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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 21 made spectrograms of the crucial “hold everything” sections. As discussed in greater detail in Appendix B, Figure 4 is a photograph of composite sound spectrograms for the full four second message. The beginning of the “...hold everything...” phrase is approximately at zero on these time scales and the impulses for the BRSW conjectured grassy knoll shot occur beginning approximately at the arrow marked 145.15s (the time of the conjectured grassy knoll shot on the BRSW time scale) and the WA impulses occur 0.2 seconds earlier. As discussed in Appendix B, the black dots mark 27 corresponding features on the two channels. It is apparent from Figure 4 that there is a marked correlation between parts of the sound spectrograms of the two channels, even though the Channel I recording has much more noise. The correlation becomes much more impressive when the spectrograms of the two Channels are compared in detail. The correlation is particularly striking when one realizes that only the initial second of the “...hold everything...” phrase can be heard clearly on Channel I, yet the sound spectrograms contain numerous matching features for the entire three and a half second sequence; note for example the impressive match in the final segment from T=3.2 to 3.6 seconds. In all cases of matching features it is clear from the text of the messages and from the signal intensities that a signal from Channel II was duplicated on Channel I and not the reverse. The sound spectrograms present much more convincing evidence in the present case than in their application to speaker identification. There, words spoken at different times, supposedly by the same speaker, are compared and a trained interpreter is often required to explain why the subjective match is significant. In the present case, the need is to identify two identical messages extending over a three and a half second interval. Not only must individual parts of the two sound spectra be alike but they must occur at exactly correct time intervals and with exactly matching frequencies. The existence of these required time and frequency correlations between the two channels imposes rigid constraints on the messages to be matched. Furthermore, all sounds that appear on both Channel I and II are useful in correlating the channels even though some are not spoken words. For example in listening to Channel II it is use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. IV. TIMING EVIDENCE FROM MATCHING FEATURES However, this tone varies in both amplitude and frequency and is also useful in correlating the two channels. 22 apparent that there is an intermittent tone that contributes to the flat portions common to Channels I and II.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 24 sections with particularly well defined frequencies on the two channels, as discussed in Appendix B-1. Such a calculation gives a ratio of recorder speeds of 1.062±0.005 in excellent agreement with the value in the preceding paragraph. Alternative analyses to minimize subjective errors in the pattern recognition are also discussed in Appendixes B-2 and B-3. To help in the visual recognition of similarities of the two patterns, sound spectrograms have been made with the speed of Channel I effectively changed by 6.7%. The results are given in Figure 4. Both frequencies and times of the two channels now appear to be quite compatible. A third approach to the investigation of whether Channel II segments are recorded onto Channel I along with the acoustic impulses was taken by a third member of the Panel and two collaborators. The Channel I and Channel II recordings were digitized and the short-term acoustic spectra were taken and stored in a digital computer. The printouts of these spectra are similar to Figures 3 and 4 and are shown in Figures B-4, B-5, and B-6. These digital spectrograms were computed directly from magnetic tapes and did not involve the use of the FBI sound spectrogram equipment. Many of the features observable in the analog spectrograms of Figure B-3 can be seen in B-6, but no use was actually made of the spectrogram patterns, instead, the actual data were used to test certain hypotheses, without human intervention. An objective measure of similarity of two spectral matches is obtained from the cross correlation coefficient, defined in Appendix B-4. This cross correlation coefficient would be reduced if one of the recordings were played at the wrong speed, or if the recording at one time were compared with the same or a different recording at a different time. The first cross correlation coefficients were made from the same Channel I and II recorded copies that were used in preparing Figures 3, 4, B-1, and B-2. It was found that the biggest peak for the cross correlation coefficient occurred for a relative warp (or speed ratio) of 1.06, in agreement with the other two manual approaches for comparing Channels I and II; a 1% deviation of warp from optimum diminished the peak substantially. Unfortunately, that Channel II copy contains many repeats caused by the use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 25 Gray Audograph machine in playback. Accordingly another tape copy was prepared by members of the Committee directly from the original Audograph plastic disk itself and by the use of a standard turntable and tone arm, thus producing a tape without compensation for the fact that the disk was originally recorded at constant linear track speed. It was this tape that was used in preparing the sound spectrograms shown in Figures B-4, B-5, and B-6. Figure 6 gives the cross correlation coefficient for the “hold everything...” segments when the relative speed was selected to give the largest peak and the 750 correlation coefficients were obtained by sliding 2.50 secs of Channel I along 10.00 secs of Channel II, 0.01 secs at a time, using frequencies in the band 600 Hz to 3500 Hz. For comparison the cross correlation coefficients of the unambiguous segment “You want...Stemmons” are plotted in Figure 7. The shape of the peak is very similar to that for the “hold everything...” segment. The background is somewhat smoother, simply because there is less noise in Channel I at this time. Channel I, however, in neither case gives a perfect reproduction of Channel II. It has lost some of the high and low frequencies, and as one would expect there are tones present on Channel I that are not on Channel II. The marked narrow peaks of the cross correlation curves clearly show by an objective test that the “hold everything...” segment of Channel II is present on Channel I at the same location as the acoustic impulses. There is no doubt that the voice (and other) sounds of Channel II are present on Channel I to an accuracy in location corresponding to a few milliseconds. We find these three sets of results to be overwhelming evidence that the “hold everything” sections of the two recordings are traceable back to a single acoustic signal from Channel II. If there is no overrecording on Channel I (as we later show to be the case), the correspondence between these two recordings of “hold everything...” would be conclusive evidence that the events analyzed by BRSW/WA were not the assassination shots, since we know from Channel II that the “hold everything” transmission was made at least 50 seconds after the Chief instructed the motorcade to “Go to the hospital.” We will discuss in Section IV-4 the possibility of there having been an overrecording on Channel I and our conclusion that there was not. Indeed, the digital analyses in themselves are used in Section IV-4 and use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. IV. TIMING EVIDENCE FROM MATCHING FEATURES Channel I radio receiver and was not added later in copying or as an overrecording. 26 Appendix D to demonstrate that the Channel II cross talk on the Channel I recording was already present at the

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 27 IV-3. TIMING OF CHANNEL I AND CHANNEL II EVENTS In the previous section, a synchronization between events on Channels I and II simultaneous with the conjectured shots was obtained by detailed analysis of sound spectrograms. Other examples of matching features on the two channels, occurring several minutes after the assassination, are so much clearer that no special technical procedures are required to establish synchronizations in these parts of the recordings—simple listening is sufficient to eliminate all doubt about these synchronizations. By timing both recordings backwards from the time of these matches, it is possible to relate the times of events in the critical portions of both recordings, independent of the correspondence established in the previous section. The clear match that occurs closest to the assassination is “You want...Stemmons,” which occurs on Channel II several minutes after the Chief said “go to the hospital.” Figure 3 shows a sound spectrogram of the match. Since Channel II was sound activated and recorded intermittently, we obtain a lower bound on the time between these two transmissions by timing the tape between them. Any halts in the recorder would cause the tape time to be less than the actual clock time between these transmissions. Time intervals were measured using two different sets of tape recordings. First, we used the tapes obtained from Bowles to time events in critical portions of the recordings. Since relative time between Channels I and II is all that is of significance in this comparison of events, time in this set of measurements was made in somewhat arbitrary Channel I elapsed time units. The timing was difficult to do because there were “repeats” (see Appendix C) on the Channel II magnetic tape and speed differences between segments of it and the Channel I tape. Appendix C describes how these timings were made and how compensations for repeats and speed differences were accomplished. The results of the spectrogram analyses just discussed were used to obtain the speed correction (a factor of about 1.06). The durations of repeats were determined from strip charts of the signal level as a function of time. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 28 The result of these timings, also given in Appendix C is that: a) On Channel II, “Go to the hospital” occurs at least 189 seconds before “You want me...Stemmons.” b) On Channel I the portion of the tape on which BRSW/WA found “shots” occurs 171 seconds before “You want me...Stemmons.” c) Since Channel II operated intermittently, any time that elapsed while the recorder was stopped would increase the 189 second interval between “Go to hospital” and “You want me...Stemmons.” There were five places where the recorder could have stopped. By this analysis, the last of the conjectured shots occurred at least 20.9 seconds after Chief Curry issued his instructions “Go to the hospital;” therefore, they could not have been the shots of the assassination. After the preceding analysis of the tapes obtained from Bowles was completed, the Committee gained access to the original Gray Audograph and Dictaphone recordings. These were transcribed, as described in Appendix C, onto tape, with care taken to minimize the 60 Hz hum that was added to the signal and to ensure that no skips or repeats were introduced in the tape recording of either channel. No break interrupted the Channel II recordings as was the case for the Bowles tapes. These recordings, of course, did not eliminate the effects of the intermittent operation of Channel II, and time interval measurements are still lower bounds. The 60 Hz hum from the original recordings was used to determine the relationship between playback speed and original recording speed and to convert the measured-elapsed time intervals to real elapsed time units. (Recall that arbitrary Channel I elapsed-time units were used for the first set of measurements made on the Bowles tapes.) It was easy to make this correction on Channel II, but difficult on Channel I, because the Dictabelt was in poor condition. The conversion method is described in Appendix C. Except for this speed-time correction, obtaining comparable measurements of use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 29 the time intervals between critical events on Channels I and II and the common “You want...Stemmons” transmission was straightforward. The result of these timings made on tapes obtained directly from the original recordings, also given in Appendix C, is that: a) On Channel II, “Go to the hospital” occurs at least 206 seconds (real time) before “You want me...Stemmons.” b) On Channel I, the portion of the Dictabelt on which BRSW/WA found “shots” occurs 178 seconds (real time) before “You want me...Stemmons.” By this analysis, the last of the conjectured shots occurred at least 30.9 seconds (real time) after the instructions “Go to the hospital”. This measurement is believed to be more accurate than the one obtained from the Bowles tapes, since the tapes obtained from the original recordings showed no evidence of skips, repeats, or breaks. Both of these results confirm the previous finding from the sound spectrograms that the section of tape in which BRSW/WA found “shots” recorded events that occurred after the assassination. Note that the results from timing events do not require a match between the two recordings of “hold eveything,” but they do not preclude such a match. Halts in the recorder would increase the time between the conjectured shots and Chief Curry's instructions. Furthermore, any delay between the assassination and the instructions “Go to the hospital” would increase the discrepancy between the timing of the conjectured shots and the actual assassination. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 30 IV-4. POSSIBILITY OF SUPERPOSED RECORDINGS The Committee has considered seriously the possibility that the impulses analyzed by BRSW/WA might have been overlaid at a later time by the “hold everything...” message. Conceivably such an overrecording could have occurred by an accidental knocking backwards of the Dictabelt or the recording head by about one minute in the first minute following the assassination or by the substitution (either accidentally or deliberately) of a new Dictabelt copy for the original, with the copy being made by audio coupling while a Channel II recording was playing in the background. The Committee found conclusive evidence that this was not the case. The evidence is of four kinds: (1) physical examination of the Dictabelt for indications of overrecording or of substitution of a copy for the original; (2) the unlikely nature of any of the highly contrived scenarios required to provide such an undetectable overrecording either accidentally or deliberately, (3) the compatibility of the timing implied by the “hold everything...” identification with other firmly established evidence, and (4) the conclusive acoustic evidence on the Dictabelt itself that the cross talk recordings were made through a radio receiver with automatic gain control. These different forms of evidence are discussed in Appendix D, where all are shown to be compatible with the recordings being made at the same time and some are incompatible with the hypothesis of later superposed recordings by audio or direct electrical coupling. Only the evidence of catagory (4) will be reviewed in this section. The digital analyses of the sound spectra can be used to demonstrate that the Channel II imprint on the Channel I recording was already present at the Channel I receiver and was not added later in the recorder or as an overrecording. The by radio nature of Channel II cross talk is demonstrated by its detailed behavior in the presence of Channel I heterodynes when another Channel I transmitter is keyed on with a more powerful carrier signal. The frequency offset between the two carriers gives rise to a heterodyne tone in the Channel I recording. However, the Channel I receiver was fitted with automatic gain control (AGC to hold the output level approximately constant; as a result, the cross talk signals decreases in intensity in a few tens of milliseconds (as does any residual use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 31 transmission from the original stuck-mike transmitter). At the end of the Channel I heterodyne, the AGC gradually increases the receiver gain, and signals on the stuck-mike transmission increase in intensity in the recording. An excellent probing signal for the Channel I gain would be a Channel II steady tone acoustically coupled from the field loudspeaker to the stuck-mike transmitter. This would come in at constant level, and the variation in level on the Channel I recorder should mimic the AGC action if the Channel II signals were present in this way. Inspection of the digital spectrogram of Figure B-4 (and digital tabulations of the data) show that numerous Channel II brief tones have constant level from beginning to end. However, a crucial demonstration is provided by the Channel I heterodyne beginning in Figure B-6 at time 32.02 seconds. The underlying Channel II brief tone is clearly substantially reduced in intensity at the beginning of the Channel I heterodyne, and gradually grows back when the Channel II brief tone results after the Channel I heterodyne ceases. More detail is available in the two digital plots of Figures B-7 and B-8. This behavior is validated by similar Channel II brief tones underlying Channel I heterodyne signals in the “You want me...Stemmons” phrase and in a phrase “I'll check...”, likewise present on both channels. This is discussed in further detail in Appendix D along with other evidence that has led the Committee to conclude that the acoustic impulses attributed to gunshots were recorded about one minute after the President was shot. use the print version of this publication as the authoritative version for attribution.