Report of the Committee on Ballistic Acoustics (1982)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

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 APPENDIX F 92 APPENDIX F POSSIBLE FURTHER STUDIES This Appendix is written in response to the Committee's assignment to recommend the kinds of tests, analyses, and evaluations needed to obtain better information from the recordings. However, the existence of this Appendix should not be misinterpreted as a Committee recommendation that these tests and analyses should be carried out. If there were to be further studies of the Dallas Police Department Channel I recording in the hope of demonstrating the validity of the conjectured shot from the grassy knoll, the information listed below could be sought. 1. The original Dictabelt could be studied more extensively for possible evidence either for or against the possibilities of the Dictabelt being a copy or containing superposed recordings. No evidence favoring either of these possibilities has so far been found in a physical examination of the belt or in studies of the recording. Further studies could include a careful search on the original belt for a second hum at about 60 Hz which would characterize a copy and an examination of the 60 Hz signal for continuity and possible indications of interceptions. Such studies, however, will now be difficult and may require the constuction of a special drum playback machine for the shrunken and stiffened Dictabelt which now causes marked flutter when it is played back on the normal machine. 2. With the information on the timing of the Channel I recording provided by the cross correlation between Channels I and II discussed in Section IV, the Channel I recording could be examined more carefully for the existence of possible shots in the portion of the recording that corresponded to the time of the assassination (between 65 and 95 seconds on use the print version of this publication as the authoritative version for attribution. 

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 APPENDIX F 93 the BRSW time scale). However, it is unlikely that evidence for shots will be found in that region, since the noise level was much higher there and that portion of the recording has already been examined by BRSW, as described on page 35 of the BRSW report, and no impulse patterns identifiable as gunfire were found; furthermore, there is some evidence that the open microphone was not in the motorcade. 3. There could be an independent analysis following generally the WA procedure but applied to all four of the conjectured shots. In the case of the conjectured grassy knoll shot, it would be of interest to see if the P value for the hypothesis of random locations of impulses cast doubt on that hypothesis. Analysis by the WA method of the impulses attributed to the three Texas School Book Depository shots would be a test both of the method and of this attribution, which contradicts the evidence that the relevant impulses occur approximately one minute after the assassination. If these impulses do fit the hypothesis of three shots, is the open microphone trajectory the same as in the BRSW studies and does it fit with the best limits that can be photographically inferred? 4. The BRSW analysis of the three shots attributed to the Texas School Book Depository could be repeated with a well defined, normalized, and objective selection process for the impulses and echoes to see if the indications of three shots associated with a reasonable microphone trajectory persisted when the unnormalized and subjective selection of impulses and echoes was eliminated. 5. Attempts could be made to see if the reliability of the analyses could be improved by utilizing the availability of amplitude information even though it is recognized that amplitude information can sometimes be misleading. Acoustic spectra and logarithmic Fourier transform studies might help. Unfortunately, one cannot deal with the Dictabelt recording as a faithful reproduction of the sound pressure at the microphone due to the distortion of the radio and recording systems, which include automatic gain control, so it will be difficult to untangle the distortion effect in retrospect. use the print version of this publication as the authoritative version for attribution. 

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 APPENDIX F 94 6. Independent analyses could be made of the probabilistic calculations both by BRSW/WA and by the present committee, with a critical review of the hypotheses on which the calculations are based. The studies could include the investigation of alternative hypotheses such as other sources of non- random impulse locations and studies of prior and posterior probabilities. 7. A study could investigate means for confirming that the open microphone was actually in Dealey Plaza. This study could examine the recording for the presence and absence of sounds of crowds, the lateness of siren sounds, the possibility of detecting a Doppler shift in the siren sounds, study of the motorcycle sounds to determine if they indicated speeds compatible with the course of the motorcycle presumed by BRSW/WA to have the open microphone, identification of the kind of motorcycle from its sound, cepstral analysis, AGC effects, etc. Bowles2 reports that Officer McLain, after hearing recordings of Channels I and II stated that there was “no way” that his mike could have been the one stuck open. As the present report was about to be printed, Officer Leslie Beilharz (who was not in Dealey Plaza at the time of the assassination) told the Committee chairman by telephone that there was a “good possibility” that his microphone may have been the one stuck open. Additional testimony could be obtained as to the location of the open microphone and attention should be given to the many questions raised in the report of James C.Bowles, including those on the microphone location. 8. A detailed analysis could be made of the interpretation of the more than 200 millisecond time displacement between the conjectured shots of the BRSW and the WA studies. 9. The Zapruder film could be analyzed further to see if the apparent incompatibility between the conjectured shots and the data inferred from the camera's angular accelerations can be removed. use the print version of this publication as the authoritative version for attribution. 

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. APPENDIX F Figure 1. Echo pattern for BRSW test shot 8 (knoll, target no. 3) received at array 3, microphones 4, 5, and 6. 95 

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. APPENDIX F Figure 2. Impulse pattern on Channel I associated with BRSW/WA conjectured grassy knoll shot. The muzzle blast for the original BRSW analyses was at A and that for the WA analyses at B. The marked time scale is different from that of BRSW. Approximately 0.9 second should be substracted from the scale to make it agree with BRSW, since A on the Figure is at 145.15 seconds on the BRSW time scale and B occurs about 0.2 second earlier than A. 96 

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. APPENDIX F 97 Figure 3. Sound spectrogram of a message on Channel II that is picked up on Channel I and is clearly understandable on both channels. 

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. APPENDIX F Figure 4. Composite photograph of sound spectrograms on each of Channels I and II, with Channel I being the upper sound spectrogram and Channel II the lower. The audible “...hold everything...” phrase begins at approximately zero on both channels, but there is no special significance to the exact location of zero time on either channel. The impulses initially identified by BRSW as arising from their conjectured grassy knoll shot occur above the arrow marked 145.15s, and those identified by WA occur 0.2 second earlier; the proper location for this arrow was determined by comparing this sound spectrogram with that of Figure 5 in the BRSW report. The letters and black dots designate corresponding characteristic features. For the reasons discussed in Appendix B, one recording was speeded up by 6.7%. Since the interpretation of sound spectrograms depends on continuing gradations on darkness, copies in a printed report lose clarity. For this reason, photographs of the sound spectrograms will be retained in the National Research Council files. 98 

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 APPENDIX F 99 use the print version of this publication as the authoritative version for attribution. Figure 5. Plot of T' versus T" for corresponding characteristics with the values of Table B-1. The marked linearity of the curve demonstrates the validity of the identification. The straight line in the figure is a plot of the given equation, which in turn is a robust linear regression fit to the plotted points. The analysis leading to this figure is given in Appendix B and Table B-1. The point furthest off the line is at T"=1.195s and is for the incorrectly identified characteristic I, as discussed in Appendix B. 

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. APPENDIX F Figure 6. Cross correlation between “Hold everything...” segments of Channels I and II sound spectrograms with time scale slightly compressed to produce the best correlation peak. The curve is produced by sliding 2.50 secs of Channel I along 10.00 secs of Channel II, 0.01 sec at a time, using frequencies in the band 600–3500 Hz. 100 

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. APPENDIX F Figure 7. Cross correlation between “You want...Stemmons” segments of Channels I and II sound spectrograms with time scale slightly compressed to produce the best correlation peak. The curve is produced by sliding 2.50 secs of Channel I along 10.00 secs of Channel II, 0.01 sec at a time, 101 

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. APPENDIX F Figure B-1. Sound spectrogram of approximately the first two seconds of the “Hold everything...” expressions on Channels I and II. The expression “Hold everything...” begins at approximately the positions indicated by the arrows. 102 

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. APPENDIX F Figure B-2. Sound spectrograms for the two seconds immediately following the sound spectrograms of Figure B-1. 103 

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. APPENDIX F Figure B-3. Composite photograph of sound spectrograms on each of Channels I and II, with the apparent time on Channel I being indicated by T' and T". The audible “...hold everything...” phrase begins at approximately zero on both channels, but there is no special significance to the exact location of zero time on either channel. The impulses identified by BRSW/WA as arising from their conjectured grassy knoll shot occur above the arrow marked 145.15s; the proper location for this arrow was determined by comparing this sound spectrogram with that of Figure 5 in the BRSW report. The letters designate the characteristic features of Table B-1, with the black dot identifying the characteristic point. The black dots were located by the procedure described in Appendix B. 104 

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. APPENDIX F B-4. Graphic plot of the digitized short-term acoustic spectra of the “I'll check all radios...” segment on Channels I and II. Times are in seconds; the frequency range is 50– 4000 Hz. Energy range shown is 20–50 dB. Channel I spectra on top, Channel II below. Note the Channel II brief tone at “C” reflected faithfully in Channel I, while the Channel II brief tone at “B” is suppressed by the Channel I heterodyne beginning at “A”. 105 

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. APPENDIX F Figure B-5. Graphic plot of the digitized short-term acoustic spectra of the “You want me...Stemmons” segment (as in Fig. B-4). Note the broadband noise at “A” which suppresses the imprint of Channel II. 106 

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. APPENDIX F Figure B-6. Graphic plot of the digitized short-term acoustic spectra of the “Hold everything...” segment. Channel II plot has been compressed by a factor 0.91125 to 0.91320 for best cross-correlation peak. Note the Channel II brief tones at 32.00–32.08 and 32.24–32.43 secs, and the interaction in Channel I spectra with the Channel I heterodyne at 32.03–32.17 secs. (Care must be taken to avoid confusing the Channel I reproduction of the Channel II brief tones with the more conspicuous Channel I tone that is 250 Hz higher in frequency. The analysis can best be made by comparing Figures B-7 and B-8.) 107 

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. APPENDIX F TONE window is delimited by the vertical bars (for which space has been made in the plot). Figure B-7. Printer plot of the Channel II spectra towards the end of the “Hold everything...” segment. The BRIEF 108 

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. APPENDIX F receiver and not added later. Figure B-8. Printer plot of the Channel I spectra for the same time range as Channel II in Fig. B-7. The attenuation of the brief tones delimited by the vertical bars demonstrates that Channel II was received by the Channel I radio 109 

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. APPENDIX F Figure C-1. Strip charts of Channel II sound level as a function of time in Channel I seconds from minus 10 to 117 seconds. 110 

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. APPENDIX F Figure C-2. Strip charts of Channel II sound levels as a function of time in Channel I seconds from 118 to 200 seconds. 111 

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. APPENDIX F Figure C-3. Time correction factor for measurement of intervals on the tape recording of Channel II, obtained directly from the original Gray Audograph record. The correction factor is a function of the location on the record and tape. 112