I am sure the answer is "it depends", so the better question is: To what extent is this possible?
The calls in question were made in the 70s, so we are in luck there. One of them can be heard here:
JFK Facts:
CNN Channel in YouTube
TIA
-Ramon
What is the purpose of this exercise? Bill O'Reilly obviously was in Dallas. Why would he be talking about getting a flight if it was a local phone call?
-- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
Yes, but I'm not going to get involved in a conspiracy theory resurrection.
In the 1970's all long lines telephony was analog. There were channel bank filters and mixers that upconverted base band audio to higher frequencies for transmission, and back down at the destination. Also known as FDM (frequency division multiplex: The conversion process is not perfect and it is possible to see mixes and intermodulation products of the carrier and local oscillator frequencies of this up/down conversion process on the resultant audio[1]. There was also about a 1 to 5 Hertz Bode frequency shift introduced to prevent feedback and oscillation. You can't hear the beatnotes and frequency shift, but you can see them with PC based spectrum analysis. I suggest: or better yet Spectrum Lab: You will need to look at the "blank" spaces between the words, where there is no voices or background noises to muddle the display. You're looking for continuous carriers, buried well under the voices. Autocorrelation: is a big help for seeing these tones by removing the audio and background rubbish.
Interpreting the residual tones, and separating them from recording artifacts, is going to be difficult. You'll need to find someone with experience in 1970's telco muxes as well as some clue as to where these recording have been, whether they were converted from previous recordings, and possibly what equipment was used. You'll also need to know which CO handled the call, which will point to which carrier handled the call (AT&T, GT&E, ITT, etc), and then what brand and model of carrier equipment might have been used. That's not going to be easy and will probably be a huge time burn for little benefit.
Hopefully, I've given you enough hints to get started. You're on your own. Don't bother sending me email as I won't help.
[1] I still do some of this looking for residual PL/DCS and control tones on stuck FM land mobile and public safety transmitters to identify the culprits. Since the frequency of operation is known, that limits the likely culprits to known licencees and a known list of equipment. However, the introduction of digital radios has made this technique both too difficult and no longer necessary due to built in transmitter ID.-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Just like e-mails, ALL OF IT can be faked. Or any combo. Name, number, voice, sound real or sound recorded, static, backgrund sounds, etc.
If you cannot figure out a possible rational explanation, then you are LOST.
I posted this question in the Stack Exchange Forum:
and was asked for an "Audio Corpus".
It is here:
In one of the audio clips, I removed some of the background noise, most likely caused by Fonzi's tape recorder.
TIA (again),
-Ramon
We wouldn't dare insulting you or professional dedication.
:-)
-Ramon
Bad idea. Every time you process and re-record that audio, you both introduce and lose important artifacts. For example, by chopping off the high end noise, you lose the tape recorders 100 or 150 KHz bias signal and its low level mixing products from the recording. The bias leakage is one of the easy ways I can tell if the recording was really made on a tape recorder, or if it was digitally faked on a PC. Also, if I see more than one tape bias carrier, I know that it was re-recorded on two different machines, which implies that it has been edited or tweaked.
For the S.E.D. readers, the 100 KHz bias leak usually shows up at around -60dB below maximum audio level, which is difficult to see under the tape hiss. The better tape machines use 150 KHz, which is almost impossible to see. Both can be found with filters if the exact frequency is known. Fortunately, junk tape recorders leak much worse, and are easier to see.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Thanks again, Jeff.
Check out Bob Primeau [kinda] colleague of yours:
He is getting lots of new clients, nobody has dropped a horse's head in his bed, etc.
Incidentally, I was privileged to work with *the* company that created the Internet, Bolt, Beranek & Newman.
They happen to be the ones who analyzed the "Dictabelt Recording": again, they gained a lot of professional respect and are in excellent health.
Regards,
-Ramon
Jeff, please bear with me. I am honestly trying to see your point of view.
Suppose there is a lawsuit and a court calls you as an *expert witness*.
We experts (you in your field, I in mine) are supposed to have high ethical standards, we are supposed to be above the yelling, accusations, etc.
How about jury duty? That is your citizen's obligation. That is the price we pay for our system, the greatest in the world.
Well, an expert is more important for Democracy than some uneducated member of the jury.
-Ramon
I have no point of view.
Expert witnesses are rarely subpoenaed. They are hired by the attorneys or by the court. "...courts hold to the traditional rule that an expert cannot be subpoenaed to serve as a witness against his or her will." The few times I've played expert witness, I testified by deposition and never appeared in court. The one time I was scheduled to testify, I sat waiting outside for days, and was never called (or paid).
I presume you haven't read much of Usenet, where yelling, accusations, character assassinations, bluster, conjecture, lying, and juvenile pissing matches are the norm. Oh yeah, welcome to Usenet.
I've been on 3 juries. Two were a waste of everyone's time. I wanted to be on a real jury so that I could experience the American legal system. What I got was a voluntary manslaughter trial, where literally everyone including the police were lying and seriously incompetent. I was the foreman. It was an interesting experience in the reality of trial by a collection of people not smart enough to get out of jury duty. If that was the greatest in the world, I would hate to see the lesser legal systems.
Cool. I've always wanted to setup a technocracy, where the government is run by the experts. However, I suspect that it's easier to obtain a decision from a jury selected from the GUM (great unwashed masses), than from a panel of university scholars, who derive so much enjoyment from endless debate and hair splitting.
In 1963, I believe that the Dallas PD was using Motorola Dispatcher radios, probably D33AAT: These were part germanium and part tube radios. Over the air, they had some interesting and obvious characteristics. The first second or more (depending on battery voltage) of each transmission was cut off as the quick heat tube filaments (1AD4 6397 2E24) warmed up. Officers using these radios had to push HARD on the PTT button, wait about 1 second, and then talk. There was no way to accidentally jam one of these radios into transmit using the PTT button. Most of the radio transmissions I heard on various recordings found on YouTube appeared to involve motorcycle police.
The D33AAT produced about 10 watts of RF at VHF at about 10% efficiency from a vibrator power supply. One could usually hear the vibrator hash on the transmissions. Despite that claim by someone on the recording that it was a motorcycle with a stuck transmitter, I doubt it because there was no vibrator hash, and the PTT on the microphone intentionally required a death grip to depress. It's been
50 years, but I'm fairly familiar with what those old radios sounded like on the air, having used them in commercial and ham service in the late 1960's. The motorcycle radio mics of the day were not noise canceling mics. Instead, to minimize wind and road noise, they simply reduced the mic gain requiring the office to yell into the microphone to be heard. An open mic wouldn't hear much beyond mechanically coupled noise from whatever it's sitting upon (i.e. engine noise).All the recordings I heard sound like noise and distortion had been added to what would normally be a very clear wide-band (+/-30Khz deviation) audio system. I've heard some crappy radios in the 1960's but nothing that awful sounding. Yet, nobody asked for a repeat transmission, which suggests that it was perfectly clear to the officers involved. Hmmm...
Anyway, have fun with your conspiracy. I'll pass.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On a sunny day (Fri, 13 Mar 2015 14:52:23 -0700) it happened Jeff Liebermann wrote in :
It is d*mn good to read somebody who knows what he is talking about. Yes, the bias issue is a good tool. There is a catch however: Some old cheap tape recorders used DC bias, I once had one like that, There is also such a thing as bias symmetry, you get the lowest tape noise for a purely symmetrical bias (so bias harmonics should or could exist too). The profi recorders in the studio had a balanced bias generator for symmetry, the cheap consumers ones just a single transistor oscillator, the latter ones achieved usually no better than -45 or at the most -50 dB noise level. When the VHS video recorders came on the market, the FM modulated video signal, so a FM carrier, was used as BIAS for an analog color chroma signal. So the bias was about 1.5 MHz (sweeping), the modulating chroma about 560 kHz IIRC. Rotating heads to get that (bias = FM video) of the tape again.
Old tape days.... For forensic investigation to know details like what you describe is of high value. Few more years an nobody remembers, Maybe google will store it a while.
Posted from s.e.d BTW :-)
During the early 1960's, when I was starting college, I worked for a repair shop that did warranty repair for various importers, mostly on tape recorders. The bottom of the line recorders had a magnet that swung in front of the tape on record. The result was a tape that was magnetically polarized perpendicular to the tape path. Play such a tape on any tape recorder often enough, and you get the thoroughly magnetized tape head, when then had to be demagnetized. I saw various schemes to self-demagnetize the heads, none of which really worked.
In the 1960's, I had a Roberts something 1/4" reel to reel tape recorder with cross field heads. I'm not certain of the timing, but I think they were introduced in that late 1960's, a few years after the assassination.
The tape bias leak is important because the recording had to be transferred from the original Dictaphone plastic belt to reproducible media, which in its day, was 1/4" reel to reel tape. It would be amusing to obtain one of these early recordings and see how many bias leaks could be found, possibly indicating how many times the audio was re-recorded. From this web page, it's been through many hands: (3 pages). My guess(tm) is that it would take several days of DSP "sweeps" across the frequencies of interest to extract coherent bias signals and probably prove nothing more than inept handling of evidence.
I skimmed through a few of these recordings and suspect this one might be good: Not much to be seen on the compressed audio using Spectrum Lab software. I did find some noise compression, which makes me suspect that it may have been "enhanced" for clarity. I found another recording claiming to be the original, which sounded far worse.
The commentary mumbles something about crosstalk between Ch1 and Ch2 in the recorder. This is the AT2C recorder used: When one 15 min belt becomes full, it switches to the other recorder so that the first belt on the first recorder can be changed without losing anything. Therefore, the alleged Ch2 -> Ch 1 crosstalk did not happen in the recorder. The alleged crosstalk probably came from the dispatch console, which likely had separate speakers for each channel, which would partially retransmit anything heard on Ch2 onto the Ch1 recording.
Enough conspiracy theory for one day. Gone to do somethine useful.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On a sunny day (Sat, 14 Mar 2015 10:43:39 -0700) it happened Jeff Liebermann wrote in :
I never had one, was popular with audiophiles I think, or at least marketed to that group. Akai?
Not sure about the timing, now we are in 1978 or so, but companding-expanding was used by some on international satellite telephone links that used FM modulation.
There is also tape press through? that creates a copy of the signal on the same reel where the turns overlap: (0)Enough conspiracy theory for one day. Gone to do somethine useful.
Yea, I am not going to listen to all that stuff, I remember Kennedy for wanting the moon, and it got done, his speeches gave me the creeps though.
I used to stay up to listen to Reagan...
That old recorder with DC bias I had, had a permanent magnet erase head :-) Did not even have a capstan, just drove the reels with a DC motor, variable tape speed, sort of a dictation machine, cheap though :-)
Yes. Akai is the parent company of Roberts. As I recall, Roberts was their trademark in the US only. Tensai and Transonic were the European names.
"Print through"
Unlikely. Print through only happens on adjacent layers of tape, requires some time to happen, and is really a problem only with thin
0.5 mil tapes. That math also doesn't work. At 3.75 inches/sec on a 7" dia reel, the longest distance and delay would be on a circumference of: 3.14 * 7" = 21 inches for a timing delay of: 21 inches / 3.75 inches/sec = 5.6 seconds The delay would be much less towards the center of the reel. At 7.5 ips, the delay would be half. The Dictaphone recording "hold everything secure" delay was something like a full minute after the assassination, so print through is probably not a suitable explanation.-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I had an Akai reel to reel from the late '60s, that I bought used in '71 or so from a friend who brought it back from Japan. It was a decent deck but it couldn't be considered "audiophile" class. It had the cross-field heads.
Roberts was the importing company that imported the first Akai tape machines. They had an exclusive contract with them, and they were private branded for them. The head of the company saw them on a buying trip to Japan, and liked what he saw.
-- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
Interesting stuff!
I assume that the digitized versions of these recordings (which is what I assume everyone is talking about analyzing here) were done at sample rates well below the 200-300 kHz needed to capture the bias signal directly. Then you'd be looking for the alias of the bias signal, at some lower in-band frequency... true?
So if the bias is normally -60 dB on the tape itself, how much of it gets through the anti-alias filter when converting to digital? Or do they digitize with special setups that use *no* (or minimal) anti-aliasing specifically to allow these sorts of analyses?
Best regards,
Bob Masta DAQARTA v7.60 Data AcQuisition And Real-Time Analysis
Yes, that's one method that barely works. The 2nd harmonic of the common 44 KHz audio sampling frequency would bring the bias signal into the audible region at 12 KHz. 48 KHz would be better with a 4 KHz mix. The problem is that the sampling frequency is usually quite symmetrical, and therefore lacks sufficient 2nd harmonic energy to do much mixing. 4 and 12 KHz are also in the audio region, making it difficult to see under that recorded audio. Originating from a computah clock, which might be dithered (spread spectrum clock) to reduce emissions, the result is a wide, dirty, low level, and useless mix. The 3rd harmonic of 44 KHz would be at a higher level, but it mixes to 32 KHz, which might be better, but is out of the range of my equipment. Might be worth a try.
In the distant past, I've detected the tape bias signal by slowing down the original 7 ips tape to 15/16 ips. That kills most of the audio, and shifts the 100 KHz bias signal down to 12.5 Khz, which can be detected. Lots of problems with this method and more than a few tricks involved, but it can be made to work. The big problem is that it has to be done with the original tape, which is often unavailable.
Much better is a ferrite tape head that offers expanded frequency response, typically to 1 Mhz. These are now commonly available but were previously rather specialized devices. They're used in systems that phase(?) lock onto the bias signal to provide an AFC (automagic frequency control) to eliminate flutter and wow from the tape: (See links at bottom of page)
I don't have any examples available, so I'm guessing from memory. I would guess(tm) a 16 bit digitized bias level would be about -100 dB below the peak audio level. That's fairly horrid when the audio band noise floor is probably about -60dB. Trying to extract a signal 40 dB into the noise is not my idea of fun. Yet, given time, it can be done. Plenty of articles on detecting signals below the noise floor:
The easiest is a sliding narrow band filter, that slowly and repeatedly scans across the 100 KHz area of interest, collecting signal level data and bin counting. I built one of these which produced its output on an x-y plotter. It was a crude autocorrelator, that looked for coherent signals. After about 1,000 passes, I could see a bump at the expected frequency, if the pen didn't rip the paper: It was also mechanically sensitive enough that I could see doors closing and changes in air pressure on the plot. The catch is that it could easily take a day or two to see anything meaningful.
Today, there are certainly better methods of audio forensics. I'm mostly familiar with older analog techniques and am somewhat lost in todays digital DSP world. The stuff I do today is far less sophisticated. Mostly it's signature analysis by looking at waterfall plots, spectrograms, sonograms, etc of radio transmissions, looking for residual tones and junk that can help identify the source. I've used your program (Daqarta) for this, but prefer Spectrum Lab for signal analysis.
The big problem with using a computah to look under the noise is that the FFT requires a huge number of samples. For example, with a common
44 Khz sampling rate, in order to resolve 0.1 Hz (to reduce the noise), I would need 880,000 data samples.I don't believe there's a single established method for extracting such signals. There are too many different types of recorders, media, and encoding schemes for one solution to work well with all of them. The wide band tape head is probably the most useful, but only with original media.
I don't know of any arrangement that does not use some form of anti-aliasing filtering to keep the audio and the bias signals from mixing. The better recorders place their cutoff frequencies quite high (about 50 KHz) to prevent group delay problems at the high end of the audio spectrum. Some people claim that they can hear phase shifts, so preserving the original waveforms has become a requirement.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
How exactly would you be expecting to get the output from a tape player to analyse for 100kHz signals?
If the player isn't right there in front of you playing the tape nothing is likely to have a frequency response up anywhere near as far as that.
-- Brian Gregory (in the UK). To email me please remove all the letter vee from my email address.
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