Report of the Committee on Ballistic Acoustics (1982) / Chapter Skim
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IV. TIMING EVIDENCE FROM MATCHING FEATURES
IV. TIMING EVIDENCE FROM MATCHING FEATURES
Pages 18-31
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From page 18... ...
Four of them are quite clear, but they occur several minutes after the assassination and involve various police communications connected with the follow-up to the shooting; however, they demonstrate clearly that there was cross talk from Channel II to Channel I As will be seen, they also provide a clear demonstration of Channel I heterodynes suppressing the recording onto Channel I of cross talk from Channel II, which suppression we later also show exists in the interval containing the impulses and shows that the cross talk was recorded through a radio receiver.
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From page 19... ...
Please IV. TIMING EVIDENCE FROM MATCHING FEATURES 19 secure until the homicide and other investigators can get there...," clearly recorded on Channel II.
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From page 20... ...
The spectrograms were prepared under the supervision of Committee members. The sound spectrograms first reproduced were from tape recordings kindly provided by James C.Bowles, Radio Dispatcher Supervisor at the time of the assassination, but a sound spectrogram with a similar pattern for the "...hold everything..." phrase on Channel I was also made from a tape supplied by James Barger, essentially identical to that used in the analysis of BRSW; later sound spectrograms were also made from new high quality magnetic tape copies of the original Channel I Dictabelt and Channel II Audograph disc.
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From page 21... ...
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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From page 22... ...
Please use the print version of this publication as the authoritative version for attribution.
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From page 23... ...
The existence of correlations between the two spectrograms over a long time interval can be demonstrated by plotting T', the time coordinate of the Channel I spectrogram, as a function of T", the time coordinate of the corresponding characteristic on Channel II. The results are shown in Figure 5.
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From page 24... ...
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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From page 25... ...
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.
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From page 26... ...
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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From page 27... ...
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.
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From page 28... ...
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.
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From page 29... ...
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)
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From page 30... ...
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.
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From page 31... ...
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.
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