Question about Dr. Donald Thomas’s Dictabelt Offset Hypothesis

[Michael T. Griffith]

It appears they never actually verified, in a controlled environment, that gunshots would record on a dicta-belt machine in any way recognizable. Correct?

No, that is not correct. They verified through numerous tests that the dictabelt contains gunshot impulses, and that those impulses were recorded in Dealey Plaza. They also had another test done in NYC by the NYPD to confirm that a patrolman's mike could record gunshot impulses even while the bike's engine was running. This is from Weiss's HSCA testimony, which I quoted in my previous reply:

Well, the effect of that can be predicted. But to confirm our understanding of this, we arranged with the New York City Police Department to perform some experiments at their shooting range in the Bronx. We went out there, and they trotted out an old Harley-Davidson motorcycle and put a transmitter on it, vintage 1963 or 1964, and an old microphone pretty much the same kind as was used by the Dallas Police Department, and we performed some experiments with people firing rifles at various locations, sometimes with the motorcycle facing the shooter, sometimes with the motorcycle crosswise to the shooter. At the same time we made recordings using high fidelity equipment of the sounds of the shots.

Now there were two kinds of recordings made. The first, as I say, was high fidelity equipment, good microphone, good recorder on the spot. The second was through the microphone which was on the motorbike, which was a microphone of the type used in Dallas, through the transmitter, and recorded downtown at the police communications laboratory. And we compared the results of these two recordings, and what we found was exactly what we had thought we would find, that is, that in the case of the high fidelity recording, we got that kind of big, first spike upward and downward, and so on . In the case of the recording made through the police microphone, that first spike was greatly attenuated and it went negative and came back up and so on. This was true, however, only in the case where the motorcycle was facing the rifle.

When the motorcycle was crosswise to the rifle, the recording made by the police microphone fairly closely matched, looks, looked pretty much like, with some distortions, but looked pretty much like the recording made using the high fidelity equipment.

So it was essentially confirmed that the windshield really does have this effect on reducing the strength of that initial, very sharp spike received, and, of course, this is what we have over here. It is consistent with the assumption that this is a microphone behind the windshield facing a rifle. . . .

[Michael T. Griffith]

For those who want to better understand the HSCA acoustical evidence, the following excerpts from the Weiss and Aschkenasy report to the HSCA should prove helpful:

During 1963, communications that were transmitted on channel 1 of the DPD radio dispatching system were recorded continuously on a Dictabelt recorder. On November 22,1963, a microphone on a mobile transmitter that was set to channel 1 apparently became stuck in the “on” position at about 12:28 p.m. and for about 5 minutes continuously transmitted sounds that it picked up.

When we first listened to this interval on the DPD recording, we found that it contained a nearly continuous noise, with occasional speech, whistles, and clicks. Also recorded on the Dictabelt in this interval were the sounds that BBN identified as probable gunshots. To the ear, these sounds resembled static much more than they did a gunshot. However, as Dr. Barger testified in September, and as we independently verified, the equipment that was used in the DPD radio dispatching system was not designed to handle sounds as intense as a gunshot, and it was therefore likely to have recorded such sounds with very poor fidelity.

Consequently, we recognized that these static-like sounds could be distorted gunshot sounds. On the other hand, such static-like sounds, theoretically could have been generated by a number of other sources, some acoustic, some related to electrical or mechanical disturbances in the DPD radio transmission, reception or recording equipment. Some test more discerning than the human ear was required to determine the probable cause of the sound impulses.

To answer the basic question, "Was the third group of recorded sounds generated by a gunshot from the grassy knoll?" with a high level of certainty, these sounds needed to be examined for some characteristic that they would have had if they had been generated by such a gunshot, and would not be likely to have had if they had not been. Of the several characteristics that can be used, the most effective and most reliable one is the sequence of delay times of the muzzle-blast echoes.

The firing of a gun generates a very loud, very brief explosive blast at the muzzle of the gun. This sound, which typically lasts about five one-thousandths of a second (0.005 seconds, or 5 milliseconds), spreads out in all directions from the gun. . . .

The time taken for the muzzle blast to be heard at some location depends solely on how fast the sound travels and how far the listener is from the gun. For example, at 65°F the speed of sound is 1123 ft/sec. A listener 112.3 feet away from a gun would hear its muzzle blast 0.1 second after the gun was fired. The time taken for the muzzle blast echoes to be heard also depends on the speed of sound and on the total distance each echo must travel, which is the total of the distance from the gun to the echo-producing object and then to the listener. Since the distance traveled by the muzzle blast to a listener must be less than the distance traveled by one of its echoes, the bang of the muzzle blast is always heard first. Then the echoes that are produced by the muzzle blast bouncing off the corners and surfaces of structures are heard. . . .

A listener cannot tell, from the sounds of a gunshot, when the gun was fired. He can determine only the times that elapse between the muzzle blast and each of its echoes. These elapsed times are called the echo-delay times. Because the echo travel times are uniquely related to the locations of the gun and the listener, the echo-delay times are unique to any given pair of those locations. Hence, if we know the temperature (and thus, the speed of sound) and the location of the echo-producing structures, echo-delay times can be used to characterize the sounds of a gunshot for any pair of shooter and listener locations. . . .

The "listener" that we have discussed, of course, could be either a human ear or a microphone. If a microphone receives the sounds and they are subsequently recorded, the recording becomes a picture of the event, not unlike a "fingerprint," that permanently characterizes the original gun and microphone locations.

Echo-delay times in such recordings can be measured easily and precisely by producing a graph of their waveforms on an oscillogram, or oscillograph. Such a graph is shown in figure 1. The narrow peaks represent individual sounds of brief duration (that is, impulse-sounds). The heights of the peaks correspond to the loudness of the impulse sounds; the spacing between peaks corresponds to the time that elapses between them. The largest of the impulse peaks is the muzzle blast. . . .

Using the fingerprint identification process as an analogy, if a latent fingerprint taken from a knife found protruding from a murder victim's body is given to the FBI for identification, it may be that no matching "known" print is on file at FBI headquarters and that the murderer cannot be immediately identified. Furthermore, the police may proceed to take fingerprint samples from all of the suspects in the case and find that none match the one found on the murder weapon. In the end, the latent fingerprint may not be identified. 

Applying the analogy to the graphs of sounds, our problem was to see if any of a number of assumed pairs of shooter and microphone locations would produce a pattern of sounds whose graph would match the graph of the sounds in question on the DPD tape.

After numerous comparisons between the echo-delay times for the sounds on the DPD recording and various predicted patterns for assumed motorcycle and shooter locations that did not match, a combination of motorcycle and shooter locations was found which mathematically produced a predicted pattern that showed strong similarities to the pattern of impulses on the DPD tape. However, to determine with a high level of certainty if these two sequences of echo delay times, which were derived from different data, represented the same source, it was not enough to show that the sequences looked alike.

They had to be shown to be alike in an objective sense, that is, by use of a method of comparison that disregarded potentially misleading appearances. Such a method was provided by a computation of the binary correlation coefficient of the two sequences. The binary correlation coefficient of two sequences is a number that is exactly 1.0 if the sequences are identical and that rapidly approaches zero as they grow more dissimilar. As used in this analysis, the binary correlation coefficient takes into account the number of echo-delay times in each of the sequences and the number of echoes that coincide. Echoes in the two sequences are said to coincide if their delay times differ by a small amount. The smaller this amount, or "coincidence window," can be made while maintaining a high binary correlation coefficient, the greater will be the probability that the DPD sequence represents a gunshot from the grassy knoll. . . .

Two different comparisons were made between the sequence of echo-delay times on the DPD tape and the most similar sequence of predicted echo-delay times. One of the comparisons was between those recorded sounds that were significantly louder than the average background noise and those predicted echoes that would have been recorded with comparable loudness. In the other comparison, the delay times of all of the recorded sounds and of all of the predicted echoes, up to a total delay of 50 milliseconds from the muzzle blast, were compared. The computed binary correlation coefficient was found to be 0.79 for the first comparison and 0.75 for the second.

In both of the comparisons described above, the coincidence window was set at ±1 millisecond. That is. a measured echo-delay time and a predicted one were said to coincide only if they were no more than 1 millisecond apart. For sequences that correlated at levels greater than 0.7 with a coincidence window of ±1 millisecond, the statistical probability was 95 percent or more that the sequences represented the same source-a sound as loud as a gunshot from the grassy knoll. Put alternatively, the probability that the sounds on the DPD recording were generated by sources other than a sound as loud as a gunshot originating from the grassy knoll is 5 percent or less. . . .

If a gun was fired from the grassy knoll during the assassination, the would-be assassin reasonably could have used either a rifle or a pistol, since the target would have been less than 150 feet away. Since rifles typically fire bullets that travel faster than the speed of sound, the firing of a rifle generates two intermixed echo sequences composed of the echoes of the muzzle blast and the echoes of the continuously generated shock wave that is created by a bullet in supersonic flight. On the other hand, most pistol bullets do not fly at supersonic speeds. . . .

The BBN analysis indicated that the gun was in the vicinity of the grassy knoll. During the acoustic reconstruction experiment that was conducted by BBN in Dealey Plaza on August 20, 1978, shots were fired from behind the wooden stockade fence on the grassy knoll. This location was consistent with available eyewitness and earwitness testimony. It was a reasonable one since it afforded good visibility of Elm Street while providing good cover for the shooter of a gun. At any other location on the grassy knoll either the visibility or the cover would have been substantially poorer. . . .

We expected to be able. to predict echo-delay times to within ±1 millisecond for specified locations of a gun and a microphone. However, it was essential to verify that this accuracy would be achieved in practice and that the identified echo-producing objects would generate significant echoes in the region of interest on Elm Street.  To test the procedure, we predicted the delay times of the echoes that would be received by a, microphone at the location of microphone 4 of array 3, as shown in figure 5, for a shot fired from the grassy knoll by the DPD shooter during the acoustic reconstruction experiment. We then compared the predicted echo-delay times to echo-delay times actually recorded on the BBN tape recording of the shot that was fired by the DPD shooter. At the time that the test shot was fired, the temperature in Dealey Plaza was approximately 90° Fahrenheit. Accordingly, the value used for the speed of sound was 1,150 feet per second. As discussed in section 4.1.5, the echo-delay time is computed by subtracting the muzzle blast travel time (185.2 msec.) from the echo travel time. The muzzle blast travel time is obtained by dividing the distance between the gun and the microphone in Dealey Plaza (213 feet) by the speed of sound. . . .

Using the methods described above, 26 echo paths were defined for 22 echo-producing objects. For some of these paths, the muzzle blast sound bounced off more than one echo-producing object. The echo-producing objects and echo paths are listed in tables 1 and 2. The travel times and the delay times for the predicted echoes are listed in table 3. Also listed are the echo-delay times determined by analysis of the time waveforms of the sounds received at microphone 4 of array 3 for the shot fired by the DPD shooter from the grassy knoll. These waveforms, which are shown in figure 6, were obtained by playing back the recording of the sounds that were picked up by the microphone, modifying the reproduced signal so as to approximate the effect that a microphone of the type used by the DPD in 1963 would have had on the signal, and then graphing the resulting signal. . . .

An analysis of the data listed in table 3 shows that the assumed locations were sufficiently accurate for the purpose of this test. The average absolute difference between the predicted and measured echo-delay times was 0.8 millisecond. The standard deviation of predicted 26 delay times about this average was 0.7 millisecond. These results are well within the accuracy required of the echo prediction procedure. . . .

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. . . .

The high degree of correlation between the impulse and echo sequences does not preclude the possibility that the impulses were not the sounds of a gunshot. It is conceivable that a sequence of impulse sounds, derived from non-gunshot sources, was generated with time spacings that, by chance, corresponded within one one-thousandth of a second to those of echoes of a gunshot fired from the grassy knoll. However, the probability of such a chance occurrence is about 5 percent.

This calculation represents a highly conservative point of view, since it assumes that impulses can occur only in the two intervals in which echoes were observed to occur, these being the echo-delay range from 0 to 85 milliseconds and the range from 275 to 370 milliseconds. However, if the impulses in the DPD recording were not the echoes of a gunshot, they could also have occurred in the 190-millisecond timespan that separated these two intervals. Taking this timespan into account, the probability becomes considerably less than 5 percent that the match between the recorded impulses and the predicted echoes occurred by chance.

Thus, the probability is 95 percent or more that the impulses and echoes have the same source--a gunshot from the grassy knoll. Stated differently, the odds are less than 1 in 20 that the impulses and echoes were not caused by a gunshot from the grassy knoll, and at least 20 to 1 that they were. (8 HSCA 6-7, 9-10, 16, 22, 24-26, 30, 32)

[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.”