Secrets of a Homicide: Acoustics

Synchronizing Zapruder and Hughes

The key to answering the question of whether or not H.B. McLain could have reached the position predicted by the HSCA acoustic experts by the time of the first shot involves synchronizing the Hughes film (which depicts McLain on Houston Street) and the Zapruder film (which depicts the shooting sequence).

The Hughes film, which shows McLain completing his turn from Main onto Houston Streets, contains no direct visual information which enables the casual viewer to determine exactly when the assassination occurs since the president’s limousine has already disappeared from view. [Exhibit 4]

Robert J.E. Hughes Jr., himself, wrote in a letter to his parents the night of the assassination that “...About five seconds after I quit taking pictures we heard the shots...” The exact number of shots Hughes heard was not reported. [104] Although some claim that the Hughes’ letter is proof that the shooting began after he stopped filming, it is important to note that human recollection is often unreliable. [105]

Although the presidential limousine is not visible during the latter moments of the sequences Hughes filmed on Houston Street – particularly the one that depicts H.B. McLain’s motorcycle – there are visual references that are common to both the Hughes film and the Zapruder film. For instance, the Hughes film not only captures the presidential limousine as it travels north on Houston but the seven motorcade vehicles and six motorcycle escorts that follow it.

The Zapruder film also captures the presidential limousine as well as a number of the same motorcade vehicles and motorcycle escorts that trail it. Several of these vehicles can be seen traveling north on Houston Street and making the turn onto Elm Street in the background of the film. [Exhibit 5]

Using these visual references and computer assisted geometric triangulation (i.e., the ability to pinpoint an object in space by triangulating its position based on two or more vantage points), it is possible to determine the relationship between the two films and, thus, synchronize them.

Stabilization Techniques

To assist in the synchronization process, the background of the Zapruder film was enlarged and stabilized using Abode Photoshop software.

The stabilization process involved loading each frame of the film into Photoshop, finding an inanimate object within the field-of-view (i.e., a tree, a lamp post, the concrete wall, etc.) and making adjustments to each frame that would keep this object fixed, or stationary, as the sequence progressed. This method removes the jitter inherent in handheld motion picture photography. When these re-centered, stabilized film frames are recompiled and viewed as a motion sequence, new details previously obscured by the movements of the camera operator are revealed. [Exhibit 6]

In addition, adjacent pairs of select frames were processed to create stereoscopic images which allowed the study of spatial relationships between objects in Zapruder’s field-of-view. [Exhibit 7]

Of particular interest was the upper portion of the frame which, at the beginning of the film, depicts the intersection of Elm and Houston, and later, as Zapruder pans the camera to his right, the northern half of Houston Street which is visible above the concrete wall of the peristyle. It is this area that shows the motorcade vehicles trailing the president’s limousine.

The Hughes film was also enlarged and stabilized using the same techniques just described. Stereoscopic images were also created from adjacent frame pairs. Of particular interest was the background area depicting the intersection of Elm and Houston, and the progression of the motorcade vehicles, including H.B. McLain’s motorcycle, trailing the presidential limousine. A comparison of the Zapruder and Hughes films reveals four vehicles, which are on-screen a sufficient period of time, upon which to base a synchronization of the two films. Those vehicles [106] are:

Secret Service Vice-Presidential Follow-up Car. The seventh car in the motorcade, a white 1963 Ford Mercury Monterey hardtop appears in both films making the turn from Houston onto Elm Streets.
National Press Pool Car. The ninth car in the motorcade, a blue/grey 1960 Chevrolet Bel Air hardtop appears in both films traveling north on Houston Street.
Camera Car 1. The tenth car in the motorcade, an off-white 1964 Chevrolet Impala convertible appears in both films traveling north on Houston Street.
Camera Car 2. The eleventh car in the motorcade, a blue/grey 1964 Chevrolet Impala convertible appears in both films traveling north on Houston Street.

Synchronization Process

The synchronization of the two films involved three basic steps:

  1. Determine the speed of each vehicle based on the Zapruder film’s average frame rate.
  2. Use the known speed of each vehicle to determine the average frame rate of the Hughes film relative to Zapruder’s camera.
  3. Use the average frame rates and computer-assisted geometric triangulation to plot the relationship between the two films.

Determining Vehicle Speed

Determining the speed of each vehicle was relatively straight forward. Portions of the Zapruder film were enlarged, stabilized and examined; the number of frames it took a vehicle of known length to pass a fixed point were counted; and a simple formula applied.

For example, a stabilized portion of the Zapruder film (Z213-236) depicts Camera Car 1 passing through Zapruder’s field-of-view. Camera Car 1 was a 1964 Chevrolet Impala with a wheelbase of 9.9 feet and an overall length of 17.5 feet. [107]

A frame count shows that it took 23 Zapruder frames for Camera Car 1 to traverse a distance equal to its own length (i.e. 17.5 feet). Dividing those 23 frames by 18.3 (the average speed of Zapruder’s camera) yields a time of 1.26 seconds for Camera Car 1 to travel its own length. That computes to a speed of 13.89 feet-per-second (or 9.5 mph). [Exhibit 8]

The speed of each of the cars visible in the background of the Zapruder film was calculated in the same manner. Slight variations in speed were noted (i.e., Camera Car 1 was moving at 9.5 mph; Camera Car 2 was moving at 9.1 mph; etc.) as would be expected in a procession of this kind.

Determining the Frame Rate of the Hughes Camera

Determining the operating speed of the Hughes camera was now a simple matter of counting the number of frames it takes for the same vehicle to pass a fixed point in the Hughes film, applying the known speed of the vehicle to the equation, and computing the frame rate of the camera. [Exhibit 9]

The answer shows that that Hughes camera was for all practical purposes operating at the same average frame rate as Zapruder’s camera (i.e., 18.3 frames per second). This fact can be confirmed by analyzing the speed of all of the vehicles common to both films. In all cases the answer is the
same. [108]

The operating speed of each amateur camera used in this analysis was calculated in the same manner – i.e., finding elements common to two of the films, determining the known operating speed of at least one of the cameras by relating it to the known speed of the Zapruder film, and using that information to determine the unknown operating speed, relative to Zapruder’s camera, of the remaining camera.

The geometric triangulation techniques described earlier and the computed operating speed of the cameras provided a way to plot the relationship between all nine amateur films.

Plotting the Relationship of the Zapruder & Hughes Films

In the case of the Hughes film, there are six different independent reference points upon which to base a synchronization of the Hughes and Zapruder films. All six independent reference points demonstrate that the two films synchronize in the same manner, as would be expected. In short, each method of synchronization is confirmed and validated by the other five independent methods of synchronization.

One of those common reference points appears in the background of the Zapruder film just as the President’s car begins to glide down Elm Street. That reference point is the seventh car of the motorcade – the Secret Service Vice-Presidential Follow-up Car – a white 1963 Ford Mercury Monterey hardtop making the turn from Houston onto Elm Street. [Exhibit 10]

This same car is also visible in the Hughes film at about the same time. [Exhibit 11] Because this vehicle appears in both films at about the same moment in time, it is possible to synchronize the two films using this vehicle as a reference point. One method of synchronizing the two films was to use the angle of the Secret Service follow-up car as it moved along the arc of its turn.

The angle of the Secret Service car as seen in the Hughes film was determined by aligning the film with a computer model of Dealey Plaza using a method known as triangulation.


Triangulation is a highly accurate way of computing the six degrees of a camera’s freedom based on camera footage. This technique is based on epipolar geometry [109] and is used by many of the world’s foremost motion picture visual effects masters to seamlessly match computer generated imagery with live action footage.

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. [Exhibit 12] Because the technique applies to any motion picture footage, historic events can be explored using this method.

It’s a tedious process that involves advancing the footage one frame at a time; aligning three or more fixed points in the footage to the same points on the model by adjusting the virtual camera’s six-degrees of freedom (i.e., moving and/or rotating the virtual camera); locking the camera’s position using key frames; [110] then advancing the footage to the next frame and repeating the process. [111]

Newtek’s LightWave software made it possible to look through the lens of the virtual camera that had been positioned to replicate the Hughes camera and see each frame of the Hughes film superimposed over this view. In other words, it was possible to look through each frame of the film (as if looking through a slide or transparency) and see the computer model beyond it.

Using the triangulation techniques just described, the fixed portions of the computer model that were visible in the virtual camera’s field-of-view were aligned with the real-world counterparts of those fixed objects as seen in the Hughes camera’s field-of-view, frame-by-frame. The result was an animated view of the computer model of Dealey Plaza that moved in frame-for-frame synchronization with the Hughes film.

Determining the Angle of the Secret Service car

Once the Hughes film was aligned to the model, a computer model of the 1963 Mercury was loaded and rotated it until it matched the angle of its real-world counterpart at Hughes frame H614. [Exhibit 13] The vehicle’s movements were then tracked frame-by-frame until it disappeared into the margin of the film; the angle of the car relative to Houston Street recorded at each frame. The last recordable angle (i.e., the last frame in which at least three points of reference were available to reliably deduce an angle) was 19-degrees at Hughes frame H631; with the average rate of change determined to be approximately seven-tenths of a degree per frame, or, 12.3 degrees of change per second. [Exhibit 14]

Next, the Zapruder film was loaded. Once again, a virtual camera was created to represent the Zapruder camera. The six degrees of freedom of this virtual camera was then matched to the Zapruder film using the triangulation technique previously described. Next, a model of the 1963 Mercury was loaded and rotated until the angle matched that shown in the film. [Exhibit 15]

The first angle obtained was taken from Zapruder frame 150, when the front of the Secret Service car emerges from behind the crowd gathered at the corner of Elm & Houston Streets.

The angle at that point was 33.5-degrees with the average rate of change over the next 26 frames found to be a little less than one degree per frame, or, 17.0 degrees of change per second. [Exhibit 16]

The data so far shows a last known angle of 19 degrees, culled from the Hughes film, and a first known angle of 33.5 degrees acquired from the Zapruder film. The question is: How much time elapsed between those two known angles? In other words, how long did it take for the angle of the Secret Service car to increase from 19 degrees to 33.5 degrees as it traveled along the arc of its turning radius? [Exhibit 17]

The two slight variations in the average rate of change of that angle – 12.3 degrees/second (culled from the Hughes film) and 17.0 degrees/second (culled from the Zapruder film) – is strong evidence that the turning radius of the car had changed slightly during the interval between the two sequences. [112] Consequently, the best that can be hoped for using this method is a range of synchronization between the Hughes and Zapruder films.

That range is somewhere between 16 and 22 frames. In other words, 16 to 22 Hughes/Zapruder frames [113] elapsed between the events depicted in Hughes frame H631 and Zapruder frame Z150. Expressed another way, Zapruder frame Z150 synchronizes to the Hughes film somewhere in the range of Hughes frames H647 to H650 [114] using this method. [Exhibit 18]

There is, however, a way of narrowing this six-frame-range of synchronization to a single frame using the speed of the Secret Service car rather than its angle to determine how much time elapsed between Hughes frame H631 and Zapruder frame Z150.

Determining the Speed of the Secret Service car

This is a relatively straight forward process whereby an average speed is calculated based upon two known speeds which is then applied to a known distance between two points to determine the unknown time period required to traverse that distance.

In this case, the unknown variable is the time period between Hughes frame H631 and Zapruder frame Z150. That unknown time period can be determined by using the two known speeds immediately before and after that period. For instance, the speed of the Secret Service vehicle immediately prior to Hughes frames H631 was determined to be 13.58 feet/sec (9.3 mph); while it’s speed immediately after Zapruder frame Z150 was found to be 10.56 feet/sec (7.2 mph).

Using these two known speeds, the average speed of the Secret Service vehicle between Hughes frame H631 and Zapruder frame Z150 can be calculated as 12.07 feet/sec (8.2 mph). [115]

At that speed, the Secret Service vehicle would have traversed the known distance of 11.5 feet between Hughes frame H631 and Zapruder frame Z150 in 0.95 seconds; or, the equivalent of 17 frames. [Exhibit 19] Hughes frame H631 plus an additional 17 frames equals Hughes frame H648. Hence, Hughes frame H648 is the equivalent of Zapruder frame Z150 (+/- one frame). [Exhibit 20] It should be noted that this single synchronization point falls within the range previously calculated.

Five additional reference points common to both the Zapruder and Hughes films – all of which provide a means of independently synchronizing the two films – validate and confirm the synchronization of Hughes frame H648 to Zapruder frame Z150 (+/- one frame), thus providing corroboration for the accuracy of this conclusion. These five validating synchronizations are the result of an analysis of the trajectory and speed of the presidential limousine, Camera Car 1, Camera Car 2, Dallas police motorcyclist Marion L. Baker, and eyewitness Rosemary Willis, as depicted in the nine amateur films listed earlier. [See, Appendix I for a complete analysis.]

McLain’s Position at the Time of the Assassination

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.

To determine McLain’s precise location at the moment the Hughes-Zapruder frames H648/Z150 were exposed, a computer model of the motorcycle was positioned to match Hughes frame H648 (the last frame of the Hughes film in which McLain appears) by noting the motorcycle’s relationship to lines-of-sight drawn between Hughes’ camera and the northwest and southwest corners of the Dal-Tex Building. [Exhibit 21] The distance between McLain’s location at Hughes H648 and the southern-most edge of the 18-foot diameter acoustic zone where McLain had to be located for the acoustic experts’ central premise to be valid, was measured at 174.38 feet. [Exhibit 22]

According to the acoustic experts, the first shot was fired at the equivalent of Zapruder frame Z160, just ten frames or 0.546 seconds after McLain had reached the crosswalk at Main and Houston; the position he occupied at Hughes frame H648 and Zapruder frame Z150.

In order for McLain to cover the 174.38 feet between his position at Main and Houston and the first shot position at Elm and Houston in the allotted 0.546 seconds, McLain would have to average a speed of 198 mph. [116] Since the Harley-Davidson motorcycle McLain was riding had a top speed of 95 mph, it would be physically impossible for McLain to cover the distance in the time specified.

Of course, McLain would actually have to travel much faster than the average speed calculated given the fact that McLain’s known speed at H648-Z150 was 14.7 m.p.h. and the presumed speed of the open microphone between shots 1 and 2, according to the acoustic experts, was 10.5 mph. [117] Simply put, McLain would be required to accelerate from 14.7 mph to a speed significantly greater than 198 mph (calculated to be approximately 2,115.4 mph – nearly three times speed of sound – in 0.2 seconds) and then slow down to 10.5 m.p.h. during the allotted 0.6 seconds. In either case, the required speed would be impossible to achieve on a motorcycle.

Consequently, Officer H.B. McLain could not possibly have been the motorcyclist with the open microphone at the location specified by HSCA acoustic experts.

What about another motorcycle officer? Could another motorcycle officer have been in a position to transmit the impulse sounds believed to have been gunshots as the acoustic experts postulated? The answer is - no. 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. [Exhibit 23]



  1. Thompson, Josiah, Six Seconds in Dallas: A Micro-Study of the Kennedy Assassination, Bernard Geis Associates, Random House, 1967, p.181 (Letter from Robert Hughes to his parents, Mr. and Mrs. Ray Hughes, November 22, 1963) [RETURN]
  2. In a 2004 email, Gary Mack, originator of the acoustic evidence and one of its leading defenders, wrote: “[Hughes] could not possibly have been confused about when the shots sounded. Before, during or after would have been definitive points in time for him…He stopped filming and a few seconds later the shooting started. So any conclusion that McLain was too far back based on the Hughes film has to show some overwhelming evidence that the shooting started while Hughes was filming, and that evidence has to explain why he never noticed shots during filming and then heard three shots after filming.” [Email message, Gary Mack to Michael O’Dell, March 9, 2004] Despite Mack’s insistence that any evidence demonstrating that the shooting began before Hughes finished filming (as this project concludes) must somehow explain Hughes’ failure to recollect the event in that manner, the overwhelming evidence presented in this document sufficiently demonstrates that Hughes’ recollection was faulty regardless of the specific reason. It has been well-documented in other studies that ear witnesses to the assassination “heard” anywhere from 2 to 10 shots beginning at various times, despite the overwhelming physical evidence that only three shots were fired. It is not necessary to the conclusions of this paper to determine why Mr. Hughes recalled the sequence of events as he did. [RETURN]
  3. The description and position of each car in the motorcade described above and throughout this document references the Presidential Motorcade Schematic Listing, November 22, 1963, Dallas, Texas, prepared by Todd Wayne Vaughan in 1992. [RETURN]
  4. Gunnell, John, Standard Catalog of American Cars: 1946-1975, Revised 4th Edition, Krause Publications, 2002, p.182 [RETURN]
  5. In a 2004 email, Gary Mack, the originator of the acoustic evidence and one of its leading defenders, claimed that because the Hughes camera (which is no longer in existence) was never tested "its running speed is unknown and unknowable." Mack wrote that FBI tests of the Zapruder and Nix cameras showed different speeds throughout the film with a variation "on the order of 10% or more." Mack noted that a speed variation of 10% over 30-seconds amounted to a discrepancy of 3 full seconds. Mack concluded that "any analysis using the Hughes film to 'prove' McLain was going to slow, or just fast enough, is misleading at best." (Email message, Gary Mack to Michael O’Dell, March 9, 2004) All three of Mack’s claims are false. First, the average speed of the Hughes camera relative to the Zapruder camera is "knowable" because the Zapruder camera was tested by the FBI, as Mack himself acknowledges. The accuracy of that relative speed is validated by the visual information contained in the film itself as it relates to other films which were synchronized to the Zapruder film using the same methods. Two, the Zapruder camera's speed varied by a maximum of 3%, not by ten percent as Mack reported. The Nix camera's speed also varied by 3%; although the FBI lab did report that the frame rate dropped to 15.75 fps during the final five seconds of runtime (a variation of 12.5% from the standard 18 fps setting). However, in calculating the average speed of the Nix camera (determined to be 18.5 frames-per-second), the FBI excluded the last five seconds of runtime "since the pertinent portions of Mr. Nix's assassination film were exposed prior to the last five seconds." Third, Mack's claim that a 10% variation in camera speed over 30-seconds would amount to a discrepancy of 3 full seconds assumes that the Zapruder camera would maintain a 10% acceleration over a 30 second period. This is demonstratively false. In fact, the FBI lab reported that when fully wound the Zapruder camera's speed increased by only 0.5% during the first ten seconds, increased an additional 1.0 to 2.0 % during the next 20 seconds, decreased 1.0 to 2.0 % for ten seconds, and decreased an additional 1.0 to 2.5 over the final 20 seconds. (FBI Lab Report, December 20, 1963) The maximum speed of the Zapruder camera was therefore only 1.5 to 2.5 % faster than the factory set speed of 18 frames-per-second. This variation would only amount to between 8 and 13.5 frames over 30-seconds; a discrepancy of just 0.44 to 0.75 seconds, not 3 full seconds as Mack claimed. [RETURN]
  6. Epipolar geometry describes the geometric relationship between two optical systems viewing the same subject and can be used to locate points or objects in space. Because a moving camera offers a new view every frame, epipolar geometry works for a single moving camera as well, and each new view is understood as a separate optical system. [RETURN]
  7. Key framing is a term used in computer animation and refers to the ability to record the positions of multiple objects at any given moment in time. [RETURN]
  8. This manual process has been largely replaced in the last few years by camera match-moving software like RealViz’s MatchMover, 2D3’s Boujou, SynaPix’s SynaMatch, and Autonomous Effect’s CameraGenie. [RETURN]
  9. The difference between the two rates of change is probably attributable to a slight change in the turning radius as the driver of the vehicle navigated the 120-degree turn from Houston onto Elm Street. For instance, a 0.28 degree change per frame in the turning radius of the Secret Service car during the one second interval between Hughes frame H631 and H648 would account for the difference in the angle of the vehicle between the two films. [RETURN]
  10. For all practical purposes, the Zapruder and Hughes cameras were found to be operating at the same speed – 18.3 frames/second. [RETURN]
  11. A splice exists between Hughes frames H648 and H649, wherein three frames are missing. These three frames are included in the six frame interval between H647 and H650. [RETURN]
  12. Calculated as 13.58 f/s + 11.87 f/s = 25.45 ÷ 2 = 12.73 feet/sec (8.7 mph) [RETURN]
  13. Calculated as 174.38 ft ÷ 0.6 sec = 290.6 ft/per/sec (198.2 mph) [RETURN]
  14. This speed was later refined by Dr. James Barger to “about 8 mph.” (Letter, Dr. James Barger to Norman Ramsey, February 2, 1982) A reduction in speed between shots one and two, as cited by Barger, would necessitate a considerable increase in speed, above and beyond the impossible speed already calculated. [RETURN]

Secrets of a Homicide: JFK Assassination © 1995-2011 Dale K. Myers. All Rights Reserved.
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