PDA

View Full Version : 16 KHz stripe in Master Open Reel Recording


guygee
2007-06-23, 05:41 AM
Trying to help somebody with this conundrum. The FA and SAs below are supposed to be from a house recording master open reel 7.5 ips (unknown deck). The transfer was done "professionally", so no details are known.
The job is to track, flac, organize and seed. Some of the previous seeds are running here now.

What boggles my mind on this recording is the 16 KHz stripe. This recording does not look like a broadcast FM to me...way too much good frequency content above 16 KHz. So why the 16 KHz spike/stripe?

I am speculating that the 16 KHz tone was injected for pitch control (playback speed control) during taping, and this tape was prepared as a pre-FM, but I would very much appreciate anyone else's informed opinion. Has anyone seen this type of thing before?

Thanks!

U2Lynne
2007-06-23, 10:46 AM
I seem to recall Five talking about getting this sort of stripe on some transfers he did and he wasn't sure why they showed up. He's off on vacation right now, but I think he's supposed to be back next week. Maybe he will have some insite.

direwolf-pgh
2007-06-23, 11:15 AM
Carrier wave/Frequency modulation

http://en.wikipedia.org/wiki/Carrier_wave
http://en.wikipedia.org/wiki/Frequency_modulation

thats my swag

paddington
2007-06-23, 11:51 AM
you guys are thinking about the 19kHz stereo 'pilot' tone in FM radio. This isn't that, unless the tape is running VERY slow.. which isn't likely.

I'd say that is line noise - electrical interference on the audio cables during recording - or playback.

We'd need to know how it was transferred to WAV to be able to guess about that. If you can post audio samples of some quiet places in the recording, I can analyze it and tell you where it probably came from.

guygee
2007-06-23, 05:08 PM
Thanks Lynne and direwolf for taking a look. Jameskg, there were a couple of small tracks marked silence, I guess from the tape lead-ins/lead-outs that have no magnetic material on them. These were truly silent, with nothing much in them at all. I guess that rules out problems on playback.

I don't think it is the pilot tone either, but your idea is that during the recording the cables could have been acting like antennas and picking up on some interference? Unfortunately I looked through the whole show, and besides those lead-in/lead-out tracks not a silent place anywhere to check...crowd noise everywhere in the background, and the same ~16 KHz stripe.

I guess the main thing I wanted to do is rule out FM broadcast...these are supposed to be from the masters...but I am still sure damn curious about that stripe.

Not having the original tapes makes this pretty hard to figure out.

Audioarchivist
2007-06-23, 11:45 PM
I recently transferred some King Biscuit Flower Hour vinyls (ZZ Top Passaic NJ 1980) that have a 16000 Hz stripe in them, too. I don't get that for any other transfers I've done, from vinyl or tape or anything. It dissappears during silence at end of sides, but is embedded in the music. I first thought it was interference (like a tv being on in the next room or something, but evidently not.
Since these albums were pressed specifically for radio broadcast, I'm thinking DIR Broadcasting put the signal in to the vinyl to carry over the radio better.
So, it doesn't mean that having a 16kHz stripe means it's POST-fm necessarily. My pre-fm vinyl source is what they played over fm. It's obviously been prepared for radio airplay when it was mastered and pressed. It's not just a mark of the radio station's transmitter...

guygee
2007-06-24, 03:19 AM
Thank you Audioarchivist, that is exactly the kind of information I am looking for. Some people claim these is no difference between a Pre-FM and a master recording (be it sbd or say mics onstage), but it seems this recording was also prepared as a Pre-FM, with the tone at about 16 KHz actually injected into the master. Many shows from this venue ended up being broadcast on FM, so it all begins to make sense.

I was looking though some old posts, and in this post (http://www.thetradersden.org/forums/showthread.php?t=13849&page=2&pp=22) ssamadhi97 identified a Westwood One promo CD (Toad The Wet Sprocket1990-04-11 Live at Park West) with the same stripe. Another true Pre-FM(?).

I would love to know "why" they put that signal into a pre-fm? Is it getting used for something, like pitch correction on playback over the radio? Or something else?

Audioarchivist
2007-06-24, 03:28 AM
I believe it's put there to enhance the way fm signals tend to deplete the highs.
I help with a pirate radio station, and we have to eq up highs and cut bass frequencies to unusual amounts to broadcast a flat response over the air...
The 16kHz stripe I guess lets high freqency signals cut through better by sort of fooling the transmitter/receiver combo a little bit...
Having that high signal present opens up the radio waves to better let other real audio signals piggyback on top of it.

paddington
2007-06-24, 01:06 PM
Let me stop you guys from rolling down the wrong track with this FM radio and 16kHz thing. What Audioarchivist is thinking about in terms of the high frequency help in FM transmission is a pre-emphasis curve of 75uS (microseconds) - which raises the modulation of the higher frequencies in a logarithmic curve that is then de-emphasised in the receivers. This allows a better S/N ratio over the entire system to combat the noise that is naturally more prevalent in the higher end of the audio spectrum.

If you record from the receiver, it should already be de-emphasised, and you wouldn't see much in the analysis to betray the presence of the processing (unless the receiver is a piece of shit). FM transmission has a response of 15kHz on each channel and rolls off sharply after that. That doesn't mean you would see a tone at 16kHz. I don't know where people get that from.

Now, you may still see the 19kHz stereo pilot tone. This tone tells the receiver to 'de-mux' the audio it gets to 2 stereo channels using the info at the second harmonic up from the pilot (38kHz). This is done to allow the same FM transmission to be received on both mono and stereo receivers. The L-R signal, or 'difference' signal is applied to the sum signal (L+R) and you get "stereo separation" to whatever degree the difference (L-R) signal is applied. In most cases, you get about 20% or so of the L-R signal. The people at Dolby stole this method when they created the original 4 channel Sourround Sound, for the back channel. It's the L-R difference signal in the mux.


Anyway.. the 16kHz noise needs to be analyzed before we can decide what it is. Don't assume it's a tone (which assumes a sine wave) - I'm betting it's white noise.

When I say "quiet" spot, I don't mean "silent" - any quiet passages in the music will be fine. The reason I ask for quiet is that the noise is likely a constant level, so any time the program audio is softer, the noise will be better isolated. If you can post some samples, I'll tell you what it is.

direwolf-pgh
2007-06-24, 02:44 PM
EMI/RFI

http://en.wikipedia.org/wiki/Radio_frequency_interference
http://en.wikipedia.org/wiki/Electromagnetic_radiation

http://www.hydrogenaudio.org/forums/lofiversion/index.php/%22http://t17212.html

There are three distinct signatures in the sources used in the original source. Each can be seen clearly in spectral analysis. A 16khz spike can be seen in two of them, one having a lower B/W of approximately 10khz, and the other have a B/W of appoximately 16khz. The third has the same 16khz B/W but without the 16khz spike. The 16khz spike is, likely, due to CRT Horizontal EMI during the recording process.
http://db.etree.org/shninfo_detail.php?shnid=32875

guygee
2007-06-24, 08:08 PM
Many thanks you guys for trying to help with this. Here is a 1.5 second stretch from a quiet part. The crowd is silent and only the electric guitar is playing a very soft riff. jameskg, I think you are right, that line looks a little too hefty for a simple sine wave. Please let me know what you think.

guygee
2007-06-24, 08:23 PM
If you record from the receiver, it should already be de-emphasised, and you wouldn't see much in the analysis to betray the presence of the processing (unless the receiver is a piece of shit). FM transmission has a response of 15kHz on each channel and rolls off sharply after that. That doesn't mean you would see a tone at 16kHz. I don't know where people get that from.

Quite apart from the issues of this recording, I've looked at FAs and SAs of many FM recordings made at the receiver, and it seems this 16 KHz signal (actually just below 16 KHz) is very often present. I've researched this topic, and found specs for modern hi-power FM receivers, and one of the features commonly mentioned is sampling at 32 KHz. Going back into the '70's and '80's I would guess that the technology was different but the effects were nearly the same (using analog filtering instead of digital sampling). Regardless, it seems this signal often survives to make it into a recording made at the receiver. ( A lot of crappy FM receivers? I wouldn't be surprised if that is the case. Or maybe many people have their TVs on while recording...thanks for that interesting angle direwolf.)

guygee
2007-06-24, 09:00 PM
One last screenshot SA - crowd goes almost silent during count-in to the song (...2, 3, fouh).

Audioarchivist
2007-06-24, 10:01 PM
I re-checked my stripe-y example, my vinyl transfer of a King Biscuit Flower Hour lp of ZZ Top.
The stripe is there sometimes and is gone other times...
There's commercials on the record, and the stripe dissappears during those breaks, and re-appears for some songs, but by the end of the show it's gone for good. I can conclude that it wasn't added on my equipment, but is embedded in DIR broadcasting's master tape.
It's in the show for side 1 and 2 but gone for side 3, and it's not in the commercials.
The first two caps are from side 1 and 2, the third is nearer the end of the show.
As I looked through the whole show, like I say, it goes away when the music fades and a commercial on the vinyl plays, so it can't be interference from my monitor or tv(which wasn't on during turntable operation, anyway)...

paddington
2007-06-24, 11:53 PM
16kHz stripe doesn't come from King Biscuit. I've transfered those myself from virgin broadcast vinyl (a couple are still posted at this site) and that stripe isn't there. It's possible that the person playing those records had the NRSC pre-emph versions and didn't know how to de-emph them.

I still say it comes from a bad transfer. People use bad cables. TVs and monitors with CRTs in them emit a 15,750Hz noise. That's is common knowlegde among people who build recording studios. You must keep your audio WAY away from them. That noise shows up all the time in transfers done by hobbyists with home computers.

The stripe coming and going could just be the environment changing during transfer. The stripe on the ones you just posted is at about 17.2kHz. If it was some standard thing, they wouldn't be all over the place. Check the SA on my Plant Biscuit torrent that is here... it's straight from broadcast vinyl transferred on pro gear. No noise at 16kHz or anywhere else.


Guygee, what I meant by sample was an audio sample :lol ... I'd like to have a minute or so of audio in those quiet spots to work with. Sorry for the misunderstanding

Audioarchivist
2007-06-25, 02:21 AM
In my case, yes the stripe does come from KBFH.
Here's some more screens that show the virgin vinyl transfer I did.
This is the show:
http://www.thetradersden.org/forums/showthread.php?t=34781
They show the stripe fading in and out for the show's opening intro, and gone for the very next thing on the record - an embedded commercial.
It then comes back through the rest of side 1's main show, and side 2, but gone from side 3, and gone for the embedded commercials...
This was a second edition of the program, perhaps their vinyl was funky from copying it from their original broadcast...?
This is from 1980. I also have the same vinyls as that Plant 83 show that was put up. It is stripeless for the transfer of my vinyl edition of it, too.
I don't think it's coincidence that it comes and goes in unison with the program.
I don't see it being interference on my part, it's too specific to the program. It shouldn't be there one minute, and gone the next, then back again like it is.
Other KBFH's I have done don't have this, and other vinyl transfers I've done have been fine before, but this one seems to have it included...

Five
2007-06-26, 06:03 PM
yes, if it was your equipment it should be steady not fading out with the commercials. so it got in there sometime before the commercials were edited in.

could be a ground loop or something coming from a faulty/cheap pickup/amp during the gig or the equipment used to record the gig ... not certain.

bass amps are often the offender, inserting a di and lifting the ground or some other transformer setup can cure this, sometimes changing which outlet the plug is plugged into can also work magic.... of course, this isn't much of an option after the fact. The stripes can be attacked using the surgical precision of an fft filter or nr applied only on the very narrow band where it is necessary, however beware of how wide and deep the settings are or else you run the risk of creating a "black stripe" lol. Generally, leave it alone unless you're 99-100% confident about what you're doing. I have a couple tutorials on this topic somewhere on my computer and can dig them up and post them if there's any interest here.

There was one act I was doing sound for at an outdoor fest and the bass player had such a bad buzz coming from his amp we actually were muting him between songs since that's when it was most noticeable. We tried everything we could think of to get rid of it another way but time ran out and as they say the show must go on.

Another show I was at in January had some steady high-pitched noise in the audio, kinda like a buzz but more high-pitched like an "eeeeeeeeee" sound audible in the room at the time. I didn't get a chance to troubleshoot the system (I was just attending), but the stripes still showed up on the open-air recording. ps it was not my recorder causing this as it was only on that show and I recall hearing it in the room.

guygee
2007-06-27, 08:23 AM
Sorry I cannot post any audio samples for the original show that started this thread as they are not mine to post. But in general all this talk of stray signals being picked up by the cables or recording equipment does not completely explain the definite bias I have seen for a small signature ~15.5Khz-16KHz in some supposed pre-fm and many fm recordings, unless it is truly interference from a TV signal either at the source or the receiver. For FM recordings I could show many examples (by no means ubiquitous, but often enough to distinguish from a case like Five's example above).

Perhaps the fact that both FM and TV transmitting stations are often located closely together in preferential locations (Empire State Building, Mt. Wilson, etc.) may contribute? I've seen this little "signature" in some old FM jazz recordings dating back into the 1950's, so I doubt the complete explanation is people recording FM while watching TV, but it may be a combination of several factors that can come into play during recording, during transmission, and/or during reception and re-recording.

I am still holding this topic open as a question mark, but the "TV signal interference" is the (IMHO) "better-than-SWAG" hypothesis that I am taking out of this discussion until/unless a better explanation comes along.

I love this forum for all of the knowledgeable people who care enough to reply. Thanks to you all.

paddington
2007-06-27, 09:15 AM
the 15.750kHz flyback problem has been around since TVs became ubiquitous.... in the 1950s. If the recording is transferred on a computer with a CRT, in goes the noise. The freq is only slightly different in Europe.

http://www.high-techproductions.com/pal,ntsc.htm

It's everywhere, and it gets into tape recordings.

Audioarchivist
2007-07-10, 10:51 AM
Check this screen out, from Police Pinkpop:
It's lineage is this: FM > Pioneer VSX-D512 receiver > PHILIPS CDR 870 (standalone CD-recorder) > CDRW > PC > EAC 0.9 > WAV > Cool Edit Pro 2.1 > WAV > FLAC
Wierd 19k ringing tinnitus in my ears

Five
2007-07-11, 05:18 PM
yeah, that's normal for an FM broadcast. try taping something off the radio at home and you'll see what I mean ;)

lowgen
2007-10-14, 12:03 PM
Anybody still following this thread?

A 16kHz stripe is the 15,734 kHz (IIRC) emanation from a TV. It comes from the horizontal oscillator used for scanning and shows up on analog recordings made with a TV nearby. Ugh!

It's a sine wave and if you slow down the recording, it's an audible whistle.

Even if you can't hear it directly (most people can't) it "dirties up" the lower freqs.




Aww. I see the question has already been aswered on page 2

paddington
2007-10-14, 12:29 PM
:lol: I was about to ask about this being an echo chamber.. good to know others are hip to the problem, though :thumbsup: