Question about Dr. Donald Thomas’s Dictabelt Offset Hypothesis

[John Iacoletti]

The supporters of the HSCA 1978 Acoustic study and of Dr. Thomas Acoustic study, admit that the 4 N-waves, the alleged “4 gunshots” are found on the recording near the phrase “Hold everything secure”. This would indicate that the alleged “4 gunshots” were recorded a minute, or perhaps a half minute, too late to have been the real gunshots. The claim is that somehow these “sounds” were offset from their true position in time.

I think this is a false premise.  Where exactly do the HSCA or Thomas "admit" that the four implulses were recorded too late to have been the real gunshots?

[Michael T. Griffith]

Michael Griffith and John Iacoletti have tried to change the subject of this thread. For those who may have forgotten, this thread is about the following question:

On the Dictabelt recording, there are 4 N-waves (I have read there are a good deal more than that scattered over the recording, but they focused on these 4) which, though they don’t sound anything like a gunshot, are actual gunshots.

The supporters of the HSCA 1978 Acoustic study and of Dr. Thomas Acoustic study, admit that the 4 N-waves, the alleged “4 gunshots” are found on the recording near the phrase “Hold everything secure”. This would indicate that the alleged “4 gunshots” were recorded a minute, or perhaps a half minute, too late to have been the real gunshots. The claim is that somehow these “sounds” were offset from their true position in time.

Question:

Can anyone come up with another example of a sound, or a spoken phrase, anything, that got offset by 30 or more seconds?

They have not answered this one basic question, but instead go off on all kinds of tangents. Clearly, the answer is no, they can’t. So, it appears everything else appears in the proper order, all the spoken phrases, everything, was recorded in the proper order. Everything except the alleged 4 gunshots.

So, when they speak of the odds that the 1963 N-waves match so closely to the 1978 N-waves, to a chance, which they have at times said was 1 in 2, or 1 in 20, or 1 in 25, consider all the hundreds of spoken phrases, and all the other sounds, and the only sound that got offset in time, was the “4 gunshots”.

And as an aside, I might point out, let’s assume, for the moment, that they are right. The 4 sound impulses were displayed in time from where they actually occurred, we don’t know if they actually occurred right when they are supposed to have occurred. For all anyone knows, if they didn’t happen 1 minute too late, maybe they really happened 2 minutes too late, or maybe 1 minute too early. There is nothing to show that the cause of these 4 N-waves happened within the period of, let’s say, z133 through z400. Nothing.

I haven't tried to change the subject. I'm saying that your entire argument shows you don't know what you're talking about, and shows you have not read the required research. If you did "read" it, then you are either trying to throw up diversionary smoke or you did not understand what you read.

I notice that not once have you mentioned the three main factors that affect the alignment of the crosstalk episodes: recorder stoppage, stylus displacements, and warps in the playback speed of the recordings. This tells me that either you haven't read the required research, or you read it but did not understand it, or you read it and understood it but are dissembling.

https://web.archive.org/web/20091026111324/http://geocities.com/whiskey99a/dbt2002.html

People who are able to understand the acoustical evidence, and who are willing to acknowledge it, will realize how clueless your argument is and/or how dishonest you are being about the evidence. No part of your inquiry addresses the real issue of the sound-distance correlations, the sound fingerprint correlations, the windshield distortion correlations, and the N-wave correlations.

As Dr. Barger noted in his reply to the NAS-NRC-Ramsey arguments, "The NAS committee did not examine the several items of evidence that corroborated our original findings." You are doing the exact same thing. No crosstalk smokescreen is going to make this evidence disappear.

Your argument is like a Flat Earther who asks, "Can anyone come up with an explanation for why boats drop out of sight when you watch them sail away from the beach?" I mean, it's just about that silly.

[Joe Elliott]

The 1978 HSCA Acoustic study that claims four shots were fired rests on 4 “N-waves” found on the recording, that don’t sound like gunshots, that don’t sound like anything, are actually gunshots. The difficulty, is that they occur about the same time Sheriff Decker is heard to say “Hold everything secure . . .”, which, on the surface, would indicate that these alleged 4 shots occurred about 90 seconds too late to have been the shots.

The claim is, that this doesn’t matter because sometimes sounds got recorded in the wrong order. This is a totally unsupported claim. It would have support if we had something like the following recording:

The motorcade has just reached Record Street (indicating the President is one block away from Dealey Plaza)
. . .
Shots have been fired at the motorcade
. . .
The motorcade has just reached Houston Street (indicating the President is just entering Dealey Plaza)

Clearly, if we had something like this recorded, then we would have some support, that at least once in a while, events were recorded out of order by the Dictabelt system. That wouldn’t mean the acoustic study has been proven valid. Even if there were rare examples that events could be recorded out of temporal order, the vast majority of the times they were not. But at least this “temporal disorder” hypothesis would have some support.



A laymen’s objection to the 1978 Acoustic study.

1.   The “gunshots” don’t sound like gunshots. Indeed, they don’t sound like anything. They are inaudible.

The breezy explanation is that the Dictabelt was designed to record voices, not gunshots. That doesn’t seem right to me. I never heard of a device designed to record voices not also being able to record loud gunshots. The Dictabelt was not designed to record Big Ben tolling the hours but I’m certain it would have. Now I can see how it might fail to record any sound if a gunshot was entirely in ultrasound, with all frequencies too high or too low for humans to hear. But fail to record sounds that human hears can plainly hear? That is a real stretch. I would at least have to see some evidence for this.

2.   The hypothesis that the Dictabelt would sometimes record sounds out of order in time, is something I would need to see an example of. It doesn’t sound likely to me.


I think I should also mention a glaring error in the 1978 Acoustic study. In 1978, the Dictabelt recorder was still used to keep a record of the police radio. So why didn’t they have the Dictabelt be used to record the sounds of their test firings of rifles at Dealey Plaza that day? This could have been easily done. So instead of just having the sounds recorded on their instruments, the sounds could also have been recorded on the Dictabelt. This isn’t a case that they could only have done one or the other. They could have easily have done both. Indeed, as usual the Dictabelt was being used by the police that day, and did record some of the test shots, which, not surprisingly, were quite audible on the 1978 Dictabelt recording. At least according to the memory of some police officers. But the Acoustic experts did not collect this Dictabelt recording at the end of the day and it, and like all routine recordings, is now gone.

Had they taken this elementary step; we would know:

1.   Does the Dictabelt record gunshots as audible sounds, that sound like gunshots, or at least audible sounds? Or as inaudible N-waves?

2.   Are events recorded out of temporal order? If so, how often does this occur? If it does, is this associated with crosstalk?

Because the 1978 Acoustic Experts did not take this elementary step, we don’t know. And, I believe the Dictabelt technology no longer exists and so unlike 1978, we can not test this, not in Dealey Plaza, or anywhere else.

This is an elemental error. At the end of the day, it doesn’t matter what their instruments recorded. It is what a Dictabelt records. That is what should have been studied. Despite their clear, elemental error, on their part, the HSCA Acoustic apologists say we should give them the benefit on the doubt. We should assume that the Dictabelt would not record gunshots as audible sounds, as if they proved this back in 1978. We should assume the Dictabelt would sometimes record sounds out of order, as if they proved this back in 1978. Because of their clear error in judgment, I am not inclined to give them the benefit of the doubt.

[Michael T. Griffith]

The 1978 HSCA Acoustic study that claims four shots were fired rests on 4 “N-waves” found on the recording, that don’t sound like gunshots, that don’t sound like anything, are actually gunshots. The difficulty, is that they occur about the same time Sheriff Decker is heard to say “Hold everything secure . . .”, which, on the surface, would indicate that these alleged 4 shots occurred about 90 seconds too late to have been the shots.

The claim is, that this doesn’t matter because sometimes sounds got recorded in the wrong order. This is a totally unsupported claim. It would have support if we had something like the following recording:

[SNIP]. . . .

A laymen’s objection to the 1978 Acoustic study.

1.   The “gunshots” don’t sound like gunshots. Indeed, they don’t sound like anything. They are inaudible.

The breezy explanation is that the Dictabelt was designed to record voices, not gunshots. That doesn’t seem right to me. I never heard of a device designed to record voices not also being able to record loud gunshots. [SNIP]. . . .

2.   The hypothesis that the Dictabelt would sometimes record sounds out of order in time, is something I would need to see an example of. It doesn’t sound likely to me.

I think I should also mention a glaring error in the 1978 Acoustic study. In 1978, the Dictabelt recorder was still used to keep a record of the police radio. So why didn’t they have the Dictabelt be used to record the sounds of their test firings of rifles at Dealey Plaza that day? This could have been easily done. [SNIP]. . . .

Had they taken this elementary step; we would know:

1.   Does the Dictabelt record gunshots as audible sounds, that sound like gunshots, or at least audible sounds? Or as inaudible N-waves?
2.   Are events recorded out of temporal order? If so, how often does this occur? If it does, is this associated with crosstalk?

Because the 1978 Acoustic Experts did not take this elementary step, we don’t know. And, I believe the Dictabelt technology no longer exists and so unlike 1978, we can not test this, not in Dealey Plaza, or anywhere else.

This is an elemental error. At the end of the day, it doesn’t matter what their instruments recorded. It is what a Dictabelt records. That is what should have been studied. [SNIP]. . . .

It is unbelievable that you would post this drivel in response to the links and research that have been presented to you. You just keep repeating the same claims about the acoustical evidence and ignoring all the evidence that refutes your claims.

The crosstalk you keep harping on has been explained by many scholars; there are perfectly plausible, reasonable explanations for the crosstalk. If you reject those explanations, then you must label as coincidence all the intricate sound-distance correlations, the windshield-distortion correlations, the N-wave correlations, and the sound-fingerprint correlations between the dictabelt impulses and the Dealey Plaza test-firing impulses. You must also believe that the dictabelt impulses that match the Dealey Plaza test-firing impulses as described above are merely bursts of static that did not even occur during the assassination.

For the sake of others who read this thread, since I suspect discussion with you is a waste of time, here are some important facts about the HSCA acoustical evidence:

* First, some news: I have learned that Dr. Josiah Thompson will include an extensive defense of the acoustical evidence in his widely anticipated book Last Second in Dallas, which will be published this November.

* The BBN scientists did notice the presence of voices on the dictabelt, some clear and some faint, but they did not analyze them because they focused on the gunshot impulses and the N-waves on the dictabelt.

* It is important to realize that the NAS-NRC-Ramsey panel claimed that the gunshot impulses identified by the HSCA acoustical experts are nothing more than bursts of static about one minute after the shooting. Warren Commission (WC) apologists still repeat this claim. Keep that in mind as we continue.

* A total of eight scientists worked on the BBN dictabelt analysis: Dr. Barger and the three other authors of the BBN report plus four other BBN scientists who assisted with the research. Dr. Barger was one of the top acoustical scientists in the world at the time.

* The BBN scientists designed five screening tests to determine whether the characteristics of the four gunshot impulse patterns on the dictabelt corresponded with the characteristics of gunfire.

* The five BBN screening tests determined that the dictabelt’s impulse patterns occur during the same timeframe the shots were fired, that the impulse patterns are unique, that the shape of the impulse patterns resembles those generated by gunfire, and that the amplitude of the impulse patterns resembles the amplitude of the echo patterns of the shots fired during the Dealey Plaza test firings.

* Five of the dictabelt’s impulses passed the BBN screening tests for gunfire, but the HSCA's chief counsel, Robert Blakey, insisted on ruling out one of the four rear-shot impulses because it came impossibly close to another rear-shot impulse and thus suggested two gunmen firing from behind. Therefore, under pressure from Blakey, the impulse at the 140.3-second mark on the dictabelt was eventually labeled as a false alarm. However, several scholars, including Dr. Thomas, argue that there is no valid reason to label the 140.3-second impulse as a false alarm.

* The Dealey Plaza test-firing sounds were processed into echo patterns. Each sound's echo pattern represented the unique "fingerprint" of gunfire sounds as heard at one location when a weapon was fired from one place to one target. The echo patterns were compared to the dictabelt’s impulse patterns to see if any of the clear fingerprints obtained during the reconstruction matched any of the sound fingerprints on Channel 1. The matching process was a binary correlation detection, a simple but powerful signal-detection system. Several echo patterns from the Dealey Plaza test firing matched sufficiently well with the four impulse patterns that BBN was able to place the motorcycle from 120 to 160 feet behind JFK’s limo.

* More than five dictabelt-test-firing impulse correlations might have been found if HSCA chief counsel Blakey had not insisted that shots only be fired from two locations during the Dealey Plaza test firings, i.e., from the grassy knoll and the sixth-floor window of the Texas School Book Depository (TSBD). Some HSCA staffers and consultants argued strenuously against this restriction, but Blakey would not budge.

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?)

This explains why the second gunshot impulse does not really trace back to the sixth-floor window if you look at the raw data for the impulse. The acoustical trajectories and echo patterns of a shot from the roof of the Dal-Tex Building and a shot from the TSBD’s sixth-floor corner window would be very similar.

* The BBN scientists noted that the loudest sound impulses from gunfire are much louder than the loudness of the sound for which the radio was designed to operate, namely, human speech. These loud impulses overdrive the radio circuitry. Because of the radio transmitter’s restricting circuits, very loud sounds are recorded in distorted fashion and appear as much weaker signals than they really are.

* The discharge of a rifle creates two types of sound impulses: the sound of the muzzle blast and the sound of the shock wave produced by the bullet as it travels at a speed greater than the speed of sound. This shock wave is also called an N-wave.

All sound impulses arriving at the microphone that were loud enough to be heard over the environmental noise would be transmitted over the radio connected to the microphone.

The environmental noise consisted mainly of the loud noise made by the motorcycle’s engine. This noise was only about 10 decibels lower than the loudest recorded gunfire impulse. Therefore, and this is a key point, only the very loudest gunfire sound impulses would be detectable above the engine noise.

This means that a gunshot fired by a gunman standing a foot or two inside a window in one of the other buildings might not have produced a loud enough sound impulse to be detectable on the dictabelt.

* The BBN scientists realized that if impulse patterns similar to those that occurred during the shooting were to be found anywhere else during the 5-minute recording of stuck-mike transmission, this would clearly indicate that the impulse patterns were caused by something other than gunfire. Therefore, they examined processed waveforms for the entire segment of stuck-mike transmissions on the dictabelt, looking for impulse patterns similar to those already identified. Only one other pattern was found. It begins about 30 seconds after the four gunshot impulse patterns and consists mostly of impulses caused by radios keying in and attempting to transmit. This sequence lasts only about 4 seconds and does not resemble the four gunshot impulse patterns.

* The gunshot impulses on the dictabelt not only have the generic structure of gunshot echo patterns, but they have the echo patterns of the gunshot impulses from the Dealey Plaza test firings.

* If the dictabelt impulses are not gunfire, then their echo patterns would be expected to match the test-firing impulses in a random manner, if they matched at all. But, the dictabelt impulses match the test-firing impulses in the same topographic order; to put it another way, the matching test-firing impulses occur in the same chronological order in which the dictabelt impulses occur. 

* 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.

* 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).

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.

* Weiss and Aschkenasy noted that the grassy knoll impulse on the dictabelt could not have been caused by a motorcycle backfire because it has a visible supersonic shockwave, or N-wave, preceding it. The N-wave comes just 24 milliseconds, or 2.4% of 1 second, before the sound impulse.

* Several scholars have noted that the grassy knoll impulse at the 145.1-second mark on the dictabelt aligns with the timing of the head shot in the Zapruder film. Blakey prevented any mention of this correlation during the hearings and in the HSCA report.

* Regarding the fact that the sound of a carillon bell is present on the dictabelt, Dr. Aschkenasy explained that this sound could have been recorded by a different patrolman’s microphone:

You are making an assumption that there was a source of a bell in Dealey Plaza, but that is your assumption. However, you have to look at the tape and the data on the tape a little more carefully, and one can see there an indication of a keying-on-transient which means that someone else tried to get onto the channel at that very time. He may have been in position to be close to a source of a carillon bell rather than anyone in Dealey Plaza, because there is associated with that carillon bell some indication of somebody else transmitting at the same time, which puts it just equally as well outside of Dealey Plaza. . . .

In fact, if you listen to the police tape recording during the entire period of the 5 minutes when the microphone on this motorcycle was accidentally on, you can in fact hear other transmitters coming on. Most of them failed insofar as all you hear is the microphone click and you hear a kind of a chirp as they try to capture the channel.

But there are a number of times where you do hear other voices coming on, other people communicating, sometimes very distorted sounds of the voices, sometimes quite clear and intelligible; and it is all during the time that this one transmitter has been on. In fact, as you go on in time past the point at which the shots occur, the ability of other transmitters to come into the channel becomes increasingly--it occurs more frequently. You hear more people coming in. You hear comments to the effect that somebody has his microphone button stuck, and it is all audible and understandable, so there are indeed several transmitters being received simultaneously during that period, and therefore it could very well have been that there was another motorcycle who happened to key on at just that point in time and picked up the sound of a bell somewhere. (5 HSCA 591-592)

[Joe Elliott]

* The BBN scientists did notice the presence of voices on the dictabelt, some clear and some faint, but they did not analyze them because they focused on the gunshot impulses and the N-waves on the dictabelt.

An incredible oversight. It was of fundamental importance to determine of these 4 inaudible N-waves occur at the correct time to be the gunshots. Why wouldn’t they focus on the voices to determine this? How else could it be determined if the 4 inaudible N-waves occurred at the correct time or not?

* The BBN scientists noted that the loudest sound impulses from gunfire are much louder than the loudness of the sound for which the radio was designed to operate, namely, human speech. These loud impulses overdrive the radio circuitry. Because of the radio transmitter’s restricting circuits, very loud sounds are recorded in distorted fashion and appear as much weaker signals than they really are.

This hypothesis could have been proven, or refuted, by using the police radio transmitters to record on to a Dictabelt recording, the sounds of the 1978 firing tests.

Question:

Why was this not done?


It was reported that the Dictabelt recording which was made in 1978, as part of the regular police operations, did record the sounds of the test firings. So, while in theory, the Dictabelt could not have recorded these gunshots as audible sounds, it appears that in reality, they could. In any case, this question could have been answered definitively had the 1978 acoustic experts not been negligent and had saved the 1978 Dictabelt recording that the police made.

[Michael T. Griffith]

The 1978 HSCA Acoustic study that claims four shots were fired rests on 4 “N-waves” found on the recording, that don’t sound like gunshots, that don’t sound like anything, are actually gunshots.

This comment shows that you have no business talking about the acoustical evidence, that you do not understand the most basic aspects of it. You haven't even read Weiss and Aschkenasy's HSCA testimony, have you? You haven't read the BBN and Weiss-Aschkenasy reports to the HSCA on the acoustical evidence either, have you?

If you have read any of these materials, I can't fathom why you would repeat the embarrassingly silly argument that the N-waves "don't sound like gunshots, don't sound like anything." That amateurish argument was answered during the HSCA hearings (and in the BBN and WA reports), and once it was answered, no one raised it again. Yet, here you are repeating it.

Furthermore, we're not talking only about the N-waves. We're also talking about the sound impulses from the muzzle blasts. You clearly do not understand that the N-waves and the muzzle-blast sound impulses are two different things. As I explained in my previous reply, when a gunshot is recorded, the N-wave is recorded a fraction of a second (about 24 milliseconds) before the sound impulse is recorded. By the way, that order of recording is exactly what the HSCA acoustical scientists found on the dictabelt. Gee, what a coincidence, hey?

Quote from: Michael T. Griffith on September 11, 2020, 07:56:41 PM
* The BBN scientists did notice the presence of voices on the dictabelt, some clear and some faint, but they did not analyze them because they focused on the gunshot impulses and the N-waves on the dictabelt.

An incredible oversight.

Actually, it is a meaningless oversight because the chronology of the crosstalk could be due to any number of factors and cannot cancel out the amazing and intricate correlations between the dictabelt gunshot impulses and the Dealey Plaza test-firing impulses.

It was of fundamental importance to determine of these 4 inaudible N-waves occur at the correct time to be the gunshots. Why wouldn’t they focus on the voices to determine this? How else could it be determined if the 4 inaudible N-waves occurred at the correct time or not?

Are you just pretending to be utterly clueless for the sake of entertainment or something? Did you only read every 10th word of my reply? I explained therein how they determined that the four "inaudible" N-waves occurred at the correct time. I explained this to you, in some detail, but you ignored the explanation--you chose not to quote it and made no effort to address it. This is not to mention the fact that the HSCA materials explain in great detail how they determined that the N-waves and the muzzle-blast sound impulses occur at the correct time on the dictabelt. Yet, you turn around and ask, "Gee, how did they determine if the four 'inaudible' N-waves occurred at the correct time?"

And, again, we're not just talking about the N-waves but also about the muzzle-blast sound impulses that come immediately after the N-waves. How can you hope to intelligently discuss the acoustical evidence when you don't understand such a basic, simple component of it?

You keep committing these blunders because you won't seriously, honestly study any research that you know contradicts what you want to believe.

Others who are reading this thread might be interested in the following excerpts from Dr. Weiss's HSCA testimony:

Well, the principles are basically the fundamental principles in acoustics, namely, that if someone makes a loud noise somewhere, like here [witness claps his hands], that sort of thing, everybody in this room can hear that noise, which means that sound moves out in all possible directions. A second principle is that that sound which they hear directly also will bounce off walls and be reflected. So they will hear not only the direct sound but also sounds called echoes bouncing from walls, corners, and other surfaces. The third principle, also very fundamental, is that the speed of sound is constant in whatever direction it may go. So that the farther you are from the source of the sound, the longer it will take for that sound to reach you, whether that source is, in fact, the original source of the sound or a reflecting surface which would cause an echo. I would like to illustrate basically what is meant by echoes at this point here. I think everybody is pretty much aware of what happens if you stand at a canyon and holler something like "Hello" and you get back a series of "Hello, hello, hello," that sort of thing. You can hear each of these echoes in such a circumstance because the reflecting surfaces are quite far apart from you and from each other. In a situation such as an echo generated in Dealey Plaza, you have reflecting surfaces, also the walls and corners of the buildings there. They, too, will generate echoes, but they will tend to come in very much more closely in sequence so that even if you have a very short, sharp sound such as a rifle firing, OK, or again a clap of the hands, you will get back what to an observer or many observers will sound like a single, loud bang type thing. . . .

As I indicated, each position in the plaza would have a unique set of echoes associated with it. If a sound heard on the police tape was, in fact, the sound of gunfire heard by a microphone-and a microphone, remember, is kind of an electronic ear--it hears the same as an ear will hear. If that indeed was the case, then I ought to be able to find a position for that microphone and a position for the gun such that I could predict a pattern of echoes that would match the sounds heard on the police tape to a high degree of accuracy. I could then say that this kind of match of a predicted pattern with the observed pattern is so close that the probability that what I am really looking at on the Dallas police tape is noise becomes very small. So we set out to be able to predict what the echo structures would be at various locations in Dealey Plaza. This was the whole art of it.

As I say, it was done by using the simple concept that sound would travel in all directions from a source and that it will reflect off surfaces and travel back. . . .

In fact, this brings up another point. If, in fact, after diligent searching we could not get a pattern of echoes, a predicted pattern of echoes, that would sufficiently closely match the impulses visible on the police tape recording, then we would have to conclude either that we did not have a shot recorded there, or that if we did have a shot recorded, then the motorcycle was not anywhere near the position we had assumed it to be, or the shooter was not anywhere near the position we assumed to be, or both conditions. . . .

So we started moving the microphone down the street at 11 miles an hour, and for this set of moved positions-now predicting what the echo pattern would be at every position as it comes on down, let's say, at what time it would receive each of these echoes.

This is a somewhat more complicated process. It is the same process; it just takes a lot longer because you have to do a lot more calculations.

As soon as we started doing that, it became immediately obvious we could quite easily find positions for the rifle and for the motorcycle, such that the match at both the early and the late echoes was getting increasingly close; and, in fact, once we were there, we were practically in the ballpark. It was a little more work, and we closed on a set of echoes that we could predict that matched the observed impulses on this pattern with an accuracy of approximately one-thousandth of a second. . . .

Mr. CORNWELL. Are you able to quantify in some fashion the probability that results from the ability to identify a large number of peaks, as you did, to that degree of precision?

Mr. WEISS. Yes, if you have a fit of some 22 points, you have a terrific fit to begin with. It really is hard to imagine this could be an accident, but you can't express it in those terms. You have to reduce it to some formal number that you can actually show is reasonable.

Now some of these echoes, and particularly the early ones coming from surfaces such as doorways over here and some corners over here, come in small. In fact, they come in below the noise level of impulse peaks in the general area of the recording where this is heard.

There is noise that is heard; there is the motorcycle noises; there is electrical noise; static is coming in. All of this is approximately at the level shown by these dashed lines on this exhibit. . . .

Now if the muzzle blast came in looking something like this, it goes up, it goes down, and then it sort of settles back, then from some of these surfaces you can quite accurately predict that it will do exactly the same sort of thing, let us say that the echo shape will be simply a mirror image replica of the muzzle blast.

Now if this is noise, then there is nothing which says that it has to start out going positive. It could equally, let us say, going upwards, the sound could equally, with equal probability, start out going this way and come back this way. But in every one of these instances where we identified an echo as coming back from a flat reflecting surface, it has precisely the correct replication quality when compared to the pattern of the muzzle blast. . . .

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. . . .

Chairman STOKES. Let me ask you this . This is 1978, this tape existed in 1963. Had this tape been given, let's say, to you or other scientists who specialized in this particular area, have you done anything new that could not have been done in 1963 with this tape?

Mr. WEISS. No, sir; the only thing that is new-this is an old technology that we are dealing with-the application is new, insofar as the use of the physics and science of acoustics for predicting the position of a microphone and/or a gun. I believe that the first application of it was only several years ago, and by Dr. Barger, in the case of the Kent State shootings. But other than that, there is nothing new in this at all. . . .

In the case of shot No. 3, since there is evidence of a shockwave preceding the muzzle blast, then it would have to be concluded that this was not a backfire, since backfires are not known to produce shockwave sounds.

We had no preconception as to what we were going to find. If anything, when we first heard the tape recording and first began to examine the data, our initial reaction was, somebody has got to be kidding; this can't be gunshots . But as we examined the data more carefully, subjected it to all the tests that we have described, the procedures that we have described, the results of the analyses themselves convinced us of where we were heading.

We can say that the bullet [of the grassy knoll shot] was not fired straight up in the air because had it been, you would not have received a shockwave impulse at that microphone position; and, indeed, if it had been fired in a direction reverse to that of the limousine, you also would not have received a shockwave impulse.

Mr. FITHIAN . Well, then, let me ask it another way. You were concerned about the alteration of the nature of the impulse by the windshield of the motorcycle?

Mr. WEISS. That is correct, only insofar as it is another means of observing a consistency between what is seen in the pattern and what is expected to be seen based upon both theory and experiment, that is, that the leading edge is much smaller than the cycle that immediately follows it. In reality, when a muzzle blast occurs, that leading edge is very much larger than the cycle that will follow it . There are two things that are reducing it as we observe it here. The first is the effect of the windshield, and the second is the effect of the compression caused by limiting action in the microphone and transmitter and almost certainly in the receiver and recorder as well.

Mr. FITHIAN. Does that in any way call into question the identification of the sound, itself, as that which reflects a gunshot from a rifle?

Mr. WEISS. Not seriously. Well, in effect, actually, rather than contradicting it, in a sense it supports it because all we see is all explainable and consistent with what we should expect to see if we take into account all the factors of the situation. (5 HSCA 557-560, 569, 581-582, 584, 588, 593, 597, 605)

[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)