15840 Hz

Today I bought a CD as a Christmas gift for my uncle. It is Charlie Haden's "Land of the Sun".  I am not very familiar with this type of music, but I heard that jazz-like thing are recorded and produced with great care. Just of curiosity, I listened to some tracks and heard something strange at high frequencies. When I looked at it in AA, it turned out that there is a constant 15840 Hz tone throughout the recording. There are also some weaker components at 17k and above. Please see the attachment.

I was really surprised by this. Is this normal? Is this a production flaw? Or something deliberate (but what for)?

I quickly checked several other CDs. The signal is not caused by the extraction process (something I wouldn't believe, but it also had to be checked) because it does appear on some disc and does not on others. When it does, the frequency and level differs across and within discs, and it is sometimes lacking before the music starts. Sometimes there are few tonal signal, or the signal is apparently modulated.

I extracted from one disc both with AA and EAC, and the result was the same.

Here are results of my tests:

CD, track (usually I looked at the beginning of each track)
frequency : level of most prominent signals (in AA's frequency analysis)

Charlie Haden 'Land of Sun', track 8
15840 : -67

George Michael 'Older', track 1
15590 : -75,  15660 : -79

track 8
15560 : -75, 15630 : -79, 15780 : -73, 15850 : -82

Slayer 'Diabolus in Musica', track 11
nothing found

Mozart Great Mass in C minor, Gardiner, track 1 and 11
nothing found

Brahms 4th Symphony, Kleiber, track 1
15680 : -91

track 2
15610 : -96, I noticed also a few smaller peaks both below and above

Beethoven 5th Symphony, Bernstein, track 1
15660 : -76

track 2
15620 : -70

Again: what is this      

Possibly some interference from a TV related circuit somewhere in the recording process. In this country the TV line frequency is 15625Hz. Was any sort of video equipment used at any stage that you're aware of?

Cheers,
Alan

Yes, that's what I was thinking - are these tracks recorded at TV shows? Mind you, that line looks pretty solid - the only way that you'd tend to get it like that is if they recorded the audio from a master VT playback channel with no filtering on the output.

...If I haven't beaten you to it.  

'Morning Steve!

Oops - got trumped by an edit!

...If I haven't beaten you to it.  

'Morning Steve!

Oops - got trumped by an edit!

Good evening, Alan!
Actually, I think it was me that got trumped...  

But for PQ's reference, there's a table here with some relevant information in it.

TV was something that came to my mind, too.  I recalled that this annoying high-frequency noise emitted by TV-sets has a similar frequency (I had measured it once).
I know nothing about TV equipment during the recordings. All the tracks come from normal, commercialy available audio CD.  Are all these musicians, from classical orchestras to pop artists, watching TV during recordings?

I find that sort of thing on more than a few LPs I record for CDR. It is not at one particular frequency, however, it varies from LP to LP and sometimes it not consistent from track to track on an LP. It is generally not loud enough for me to notice, although perhaps in the days when I had to sit as far as possible from a TV, in order to escape its howl, the LPs might have been annoying too.

I know nothing about TV equipment during the recordings. All the tracks come from normal, commercialy available audio CD.  Are all these musicians, from classical orchestras to pop artists, watching TV during recordings?

Quite a few studios use TV monitoring between control room and studio - often in both directions, but I don't think that this is the mechanism, because that line wouldn't be anything like as constant as it is. You'd have to have a mic pointing pretty directly at the source to pick this up, and I can tell you from first-hand experience that this really doesn't happen.

But if a performance gets recorded in a TV studio, and it's done the way that it often is these days, where the band or singer in the band sings to a backing track, and the entire result is recorded on VT, then it's not that difficult at all for line sync signals to pollute the audio lines. If you looked at the patching arrangements in most studios, you would begin to realise why!

It's not that unusual for 'cheap' CDs to be released from performances like this, and if no attempt is made to filter it out, there it stays...

I'm not saying that this is the definitive answer, but I'd be very surprised if TV line sync doesn't come into it somewhere...

It's not that unusual for 'cheap' CDs to be released from performances like this, and if no attempt is made to filter it out, there it stays...

I can't check the first (Charlie Haden) disk right now, but none of the other CDs with the signal was a cheap one... And they do not seem to be recorded in TV studios.
Brahms and Beethoven was recorded in Vienna, in Großer Saal of the Musikverein, in 1980 and 1977, respectively. The CDs are from Deutsche Grammophon.
George Michael's 'Older' was recorded at Sarm West Studio (Steve, don't you know the place?) in London probably around 1995. This CD is from Virgin.

If these are cheap and carelessly prepared CDs, which are expensive and properly recorded then?  

I have seen similar fixed frequency lines as the result of a resampling for real-time sample-rate change (e.g., 48 to 44.1), but I don't think the frequency is right for that in this case.  

On LPs it can be oscillation in the drive to the cutter.  I once had two different LP cuts of a particular recording, one with a c.10kHz tone for the first few minutes, and the other without; I now have two commercial CD transfers of the same recording, and one has the 10k tone, the other not!

Paul

Here I've got  Jaques Loussier CD from the late 80's with a fixed low level frequency of 15633.  It shows in spectral view, and in quiet passages, but no in a frequency analysis scan due to its low level.  Must be a jazz thang...

I see the same artifact in the hi-fi audio on S-VHS recordings.  Some consumer brands, and most "professional" S-VHS VCRs seem to be "quieter" than others with regards to this signal -- although in truth I can't say I actually hear the noise under normal listening conditions.  I assumed it's part of the process of multiplexing the audio into the video signal on the tape... on some machines it nearly disappears when the audio signal goes quiet.

If I'm concerned with the impact on the audio,  the AA Frequency Space editor makes short work of it.  But I'm usually recording voice for lo-fi uses anyway, so I generally don't have to worry about anything above 11k.

I've been wondering a lot about this, because it doesn't altogether make a lot of sense - as I'm sure that anybody reading the thread has realised. What I've been trying to come up with is a plausible explanation for this at all, because clearly TV itself doesn't get implicated in several of these recordings.

My current thoughts are centred around Sony and some of the machines that were used for digital mastering back in the 70's, and have continued in use until quite recently in some cases. I'm just wondering whether an out-of-adjustment Sony 1630 or any of the F1 variants could do this? Considering that they are all based on video technology (and some were used for mastering stuff that was only ever released on vinyl, I believe), then this could possibly be the missing link...

Welllll.... don't know if this helps as a clue, or further confirmation.  For the live recordings I have to do, a Sony Minidisc machine receives the soundboard's signal first, then passes it out to other places including my soundcard via the SPDIF connection.  Only every once in a while will I also get this peak around 15 - 16K.  But, since it's intermittent maybe this doesn't qualify as evidence of Sony's involvement.