Acoustics

In recent years, numerous authors and researchers have resurrected the ostensible acoustics evidence that the House Select Committee on Assassinations primarily based its conclusions on surrounding the probability of there being a conspiracy in the assassination of JFK. For context, the Committee, now referred here on as "HSCA", utilized a Dictabelt recording that contained a Dallas police motorcycle, through an open microphone, accidently continuously transmitting over Channel 2. This subsequently led to the possibility of that motorcycle having accidentally recorded the assassination itself. Although no gunshots are audible through the human hear from the Dictabelt recording, James Barger et al felt that specific acoustical "impulses", because they had a statistically significant correlation with a spectrogram of a gunshot, were in-fact gunshots. Below is the segment containing the "impulse sounds":

Now observe what a spectrogram of a actual rifle shot taken during a reenactment of the assassination looks like:

Do they appear at all the same? Below is a table of the ostensible correlations (utilizing Pattern Cross-Correlation) between the two:

However, this correlation is rendered moot when we become cognizant of the objective fact that there are, also, statistically significant correlations between the spectrograms of gunshots and vocal patterns! Below is a spectrogram, created by myself, saying "K" (also, credit to Michael O'Dell for originally pointing this fact out):

And below is me stating "hold everything secure", which is what Sheriff of Dallas County Bill Decker transmitted over Channel 2:

Because of this fact, the acoustical "impulses" and their correlations to the spectrogram of gunshots are inconsequential. Nonetheless, the National Academy of Sciences, at the behest of the Department of Justice, analyzed the acoustics and found that "crosstalk", instances in which speech was transmitted over both channels simultaneously (specifically the HOLD crosstalk), demonstrates that the acoustical impulses the HSCA used occurred, objectively, 60 seconds after the assassination (although later corrected by Michael O'Dell to 29 seconds). Moreover, Sonalysts, Inc, commissioned by University of Virginia political science professor Larry J. Sabato, found that attempts by D.B. Thomas and Josiah Thompson to postulate correcting crosstalk (specifically the CHECK crosstalk) were invalid once they conducted a "Time-Frequency Reassignment" of the two tapes and discovered that the CHECK "crosstalk" is not an actual instance of crosstalk because of the incongruences of the frequencies of the tapes within the time period. Here is the link summarizing their research and rebuttal to D.B. Thomas:

Further_research_analysis_and_commentary_on_the_Dallas_Police_Department_recordings_of_November_22_1963.pdf (thekennedyhalfcentury.com)

Finally, the HSCA and James Barger opined and held as essential the positioning of Dallas police motorcyclist H.B. McLain in recording the assassination through the motorcycle. As James Barger testified:

"The officer was able to remember–I was very pleased to hear–that when he was around the corner from Main onto Houston he could see the Presidential limousine disappearing around the corner here from Houston onto Elm. That distance would be on the order of 180 feet. So he would then be somewhere around 180 feet, perhaps a little less, from the Presidential limousine at that time. Now, the distance from where we think that he was at the time of the first shot, which is here, to the distance where the Presidential limousine was at the time of the first shot is about somewhere between 120 and 138 feet. Again, there is an 18-feet uncertainty. I just said that we have located with our acoustic analysis the result that the motorcycle was 120 to 138 feet behind the limousine at the time of the first shot, which is right about here."[1]

Yet, Dale Myers in his study utilizing epipolar geometry (which is the use of 2-dimensional photographs to construct a 3-dimensional location and the position of objects in that location) found that McLain was not in the requisite position to actually record the assassination as dictated by the acoustical "impulses":

"Through triangulation, it is possible to determine a camera’s position in 3D space by taking any film or video footage that a camera has recorded; superimposing that footage over a three-dimensional model of the scene recorded; and triangulating three or more fixed points that are visible within its field of view…The geometric analysis of the photographic record demonstrates that Dallas police motorcyclist H. B. McLain was near the crosswalk at Main and Houston at the time that Hughes frame H648 and Zapruder frame Z150 were exposed" After finding that McLain was 174.38 feet behind the acoustical zone that had a diameter of eighteen feet that McLain is required to be in in order to record the assassination on his motorcycle: “The filmed record clearly shows that there were no other motorcycle officers between the presidential limousine and Officer McLain at the time the shots was fired, and therefore, no motorcycle officers could have been in the position dictated by the acoustic evidence."[2]

Sources:

1.AARC Public Digital Library - HSCA Hearings - Volume V, pg (aarclibrary.org)

2.SECRETS OF A HOMICIDE: ACOUSTICS - EPIPOLAR GEOMETRIC ANALYSIS OF AMATEUR FILMS RELATED TO ACOUSTICS EVIDENCE IN THE JOHN F. KENNEDY ASSASSINATION (jfkfiles.com)