The HSCA Acoustical Evidence: Proof of a Second Gunman in the JFK Assassination

[Joe Elliott]

Mr. Elliott's surprising claim that the windshield-distortion correlations originated with Jason Perdue's book People in High Places deserves further comment. Anyone who has read the HSCA materials knows that not only did Weiss and Aschkenasy note these correlations in their testimony and in their report, but that the HSCA report noted them as well.

I had never heard of Perdue's book until I read this reply. I tracked down an online copy of the book (2nd edition). Perdue does not say the grassy knoll shot had no windshield distortion. He correctly observes that the final shot was the one that was found to have no windshield distortion, not the grassy knoll shot (pp. 69-70).

Coincidentally, just before I looked up Perdue's book, I realized that the fourth shot was the no-windshield-distortion shot after I went back and re-read the HSCA report's section on the acoustical evidence. I have revised my article on the acoustical evidence accordingly.

When you look at the position of the motorcycle for the third shot and the fourth shot, it makes perfect sense that the fourth shot does not contain any windshield distortion. For the grassy knoll shot, as with the two previous shots, the windshield was still between the rifle and the microphone, but this was not the case for the fourth shot. This is an astonishing coincidence if the dictabelt tape does not contain JFK assassination gunfire.

Several folks who have read Weiss's testimony on this subject have inferred that he was implying that the grassy knoll shot was the shot with no windshield distortion. This is how I had read his testimony as well. This is even how Dr. Chambers read his testimony. With tongue in cheek, I blame Dr. Weiss for not specifying by number the shots with windshield distortion ala the HSCA report! The HSCA report sets the matter straight:

So, now that we have cleared up the confusion about which shots were and were not found to contain windshield distortion, we see that the windshield-distortion correlations are powerful, convincing evidence that the police tape contains at least four gunshots. Again, if these correlations are all just a coincidence, they are an astounding, astronomically improbable coincidence. When you think about the number of factors that would have to align by pure chance to make it theoretically possible for these correlations to be mere coincidence, you realize that the only rational conclusion is that they are not a coincidence but are hard evidence that the HSCA acoustical experts were correct.

I did make an error. I found a phrase you quoted from an unnamed source, did a google search, and found it in a book published by Jason Perdue’s book, “People in High Places”. So, you were not quoting Jason Perdue. You were both quoting an HSCA report. But this was not clear from your original post.

Coincidentally, just before I looked up Perdue's book, I realized that the fourth shot was the no-windshield-distortion shot after I went back and re-read the HSCA report's section on the acoustical evidence. I have revised my article on the acoustical evidence accordingly.

https://www.archives.gov/research/jfk/select-committee-report/part-1b.html

And here is the paragraph from Weiss and Aschkenasy. It straddles Page 73 and 74:

Weiss and Aschkenasy also considered the distortion that a windshield might cause to the sound impulses received by a motorcycle microphone. They reasoned that the noise from the initial muzzle blast of a shot would be somewhat muted on the tape if it traveled through the windshield to the microphone. Test firings conducted under the auspices of the New York City Police Department confirmed this hypothesis. Further, an examination of the dispatch tape reflected similar distortions on shots one, two, and three, when the indicated positions of the motorcycle would have placed the windshield between the shooter and the microphone.11 On shot four, Weiss and Aschkenasy found no such distortion. (55) The analysts' ability to predict the effect of the windshield on the impulses found on the dispatch tape, and having their predictions confirmed by the tape, indicated further that the microphone was mounted on a motorcycle in Dealey Plaza and that it had transmitted the sounds of the shots fired during the assassination.

So, yes, the shot that that Weiss and Aschkenasy found no windshield distortion was the four BBN shot, or the fifth Thomas shot, the last shot. And it was determined to be from the TSBD.

I’m still a little perplexed about this though. Yes, the windshield would not be in the way of this last shot. But Officer McLain’s torso would have been squarely in the way. So, I am not too impressed with Weiss and Aschkenasy finding no distortion in this last impulse, as they had found in the first three. Why wouldn’t Officer McLain’s torso cause distortions, when the sound waves were forced to bend around his torso, just as the wound waves had to bend around the windshield from the first three shots.

Several folks who have read Weiss's testimony on this subject have inferred that he was implying that the grassy knoll shot was the shot with no windshield distortion. This is how I had read his testimony as well. This is even how Dr. Chambers read his testimony. With tongue in cheek, I blame Dr. Weiss for not specifying by number the shots with windshield distortion ala the HSCA report! The HSCA report sets the matter straight:

How could Dr. Chambers be ignorant of all this?
How could he not know that for the “grassy knoll” shot, the grassy knoll would be almost directly ahead of the motorcycle?
How could Dr. Chambers have concluded that the Weiss and Aschkenasy found no windshield distortion for the grassy knoll shot?

I thought Dr. Chambers was supposed to be a big expert on the acoustics of this case. It sounds like he doesn’t even know the basics. For you or me to make such an error is understandable. Not for Dr. Chambers.

And by the way, I don’t see anything in Dr. Weiss’s testimony that implies the grassy knoll shot would have no windshield distortion. So, I don’t see how Dr. Chambers got that idea, either from the testimony nor from the final report.

Question:
How did Dr. Chambers make two such large errors?
1.   Believed the grassy knoll would be off to the side of the motorcycle when it recorded the next to last shot.
2.   Believed that Weiss and Aschkenasy found no windshield distortion with the grassy knoll shot.

I see nothing obvious in the testimony or the final report that could lead to such errors.

[Jerry Freeman]

How exactly would a stuck microphone confuse the activities in Dealey Plaza?

DUH...communication breakdown just at the exact time of the shooting. Another remarkable coincidence huh?

[Joe Elliott]

When I first heard the police tapes...I came to the conclusion that the "stuck microphone" was a deliberate act to confuse the activities in Dealey Plaza. I still think so.

How exactly would a stuck microphone confuse the activities in Dealey Plaza?

DUH...communication breakdown just at the exact time of the shooting. Another remarkable coincidence huh?

Yes, but my question stands What practicable effect do you think a “stuck microphone” to have?

Do you imagine that without a stuck microphone, the Dispatcher would immediately direct these two policemen to this spot, those two policemen to that spot, maximizing the odds of catching someone? No, the only practicable effect is that without a stuck microphone, the Dispatcher could send in other units to Dealey Plaza immediately to help with the search. But even with an immediate response, it will take many minutes for units to arrive from other parts of Dallas. In the meantime, any shooter can leave the area, even if only moving at a walking pace.

With or without a stuck microphone, either the policemen already at Dealey Plaza are going to, on their own, in the first ten minutes, catch a shooter, or they are not. The radio network, the Dispatcher, policemen who are elsewhere, aren’t going to make a difference in the immediate search.

As it was, what effect did the stuck microphone have on the search? None. Officers, acting without instructions, went looking for the shooter. Officer Baker went into the building and climbed the stairs, on his own initiative. He did not need the Dispatcher to tell him what to do. If the microphone was not stuck, he still would not call in for instructions. That takes too much time and ties up the radio for everyone else. In a situation like this, everyone has to do what they think is best. Any coordination is going to have to come from senior officers already on the spot. Not from the radio network.


And these communication breakdowns, a stuck microphone key, was hardly an unknown event and was always plaguing the police department.

[Michael T. Griffith]

I’m still a little perplexed about this though. Yes, the windshield would not be in the way of this last shot. But Officer McLain’s torso would have been squarely in the way. So, I am not too impressed with Weiss and Aschkenasy finding no distortion in this last impulse, as they had found in the first three. Why wouldn’t Officer McLain’s torso cause distortions, when the sound waves were forced to bend around his torso, just as the wound waves had to bend around the windshield from the first three shots.

This won't work. The sound waves would have been coming from high above McClain and at a lateral angle from this right. At most, some of the waves might have encountered a portion of the top part of his right shoulder, resulting in minimal distortion, if any.

But the HSCA acoustical experts tested for windshield distortion and found that it significantly weakened the recorded sounds, by 3-6 decibels, when the windshield was between the rifle and the microphone (8 HSCA 31). They also found that shots received from the sides and rear were not affected by the windshield:

Obviously, sounds received from the sides and rear of the motorcycle would not be affected by the windshield. (8 HSCA 31)

Just the fact that the first three shots all contain windshield distortion is an amazing correlation. The fact that the fourth shot shows no such distortion is equally remarkable. The four correlations combined constitute powerful evidence that the dictabelt tape recorded assassination gunfire.

How could Dr. Chambers be ignorant of all this?
How could he not know that for the “grassy knoll” shot, the grassy knoll would be almost directly ahead of the motorcycle?
How could Dr. Chambers have concluded that the Weiss and Aschkenasy found no windshield distortion for the grassy knoll shot?

I thought Dr. Chambers was supposed to be a big expert on the acoustics of this case. It sounds like he doesn’t even know the basics. For you or me to make such an error is understandable. Not for Dr. Chambers.

And by the way, I don’t see anything in Dr. Weiss’s testimony that implies the grassy knoll shot would have no windshield distortion. So, I don’t see how Dr. Chambers got that idea, either from the testimony nor from the final report.

Question:
How did Dr. Chambers make two such large errors?
1.   Believed the grassy knoll would be off to the side of the motorcycle when it recorded the next to last shot.
2.   Believed that Weiss and Aschkenasy found no windshield distortion with the grassy knoll shot.

I see nothing obvious in the testimony or the final report that could lead to such errors.

Well, hold on now. Let's be fair and accurate about this. Dr. Chambers was correct in saying that the HSCA experts found windshield distortions in the shots that should have contained them and did not find such distortions in the shot that should not have contained them. That, after all, is the main point. He simply misidentified which shot does not contain windshield distortion. It's an error, to be sure, but it does not affect the main point. So it's not like this is some horrendous gaffe.

But, yes, even very good experts with exceptional qualifications make a mistake every now and then.

Dr. Chambers' chapter on the acoustical evidence is far superior to Sturdivan's errant and misleading chapter on the subject.

[Joe Elliott]

This won't work. The sound waves would have been coming from high above McClain and at a lateral angle from this right. At most, some of the waves might have encountered a portion of the top part of his right shoulder, resulting in minimal distortion, if any.

It appears it will work. McLain’s torso should block the direct path to the microphone.


Basic assumptions:
•   Microphone is on level with the handle bars, to be easy to reach.
•   Microphone is just forward of where the hands hold the handlebars, about 18 to 24 inches in front of the torso.

First, let’s talk about the horizontal angles.

Form previous work, I made a program that calculated the angles and distances for the limousine. At the time the fourth of five “shots” was fired, the motorcycle was in the fourth circle. This works to be about the position of JFK at Zapruder frame z174. At that moment, the horizontal angle back to the TSBD sniper’s nest was 20 degrees. The microphone would be, I think about 18 to 24 inches in front of his torso. Now coming in at a 20-degree angle, the center of the “acoustic shadow” would be displaced to the left by:

Between:
          18 * tan (20) = 6.6 inches
 And:
          24 * tan (20) = 8.7 inches

Where was the microphone? In the center behind the windshield? No.

http://mcadams.posc.mu.edu/russ/jfkinfo2/jfk5/hscashot.htm

Mr. ASCHKENASY - However, they will not look the same, because at the locations where they were picked up the motorcycle was in different orientation relative to the sound source, and as was discussed earlier, the windshield has an effect, the position of the microphone, which we suspect was on the left side of the motorcycle, those all would affect the quality, if I can call it that you know, the shape of the received muzzle blast.

So, the acoustic data that Weiss and Aschkenasy, seemed to indicate the motorcycle microphone was on the left side of the motorcycle.

So, about 6 to 9 inches offset of the acoustic shadow. Officer McLain was pretty big, I understand, so let’s say his torso was 22 inches wide, a bit of a conservative guess. So, his “acoustic shadow” would be offset about 8 inches. So instead of covering everything between -11 to + 11 inches (0 being the center), it would cover more like (-18 to + 4 inches). I doubt the microphone would be outside his hands. I think the maximum to the left it would be would be around -15 inches. So, I think horizontally, the microphone would very likely be in that ‘Acoustic Shadow’.


Of course, one could get around this by saying Weiss and Aschkenasy were mistaken. The microphone was on the right. But this would discredit them. They couldn’t tell from the acoustic data if the microphone was near the left edge of the microphone or the right?


Well, what about the vertical angle. At z174 the angle relative to the street would have been about 23 degrees. The sound wave would have to come down about 15 inches, with the microphone at the same level as his hands. How far would it down?

Between:
          18 * tan (23) = 7.6 inches
 And:
          24 * tan (23) = 10.2 inches

The “acoustic shadow”, 18 to 24 inches in front of Officer McLain, would only come down about 7 to 10 inches, at least 5 inches too high to miss exposing the microphone to a direct line to the sniper’s nest. And this is only taking into account the torso, not the head and helmet.



I think it likely the microphone should be in the acoustic shadow of the torso of Officer McLain.

But the HSCA acoustical experts tested for windshield distortion and found that it significantly weakened the recorded sounds, by 3-6 decibels, when the windshield was between the rifle and the microphone (8 HSCA 31). They also found that shots received from the sides and rear were not affected by the windshield:

Just the fact that the first three shots all contain windshield distortion is an amazing correlation. The fact that the fourth shot shows no such distortion is equally remarkable. The four correlations combined constitute powerful evidence that the dictabelt tape recorded assassination gunfire.

Not that remarkable, since it is likely they should have found distortion in the fifth shot, from the TSBD, due to Officer McLain’s torso. But let’s say they are right. How remarkable is this? One out of five.

Let’s not forget their other scores. They said the shots came from the TSBD, TSBD, TSBD, KNOLL, TSBD. Of the 15 impulse pairs with a strong correlation, how many fit this scenario? First of all, we have to subtract 4, because the determination of whether it was the TSBD or the KNOLL was based on what they felt was the strongest correlation, so those 4 are going to be automatically “right”. Of the other 11 less strong correlations, only 7 of 11 were correct. Not too far from 50-50. Not too impressive.

For the target, comparing where the target should be, based on the time, compared to where the target was, from the acoustic evidence, they were right 4 out of 15 times. About what one would expect from random results with only 4 targets. They were right about 1 out of 4 times.

Location of the limousine? Harder to judge, because I can’t find a good map showing the microphones for the second group ( 2 ( 1 ) through 2 ( 12 ) ). But fairly good but far from perfect. Yes, yes, I know, the correlation with the microphone locations is a “remarkable” match for a motorcycle moving pretty steadily along at 11 mph. A remarkable match, provided one first tosses out all the “false alarms”. Assuming one cherry picks the best microphone locations of the 15 correlations found.

Of course, if I cherry pick the microphone locations from the same data., the results are not so remarkably good.

Shot 1: Motorcycle at 2 (5 )
Shot 2: Motorcycle at 3 ( 5 ), motorcycle has shot forward at high speed and is near where it should be to record the shot at z313
Shot 3: Motorcycle at 2 ( 11 ), motorcycle has reversed course and headed back toward Houston Street
Shot 4: Motorcycle at 3 ( 8 ), motorcycle has reversed course again and is back to following the limousine at high speed.
Shot 5: Motorcycle at 3 ( 5 ), motorcycle has reversed course again and is heading back toward Houston Street a second time.

You see, the remarkable correlation of the data with the expected motorcycle speed depends heavily on which correlations are chosen as “good” and which are chosen as “false alarms”.


And we don’t know, but his may have been assisted by a partial search for matches. Not searching for matches where they couldn’t be. Like looking for a match with an early shot way down Elm street. Or looking for a match for a later shot on Houston Street. We still have no definitive statement from the BBN that all possible 2,592 combinations were hand checked in the 10 days available.

Well, hold on now. Let's be fair and accurate about this. Dr. Chambers was correct in saying that the HSCA experts found windshield distortions in the shots that should have contained them and did not find such distortions in the shot that should not have contained them. That, after all, is the main point. He simply misidentified which shot does not contain windshield distortion. It's an error, to be sure, but it does not affect the main point. So, it's not like this is some horrendous gaffe.

But, yes, even very good experts with exceptional qualifications make a mistake every now and then.

Dr. Chambers' chapter on the acoustical evidence is far superior to Sturdivan's errant and misleading chapter on the subject.

No. Dr. Chamber’s gaffe is pretty serious.

He wrote a book about the assassination. He wrote a chapter about the acoustics. He gave us the impression that he was looking independently into the evidence, and found that Weiss and Aschkenasy did analyze the evidence correctly. But we know he did not do this.

•   He did not look at the waveforms for the “grassy knoll” shot and found that there were, indeed, no distorted waveform there. We know that because Weiss and Aschkenasy did find this waveform to be distorted.

•   He did not check the BBN map, as I did, to make certain that Weiss and Aschkenasy were correct that the motorcycle position would not cause the windshield to distort the sound from the grassy knoll shot.

•   He didn’t even check the HSCA reports to confirm that it was, indeed, the grassy knoll shot that would not cause windshield distortion, according to Weiss and Aschkenasy.

Oops.

Instead, it looks like Dr. Chambers just went with his impressions, that Weiss and Aschkenasy said the grassy knoll shot should not contain windshield distortions, and indeed did not contain windshield distortions, and just rubber stamped the claim he thought they had made. And said, “yes, they got it right alright”. That is what it looks like to me. Not impressive.

[Michael T. Griffith]

In order to fully understand and appreciate the HSCA acoustical evidence, one must understand the phases and nature of the acoustical analysis.

* When BBN received the Dallas police dictabelt recording, they understood that “if gunfire had been recorded on Channel 1, the analysis of that tape could be expected to reveal patterns of transient waveforms that would be generally characteristic of the shock wave produced by the bullet, of the loud and impulsive noise of the muzzle blast, and of echoes of each” (8 HSCA 42). They also knew that “it could further be expected that the major components of the shock wave would appear in the 1-kHz to 3.2-kHz frequency band” (8 HSCA 42).

Thus, the BBN experts knew that, if they were dealing with impulse patterns caused by gunfire, each of their sounds would come in a specific order: they knew that the shock wave (or N-wave) would come first, followed by the muzzle blast, followed by echoes of the shock wave and the muzzle blast. They also knew that the presence of these patterns would depend on whether the microphone was in position to record them.

* In order to determine if gunshot waveform patterns were present on the police tape, the BBN acoustical scientists first had to apply two filters to the tape to filter out sounds that were outside the 1.0 to 3.2-kHz frequency band and to filter out background noise, especially the engine noise, that could mask the presence of gunshot-like impulse patterns.

* BBN applied the two filters to the entire 5-minute police tape (8 HSCA 42).

* BBN then took the recorded outputs from both filters for the entire 5-minute tape and converted the sounds into images, such as oscillograms and spectrograms, so that they could analyze the impulse patterns in minute detail. An example:



* The BBN scientists then analyzed the peaks and lines of all the impulses on the dictabelt recording. They did not just examine this or that part of the graphically displayed tape, but the entire tape.

* Also, at this point, the BBN scientists did not know if any of the impulse patterns would pass the initial five gunfire screening tests, and they had no idea which motorcycle may or may not have recorded gunfire in Dealey Plaza. They were simply looking for any and all patterns that resembled waveforms with the general characteristics of gunshots.

Keep in mind that they had no test-firing data from Dealey Plaza yet, because the test firing had not yet been conducted. Also keep in mind that they had not yet even subjected any of the impulse patterns to the five screening tests. 

* When the BBN scientists analyzed the graphical representations of all of the dictabelt tape’s impulse patterns, they found six patterns that they believed should be subjected to the five screening tests.

* BBN then applied the five screening tests to the six impulse patterns. If a pattern failed even one of the screening tests, it was disqualified from further analysis. Five of the six impulse patterns passed the screening tests.

The one pattern that did not pass failed three of the five screening tests: it failed the test for duration, the test for amplitude, and the test for shape. The test for shape examined whether the impulses within the pattern resembled the general characteristics of a shock wave and a muzzle blast.

Until today, I believed that the failed impulse pattern—the 4-second pattern discussed in previous replies--failed two of the five screening tests, but a closer reading of the BBN report clearly shows that it failed three of them. The BBN report notes that the 4-second impulse pattern was not only too short and of insufficient amplitude, but that it lacked “shapes similar to the expected characteristics of a shock wave and of a muzzle blast,” whereas the five other impulse patterns had those characteristics (8 HSCA 43).

This was the end of the preliminary analysis.

* At this point in time, the BBN scientists had no information on any motorcycle’s location in Dealey Plaza; they had no microphone-location data from the test firing to determine any possible motorcycle positions; and they did not even know if any of the five passing impulse patterns would pass the far more rigorous analyses based on the test-firing data.

* After studying the results of the screening tests in the preliminary analysis, the BBN scientists contacted the HSCA and advised the committee that they needed to conduct a test firing in Dealey Plaza before they could do further analysis of the dictabelt recording. The HSCA then asked two acoustical experts from Queens College, Mark Weiss and Ernest Aschkenasy, to review the BBN analysis and the BBN test-firing plan. WA found the BBN analysis to be accurate and the BBN reconstruction plan to be sound.

* The Dealey Plaza test firing was then conducted. Shots were fired from two locations: the sixth-floor Texas School Book Depository window that Oswald allegedly used and a spot on the grassy knoll. 36 microphones were placed on Houston Street and on Elm Street to record the sounds of the shots.

* The impulse patterns from the test-firing shots were then compared with the dictabelt impulse patterns that passed the gunfire screening tests. All five of the dictabelt impulse patterns were found to match patterns of some of the test-firing shots. The matches were based on the echo patterns of the respective impulse patterns. The odds that these correlations were due to chance are astronomically low.

We can suppose that one or perhaps two random noise patterns might, by rather remarkable chance, match the echo patterns of shots fired in Dealey Plaza within a 10-second period. But the idea that random noise patterns would match the echo patterns of five shots fired in Dealey Plaza within a 10-second period seems impossibly far-fetched.

And note that the acoustical scientists had not yet attempted to determine if the matches occurred in the correct topographic (locational) order in relation to the movement of the motorcycle. So the suggestion that the BBN scientists "only checked for matches where they anticipated where the motorcycle might be" is not only erroneous but displays a misunderstanding of the nature and timeline of the acoustical analysis.

* When the HSCA acoustical scientists studied the correlations further, they made two surprising discoveries. They found that when the locations of the microphones that recorded the matches were plotted on a graph showing time and distance, the microphones were grouped around a line on the graph that matched the known average speed of JFK’s limousine on Elm Street.

More important, they found that the matches occurred in the correct topographic (locational) order. The first dictabelt gunshot impulse pattern matched a test shot recorded on a microphone on Houston Street, close to the intersection with Elm Street. The next dictabelt gunshot impulse pattern matched a test shot recorded at the next microphone farther north on Houston Street. The third dictabelt gunshot impulse pattern matched a test shot recorded on a microphone in the intersection of Houston and Elm. The fourth dictabelt gunshot impulse pattern matched a test shot recorded on a microphone farther down on Elm Street. And the fifth dictabelt gunshot impulse pattern matched a test shot recorded on the next microphone on Elm Street.

The odds that these stunning topographic correlations could be coincidence are 125 to 1 against. Why? Because there are 125 ways that any five events can be sequenced, e.g., 5-2-4-1-2, 2-1-4-5-3, 4-5-3-1-2, 3-5-4-2-1, 3-2-4-1-5, etc., etc. Only one of those 125 ways is 1-2-3-4-5. In other words, the odds that these locational correlations are the result of chance are 124 out of 125, or 99.20%, against.

* The HSCA acoustical experts found four more impressive correlations.

They found that each dictabelt gunshot impulse pattern that was recorded when the motorcycle was in position to record the shot’s N-wave does in fact include an N-wave.

They found that in each shot with an N-wave, the N-wave comes in the correct order and interval in relation to the muzzle blast that comes behind it. When a rifle shot is fired, the first sound to reach a properly placed microphone will be the N-wave, followed by the muzzle blast, followed by the echoes of the N-wave and of the muzzle blast. N-waves come 10-30 milliseconds before the muzzle blast, depending on the rifle’s muzzle velocity and other factors. The N-wave in the dictabelt grassy knoll shot comes 24 milliseconds before the muzzle blast.

They found that each shot with an N-wave includes echoes of the N-wave and of the muzzle blast, as it should, and that the echoes come in the correct order and interval in relation to the N-wave and the muzzle blast.

Finally, the HSCA experts found that windshield distortion occurs in the dictabelt gunshots where it should occur, and does not occur in the one gunshot where it could not have occurred. The HSCA acoustical experts tested for windshield distortion because they knew it could substantially affect how the sounds of gunshots were recorded. They found that the dictabelt impulse patterns that contain windshield-distortion characteristics were recorded when the motorcycle’s windshield was between the shooter and the microphone. Conversely, they found no signs of windshield distortion in the one dictabelt impulse pattern that was recorded when the windshield was not between the shooter and the microphone. These are stunning correlations.

The HSCA report’s comments on the windshield-distortion correlations deserve another reading:

Weiss and Aschkenasy also considered the distortion that a windshield might cause to the sound impulses received by a motorcycle microphone. They reasoned that the noise from the initial muzzle blast of a shot would be somewhat muted on the tape if it traveled through the windshield to the microphone. Test firings conducted under the auspices of the New York City Police Department confirmed this hypothesis. Further, an examination of the dispatch tape reflected similar distortions on shots one, two, and three, when the indicated positions of the motorcycle would have placed the windshield between the shooter and the microphone. On shot four, Weiss and Aschkenasy found no such distortion.(55) The analysts' ability to predict the effect of the windshield on the impulses found on the dispatch tape, and having their predictions confirmed by the tape, indicated further that the microphone was mounted on a motorcycle in Dealey Plaza and that it had transmitted the sounds of the shots fired during the assassination. (HSCA report, pp. 74-75)

[Joe Elliott]

More important, they found that the matches occurred in the correct topographic (locational) order. The first dictabelt gunshot impulse pattern matched a test shot recorded on a microphone on Houston Street, close to the intersection with Elm Street. The next dictabelt gunshot impulse pattern matched a test shot recorded at the next microphone farther north on Houston Street. The third dictabelt gunshot impulse pattern matched a test shot recorded on a microphone in the intersection of Houston and Elm. The fourth dictabelt gunshot impulse pattern matched a test shot recorded on a microphone farther down on Elm Street. And the fifth dictabelt gunshot impulse pattern matched a test shot recorded on the next microphone on Elm Street.

The odds that these stunning topographic correlations could be coincidence are 125 to 1 against. Why? Because there are 125 ways that any five events can be sequenced, e.g., 5-2-4-1-2, 2-1-4-5-3, 4-5-3-1-2, 3-5-4-2-1, 3-2-4-1-5, etc., etc. Only one of those 125 ways is 1-2-3-4-5. In other words, the odds that these locational correlations are not the result of chance are 124 out of 125, or 99.20%.

Mr. Griffith corrected me on proper English, on when to use “it’s” and “its”. Something I should have learned in high school. Let me correct him on a little math on something he should have learned in high school.

What are the odds of five things ending up in the correct order? One out of 125? How did he get that? Five to the third power?

No, the number of permutations of a set with “n” members is n-factorial. This is:  n * (n-1) * (n-2) * . . . 2 * 1. So, the number of ways to order a set with 5 members is 120.


Now, what about the remarkable order of the apparent position of the motorcycle over time. How it appears to be moving up Houston and then down Elm Street at a study pace. Well, it turns out, that this depends heavily on cherry picking the data, as the BBN did. For instance, the BBN found correlations for the microphones for the first “shot” at microphones 2 ( 5 ), 2 ( 5 ), 2 ( 6 ) and 2 ( 6 ). Quite good. For the second “shot” at microphones 2 ( 6 ), 2 ( 6 ), 2 ( 10 ) and 3 ( 5 ). Wildly bad. They found correlations along a stretch of about 84 feet along Houston and Elm. But the rest were not as bad.

If you make careful selections of which correlation that is considered “good”, then for the 5 shots (including Dr. Thomas’s fifth shot) you get:

2 ( 5 ), 2 ( 6 ), 2 ( 11 ), 3 ( 4 ) and 3 ( 5 ). If the first microphone at 1 ( 1 ) is considered at distance 0, and we assume a distance of 12 feet between each microphone, we get distances along this track of:

168, 180, 204, 252, 264 feet.

Note: These distances are very rough. And the second section of microphones 2 ( 1 ) through 2 ( 12 ), is much shorter than the other two, because they did not arrange these microphones in a linear line but bunched them up over a short distance around the bend of Houston to Elm, where the street was widest.

Ok. This is quite good. We get a nice steady pace of around 11 mph. Sounds quite plausible.


But what if we make a different selection of which correlations are considered good? In that case we can get:

2 ( 5 ), 3 ( 5 ), 2 ( 11 ), 3 ( 8 ), 3 ( 5 ). This gives us the distances along this track for the 5 shots of:

168, 264, 204, 300, 264 feet.

This gives us a much more erratic pattern. It appears the motorcycle initially speed forward at a tremendous speed between shots 1 and 2, then reversed direction to head back toward Houston to record the third shot, then again reversed direction and rode down Elm Street to record the fourth shot, before reversing direction for the third time and heading back toward Houston to record the fifth shot.

You see, a lot depends on which correlations you decide you like. And which ones you decide to reject as “false alarms”.


Ok, let’s do it one more time. This time, not trying to make the data look good or bad. Whatever correlation we get, we will accept its position, then select the average of all the correlations for that shot. In that case, we get the distances of:

174, 207, 204, 280, 280 feet.

Well, not too bad. A couple hiccups here and there. An apparent reversal between the second and third shot. And the motorcycle appears stopped for the fourth and fifth shot. But still, not too bad.


Well, why didn’t they do the obvious thing? Make their position estimate of the motorcycle based on the average result they got from their data. Because their data seemed in many ways to be random.

For different widely space targets were used. Of the 15 found correlations, only 4 corresponded with the location of the limousine at that time. About a success rate of 1 in 4, exactly as to be expected with random results.

For the source of the gunfire, the correlations were not consistent. Of the four judged shots with multiple correlations, three of them gave two different location for the source of the fire, the TSBD and the Grassy Knoll. Only the last shot, with three correlations, did all three agree on the same source, the TSBD. Of the 12 test shots, 8, or 67 percent came from the TSBD. Of the 15 found correlations, 12, or 80 percent, came from the TSBD. Again, the results are close to what one would expect of random data.

Only with the location of the limousine could a case be made for good, non-random data. Provided the data was cherry picked. If this was done, then it could be argued, as the BBN did, that the data supports a plausible, fairly constant 11 mph speed for the motorcycle with the stuck microphone.


But how did they make their case? Did the propose using cherry picked data. And also presented arguments in favor of using all their data, and using the average location to show the position of the motorcycle. But argue for why the cherry-picked method is better. No. they never made any arguments about why using cherry picked data is superior to using the averages of the data. They simply presented their cherry-picked data, in the form of a map of Dealey Plaza with four circles, nicely spaced, which support a near constant speed of 11 mph for the motorcycle.



One can still argue, well maybe there is not a 1 in 120 chance that we get such a correlation of the speed of the motorcycle with a 11-mph steady progress. But the data is consistent with a motorcycle progressing up Houston and Elm in generally the right direction. This suggests that the data is not random. But there is one more thing to considered, beyond cherry picking which correlations to use, that could skew the data. And that is deciding which part of the raw data to search for comparisons. It would be natural to assume they searched for all possible 2,592 combinations, of the:

•   432 recordings from the 1978 tests, 36 microphones, each recording 12 test shots.
with:
•   The six suspect impulses from the 1963 Dictabelt recording.

But they had only 10 days to do all these comparisons, and the associated calculations, to find the strongest correlations. So, it is plausible they only searched for where there could be a valid correlation. So, after finding one shot, likely the second, skip searching the hundreds of possible comparisons of early shots with the microphones that are on Elm Street, where they couldn’t be. And skip searching the hundreds of possible comparisons of the later shots along Houston Street and around the bend, where they couldn’t be. This approach may have been dictated by time constraints, 10 days between the shooting tests and the making of the phone call to the HSCA reporting on the finding of 15 correlations.

And the search may have been a good deal more focused than that. After finding one shot, let’s say the second shot, they might initially search the section that is consistent with a 11 mph for the first shot. Upon finding random correlations that convince them that the motorcycle is indeed moving at about the same speed as the limousine, they could do the same with the third, fourth and fifth shot, resulting in data that matches fairly well, with a 11-mph motorcycle. Even though the data is random noise.


BBN did all they could to make the case that their data was good. Cherry picked their data. Drew a map with 4 circles that showed how consistent this cherry-picked data was with a 11-mph motorcycle. If there was more there could have been done, they would have done it.

They could have said “It takes about ‘x’ minutes to make one comparison and the associated calculations”. The rate can be maintained for 6 hours during a hard-working day. We had ‘y’ men on this job. After a couple of days, we could process ‘z’ combinations per day. By the eighth day, we had completed all 2,592 combinations. This would help nail down the somewhat good correlation with the data and the location of the motorcycle. But there is no statement to this effect. No statement that unequivocally states that all 2,592 comparisons where actually done and completed.

Combined with the randomness of the data, except in regards as to the apparent speed of the motorcycle, I believe that only a subset of the 2,592 comparisons was actually made.

[Jerry Freeman]

Yes, but my question stands...

That is [I guess] agreement that it was another 'remarkable coincidence'. To quote your previous statement...."What are the odds"?

And these communication breakdowns, a stuck microphone key, was hardly an unknown event and was always plaguing the police department.

  Really? I would like to see some documentation of this.
I believe this acoustical jive is a waste of web space so if you don't reply...no loss of skin.