_______________________________________________________________________________________________
The Kennedy Assassination for the
Novice
Presents
CROSSTALK
Synchronization of Putative Gunshots with
Events in Dealey Plaza
JFK Lancer’s
November
in Dallas Conference
November 23, 2002
By
Dr. Donald B. Thomas
(copyright, 2002 by Donald B. Thomas)
(Reprinted here with the author’s
permission)
During the tenure of the House
Select Committee on Assassinations, Acoustical experts determined that the
sounds of the Kennedy assassination had been captured by a Dallas Police radio
microphone and recorded by their communications recording system. It was
further determined that among the sounds determined to be gunshots was one
which had been fired from the Grassy Knoll [1]. Because of the considerable
historical significance of this evidence another opinion was sought and the
findings of the first laboratory were confirmed by a second [2]. These findings
led to the official conclusion of the Assassinations Committee that there
probably was a conspiracy behind the death of President Kennedy [3]. A formal
request was made to the Department of Justice to reopen the case for the
purpose of identifying the perpetrators. The Justice Department chose instead
to commission yet further study of the acoustical evidence. This third study,
conducted by a panel organized by the National Research Council found that the
HSCA conclusion was invalid on the grounds that the sounds alleged to be the
assassination gunfire had been deposited on the Dallas Police recordings at a
point in time after the assassination was over [4]. The purpose of my
presentation today is to address this issue and to explain how one might arrive
at a different conclusion.
On the fateful day that John F. Kennedy
visited Dallas in November 1963, the Dallas police were recording their radio
transmissions over two channels. A frequency designated as Channel One (CH-1)
was used for routine police communications. A second channel, designated
Channel Two, (CH-2) was an auxiliary channel, which on this day was dedicated
to the President's motorcade. Up until the time of the assassination, most of
the broadcasts on this channel consisted of Police Chief Jesse Curry's
announcements of the location of the motorcade as it wound through the streets
of Dallas (James C. Bowles, head of the DPD communications department in 1963
has published transcripts of the police tapes [5] and all excerpts cited herein
follow his interpretation). Chief Curry was in the motorcade's lead car.
President Kennedy's limousine was the second car in line. The context of the
broadcasts on CH-2 allows us to fix the approximate time of the assassination.
In accordance with established radio protocol, the dispatcher on each channel
regularly announced the time, frequently appending the notation to his calls.
Fifteen seconds after the dispatcher on CH-2 had noted the time at 12:30, Curry
began shouting into the microphone,
"Go to the Hospital,
We're going to the hospital,
Officers, Parkland
Hospital."
This was the first of a series of calls
concerning the assassination and allows us to place the shooting at between
12:30 and 12:31 by the CH-2 dispatcher's clock. Meanwhile, over on CH-1, a most
fortuitous event occurred. Beginning at about 12:28, by the CH-1 dispatcher's
clock, and lasting until about 12:34, a microphone on a police motorcycle radio
stuck open. For about 5-1/2 min, the CH-1 broadcast was dominated by the sound
of the motorcycle's motor. Unable to communicate effectively, police officers
began to switch over to CH-2. At 12:33 the CH-1 dispatcher broadcast,
"There's a motorcycle officer up
on Stemmon's with his mike stuck open.
Could you send someone up there to
tell him to shut it off!"
A relevant question is, what made the dispatcher
so certain that the motorcycle with the open microphone was on the Stemmons
Freeway? An important clue is that around 12:32 the open microphone had
captured the sound of sirens. The only emergency in Dallas at that moment was
the assassination and at 12:32-33 the President's motorcade was on the Stemmons
Freeway en route to Parkland Hospital. There were 18 motorcycles escorting the
President's motorcade and evidently the dispatcher had inferred from the sirens
that the unit with the stuck microphone was among them.
If this inference was correct, then there
was a strong possibility that the motorcycle and its open microphone was one of
the 13 police motorcycles that were in Dealey Plaza at the time of the
assassination, and if so, it could have captured the sounds of the gunfire on
the police recording system. Eventually acoustical experts did find suspect
sounds with the characteristics of gunshots recorded during the motorcycle
sequence. The suspect sounds occur in a nine second interval that begins
approximately two minutes into the stuck microphone sequence. The NRC panel
concluded that this nine second interval was not coincident with the time of
the assassination.
If the suspect sounds truly are the
assassination gunshots they would have been deposited on the police recording
system coincident with the murder. If they are not the assassination gunshots
then it is much less likely that they would be coincident. Thus, an analysis of
events on the separate police channels provides us with an independent test of
the hypothesis that the gunfire has been correctly identified. Several
broadcast events are common to both channels during or close to the motorcycle
segment. Recall that officers were switching between channels because of the
problem on CH-1. This channel surfing, combined with the urgency of numerous
callers trying to reach the dispatcher with information related to the incident
at the same time, resulted in several instances of crosstalk. Crosstalk is a
phenomenon that happens when a broadcast over one channel is picked up by a
live microphone on a radio tuned to the other channel. The result is a
simulcast; the simultaneous broadcast of one call over both channels.
There are five such simulcasts during the
motorcycle segment. The crosstalk instance which occurs closest to the time of
the assassination, as judged by the context of the broadcasts on CH-2, was a
broadcast by Deputy Chief Fisher. I will now play a three minute section of the
CH-2 recording, ending with Chief Curry's call "Go to the Hospital."
A transcript is provided (Table 1) to aid in following along with the recording
at the time of the last calls.
Table 1.- Transcript of CH-2 DPD Radio
Broadcasts at around 12:30 p.m.
________________________________________________________________________________
Speaker Broadcast
________________________________________________________________________________
LAWRENCE:
"I'm at the Trade Mart now. I'll head back out that way."
FISHER: “Naw,
that's all right. I'll check it."
LAWRENCE:
"10-4."
CURRY:
"At the Triple Underpass."
DISPATCHER: "10-4, One. 15 Car 2.”
DISPATCHER: "12:30,
KKB364.”
LAWRENCE: "125
to 250."
DISPATCHER: "15
Car 2."
CURRY:
"GO TO THE HOSPITAL. WE'RE GOING TO THE HOSPITAL,
OFFICERS."
________________________________________________________________________________
Part of Fisher's broadcast on CH-2, the
phrase, "I'll check it," crossed over to CH-1. I will now play the
CH-2 phrase followed by the gunfire sequence on CH-1 so that you can hear for
yourselves the crosstalk under discussion and the putative gunshot sounds that
follow two seconds later.
Table 2.- CH-1 DPD Radio
Broadcasts near 12:30 p.m.
________________________________________________________________________________
FISHER: "I'll check it."
[STATIC LIKE SOUNDS ALLEGED TO BE
THE GUNSHOTS]
DECKER: "Hold everything
secure..."
________________________________________________________________________________
Two seconds after the Fisher phrase on
CH-1 the gunfire sequence begins. Two seconds after the Fisher phrase on CH-2
one finds Curry's announcement that he is, "At the Triple Underpass."
Ergo, the first putative gunshot sound was recorded synchronous with a time
when the lead car of the motorcade was in a position near the Underpass. By
referring to this aerial photo of Dealey Plaza we can get some perspective on
the topology of events. The Triple Underpass is the railroad bridge at the east
end of Dealey Plaza. Chief Curry must have been on Elm Street somewhere in the
vicinity of what is now called the "Grassy Knoll" when he made his
broadcast. The question is, where was the President's limousine at this time?
In this photograph, a polaroid taken by witness Jack Weaver, we can see both
the lead car and the President's limousine in Dealey Plaza moments before the
assassination. The lead car is approximately 150 ft ahead of the limousine on
Houston Street at this time. Another film in which the two cars appear together
is in the famous Zapruder film, which shows the two cars arriving together at
the Triple Underpass after the shooting. The proximity of the two cars shown by
the filmed evidence demonstrates that the President's limousine must have been
on Elm Street when Curry made his call and hence, the juxtaposition of the
broadcasts relative to the alleged gunfire sequence, and the juxtaposition of
the cars on Elm Street relative to the real gunfire are found to give a close
match.
There is a problem with this scenario,
however, as straightforward as it may seem. The issue is whether or not one can
rely on the crosstalk instances to provide an unequivocal timeline of events.
For example, the NRC panel relied on a different instance of crosstalk, a
broadcast by Sheriff Decker which occurs at least one minute after the
assassination, or at least one minute after Chief Curry's call to "Go to
the hospital." On CH-1 a fragment of Decker's broadcast, "Hold
everything secure," crossed over from CH-2 and is found at the end of the
gunshot sequence. The NRC panel relied on the Decker crosstalk as evidence that
the putative gunshots were actually recorded one minute after the
assassination. The problem is that the elapsed tape time between Fisher's and
Decker's broadcasts on CH-2 is 98 seconds, but the elapsed tape time between
Fisher and Decker crosstalks on CH-1 is only ten seconds. Clearly there is a
serious time discrepancy involved. Moreover, there are five simulcast events
between the two channels at the time of the motorcycle segment, but the time
intervals between any pair is different on the separate channels (Tables 3
& 4). As a consequence, the crosstalks misalign regardless of which pair of
simulcasts one chooses as the tiepoint. This is demonstrated in the graphic
representation of the timelines where I have used the two close crosstalks by
Sergeant Bellah as the tiepoint.
Therefore, in order to have confidence in
the synchronization of events on the two channels we must first resolve the
time discrepancies between the crosstalks. To do that we require two things:
firstly, we need to understand the phenomena that are responsible for the time
discrepancies, and secondly, we must have an independent source of information
on the real lapse of time between events.
Table 3.-
Simulcasts Between DPD Channels (12:28 TO 12:36)
CH-2 TIME*
BROADCAST BROADCASTER
12:29:50 "I'll check it" Fisher
12:31:28 "Hold everything secure" Decker
12:33:38 "Check those radios" Bellah-1
12:33:50 "You want me ... Stemmons" Bellah-2
12:35:21 "Attention all ... vehicles" Henslee
________________________________________________________________________________
*Times
anchored to notation of 12:30 on FBI 60 Hz adjusted playback.
Table 4.- Playback
Time Intervals* Between Crosstalks by Channel
Crosstalks Channel 1 Channel 2
Fisher
to Decker 10 98
Decker
to Bellah-1 158 130
Bellah-1
to Bellah-2 15 12
Bellah-2
to Henslee 114 91
Fisher
to Henslee 297 331
________________________________________________________________________________
*Times
from 60 Hz adjusted playback reported by Michael O'Dell.
Time
Warps
The crosstalk
misalignments result from three primary factors: recorder stoppage, stylus
displacements, and warps in playback speed of the recordings.
A)
Playback Speed.- Speed
warps during playback cause measured time intervals to differ from real time.
For those of you who still remember phonograph records, this problem is exactly
the same as one would get by playing a 33 rpm record at 45 rpm. In this case
the speed warp resulted from using a playback instrument different from the
instrument that made the original recordings. Captain James C. Bowles, a
supervisor with the police communications department in 1963, rented a dictaphone machine to playback the
police dictabelt for copying and transcription. Because the DPD dictaphone
machine was in constant use, Bowles had to use the rented machine to make his
copies of the CH-1 dictabelt. The problem with dictaphone machine is that there
is no set recording or playback speed. It had a knob for adjusting the belt
speed (presumably as an aid to transcription) but there are no increments or
standard settings. By using a different machine for playback it was inevitable
that a chronic speed warp would be introduced. The problem was not as large or
as obvious as playing a 33 record at 45 speed, but only about a 5% difference.
But even a 5% difference becomes significant. Over a 6 min segment of recording
the timeline error would be about 18 sec, which is too large to ignore. The
degree of warp was measured by the HSCA's acoustical experts by using the 60 Hz
power hum from the motor that drove the dictabelt. It was found that when
Bowles made his tape recorded copy of CH-1 his rented dictaphone machine drove
the belt about 5% faster than when the original recording was made. Thus, time
intervals on the Bowles tapes are shorter than real time and need to be
decompressed by a factor of 1.05 to correct for the difference in the
instrument settings. The NRC panel confirmed this warp when it measured the
interval from HOLD to YOU on the Bowles CH-1 tape at 171 sec, but when the
dictabelt itself is played back at a speed set to match the 60 Hz power hum the
same interval is 178 sec, equivalent to a warp factor of 1.045. The time
intervals shown in Tables 3 & 4 have been corrected using the 60 Hz power
hum.
B)
Stylus displacements.-
Both original recording instruments recorded and played back with a stylus
which etched an acoustical groove or tracked an acoustical groove, and as in
the familiar case of a worn phonograph record, the recordings were susceptible
to stylus displacements. Displacements could be forward or backward resulting
in, respectively, skips or repeats, both of which are readily detectable in the
instances when they take place during voice transmissions, but which are not
readily detectable if any occurred during silences. Stylus displacement was a
particular problem during playback of the audograph disc. As a result of the
wear and tear from the transcription process, the disc would not playback
without jumping. Thus, the Bowles tape of CH-2 contains multiple repeats as
well as missing broadcasts, and in fact, this is the reason that every bootleg
version of CH-2 differs from each of the others. Because a skip will reduce
playback time, and a repeat will add playback time, one would certainly want to
resolve the number of skips and repeats in order to
arrive
at an accurate measure of original recording time. As it turns out, the problem
is not as serious as it might have been because the audograph mechanism tended
to compensate for skips. The stylus on this machine is fixed - not free to jump
as in a phonograph player. In the case of a phonograph record, for example, a
scratch could induce a needle jump such that a record could play for an hour,
constantly repeating the same section of groove. The audograph machine was
designed so that such couldn't happen. Unlike a record player, the audograph
disc plays from the inside out. Moreover, the turntable is driven by a screw
drive which pushes the axis of the turning disc in a direction perpendicular to
the fixed stylus during play. As a consequence the tension on the stylus
induced by displacements tends to cause the stylus to skip in the opposite
direction if and when it next displaces. The stylus is inexorably driven
towards the outer rim of the disc by the screw drive as the disc turns. The
compensatory skip may not occur immediately but it becomes highly unlikely that
there will be an accumulation of significant added time. Of course, with regard
to any given time interval there is a possibility that a repeat has added time
and that the compensatory skip hasn't yet occurred, and therefore any given
time interval is likely to be off by about 3-1/2 sec or so (the rotation time
of the disc).
C)
Recorder Stoppage.-
The recorders on both channels were sound actuated and would stop recording
when there was dead air. The actuation switch was programmed to shut off the
recorders anytime there was more than about four sec of dead air. However, Jim
Bowles states that line noise was often sufficient to keep the recorders
running. On CH-1 this was not a problem because the motorcycle motor noise kept
the recorder active. On CH-2 however it is clear that the recorder did stop.
Those of you familiar with these recordings know that during the time period
before the assassination, from about 12:15 to 12:30, by the dispatcher’s time
notations, there is only about 5 min of recorded tape time. It is problematic
that recorder stoppage cannot be detected directly, nor is there is a direct
way to measure the duration of the stoppage when it occurred.
Dispatcher
Time Notations
An important aspect of the police radio
protocol was that the dispatchers regularly noted the time. Each dispatcher had
his own clock. These were analog clocks which were synchronized regularly to
keep them within one minute of one another. Typically the dispatcher would
append a time notation to one of his regular calls. Thus, there would often be
more than one time notation during a minute of time if there were many calls,
or there would be no notation during some minutes if no call was made. Because
the time notations were not meant to be precise to within seconds the intervals
between notations will not be exactly 60 sec. However, over segments of time of
many minutes, the time interval between notations will average out to 60 sec if
there is no interruption in recording time. That is why the time notations are
critical in resolving the discrepancies in the time intervals between the
crosstalks. The time notations give us an independent measure of actual time
passage between events on the recordings.
Reconciliation
of Misalignments
The
misalignments between the crosstalks can be resolved if one pays attention to the
factors that cause the time warps and the passage of real time denoted by the
dispatchers announcements. For example, note the small discrepancy between the
two Bellah crosstalks, an interval of about 15 sec on CH-1 but only about 12
sec on CH-2. When one factors in the 5% warp in tape speed the actual
discrepancy is 3.4 sec. That amount matches the rotation time of the audograph
disc and therefore the discrepancy can be explained as a stylus displacement; a
skip of one groove. Because the amount of time involved is so small it isn’t
necessary to prove that our explanation is true, but only that the discrepancy
is susceptible to explanation by the phenomena that we know are causing warps
in the
timelines. Moreover, one cannot add 3.4 sec to the timeline because of the
compensating effect of the audograph playback. This skip may well have
compensated for an earlier repeat.
The
next largest misalignment occurs between the second Bellah crosstalk (You want
me...Stemmons) and Dispatcher Henslee’s deliberate simulcast (Attention all
emergency vehicles). The 60 Hz adjusted interval is 114 sec on CH-1 but only 91
sec on CH-2. The difference, 23 sec is easily explained by a recorder stoppage
on CH-2. But just because there is a simple explanation is not evidence that
the explanation is correct. In theory the discrepancy could be due either to
lost time on CH-2 or added time on CH-1 or a combination of both. The
corroboration for the resolution is found in the dispatcher’s time notations.
The time notation sequence is shown in Table 5. Regression analysis is a
mathematical test of linear
relationships. In this test we are comparing the actual timeline (recorded
time) and the corrected timeline by adding the hypothetically missing 23 sec to
the actual time lapse shown by the dispatchers time notations.
Table 5.- Regression analysis of Dispatcher time notations against
recorded time
on CH-2 (in sec)
to test hypothesis of recorder stoppage.
Notation Expected Actual
Corrected
12:30 0
0 0
12:31 60
95.8 95.8
12:32 120
121.2 121.2
12:34 240
212.8 212.8
12:35a
300 268.9 268.9
12:35b 300
300.3 300.3
12:36a 360
329.9 352.9
12:36b 360 358.8
381.8
All Notations Slope
.902 .944
[Minus 12:31] Slope
.947 .998
Regression statistics for Regression Statistics for
uncorrected time notations corrected time notations
intercept a = .1876 intercept a = -5.5
slope b = .947 slope b = .998
s.e. of b = .0472 s.e. of b = .0606
Correlation r² = .988 correlation r² = .982
t
= 20.15, df = 5, p = 2.797 x 10-6 t = 16.46, df = 5, p = 7.56 x 10-6
F
= 483.2, df = 1,6 p = 5.792 x 10-7 F = 325.5, df = 1,5, p = 9.61 x 10-6
mean x = 240, mean y = 227.4
mean x = 240, mean y = 234
In the
regression test a slope of 1.0 would be perfect agreement; there would be a one
to one agreement between recording time and real time. The actual slope is .902, a fair agreement, but far from
perfect. Part of the problem is with the 12:31 time notation. This notation is
way off line, coming 36 seconds later than it should. But there is a logical
explanation. Sixty seconds after the 12:30 time notation Sheriff Decker was
transmitting orders to his men. As soon as Decker stopped transmitting the
dispatcher made the 12:31 time notation. Radio protocol included making regular
time notations but it did not include interrupting broadcasts for that purpose.
If we delete this aberrant notation the agreement between actual and expected
increases to .947, essentially a ninety-five percent agreement. If we then add
the hypothetically missing 23 sec between the second 12:35 and first 12:36 time
notations, we not only increase the agreement, but arrive at a near perfect
slope of .998. Thus, the dispatcher’s time notations provide us with
independent corroboration that the hypothesis of recorder stoppage to explain
the 23 sec discrepancy is correct.
By
making this correction we achieve a coherent timeline for CH-2 because there is
now good agreement between recorded time and real time. Most importantly, the
timeline is achieved with evidence completely independent of the juxtaposition
of the putative gunshot sounds on CH-1 and of the broadcasts that establish by
context the time of the assassination on CH-2. Using this rational timeline the
period from the Fisher crosstalk to the Henslee crosstalk on CH-2 is 354 sec.
This brings in to focus the real problem with the DPD recordings because the
same time interval on CH-1 (Fisher to Henslee) is only 297 sec.
Aligning
the two timelines (CH-1 and CH-2) using the Bellah-1, Bellah-2 and Henslee
simulcasts as anchors, the Decker and Fisher broadcasts still fail to align.
Moreover, it becomes evident that the reason for the misalignment is that about
a full minute of time is missing (57 sec) from CH-1 between the Fisher and
Bellah-1 broadcasts. The missing time is too great to be attributed to
recording speed, and besides, we have already measured and applied this
correction. Similarly, recorder stoppage cannot explain the missing time
because the motorcycle broadcast would have kept the recorder active. The one
phenomenon that works is a stylus displacement. There are some conspiracy
minded folks that envision sinister forces at work. However, the fact is that
the dictaphone machine had to be serviced about every half hour or so because
of the limited amount of recording space on the dictabelts, and if the person
changing the belts (or someone else) accidentally bumped the instrument, this
could have induced the displacement. Under this scenario, at approx. 57 sec in
real time after Fisher's broadcast, the stylus could have displaced backward
landing in a track 31 sec before the Fisher broadcast and from there continued
to over-record until the point where the stylus originally displaced, in the
process superposing the crosstalked Decker broadcast 10 sec after the Fisher
broadcast on this channel. The needle jump hypothesis explains the 88 sec
misalignment between the Fisher and Decker broadcasts while simultaneously
explaining the 57 sec misalignment between the Fisher and Bellah crosstalks. No
other phenomenon does both.
Ultimately, the misalignments can be
explained and resolved by the factors that we know to be causing time
displacements on the recordings: recorder stoppage, speed warps and stylus
displacements, establishing timelines independent of whether or not there are
gunshots on the recordings and independent of the juxtaposition of the suspect
sounds to the broadcasts concerning the assassination. That being so, the
timeline evidence does support that the putative gunshots are synchronous with
the time of the shooting by reliance on the crosstalk closest to the
assassination, the Fisher broadcasts, and remain synchronous with the time of the
shooting using all of the crosstalks once the discrepancies are resolved.
Conclusions
Any evidence is subject to different
interpretation and that is the case here. Many of these crosstalk instances are
difficult to hear, which is why I have played them for you so you can make up
your own minds and believe your own ears. Different listeners have reported
different interpretations of the broadcasts, even the more audible CH-2, as
witness the various transcripts that have been published. In part because they
were captured over a second intervening microphone and in part because the
motorcycle motor on CH-1 is contributing unwanted noise, the crosstalks are
anything but loud and clear. A digital voiceprint analysis has not been applied
to the Fisher broadcasts, as it has to the Decker and Bellah crosstalks, so
caution is advisable. Bowles identification of the call on CH-1 as a fragment
of Fisher’s call might be mistaken. Moreover, given some of the problems with
the aforementioned voice-print analyses, such a study still might not be
conclusive. Whether or not the Fisher broadcast crossed over on to CH-1, the
time warps are real and this makes any synchronization based on common signals
subject to some doubt, regardless of how rational our corrections to the
timelines seem. The point I wish to make in conclusion is that the NRC panel’s
reliance on a single instance of crosstalk, the Double Decker, does not
establish asynchrony between the sounds identified as gunshots and the time of
the assassination. As a consequence, the acoustical identification of the
assassination gunfire on the Dallas Police recordings has yet to suffer a
substantial challenge.
Acknowledgements
I am indebted to Jim Barger, Gary Mack,
and Michael O’Dell for comments, information, and some of the photographs that
contributed to this presentation.
References
1. Barger, J.E., S.P. Robinson, E.C.
Schmidt & J.J. Wolff. 1979. Analysis of
recorded sounds relating to the assassination of President John F.
Kennedy. Bolt, Barenek & Newman, Inc. Cambridge MA. Proceedings of House
Select Committee on Assassinations Vol. 8. p. 116.
2. Weiss, M.R. & A. Aschkenasy.
1979. An analysis of recorded sounds relating to the assassination of President
John F. Kennedy. Dept. Computer Sciences, Queens College, City University New
York. Proceedings House Select Committee on Assassinations Vol. 8. p. 32.
3. U.S. Congress, House of Representatives,
1979. House Report Wo. 95-1828. Select Committee on Assassinations. Final
Report, p. 76. U.S. Gov’t Printing Office. Washington D.C.
4. National Research Council. 1982.
Report of the Committee on Ballistic Acoustics. Prepared for Dept. of Justice,
Washington D.C. Report No. PB83-218461, p. 16.
5. Bowles, J.C. 1993. The Kennedy
assassination tapes: a rebuttal to the acoustical evidence theory. Pp. 313-410
in: G. Savage, JFK: First Day Evidence. Shoppe Press, Monroe, LA.