I did all of it up to the point where it was glass-mastered. And what's really weird about that is that there's a very faint line at about 18k on it that's definitely not on the file supplied for the glass mastering - I checked carefully. And it's not consistent, either. This is at a level which is, quite frankly, completely immaterial; it's around the -80dB mark.

So now, I have no idea what's happened here at all. But you have to be a little suspicious about the glass mastering process - especially one where it's not doing this consistently - and this seems to apply to a lot of CDs.

Just curious, where are you guys getting 15625hz?

Original B&W NTSC Standard:
30fps x 525lines per frame = 15750hz horizontal scan rate

Color NTSC:
29.97fps x 525lines per frame = 15734.25hz

JTC

Whoops!  Just read the thread again and realized many of you are well outside the land of NTSC.  Apologies all around.  It does sound like a video related noise source.

JTC

OK, so PAL runs 625 lines at 25 frames per second, which gives you 15,625.  But you're right, since we're in NTSC land over here, I should be talking about 15,750.

I've only had the opportunity to inspect audio both before and after glass mastering five times, and have never found a single bit to be different -- the result one would hope for.  Steve, could some other mastering step be involved?  Say the digital master went through one of these places that seem to be all the rage these days, passing the signal through an analog step in the chain, and a tiny bit of interference is picked up along the way.  I'd vouch for re-digitization, in any case.

And for those with the whine more on the left channel, well, I guess the video monitor was on the left side!  But why would this be so consistent?  (Ours would be heavier on the right, for what it's worth!)

I've only had the opportunity to inspect audio both before and after glass mastering five times, and have never found a single bit to be different -- the result one would hope for.  Steve, could some other mastering step be involved?  Say the digital master went through one of these places that seem to be all the rage these days, passing the signal through an analog step in the chain, and a tiny bit of interference is picked up along the way.  I'd vouch for re-digitization, in any case.

Remember that this was a higher frequency - something strange is happening in the transfer process, I think. With the particular one I mentioned, I watched the courier depart to the place where they only have glass mastering and pressing - the only thing that happened before it went was that we picked the master copy that had the lowest BLER - and that's a read-only process. What I was looking at is, I suspect, something different.

But as far as the others are concerned, what is quite intriguing is the CDs where this comes and goes. I haven't yet seen one where the spectrum line is as well defined as PQ's example - all the ones I've seen have close sideband noise, which has the effect of blurring the line. That could be the result of the FFT spectrum though - I'll have to try altering it and see what changes. One of the things that puts this firmly into line rate territory is the absence of other spurii - the harmonics of this would be outside the audio band. The other thing to note is that this would have to be an effect where the spurious frequency was added to the original at the point where it was digitised - which makes any of the earlier digital mastering machines rather more suspect, because they were all based on modified video recorders. Or in some cases, unmodified video recorders. The world standard machines were all NTSC ones, though - that's what a Sony 1630 is. PAL ones weren't used for this at all. Since the digitised audio was spat into these things in video frames (that's how you got away with unmodified machines) and the resulting video was reclocked into a continuous stream sent to the glass mastering machine, it's quite easy to see how spurious signals could be injected by a machine that wasn't set up particularly well.

The slight variations in frequency also make slightly more sense if this is the scenario, as well. The U-matic VCRs have some lattitude in what they record, and effectively derive their clocking sources from the incoming signals. You can drift the sync signals quite a bit before the machine refuses to lock up, and in theory this doesn't matter, because the digital stream is reconstituted in a separately clocked FIFO afterwards anyway. What this means is that the frequency you see might appear to drift slightly - even though in most cases, it won't.

Anyway, this is my currently preferred (theoretical) source - unless somebody's got another they wish to postulate!

Just in case, I heaved out the my first ever CD (double) that I recorded for Philips back in April '84 - on an F1/SLF1 system, edited on the Sony Umatic systems then in use (at HHB when they were working out of a garage).  No sign of the mystery tone.  I also took the opportunity of checking the 1997 re-release / repackage of the CD with other works, and it inverts nicely, which shows they didn't monkey with it at that point.

Aha - but in the non-Ozpeter tracks, which are on the second half of the second CD of the re-released set, there is a faint trace of the tone - I nearly missed it at first glance.  The date of that recording was Sept 85 - I know not how it was done, apart from it being an in-house Philips production in a Swiss studio.

Note that no TV equipment other than the F1/SLF1 was present at my original recording.

Make of that evidence what you will!

I don't know if any of you susbscribe to Gramophone magazine, but the opening track on this month's cover disc, from a new DGG release of Beethoven Piano Concertos, suffers from 4 mystery tones.

Spectral view in AA shows a continuous line at 15625Hz, an intermittent line at about 15585Hz and two higher solid lines at 19235Hz and 19335Hz.

I had ripped this track (which is from a live recording) because there was so much rustling noise at the start I wondered whether AA could get it out. I'll admit I'd not heard the tones, but of course I couldn't miss them in spectral view...

Only FWIW because it's consistent, whereas what others are reporting here seems to be INconsistent:  When dithering is performed, at least on Triangular 48kHz, there is always a low-level peak from 20500 - 21000kHz.  It's never heard, but always there, and always in those frequencies.  In spectral view it shows up as a very similarly solid line as what Pawel showed.

I think that these tones are so low in amplitude that they're just not heard, just as dither isn't heard.  But Cal, I hope you're not inferring that this is a byproduct of dither.

When you get into the current generation of recording and start seeing tones at frequencies other than 15,625 or 15,750, we need to take into consideration other electronic devices that may be present.  In particular we can blame computer monitors, which can have many different possible horizontal frequencies.  I don't know about PDAs, Segas, Gameboys, or other toys the percussion section might have stayed amused with...

But Cal, I hope you're not inferring that this is a byproduct of dither.

Aha... and that's why you won't find my name in any of the technical threads.  Like Sergeant Shultz says: "I know nothinkkkk!!!!"

My technical knowledge about all this renders me hard-pressed to make any knowledgeable informed statements that could actually mean anything.  But by accident?  For sure, there.  

No... my only reason to mention dither in this thread was only as a by-the-way type comment, since I'd seen similar displays of the dither signal that looked even remotely like what Pawel showed.... just in case you guys who can talk the talk might have missed anything.  But that's why I qualified my comment by stating I recognized there probably is a difference between dither and what is being discovered in some of this audio data.  And you've just confirmed that.

So I can offer this Dither Disclaimer: Any mention of dither by me in this thread is probably spurious and totally confusing the issue.  Please disregard.

(Whewww.... off the hook now), and I'm puhlennnty content to keep these type subjects as READ-ONLY by me.

 

When you get into the current generation of recording

.. and Steve tentatively blamed older equipment

I would like you to know that the Charlie Haden's CD, where I first noticed the mysterious tone, was released in 2004 and, apparently,  recorded in 2003 or 2004 ("Land of the Sun  had its genesis in 2003 when Haden met with..." -  from the Verve record website). The signal was stronger here than on any other album I've checked, and the other albums were older.

BTW, I realized that the apparent strength of the signal as seen in the Spectral View might be misleading because it depended on Display parameters. As far as I remember, these were: 120 dB range, logarithmic energy plot, FFT:1024, Hanning window, 50% Window width.

For a more precise view of the signal please see the current attachment. This is the same track, bass intro - same as before, but other part of the intro.

.. and Steve tentatively blamed older equipment

The reason that this is tentative is that I believe that in some places, it is still being used to present masters to pressing plants for glass mastering. It's certainly currently listed as an acceptable transfer mechanism, along with DAT, and there may well be material still being presented today in this format. It's not one I ever used for the purpose, though. This might account for why the artefacts are there. Certainly, the older and further out of adjustment one of these machines gets, the better the chances of additional spurii.

The only way you could find out easily would be to ask the CD pressing plant, I'd think.

So far no-one has mentioned SSL consoles which, apparently, were well known for injecting these tones from their video display. In my younger days I used to hear 15kHz or so on many records and I just put it down to having better hearing than the mastering engineers at the time. Using a Decca FFSS cartridge which probably resonated at around that frequencydidn't help either.

Cheers

James.

I think that I can explain these signals .  The governments work together with record companies and transmit subliminal messages to our brains using the 15625 signal as a carrier   . This signal is exactly the thousandth harmonic of brain beta waves' frequency and therefore allows to control our minds by interfering with these waves   .  That the frequency of the signal is very similar to the frequency emitted by TV sets is not just a coincidence. The plot includes the makers of audio-video devices as well      

     

This is quite true. It's no coincidence that we tend to fall asleep in front of the TV. This puts our minds into a state where we are much more receptive to these insidious messages. How else can we explain the re-election of George W and Little Johnny Howard? Removing these signals from our TV sets would have the twofold advantage of allowing us to enjoy our programs through to the end and freeing our minds of the evil propaganda of our politicians.