Monday, November 22, 2010

Dealey Plaza Echo Analysis - Acoustical Forensics

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Dealey Plaza Echoes


- Acoustical Forensics 101

By William E. Kelly

On November 22, 1963, when shots rang out at Dealey Plaza in Dallas, many witnesses looked for a smoking gun on the grassy knoll, searching for irrefutable evidence of conspiracy and an elusive gunman who didn’t take credit for shooting the president.

Those shots are still reverberating in the halls of justice, where attorneys keep asking for more studies of the acoustical evidence that indicate there were at least four shots, two guns, an ambush and conspiracy to kill the President.

It was four days after Christmas 1978 when a college physics professor was brought into the congressional hearing room and placed under oath. In a cold objective scientific manner he testified about his experiments on the sounds contained on a Dallas police department dictabelt tape.

In summary he told the congressmen, committee counsel and reporters present that, “It is our conclusion, that as a result of a very careful analysis, it appears with a probability of 95 percent or better that there was indeed a shot fired from the grassy knoll.”

The addition of acoustical evidence came early in the course of the House Select Committee on Assassination (HSCA) inquiry when it was discovered that a Dallas police officer kept some memorabilia in an attic trunk, including the dictabelt of police radio broadcasts of November 22, 1963. A study of that tape revealed that a police radio switch was locked on and continually broadcasted for approximately five minutes, during which time the assassination took place.

The HSCA hired an acoustics expert Dr. James Barger, to evaluate the tape to determine if the microphone with the open switch was in Dealey Plaza, and if the sounds of gunshots were on the tape. Dr. Barger, a sonar projects officer at the U.S. Navy Underwater Sound Laboratory, and chief scientist at Bolt, Beranek & Newman, Inc., had previously studied the White House Watergate tapes as well as the recordings of the shootings at Kent State.

In August of 1978 Dr. Barger had microphones set up along Dealey Plaza and recorded the sounds of rifles fired from the sixth floor of the Texas School Book Depository and the grassy knoll. Those recordings were refined, measured on an oscilloscope, and compared to the graphs of the sounds recorded in 1963 by the Dallas Police dictabelt.

When he testified before the HSCA in September 1978, Dr. Barger concluded that 1) the microphone with the open switch was indeed in Dealey Plaza at the time of the assassination, 2) there is a 97 percent probability that two of the impulses on the tape were caused by gunshots, 3) that there is a 65 percent probability that there are three shots recorded on the tape, and 4) there are indications of a fourth shot, given a 50-50 probability this shot came from the grassy knoll.

In a refined analysis of the one impulse on that tape that Dr. Barger identified as possibly originating from the grassy knoll, two other acoustical experts, Professor Mark Weiss and Mr. Ernest Aschkenasy, were asked to see if they could come up with more precise statistics.

After identifying the location of the microphone, thus reducing their chance of error, they reported that they had increased the probability of a shot originating from the grassy knoll from 50 percent to 95 percent.

What’s more, Weiss testified, their analysis wasn’t the result of some arcane experiments that used imprecise measuring devices, but instead they used principles in physics that could be understood (and thus duplicated) by high school students. Nor did the tests involved any subjective judgments, but were based on everlasting and relatively simple mathematical principles.

“If I were a lawyer,” Weiss testified, “I probably would express it as beyond a reasonable doubt that shot took place.”

Mr. Weiss: “We had no preconceptions as to what we were going to find, if anything. When we first heard the tape recording and 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, subjecting it to all the tests that we have, the results of the analysis convinced us. We did not have any objective other than to do the best we could to find out what these data really represent.”

Mr. Aschkenasy: “The numbers could not be refuted. They just came back again and again the same way, pointing only in one direction, as to what these findings were. There just doesn’t seem to be any way to make these numbers go away, no matter how hard we tried.”

Mr. Weiss: “The principles we used are basically the fundamental principles in acoustics, namely that sound moves out in all directions, it is reflected, and the speed of the 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 or not it is the original sound or the reflecting echo.”

“In a situation such as an echo generated in Dealey Plaza, you have reflecting surfaces in the walls of buildings, fences, etc., so if you have a very short, sharp sound, such as a rifle firing, you would hear something like – bang, bang, bang, and diminishing in amplitude as you get echoes over a larger period. If the buildings are the same 15 years later, as they are in Dealey Plaza, and a rifle is shot form exactly the same spot, you would have exactly the same sequence of echoes.”

“These acoustical principles have been established a very long time, they have been known for several hundred years. These are fundamental things in acoustics, the things taught in high school or undergraduate level college physics.”

“Bascially we used a large survey map of Dealey Plaza, on a scale of one inch corresponding to ten feet, a ruler that could be extended, a hand calculator for computing some very simple things, and an oscilloscope for observing the wave shapes of the sounds that we get when we played back the tape recordings, and a device that enabled us to plot these patterns on paper to examine them in very fine detail.”

“The basic idea is that if a sound heard on the police tape was the sound of gunfire, then I ought to be able to find a position for that microphone and a position for that gun such that I could predict a pattern of echoes that would match the sounds to a high degree of accuracy. The graph made by the sound of the shot, and the echoes that were received by the microphone on Dealey Plaza can be likened to fingerprints. The pattern of sounds is unique and that pattern is as much a fingerprint that identifies two things – the location of the sound – the rifle, and the location of the receiver – the microphone.”

“Although they were smudged by noise, we sought to match the fingerprints we had that had been recorded in 1963. We did that match in a numerical way that allowed us to score each match. I could then say that the match of a predicted pattern with the observed pattern is so close that the probability that the sound is something other than a gunshot becomes very small.”

“So we start out to predict what the echo structure would be at various locations at Dealey Plaza 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. We have become familiar with the acoustical structure of Dealey Plaza by using the map to know where the echo reflecting surfaces are, and we had to know where the source of the sound, where the shooter was.”

“If after diligent searching we could not get a pattern of echoes, a predicted pattern of echoes that would clearly match the impulses visible on the police tape, then we would have to conclude we did not have a shot, or the microphone and/or the shooter was not anywhere near the positions we assumed.”

“Both are variables. So we moved them around, a process of experimentation, trial and error, until we closed in on a set of positions that gave us a reasonable accurate match. We got a set of positions which gave an extremely good match to this early set of echoes, but this set of data was not as good for the other echoes that were out at a distance.”

“The committee asked us if there was any way to take Dr. Barger’s statement of 50-50 percent and move it off center either way, and it really didn’t matter to us which way it moved. We were totally independent. So we adjusted again until the light finally dawned, that we weren’t dealing with a shooter here and a microphone here. We were dealing with a stationary shooter alright, but also with a microphone that was in motion, going down the street – a microphone on a motorcycle in the motorcade.”

“So we started moving the microphone down the street at 11 miles an hour, the speed of the motorcade, now predicting what the echo pattern would be at every position. As soon as we started doing that, it became obvious immediately that we could quite easily find positions for the rifle and the motorcycle.”

“In fact, there are 22 peaks for which I can predict an echo path that will match it to within one-thousandth of a second, a terrific fit to begin with. Once we knew approximately where everything was, we then tried to adjust positions, and we found that if you moved the shooter five feet you could compensate for the initial moving of the microphone by about one foot and get a range of fit of prediction to greater than one millisecond.”

At that point in the proceedings, one of the committee counsel asked, “So the only two locations in Dealey Plaza which would produce this echo pattern would be a microphone moving at 11 miles per hour within about one foot of a designated spot approximately 120 feet behind the president’s limo, and a rifle firing from the grassy knoll within an area five foot in circumference?”

Mr. Weiss: “That is correct.”

G. Robert Blakey: “The results of the acoustical project not only led the committee to reexamine the FBI firing data, but it also led us to look for a motorcycle policeman about 120 feet behind the president’s limo, to the left side of the road, with a microphone on the left handlebar that had a faulty switch.”

“Ultimately, the committee found film coverage of a motorcycle policeman on Houston Street several car lengths behind the president’s limo as it turned in front of the Texas School Book Depository, from Houston onto Elm, the place that the acoustical experts suggested it would be. The officer riding the motorcycle was identified as H.B. McLain, who rode 120-180 feet – five to seven car lengths behind the president’s limo, who was on the left side of the motorcade, with a microphone, unlike other Dallas police motorcycles, mounted on the left handlebar. Officer McLain testified before the committee that his microphone also stuck open quite frequently without his knowledge.”

“It is hard to imagine this could be an accident,” Weiss testified, “but you can’t express it in those terms. There is noise, motorcycle engine noise, electrical noise, static coming in, so we excluded from consideration anything that was at that level. We took into account everything that might affect the accuracy of our predictions. We took into account the map’s accuracy, the temperature, the change in architecture of the Plaza, distortion of the microphone and transmitter, static produced by the recorder, and if there is any weakness in the results of our analysis it has escaped us entirely. Anything that would have significant impact on the measurements we have made would be contrary to anything I can imagine.”

Mr. Weiss: “This procedure has nothing to do with human responses or interpretations, such as a polygraph, which may vary from one observer and evaluator to another. This is pure, basic physics and geometry.”

“The impulses we studied couldn’t have been produced by a motorcycle backfire because it has a visible supersonic shockwave preceding it, and even if a motorcycle backfire could produce such a shockwave, that motorcycle as up there on the grassy knoll behind the stockade fence in Dealey Plaza.”

Dr. Barger: “Once we checked the procedures used by Professor Weiss, their parameters and their echo-producing objects, we received from them the results of their match. Drs. Kalikow, Rhyne, and Mr. Schmidt and I, at Bolt, Beranek and Newman, reviewed their results, and we concluded they had successfully achieved a match having a high correlation coefficient, with a plus or minus of one-one-thousandth of a second error for each match. Whereas we had used a plus or minus six one-thousands of a second error, a larger acceptance window, because we didn’t know where the motorcycle was exactly. The effect of reducing this acceptance window is to greatly reduce the likelihood that noise bursts that occur could mimic the fingerprint of a shot from any place and received at that microphone. It reduces it very substantially.”

Mr. Aschkenasy: “If there are any other sounds which resemble sounds produced by a bullet in a supersonic flight followed by the sound of muzzle blast, then they must be considered, but I don’t know that there are.”

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

Representative Louis Stokes, Chairman of the committee, told Weiss that his testimony might very well “change the course of history.”

Stokes told Weiss, “as a scientist you are aware of the enormous impact that your testimony has here today, because if the committee accepts your testimony, the committee accepts, in effect, the fact that on that particular day in 1963 when the President was assassinated, there were two shooters in Dealey Plaza.”

Although most of the HSCA members were impressed with the acoustical evidence, Rep. Robert Edgar (R. Pa.) asked Dr. Author Lord, a physics professor at Drexel University in Philadelphia, to listen to the acoustic expert’s testimony and evaluate their presentation. Dr. Lord later said, “Weiss and Aschkenasy did a nice job. They used a neat technique, I guess you’d call it acoustical forensic pathology, but it’s never been done before. They look good, but there’s no precedent for it.”

Longtime critics of the official inquiries were also skeptical of the acoustical findings. They warned that the acoustics could be a red herring, and draw attention away from other, even more significant evidence. They reason that if the HSCA base its conspiracy conclusion only on the acoustical evidence, and the acoustical experts who restudy the evidence disagree, they can then eliminate the reason for instigating a proper investigation of all the evidence.

The acoustical evidence isn’t the only evidence of conspiracy, and it isn’t probative evidence that bears on the identity of those responsible for the crime, but it is objective, scientific evidence that can be duplicated and confirmed, and used to help convince those with the authority to instigate a proper criminal investigation.

After the Justice Department asked the National Science Foundation (NSF) to evaluate the acoustical tests, a $23,000 grant was awarded to a team of scientists to evaluate the previous studies done by Barger, Weiss and Aschkenasy. The director of this task force was Harvard University physics professor Norman S. Ramsey.

At the same time, Barbara Jorgenson of the Academy of Sciences said the results of these studies of the acoustical evidence “is not going to end the controversy. This is only going to answer one small part.”

The acoustical study is only one small part of all the available evidence, the relevancy and meaning of which is questionable, but it is the only officially funded study (up to that time), and was the last report due before the Congress and Justice Department were to take any further action.

This “hot potato” became a time-bomb as the acoustical tapes and scientific reports filtered down through government agency channels.

The “red herring” theory began to take effect first, when the FBI released a report in December, 1980, even though they weren’t asked for their opinion. The FBI stated the HSCA acoustics experts did not show that the gunshots were on the dictabelt or that other sounds originating in Dealey Plaza were recorded on it.

In an interview with the Dallas Morning News reporter Earl Golz, Blakey called the FBI study a “sophomoric” analysis, and “irrelevant because they critiqued something we didn’t do….they didn’t have an understanding of the uniqueness of the acoustical pattern of Dealey Plaza and the probability that the shots heard on the tapes were fired there.”

Over a year went by before the contract for the study was awarded, and another year would come and go before the Ramsey group’s report was due. After breaking two deadlines, it seemed like they would release it whenever they agreed on a conclusion, and that didn’t seem likely to happen quickly.

Although Ramsey himself wouldn’t comment on his study until it was finished and released, one member of the Ramsey task force, University of California physics professor Luis W. Alverez, said he strongly disagreed with the method by which the HSCA acoustical expert James E. Barger found a gunshot sound from the grassy knoll.
Facilited by the production and release of a plastic 45 rpm recording of the tape by Gallery, a girlie magazine, amateur electronics sleuth were not discouraged from offering their opinions either, and Anthony J. Pellicano, Gary Mack and Steve Barber all submitted their analysis to the acoustical teams. Pellicano pointed out some inconsistences on the tape, including the sound of a carillion bell. Mack responded with the fact that there were two such bells near Dealey Plaza in 1963, but they are no longer there today.

Steve Barber, a drummer from Mansfield, Ohio also sparked controversy by noting that on the tape there’s the broadcast of Dallas County Sheriff Bill Decker, saying, “send all my available men up there to the railroad…” over the radio approximately 30 seconds after leaving Dealey Plaza, which forced Barber to conclude the sounds on the tapes were not recorded in Dealey Plaza at the time of the assassination.

Others have attributed this to “cross talk” where the tape skips.

When former HSCA chief counsel G. Robert Blakey was asked about the new studies, he responded by saying, “It’s almost diabolical, it’s outrageous what they are doing. They have put the acoustical evidence in a process that is guaranteed to raise questions about it. No scientist worth his salt is even going to come in and say everything is perfect. The typical way that scientists do things is to find things that are wrong.”

Instead of following standard scientific procedure for authenticating test results by duplicating the previous tests to see if the same results can be independently obtained, the Ramsey group studied the HSCA acoustical reports prepared by Barger, Weiss and Aschkenasy, and sat back and criticized it.

Even though the HSCA acoustical experts said that most high school physics students could duplicate their experiments with an oscilloscope and a calculator, the $24,000 Ramsey study never conducted any such experiments to confirm or refute the original HSCA tests.

Before it was even released, Blakey called the Ramsey report “a great study of a study.” He predicted that, “The ball will be handled so that it will be back in the Congress’ lap and the Department of Justice will have gotten out from it entirely. Nothing else is going to be done about it. They just want this case to die.”

Congressman Edgar’s consultant, Dr. Lord of Drexel, said that the acoustical studies must be done over a long period of time. “The analogy that the acoustics is like a fingerprint is good, but you can’t say that on the basis of seeing one fingerprint that all fingerprints are different.”

Well there are now a number of case studies worth considering, including Kent State and new recordings found of the assassination of Robert F. Kennedy, as well as a tape of the shotgun death of Oswald’s friend George DeMohrenschildt, as well as the March, 1981 attempted assassination of President Reagan.

Accoustical forensic pathology – it’s new, it’s interesting, it’s worth studying, but Justice shouldn’t rest on it, and as evidence in a homicide, it shouldn’t be the deciding factor, at least until more tests are done.

“If this were an active, current case, they wouldn’t be taking this kind of time,” Blakey said. “They just want this thing to die. They want to cloud it with enough uncertainty and questions that it will not continue to be a matter that is of concern to people.”

“There was a conspiracy to kill my president, and yours, and for some reason that entirely escapes me, people don’t want to investigate it further.”


Barger Report:

Testimony of Weiss and Aschkenasy:

Weiss and Aschkenasy Report:

Testimony of H. B. McLain:

HSCA Report: - analysis

NAS Ramsey Report:

Don Thomas :

Don Thomas : Echo Correlation Analysis

Don Thomas Overview: (3 parts)

Washington Post (George Lardner, 2001) :

Wiki Links:

Dale Myers:

More Myers: - entry212818

Michael O’Dell :

J.C. Bowles :


Unknown said...

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jhon said...

Mack's visual interpretation, a uniformed police officer can be seen standing behind the stockade fence, his face obscured by muzzle flash but with a badge like object on his fence