Question: What did acoustic experts review in regards to the Kennedy assassination?
About the article "Assassination of Robert F. Kennedy", section "Second gunman theory".

Candidate passages:
In 1979, after a review of the evidence and of prior investigations, the United States House Select Committee on Assassinations (HSCA) largely concurred with the Warren Commission and was preparing to issue a finding that Oswald had acted alone in killing Kennedy.
However, late in the Committee's proceedings a dictabelt recording was introduced, purportedly recording sounds heard in Dealey Plaza before, during and after the shots were fired.
After an analysis by the firm Bolt, Beranek and Newman appeared to indicate more than three gunshots, the HSCA revised its findings to assert a "high probability that two gunmen fired" at Kennedy and that Kennedy "was probably assassinated as the result of a conspiracy."
Although the Committee was "unable to identify the other gunman or the extent of the conspiracy," it made a number of further findings regarding the likelihood or unlikelihood that particular groups, named in the findings, were involved.
Four of the twelve members of the HSCA dissented from this conclusion.
The acoustical evidence has since been discredited.
Officer H.B.
McLain, from whose motorcycle radio the HSCA acoustic experts said the Dictabelt evidence came, has repeatedly stated that he was not yet in Dealey Plaza at the time of the assassination.
McLain asked the Committee, "‘If it was my radio on my motorcycle, why did it not record the revving up at high speed plus my siren when we immediately took off for Parkland Hospital?’” In 1982, a panel of twelve scientists appointed by the National Academy of Sciences, including Nobel laureates Norman Ramsey and Luis Alvarez, unanimously concluded that the acoustic evidence submitted to the HSCA was "seriously flawed", was recorded after the President had been shot, and did not indicate additional gunshots.
Their conclusions were later published in the journal "Science".
In a 2001 article in the journal "Science & Justice", D.B.
Thomas wrote that the NAS investigation was itself flawed.
He concluded with a 96.3 percent certainty that there were at least two gunmen firing at President Kennedy and that at least one shot came from the grassy knoll.
In 2005, Thomas' conclusions were rebutted in the same journal.
Ralph Linsker and several members of the original NAS team reanalyzed the timings of the recordings and reaffirmed the earlier conclusion of the NAS report that the alleged shot sounds were recorded approximately one minute after the assassination.
In 2010, D.B.
Thomas challenged in a book the 2005 "Science & Justice" article and restated his conclusion that there were at least two gunmen. 
The Assassination Records Review Board was created as a result of an act passed by the US Congress in 1992, entitled the "President John F. Kennedy Assassination Records Collection Act."
The Act mandated the gathering and release of all US Government records related to the Assassination of John F. Kennedy.
The Act was passed following the public outcry about the assassination after the 1991 premiere of Oliver Stone's film "JFK", which proposed Kennedy assassination theories involving plots to kill the President.
The ARRB collected evidence starting in 1992, then produced a final report in 1998.
According to Douglas P. Horne, the ARRB's chief analyst for military records,The Review Board’s charter was simply to locate and declassify assassination records, and to ensure they were placed in the new “JFK Records Collection” in the National Archives, where they would be freely available to the public.
Although Congress did not want the ARRB to reinvestigate the assassination of President Kennedy, or to draw conclusions about the assassination, the staff did hope to make a contribution to future ‘clarification’ of the medical evidence in the assassination by conducting these neutral, non-adversarial, fact-finding depositions.
All of our deposition transcripts, as well as our written reports of numerous interviews we conducted with medical witnesses, are now a part of that same collection of records open to the public.
Because of the Review Board’s strictly neutral role in this process, all of these materials were placed in the JFK Collection without comment.
According to Horne, the ARRB's work showed that:(1) The autopsy report in evidence today, Warren Commission Exhibit 387, is the third version prepared of that report; it is not the sole version, as was claimed for years by those who wrote it and signed it.
(2) The brain photographs in the National Archives that are purported to be photographs of President Kennedy’s brain are not what they are represented to be; they are not pictures of his brain, but rather are photographs of someone else’s brain.
Normally, in cases of death due to injury to the brain, the brain is examined one or two weeks following the autopsy on the body, and photographs are taken of the pattern of damage.
Following President Kennedy’s autopsy, there were two subsequent brain examinations, not one: the first examination was of the President’s brain, and those photographs were never introduced into the official record; the second examination was of a fraudulent specimen, whose photographs were subsequently introduced into the official record.
The pattern of damage displayed in these ‘official’ brain photographs has nothing whatsoever to do with the assassination in Dallas, and in fact was undoubtedly used to shore up the official conclusion that President Kennedy was killed by a shot from above and behind.
(3) There is something seriously wrong with the autopsy photographs of the body of President Kennedy.
It definitely is President Kennedy in the photographs, but the images showing the damage to the President’s head do not show the pattern of damage observed by either the medical professionals at Parkland hospital in Dallas, or by numerous witnesses at the military autopsy at Bethesda Naval hospital.
These disparities are real and are significant, but the reasons remain unclear. 
The sole acoustic evidence relied on by the committee's experts to support its theory of a fourth gunshot (and a gunman on the grassy knoll) in the JFK assassination, was a Dictabelt recording alleged to be from a stuck transmitter on a police motorcycle in Dealey Plaza during the assassination.
After the committee finished its work, however, an amateur researcher listened to the recording and discovered faint crosstalk of transmissions from another police radio channel known to have been made a minute "after" the assassination.
This was supported by the National Academy of Science article.
Further, the Dallas motorcycle policeman thought to be the source of the sounds followed the motorcade to the hospital at high speed, his siren blaring, immediately after the shots were fired.
Yet the recording is of a mostly idling motorcycle, eventually determined to have been at JFK's destination, the Trade Mart, miles from Dealey Plaza.
In 1992, author Bonar Menninger dismissed the committee report as "Blakey's $5 Million Folly".
In 2001, this criticism of the Committee's acoustic evidence was rebutted in a "Science & Justice" article written by D.B.
Thomas, a government scientist and JFK assassination researcher.
He concluded the HSCA finding of a second shooter was correct and that the NAS panel's study was flawed.
Thomas surmises that the Dictaphone needle jumped and created an overdub on Channel One.
The 1981 Committee on Ballistic Acoustics was charged with reviewing the HSCA’s acoustic evidence.
They concluded that the acoustic evidence of conspiracy was invalid.
Donald Thomas who reportedly performed the first independent peer review of the HSCA’s work and who people think was “an expert on acoustic testing” never read Thomas’ own report on his work with the acoustic evidence in which he acknowledges that "he is not an acoustic expert."
In 2003, computer animator Dale Myers used various films from the day of the shooting to plot the locations and speeds of the motorcycle police officers during the assassination, and concluded that no police motorcycles were anywhere near the precise microphone location on Houston Street required by the Committee's acoustic experts.
Myers' study confirmed the same misgivings voiced by HSCA photographic consultant Richard E. Sprague in 1978.
A majority of witnesses who testified on the source of the shots said they came from the direction of the Depository.
However, many witnesses thought the shots came from the direction of the Knoll.
Only five witnesses, from a total of over one hundred, thought the shots came from two directions simultaneously.
"The Mitrokhin Archive--The KGB in Europe and the West", by Christopher Andrew and Vasili Mitrokhin, documents extensive manipulation by the KGB in creating and fostering conspiracy theories regarding the Kennedy assassination.
The origin of the infamous forged letter, purported to be from Oswald to E. Howard Hunt, remained inconclusive in the final opinion of the Committee, leaving, in the words of Hunt, "an article of faith that I had some role in the Kennedy assassination.
"In 2003, Robert Blakey, staff director and chief counsel for the Committee, issued a statement on the Central Intelligence Agency: ...I no longer believe that we were able to conduct an appropriate investigation of the Intelligence Agency and its relationship to Oswald... We now know that the Agency withheld from the Warren Commission the CIA-Mafia plots to kill Castro.
Had the commission known of the plots, it would have followed a different path in its investigation.
The Agency unilaterally deprived the commission of a chance to obtain the full truth, which will now never be known.
Significantly, the Warren Commission's conclusion that the agencies of the government co-operated with it is, in retrospect, not the truth.
We also now know that the Agency set up a process that could only have been designed to frustrate the ability of the committee in 1976-79 to obtain any information that might adversely affect the Agency.
Many have told me that the culture of the Agency is one of prevarication and dissimulation and that you cannot trust it or its people.
Period.
End of story.
I am now in that camp. 
The Assassination Records Review Board was not commissioned to make any findings or conclusions.
Its purpose was to release documents to the public in order to allow the public to draw its own conclusions.
From 1992 until 1998, the Assassination Records Review Board gathered and unsealed about 60,000 documents, consisting of over 4 million pages.
All remaining documents are to be released by 2017. 
According to the House Select Committee on Assassinations, a Dictabelt recording of the Dallas Police Department radio dispatch transmissions from November 22, 1963, was analyzed to "resolve questions concerning the number, timing, and origin of the shots fired in Dealey Plaza".
The Committee concluded that the source of the recording was from an open microphone on the motorcycle of H.B.
McLain escorting the motorcade and that "the scientific acoustical evidence established a high probability that two gunmen fired at President John F. Kennedy.
"The acoustical analysis firm hired by the Committee recommended that the Committee conduct an acoustical reconstruction of the assassination in Dealey Plaza to determine if any of the six impulse patterns on the dispatch tape were fired from the Texas School Book Depository or the grassy knoll.
The reconstruction would entail firing from two locations in Dealey Plaza—the depository and the knoll—at particular target locations and recording the sounds through numerous microphones.
The purpose was to determine if the sequences of impulses recorded during the reconstruction would match any of those on the dispatch tape.
If so, it would be possible to determine if the impulse patterns on the dispatch tape were caused by shots fired during the assassination from shooter locations in the depository and on the knoll.
In 1978, at the behest of the House Select Committee on Assassinations, members of the Dallas Police Pistol Team participated in an acoustical reconstruction by firing both rifles and pistols from the locations selected by the researchers.
During the acoustical reconstruction, the Dallas Police marksmen had no difficulty hitting the targets.
The House Select Committee's firearms experts "...testified that given the distance and angle from the sixth floor window to the location of the President's limousine, it would have been easier to use the open iron sights."
The Warren Commission tests had been carried out on the assumption that Oswald, who they and the Committee concluded fired the shots, used the telescopic sight.
An article which appeared in "Science & Justice", a quarterly publication of Britain's Forensic Science Society, found there was a 96% certainty, based on analysis of audio recordings made during the assassination, that a shot was fired from "the grassy knoll" in front of and to the right of the President's limousine.
The acoustical evidence has since been discredited.
Officer H.B.
McLain, from whose motorcycle radio the HSCA acoustic experts said the Dictabelt evidence came, has repeatedly stated that he was not yet in Dealey Plaza at the time of the assassination.
McLain asked the Committee, "‘If it was my radio on my motorcycle, why did it not record the revving up at high speed plus my siren when we immediately took off for Parkland Hospital?’” In 1982, a panel of twelve scientists appointed by the National Academy of Sciences, including Nobel laureates Norman Ramsey and Luis Alvarez, unanimously concluded that the acoustic evidence submitted to the HSCA was "seriously flawed", was recorded after the President had been shot, and did not indicate additional gunshots.
Their conclusions were later published in the journal "Science".
In a 2001 article in the journal "Science & Justice", D.B.
Thomas wrote that the NAS investigation was itself flawed.
He concluded with a 96.3 percent certainty that there were at least two gunmen firing at President Kennedy and that at least one shot came from the grassy knoll.
In 2005, Thomas' conclusions were rebutted in the same journal.
Ralph Linsker and several members of the original NAS team reanalyzed the timings of the recordings and reaffirmed the earlier conclusion of the NAS report that the alleged shot sounds were recorded approximately one minute after the assassination.
In 2010, D.B.
Thomas challenged in a book the 2005 "Science & Justice" article and restated his conclusion that there were at least two gunmen.