Acoustic Evidence of Conspiracy?
On the basis of "acoustic evidence" provided by a Dallas Police Department Dictabelt tape, the House Select Committee on Assassinations concluded that there were at least four shots in Dealey Plaza, and that one of them came from the Grassy Knoll. The Dictabelt recorded a cop's microphone that had stuck in the open position during the minutes of the assassination. Nobody can actually hear shots on the Dictabelt, but an elaborate statistical analysis isolated fours sets of "impulses" that the House Committee's acoustic consultants asserted were shots.
An explosive finding, if true.
But the "acoustic evidence" has had a tough time since it was first announced by the Committee in 1979. The attack on the "acoustic" finding has come from three directions:
- A perceptive researcher noticed something on the dictabelt that the high-priced experts had failed to notice.
- Other researchers found holes in the logic of the House Select Committee's reconstruction of the events whereby the "shots" were recorded.
- A high-powered scientific panel trashed almost every aspect of the "acoustic" study.
What Happens When You Simply Listen Carefully?
The fellow at the right is Steve Barber, as he appeared on PBS' "Nova" in 1988. He was a researcher intrigued by the "acoustic findings" who wanted to study them further. Unable to get a copy of the Dictabelt tape from the National Archives, he eventually managed to listen to it when Gallery Magazine included, in an issue full of conspiracy articles, a recording of the tape. Greg Jaynes, who now owns the original, supplied this photo.
Playing the flimsy record over and over, Barber noticed something that the House Committee experts had not: the voice of Sheriff Bill Decker saying "hold everything secure" in the exact place where the shots supposedly occured. Yet Decker was known to have said "hold everything secure" about a minute after the real shots in Dealey Plaza. Thus the "shots" discovered by the House Select Committee could not actually be shots.
And here is the segment from the dictabelt tape. Listen very closely -- Decker's statement is there.
Barber's own experiences, first in finding the Decker statement and then in dealing with conspiracy-oriented researchers after his finding had been revealed, are the subject of this fascinating and very personal memoir.
Reconstructing the Stuck Microphone
In this essay, Greg Jaynes provides a good briefing on the "acoustic evidence," and particularly on the issue of whether the stuck microphone could have been on Officer McLain's motorcycle, and whether McLain's motorcycle could have been where the "acoustic evidence" requires it to be at the time of the supposed Grassy Knoll shot.
If Jaynes survey of witness testimony (see above) fails to support McLain's motorcycle being where it needed to be to support the "acoustic evidence," what does the photographic evidence show? In a presentation to the JFK Lancer Convention in 1997, Jaynes showed that McLain was several car lengths behind the place in the motorcade where the Committee placed him.
What do the Scientists Say?
Faced with the fact that the shots are found on the Dictabelt tape at the same time as Decker's "hold everything secure" statement, defenders of the "acoustic
evidence" claimed that the needle of the Dictaphone may have skipped and
overlaid the Decker statement over the real assassination shots.
This passage from Science magazine recounts the NAS examination of this issue.
The entire article from Science is interesting reading, and gives a good, rigorous rundown of the problems with the "acoustic evidence."
The "acoustic evidence" got a boost in 2001, when a scientist named D.B. Thomas published an article claiming to have corrected the statistical treatment in earlier studies and found clear evidence of a shot from the Grassy Knoll. However, a recent careful study of the timing on the events on the tape by Michael O'Dell vindicates the discovery of Steve Barber and the position of the Committee on Ballistic Acoustics that the "shots" happened to late to actually be shots. Thus the "acoustic evidence" was to acoustic science what cold fusion was to physics: an example of how even reputable scientists can jump to conclusions when faced with the possibility of an "explosive" discovery.
The following resources are available on Dave Reitzes JFK Online web site.
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