Question about Dr. Donald Thomas’s Dictabelt Offset Hypothesis

[Joe Elliott]

I see no mention (in the quoted text) of a dictabelt recorder being part of the recording chain in the controlled setup (NYC/NYPD) or any other controlled setup to verify what the dictabelt is capable of, but I could have missed it.

I'm not interested what they think they heard or measured on the original recording.

No mention on the NYC/NYPD using a Dictabelt recorder. And no mention of the NYC/NYPC tests showing the recordings they did get were audible or inaudible.

Common sense says a recording of gunshots should be audible. In support of this, it was reported that the Dallas police noticed on their daily Dictabelt recording from 1978, audible, not inaudible, but audible sounds from the 1978 acoustic test firings. Very unlike the inaudible N-waves on the 1963 recording. But the acoustic experts had no interest in what a Dictabelt would record, only what their instruments would record. But their instruments weren’t there in 1963, so no direct comparison could be made, as could have been done had they made use of the Dictabelt system that was still there in 1978.

1.   The “gunshots” on the 1963 recording are inaudible, but it appears on the 1978 recording they were audible.

2.   The “gunshots” appear to occur at the wrong time, about when Sheriff Decker says “Hold everything secure”.

3.   The predicted location of where the motorcycle that recorded these shots occurred, does not have a motorcycle there, or anywhere within 100 feet of that location, the intersection of Houston and Elm.


The “gunshots” are made at the wrong time, recorded from the wrong location, are not audible, and are found on the 1963 Dictabelt recording more than 4 or 5 times (8 shots? 16 shots?), as the acoustic experts admitted back in 1979. Beside all of this, there doesn’t seem to be any real problem with their hypothesis.


As an aside, I have to admit that much of this acoustic information is way too technical for me. However, I think there is an easier way to tell it is wrong. Check out the topic I started today on:

Dictabelt Acoustic Question – Who Rode the Motorcycle

Where I think it is very clear that the conclusions reached by the acoustic experts in 1978 are false.

[Joe Elliott]

Michael Griffith hits me with a blizzard of arguments which are too many for me to deal with. Not because each of these arguments are so irrefutable, but just from the sheer number of them. It gives me the impression that he is trying to make up for the lack of quality of these arguments with quantity.

Michael Griffith also cannot resist mentioning how ignorant I am about the case. There is some truth to this. I doubt I have spent a fraction of the time reading on this case as he has. I try to broaden my reading to cover a lot of subjects, science, particularly geology, plate tectonics, ancient life, evolution. And history, and mostly history not involving the Kennedy assassination. Yes, a strong interest in the past, and not speculating about the future. The past seems more real to me. Who knows what’s going to happen in the next thousand years?

And besides, I think it’s hard for a LNer to put as much passion into the case as a CTer who hopes to be the first to make the truth clear to all. Or maybe the 153rd. But what good is spending so much time researching the Kennedy assassination, when you already have your conclusions. What Pro Conspiracy argument does Mr. Griffith not believe in? I suspect only ones that contradict a more favored pro conspiracy theory.

But even here, not always. I saw he wrote an article back in 1996 about maybe Officer McLain could not have been the motorcycle officer who trailed behind the Presidential limousine by 120 to 160 feet. Maybe it was Officer Hargis who in the perfect position to record the sounds of the shots that match the 1978 testing. This is curious for three reasons. One the Zapruder film shows him right where he is supposed to be, about even with the rear bumper of the Presidential limousine. This can be explained away because the Zapruder film is faked, right? And maybe the Altgens photograph at z255 was faked as well, why not? But he also argues that Hargis was right behind the President when his head exploded from the headshot. How could Hargis be splattered with blood while 120 to 160 feet behind the President? So, it seems that Mr. Griffith is quite capable of believing in two different Pro conspiracy arguments that contradict each other. Officer Hargis was both right behind the President and 120 feet behind at the same time. It may have something to do with Quantum Physics. I’ll leave Mr. Griffith to explain it.

In any case, let’s deal with a few of the points Mr. Griffith made.

* When you calculate the speed of the dictabelt motorcycle based on the echo correlations with the test-firing impulses, you get a speed that is almost identical to the average speed of JFK’s limo. The distance from the first matching microphone to the last was 143 feet. The time between the first and last gunshot impulse on the dictabelt is 8.3 seconds. In order for the motorcycle with the stuck mike to cover 143 feet in 8.3 seconds, it would have had to travel at a speed of right around 11.7 mph. This speed fits almost perfectly with the FBI's conclusion that Kennedy’s limo averaged 11.3 mph on Elm Street. If this is a “coincidence,” it is an amazing, stunning coincidence.

No, I don’t see this as any sort of coincidence at all. The Warren Commission’s Report stated that the average speed of the motorcade was 11 mph. So, going into this, the acoustic experts were looking for results that are consistent with a motorcycle going 11 mph. They know a correlation consistent of a motorcycle going 2 mph, or 30 mph, or 10 mph backwards is not going to do them any good.

Seek and you shall find. If they found a correlation between one location and the first shot, where would they check for the second shot 1.6 seconds later? Elementary. It would have to be 16.1 feet (11 mph is about 16.1 feet per second) times 1.6 seconds or 25 feet down the road. And then go check the next appropriate spot.

As an aside, I think this point shows the big difference between Mr. Griffith and myself. Mr. Griffith values taking in as much information as possible. To read voraciously to amass as many new facts as possible, so long as they are facts that support the Pro conspiracy side, of course. I don’t do nearly as much as that. But I am critical to the hypotheses I consider adopting. I don’t see this in Mr. Griffith. A little reflection would have told them that whether the 1978 acoustic study was valid or not, either way, they were going to find a result consistent with a motorcycle driving alongside the motorcade.

* Acoustical experts Weiss and Aschkenasy determined that the odds that the correlations between the dictabelt grassy knoll shot impulse and the test-firing grassy knoll impulse were a coincidence were “less than 1 in 20” (8 HSCA 32).

Yes, but there are lots of places they might look for a correlation.

Maybe starting with the stretch of road starting at the corner of Main and Houston and the next 143 feet.
And the stretch starting from 20 feet from Houston for the next 143 feet (that stretch would have been a jackpot).
And the stretch starting from 40 feet from Houston for the next 143 feet.
And so on, ending with the stretch starting 180 feet down Elm for the next 143 feet.

Now, it may have been true, that they found a stretch of road, that the acoustic tests found matched the patterns found on the Dictabelt recording, and the odds of this happening are 20 to 1. But if they tested 20 stretches of road, that would really not be that amazing a coincidence.

And in any case, regardless of the odds, if a motorcycle is not where they predicted it must be, their odds go from 95% to zero.

Incidentally, Weiss and Aschkenasy said that before they began their research, they did not believe there were any shots on the dictabelt, much less four or more.

Yes, they said a lot of things. But I don’t believe everything I hear. Sometimes people tell themselves stories going into a case, like, it really doesn’t matter to them if they make the discovery of the century or not. It’s all the same to them. Yes, that all sounds perfectly plausible to me.

In limiting the test firings to two locations, Blakey ruled out the possibility that any of the unmatched sounds on the dictabelt could be matched with impulses of shots fired from other locations, such as from the nearby Dal-Tex Building or the County Records Building, both of which would have provided logical sniper positions. (Interestingly, Mafia man Eugene Brading was arrested in the Dal-Tex Building shortly after the assassination. Just a "coincidence", right?)

Again, I wonder if Mr. Griffith questions his beliefs.

The Dal-Tex Building. Yes, that gives some excellent angles for firing down Elm Street. The Court Records Building? Not so much. A shooter from this building will be dealing with a target on Elm Street moving at a high angular velocity. An unnecessary complication, when a location in the TSBD or the Dal-Tex Building gives a pretty much straight shot down Elm Street with the limousine moving almost directly away. But I don’t suppose Mr. Griffith thinks about this very much. Any location other than the TSBD makes a logical sniper position. Heck, even the Grassy Knoll, firing almost at right angles to the motion of the limousine is a logical firing position.

[Joe Elliott]

I didn't think less than an expert's opinion counted...

If you stumble upon any real experts on this forum, like me know. Well, I think we can count Steve Barber was a real expert. His contributions are well known. His observations have become the eye of the HSCA 1978 Acoustic debate. And there may be some others. But far more common are posers.

[Michael T. Griffith]

I see no mention (in the quoted text) of a dictabelt recorder being part of the recording chain in the controlled setup (NYC/NYPD) or any other controlled setup to verify what the dictabelt is capable of, but I could have missed it.

I'm not interested what they think they heard or measured on the original recording.

So you doubt that the dictabelt could have recorded gunfire? Why? It recorded a wide variety of other sounds. Why would it not have recorded gunfire? The acoustical experts explained why the gunshots showed up on the dictabelt in an aurally reduced form.

You don't care what the acoustical experts measured? Then you don't care about science. The measurements were based on long-established principles of physics and acoustics. A supersonic shockwave is not going to magically appear for no reason on a recording. The recording must contain the sound impulse of an object traveling faster than the speed of sound in order to record an N-wave milliseconds before the sound impulse appears. They explained this undisputed phenomenon in their reports and during their testimony.

No mention on the NYC/NYPD using a Dictabelt recorder. And no mention of the NYC/NYPC tests showing the recordings they did get were audible or inaudible.

Gosh, this again? This is explained in the HSCA materials. The materials explain how the DPD recording system's limiting circuitry would have affected how the gunshots were recorded. Again, the problem is that you simply refuse to honestly, sincerely read any research that you know disagrees with what you want to believe.

Common sense says a recording of gunshots should be audible.

Common sense says that at some point, in order to stop embarrassing yourself by making amateurish arguments that were answered decades ago, you should have the integrity and objectivity to read the HSCA research before you say another word on the subject.

In support of this, it was reported that the Dallas police noticed on their daily Dictabelt recording from 1978, audible, not inaudible, but audible sounds from the 1978 acoustic test firings. Very unlike the inaudible N-waves on the 1963 recording. But the acoustic experts had no interest in what a Dictabelt would record, only what their instruments would record. But their instruments weren’t there in 1963, so no direct comparison could be made, as could have been done had they made use of the Dictabelt system that was still there in 1978.

This is unbelievably silly, not to mention misleading. They knew "what a dictabelt would record" because, umm, they had the DPD dictabelt! And when they did the NYC test, they used vintage microphones very similar to the ones used by the DPD in 1963. The issue was not what the dictabelt could record, because the dictabelt could only record the sounds sent to it by the patrolmen's microphones; the issue was what the patrolmen's microphones could hear and transmit to the dictabelt. 

1.   The “gunshots” on the 1963 recording are inaudible, but it appears on the 1978 recording they were audible.

Sigh. . . .  Gosh. . . .  You complain that I call out your ignorance, and then you repeat this ignorant stuff because you still have not read the HSCA materials. I guess you know nothing about the episode during the hearings when one of the members of the committee declared that he could not hear the shots on the dictabelt, but it turned out he was listening to the Dealey Plaza test-firing recording.

Dr. Barger explained why one cannot hear the gunshots on the dictabelt by just listening to it with the unaided ear:

Now it was perfectly clear that these sounds were not clearly audible. There is in the field of detection theory a favorite approach called matched filtering. The matched filter is a device that is used to detect events that you have some understanding of, even though they are subaudible. Matched filters are used in radar sets commonly to detect the presence of impulsive signals in noise, even though they are not visible or audible in the raw data. There was reason to believe that applying these techniques we might be able to detect the impulsive sounds of gunfire.

The most serious problem was the motorcycle noise. There is a way to help reduce that. It is a technique called adaptive filtering. It considers that the motorcycle is a repetitive device . As the cylinders fire, they do so periodically. The adaptive filter can learn to understand the event and project what will happen the next time the piston fires and subtract that noise out from the tape.

We thought once the adaptive filtering was conducted, the tape might then be noise-free enough to attempt a detection of the sounds of gunfire. . . . .

Initially we listened to the whole tape and we found at one point on the tape a 5 1/2-minute segment in which the sound of a motorcycle engine and other noises were heard continuously. This particular 5 1/2-minute segment was the period of the stuck microphone button that Professor Blakey described earlier.

The sound in that 5 1/2-minutes was mostly motorcycle noise. . . .

Now, as I said, we realized from the outset that we were seeking to detect sub-audible events, or at least not audibly recognizable events, and this is helped by looking at the electrical waveform that represents the sounds in a form called a waveform chart. So the first thing we did was to digitize the sounds in this 5 1/2-minute tape recording to form a computer file of the information contained by that digitalization, and then plot out a chart showing the waveform on the tape. (2 H 18, 27)

2.   The “gunshots” appear to occur at the wrong time, about when Sheriff Decker says “Hold everything secure”.

Only if you accept the Decker crosstalk as determinative, but to do that you must ignore all the correlations between the dictabelt shots and the test-firing shots, and you must ignore the other cases of crosstalk on the recording.

Why do you suppose that the NRC-Ramsey panel offered no alternative explanation for the sound impulse and N-wave of the grassy knoll shot? They strenuously objected to the grassy knoll shot, but they offered no explanation for the echo-pattern correlations and the presence of the N-wave for that shot. Why not?

3.   The predicted location of where the motorcycle that recorded these shots occurred, does not have a motorcycle there, or anywhere within 100 feet of that location, the intersection of Houston and Elm.

We both know that you don't know this, and that you are just repeating what some other WC apologist has said. I know you have not done any study of the evidence relating to the location of the motorcycle. Let's try this getting you to answer some simple questions about relating to the motorcycle's presence in Dealey Plaza:

* How could the dictabelt contain sound impulses that match the acoustical fingerprints and echo patterns of at least four shots fired during the Dealey Plaza test-firing, if those impulses were not recorded in Dealey Plaza? How did they get on the dictabelt if they were not recorded when a microphone in Dealey Plaza transmitted them to the dictabelt?

* How did supersonic shockwaves get on the dictabelt, and why do those shockwaves always come, as they should, milliseconds before the sound impulses that match the acoustical fingerprints and echo patterns of shots from the Dealey Plaza test firing, if the dictabelt does not contain gunfire from Dealey Plaza?

N-waves are distinct. Their acoustical fingerprints are different from those of any of the other measured sounds on the dictabelt and on the test-firing recording. So once you detect an N-wave on a recording, your next task is to determine the echo pattern, and that pattern will depend on where the rifle was pointing and whence it was fired. Dr. Barger:

As I have explained, the pattern of the N-wave shed from the bullet is distinct, so the echo pattern at any one point depends upon the direction in which the rifle is pointing, as well as the place where it is fired from. (2 H 48)

* How could it be that the windshield distortions of gunfire detected during the Dealey Plaza test firing show up when they should and when they should not on the dictabelt, if the dictabelt does not contain gunfire from Dealey Plaza? Can you even fathom how this kind of specific correlation could be a coincidence?

* Does the photographic record of the assassination provide a sufficiently comprehensive record to allow us to identify where every motorcycle, witness, car, and object was at any given time during the shooting? No, it does not.

Also, if you ever get around to reading the HSCA materials, you will learn that when BBN did their analysis, they made on assumptions about the location of the motorcycle that had the stuck mike. Dr. Barger:

We presumed nothing about the location of the motorcycle or its speed or even direction of motion. The matches were made without any presumption whatsoever about the position of the motorcycle, in fact, of course, without any knowledge that the motorcycle was even there.

After having made the matches, however, the position, I should say, the location of the microphones through which we found matches did in fact progress down the motorcade route at the times that the four subsequent periods on the tape showed matches. And as I indicated previously, the locations of the microphones where the matches were found at the four different times were moving down the motorcade route at approximately 11 miles an hour. (2 H 70)

Your bottom line, like it or not, is that all of the echo correlations, sound fingerprint correlations, windshield-distortion correlations, and N-wave correlations documented by the HSCA acoustical experts are all just one big whopping coincidence, and that the identified gunshot impulses are all just random bursts of static that did not even occur during the shooting. You and other WC true believers base this on the NAS-NRC-Ramsey panel's claims, even though that panel did not include a single acoustics experts, and even though one of its members was an ardent WC apologist who was caught rigging his ballistics tests and misrepresenting his test data, even though the NAS-NRC-Ramsey panel failed to address any of the evidence that corroborated the initial BBN findings.

Here is what Dr. Barger, speaking on behalf of all the HSCA acoustics experts, said about the NAS-NRC-Ramsey panel's claims:

Upon reading the NAS report, we did a brief analysis of the Audograph dub that was made by the NAS Committee and loaned to us by them. We found some enigmatic features of this recording that occur at about the time that individuals react to the assassination. Therefore, we have doubt about the time synchronization of events on that recording, and so we doubt that the Barber hypothesis is proven. The NAS Committee did not examine the several items of evidence that corroborated our original findings, so that we still agree with the House Select Committee on Assassinations conclusion that our findings were corroborated. (Letter from Barger to Robert Blakey, February 18, 1983)

[Michael T. Griffith]

No. When did I say that?

I don't doubt it, I question why the "experts" didn't establish a baseline for what the Dicta-belt would record in case of a gunshot under various conditions.
 
That you can't hear?

Correct. You can't hear most of the sounds because of the way that the dictabelt system's circuitry processed incoming sounds. The HSCA acoustical experts explained this several times. I've quoted from three of those times.

How would I know. Have you seen the wave forms KNOWN to be from gunshots on a Dicta-belt?

Sound waves follow the laws of physics, and we know the factors that affect how sound waves travel. We also know how dictabelts recorded sound, just as we know how sound was recorded onto vinyl records. We also know how to obtain acoustic fingerprints of sound waves, how to measure the travel of sound waves, how to measure the echoes of sound waves, etc. We also know how the DPD's recording system affected how incoming sounds from the microphones were recorded onto the dictabelt, such as how they changed the amplitude of some sounds. We also know what causes N-waves and how to measure them and how to graph their characteristics.

If anyone is saying otherwise, then they need to explain all the intricate correlations between the identified gunshot waveforms on the dictabelt and the waveforms of gunshots from the Dealey Plaza test firing, plus the correlations between the dictabelt and test-firing N-waves. If the gunshot impulses on the dictabelt are not gunshots, then someone needs to explain all the correlations with the impulses from the Dealey Plaza test-firing shots. The NAS-NRC-Ramsey panel did not address a single one of the lines of evidence relating to those correlations. 

What they assumed to be gunshots.

No, they determined they were gunshots after running numerous screening tests and then comparing the impulses that passed the screening tests with the impulses from the test-firing. Again, if those impulses are not gunshots, then all the specific, scientifically established correlations between them and the test-firing impulses need to be explained.

Correct, unless they had a Dicta-belt reference. I certainly do, that's why I'm pointing out their method was unsound. yadayada

How was their method unsound? It was based on standard, long-known principles of physics and acoustics. Somehow those impulses got on the dictabelt. If they were not recorded by a patrolman's mike during the shooting, then someone needs to explain why they match impulses from the Dealey Plaza test firing in their echo patterns, windshield distortions, N-wave patterns, and speed-of-microphone pattern.

They supplied no experimental evidence said impulses would record on a Dicta-belt in a way they assumed.

I don't understand your argument. They already knew how dictabelts recorded sound, just as they knew how vinyl records recorded sound. There was no mystery or debate about this. The sounds were already on the dictabelt, so, obviously, they knew the dictabelt had recorded them. I'm not being flip: I'm just saying that there was no mystery or issue about how the dictabelt recorded sounds. So I don't understand your argument that they had no "experimental evidence" that the impulses would record onto a dictabelt in the way they "assumed." They didn't "assume" anything. The dictabelt's recording properties were long-known, undisputed science.

There was no issue about how the dictabelt recorded sound, but there was a question about how the DPD patrol bike microphones transmitted sound back to the dictabelt, and the HSCA acoustical scientists determined this by testing very similar microphones in the NYPD test.

The scientists did the Dealey Plaza test firing to establish a control, a baseline, against which the sounds on the dictabelt could be analyzed, since they knew shots were fired in Dealey Plaza during the time in question. If the gunshot impulses on the dictabelt had not been recorded in Dealey Plaza, then they would not have matched four or more of the Dealey Plaza test-firing impulses in their N-wave sound-distance properties, their muzzle-blast sound-distance properties, their windshield-distortion properties, and their waveform properties. Dr. Aschkenasy put it this way regarding the grassy knoll shot during his testimony:

"If someone were to tell me that the microphone that picked up that impulse was not at Dealey Plaza, and that in fact it was transmitting from another location, then I would go there and expect to find a replica of Dealey Plaza at that location. That is the only way it can come out.”

[Michael T. Griffith]

The gain control (AGC) discussed is not that of the Dicta-belt machine. If you believe it is be specific in you quote.

Okay, let's see if we can clear this up. We need to understand that the dictabelt machine was the medium on which the sounds were recorded; the dictabelt itself did not control how the sounds were processed before they arrived, before they were recorded. The dictabelt received sounds from the DPD dispatch system. The DPD dispatch system included an AGC circuit, among other circuits. The AGC circuit greatly affected how sounds were processed before they arrived at the dictabelt. I quote from the Weiss and Aschkenasy report to the HSCA:

The DPD radio dispatching system contained a circuit, that would have greatly affected the relative strengths of the recorded echoes of a muzzle blast. This circuit, the automatic gain control (AGC), limited the range of variations in the levels of signals by reducing the levels of received signals when they were too strong and increasing their levels when they were too weak. It responded very rapidly to a sudden increase in the level of a signal, but comparatively slowly to a sudden reduction in a signal level. Consequently, the response of the AGC to the sound of a muzzle blast would greatly reduce the recorded levels of echoes and background noise received shortly afterward. Progressively during the next 100 milliseconds, the AGC would allow the recorded levels of received signals to increase until full amplification was finally restored. The effect on the predicted echoes would be to make the recorded levels of late-arriving echoes verv nearly the same as those of the early ones. (8 HSCA 30)

No, we don't know how sound in the case of gunshots were recorded since no baseline recording of gunshots involving a Dicta-belt machine was conducted.

We'll have to agree to disagree. I see this as a baseless and irrelevant argument. The sound impulses were heard by the microphones, processed through the DPD dispatch system's circuits, and recorded on the dictabelt. They were recorded on the dictabelt the same way  all the other sounds were recorded.
 

http://mcadams.posc.mu.edu/odell/

Oh, yes, O'Dell's article. I just re-read it because I had not read it in quite some time. O'Dell's article will probably convince newcomers, but it won't convince anyone who has read the HSCA materials and the defenses of those materials.

O'Dell proposes the same basic explanation that the NAS-NRC-Ramsey panel offered; he simply identifies a different voice transmission as the alleged source of the grassy knoll shot.

If you've read the HSCA materials and their defenses, and if you then read O'Dell's article, one of the first things you notice is that O'Dell never specifically explains the sound-distance-waveform correlations between the dictabelt and the Dealey Plaza test-firing impulses, and he does not even mention the windshield-distortion correlations.

O'Dell even suggests that the HSCA acoustics scientists mistook the waveform of the "hold everything" crosstalk for an N-wave because the waveform of the crosstalk has one feature that looks like that of an N-wave. Leaving aside the problem of the precise timing between the N-wave and the sound impulse that follows it (O'Dell never addresses this point), and leaving aside the problems with the timing and properties of the crosstalk, what about the other N-waves? What crosstalk episodes can O'Dell, or anyone else, nominate to explain the other N-waves? What about the windshield distortions and the fact that they occur and don't occur exactly as they should for a recording made from a patrolman's microphone in Dealey Plaza?

Dr. Thomas deals with O'Dell's arguments at some length in his chapter that responds to attacks on the acoustical evidence in his book Hear No Evil, pp. 632-644. We can say the same thing about O'Dell's article that Dr. Thomas notes about the two NAS-NRC attacks on the acoustical evidence:

Neither this nor the original NRC study attempted to refute the core evidence at the heart of the HSCA conclusion: the fact that the suspect sounds on the police recording matched the test shots fired in Dealey Plaza, and that the matching data was ordered in a way that would not have happened if the matches were spurious. (p. 613)

Incidentally, Dr. Thomas also tackles the assertion that McClain was not in the right location to have recorded the gunfire sounds. Dr. Thomas shows that when you look at the totality of the photographic evidence, that evidence suggests that McClain was in the correct position and that his microphone did record the gunfire impulses (pp. 667-689). Says Dr. Thomas,

Although no films show the specified locations at the requisite times, a motorcycle ridden by a patrolman named H. B. McClain was in a position both before and after the shooting such that with a reasonable trajectory he could have been in the specified locations. (p. 687)

No control for all this stuff was established on a dicta-belt. Deal with it.

Nobody saw a need for such a "control" because the science involved with how a dictabelt records sounds was already well known and undisputed. 

Fine, then show me the specs for the Dicta-belt recording gunshots and inaudible pulses.

What "specs"? What are you talking about? Again, there's never been any dispute or mystery about the process by which sounds of any kind are recorded on a dictabelt. Similarly, the science behind the phenomenon of sub-audible sounds being recorded on sound-recording media was already well known back in the 1970s. This is basic stuff that was explained by the HSCA acoustical scientists. Have you read the BBN and W&A reports?

Straw man arguments doesn't work. Not my claim.

But it does involve your claim. Your claim, as far as I can tell, is that there are no gunshot impulses on the dictabelt but only random bursts of static and crosstalk from other microphones, and that the HSCA acoustical scientists mistook this static and crosstalk for gunshot impulses and their associated N-waves.

Herb Blenner, an electronics engineer, has written some excellent articles on the acoustical evidence. Here are excerpts from some of his articles that address the NAS-NRC-Ramsey claims:

No matter what the critics say they cannot make the pulse patterns attributed to gunfire vanish from the acoustic records. These patterns contain very special pulses that distinguish themselves from all the other snaps, crackles or pops. I call these special signals limiting pulses.

Playing a wave file of these limiting pulses at progressively slower speeds provides audible evidence of the special nature of these pulses.

Reducing playing speed dramatically lowers the pitch of the voice and has a similar effect upon a brief heterodyne and the background noise. However, the pitches of the limiting pulses initially resist lowering and change slightly at greatly reduced playing speeds. This demonstration shows that the high frequency contents of the limiting pulses are widely dispersed and extremely rich. These uncommon characteristics are further evidence that these special pulses are the responses of the radio system to impulses generated by the limiting circuit in the audio stage of the transmitter.

BBN documented a level of 100 db re 2 X 10-5 Newton per square meter at the microphone as the threshold for activation of the limiting circuit. This means that ears near that microphone would have heard sounds reminiscent of moderately distant gunfire.

Two choices arise. One may assert that the Dictaphone recorded gunshots on the Dictabelt or a studio added the limiting pulses and made an untrue acoustic record. . . .

The fundamental problem with this conclusion [that the crosstalk was recorded through a receiver with AGC] is the presented evidence does not show that the cross talk recordings were made through a radio receiver. Although the Committee on Ballistic Acoustics [the formal name of the NAS-NRC-Ramsey panel] should have tested heterodynes for frequency modulation as conclusive evidence of the by-radio nature of the cross talk, they pursued fallacious arguments. In fact, a quantitative detail provided by the committee showed AGC acted on audio. Even worse, they concentrated on attack characteristics that are ambiguous evidence of AGC action and misinterpreted the decay characteristics, which showed AGC acted at two or more places within the system. Not surprising the Committee on Ballistic Acoustics began by confusing the subject that provided a technically correct method of showing by-radio nature of the cross talk. . . .

In a communications system, frequencies below one thousand hertz contain most of the audio power. Now a gain control circuit requires many and perhaps tens of milliseconds to sample a few cycles. Without doubt, the sluggish decrease in cross talk intensity conclusively demonstrates the by-audio nature of the change.

The Committee on Ballistic Acoustics mistakenly attributed every decrease in cross talk volumes to AGC actions in response to heterodynes. . . .

Contrary to the declaration of the Watson Research Center, the frequency response of Channel-I was adequate to respond to the Channel-II brieftone. In fact, spectrographs of Bellah's broadcast and its crosstalk show the narrower frequency response of Channel-I attenuated the brieftone by less than four decibels relative to the voice.

Similarly a brieftone mars Decker's Channel-II hold everything secure broadcast. In both cases the brieftones are excessively loud signals and only their narrowband characters prevent them from obscuring the broadcasts.

Unlike the Bellah crosstalk where the loudness of the brieftone is comparable with the voice, the alleged Decker crosstalk contains no audible nor measurable brieftone.

The missing brieftone is the first clue that the alleged Decker crosstalk does not match the corresponding portion of the Decker broadcast while the badly garbled voice of the alleged Decker crosstalk that contrasts sharply with the clarity of the Bellah crosstalk is the second hint. (https://jfk.boards.net/thread/201/problems-acoustic-evidence)

[Michael T. Griffith]

Quote from: Joe Elliott on September 09, 2020, 01:44:14 AM
Question about Dr. Donald Thomas’s Dictabelt Offset Hypothesis

The “Hold Everything Secure” phrase, which was said about a minute after the assassination, and the “four impulse patterns” occur at about the same time on the Dictabelt recording. Dr. Donald Thomas explained this away by saying the two channels could drift apart from each other by a minute.

Would you have a source for this "offset" being explained (away)?

He doesn't understand what he's reading, or he's repeating some other person's mischaracterization of this issue.

There is no doubt there are offsets. Nobody denies this. Rush and O'Dell acknowledge there are offsets. The NRC panel acknowledged there are offsets and cited the AGC effect on the heterodynes (high-pitched feedback squeaks) and posited recorder stoppage to explain them. The question is, Was the offset in question imposed on Channel 1 or on Channel 2? NRC defenders claim that the offset was imposed on Channel 2 (or caused by impositions on Channel 2) via recorder stoppage. HSCA defenders assert that the offset was imposed on Channel 1 (or caused by impositions on Channel 1), and they note that this explanation agrees with the dispatcher's time notations. For a full discussion on the offset issue, see Thomas, Hear No Evil, pp. 638-643.

As Dr. Thomas observes, any discussion on the offset issue must consider the multiple intricate correlations between dictabelt gunshot impulses and the Dealey Plaza test-firing impulses.

[Michael T. Griffith]

Mr. Elliott certainly got one thing right: your arguments always result in a copy-paste circus and now it's Herbert Blenner's turn.

So you object that I often include quotes in my replies. Well, sorry about that. Some people like to back up their points with direct quotes instead of always paraphrasing.

I doubt you actually understand what he's saying, he just happens to support your case.

I can tell by your arguments that I understand a whole lot more about this issue than you do.

I know of Blenner and consider him one of the worst technical writers I've encountered. It's a mystery to me what he's driving at and what he's trying to confirm or debunk.

You don't get his point? If so, that's because you don't know enough about the acoustical evidence to grasp his point. Let me simplify his point for you: Blenner was refuting the claim that the dictabelt's grassy knoll shot identified by the HSCA experts is just random noise, and he was explaining some of the reasons that the crosstalk cannot explain away the evidence of gunfire on the dictabelt. I thought that was already plainly obvious from Blenner's first sentence:

"No matter what the critics say they cannot make the pulse patterns attributed to gunfire vanish from the acoustic records. These patterns contain very special pulses that distinguish themselves from all the other snaps, crackles or pops."

And then he went on to point out some of the errors made by the NAS-NRC-Ramsey panel. But you still did not grasp his point. Well, now, hopefully, you do.

I'm not saying he doesn't know his stuff, I just don't have the patience to deal with him.

If you had done your homework, you would have no problem understanding Blenner's research. Blenner is not the greatest writer, but if you've done the necessary homework, you should be able to readily understand his articles. I might add that his writing is not as bad as that of some WC apologists who frequent online discussion forums.

BTW, being unfamiliar with the term specs tells me you haven't got a clue about audio equipment

Huh? Where do you get the ignorant claim that I don't know the term "specs"? I asked you to explain what specs you were talking about in the context of how the dictabelt would have recorded gunfire, since you seem to have the mistaken idea that it recorded gunfire differently than it recorded all other sounds.

You keep repeating this drivel about the "failure" to establish how the dictabelt recorded gunfire. As I've told you several times now, it recorded gunfire the same way it recorded every other sound.

and I'll bet you have no clue whatsoever how the circuitry of the dictabelt machine would affect the input signal to be recorded.

This is mighty bold talk, not to mention rude talk, from somebody who couldn't understand Blenner's point.

Anyway, first of all, Mr. I Can't Understand Blenner, the dictabelt machine had no "circuitry" that had anything to do with signal processing. The circuitry that affected how sounds were processed and transmitted to the dictabelt was external to the machine. The dictabelt itself had nothing, nothing, nothing to do with this--it was just the recording medium on which the sounds that were sent to it by the DPD dispatch system were recorded. You seem unable to grasp this basic point.

As for how the DPD dispatch system's circuitry affected the sounds that were transmitted to the dictabelt, I discussed this very issue in my last reply to you, and I've addressed this issue at least twice in other replies. In my previous reply, I quoted a detailed explanation from the W&A report about how the AGC circuit affected the processing of the sounds before they were transmitted to the dictabelt. Did you somehow miss all that?

Reading just the first few pages of the HSCA report Vol. III explains a lot. It's unclear in the Foreword what "authorized" means, but if they (BBN) were commissioned I hope they were handsomely paid. It's evident from section 1.2 they were provided three tapes containing Hi-Fi recorded stuff and they seemed to have blind faith in those tapes. Moving on to section 1.7 (p11) it's clear that the quality of the dictabelt recording was so bad that they had to speculate that what they termed "continuous noise" was believed to be the sound of a motorcycle engine. This is repeated on page 12. It immediately raises the question why the noise on the Hi-Fi recording could not be identified as engine noise from a bike and that didn't bother them? Especially in view of this found on a wiki page (I know, it's wiki and the source is Bugliosi) https://en.wikipedia.org/wiki/John_F._Kennedy_assassination_Dictabelt_recording): 

There's nothing to disagree about, I'm stating the facts.

Oh, boy. . . .  These arguments are laughable. They are ignorant jibberish.

As for Bugliosi, he was a total idiot on the acoustical evidence. He knew next to nothing about the acoustical evidence, didn't understand the HSCA research, grossly misrepresented the HSCA research, grossly misrepresented Dr. Scheim's and Dr. Thomas's research, and ignored all responses to his ignorant babbling on the subject after his book was published.

When you are ready to discuss the intricate correlations between the dictabelt gunshot impulses and the impulses from the Dealey Plaza test firing, let me know. But let me save you some time: If your plan is to once again go running to pro-WC sites or to read the NAS-NRC-Ramsey report, be advised that none of these sources ever gets around to dealing with those correlations.

I suspect you are another Joe Elliott in that you won't seriously read anything that you know contradicts what you want to believe. However, on the off chance that you ever decide you really want to study the other side, you might start with chapters 16-19 of Dr. Thomas's book Hear No Evil.

And, Dr. Josiah Thompson will include a detailed defense of the acoustical evidence in his highly anticipated book Last Second in Dallas, which will be published in November. Dr. Thomas and other scholars have been working with Thompson on the acoustics section.