Report of the Committee on Ballistic Acoustics (1982) / Chapter Skim
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APPENDIX B ANALYSES OF SOUND SPECTROGRAMS OF "HOLD EVERYTHING..."
APPENDIX B ANALYSES OF SOUND SPECTROGRAMS OF "HOLD EVERYTHING..."
Pages 41-59
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From page 41... ...
The first observer, looking at the sound spectrograms of both Channels I and II but making no measurements, marked on Channel II 27 points which he felt were sufficiently characteristic and sufficiently well reproduced on Channel I to be identifiable there by an independent observer. Then a series of 27 xerographic copies were prepared of different portions of Channel II, extending 1/2 second to each side of the single identified characteristic and with no indication of time scale on any of the Channel II strips.
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From page 42... ...
use the print version of this publication as the authoritative version for attribution.
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From page 43... ...
Please use the print version of this publication as the authoritative version for attribution.
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From page 44... ...
Under the copy hypothesis that the signal on Channel I is a noisy copy of that on Channel II, the values of u are determined by measurement errors in the presence of noise, and there may occasionally be an outlier due to the matching noncorresponding features on the two channels. The robust linear regression routine RLIN in the Minitab 80.1 interactive statistical package5 yields the estimated fit T'= -0.0253+1.0599T"+u*
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From page 45... ...
To be more specific, let us suppose (i) that the Channel II markings are precise, (ii)
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From page 46... ...
Also ∆F=F'−β−1F" has mean 0 and standard deviation use the print version of this publication as the authoritative version for attribution.
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From page 47... ...
Please APPENDIX B 47 the relation is approximately maintained by the estimates. Could the observed coincidences have occurred even if the message on Channel I were not a copy of that on Channel II?
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From page 48... ...
Please use the print version of this publication as the authoritative version for attribution. APPENDIX B except for a few points, such as I, that have been adjusted for a better fit in Figure 4.
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From page 49... ...
Since the analysis of the preceding section shows that the measured times between corresponding events on Channel I are longer than on Channel II, by about 6%, it seemed worth measuring the frequency ratios of corresponding signals that were particularly well suited for frequency measurement; if the two sound spectrograms really did originate from a single 3.5 second long signal on Channel II, which was fed by cross talk onto Channel I, then the frequency ratio must depart from unity by that same approximately 6%. This was our working hypothesis at the time, so the frequency ratio measurements provided a test of the hypothesis -- if the frequency ratio was not approximately 1.06 the hypothesis would have been totally disproved.
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From page 50... ...
Another Committee member made independent measurements of the average of the same frequency ratios and found a mean value of 1.063±0.007 use the print version of this publication as the authoritative version for attribution.
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From page 51... ...
Please use the print version of this publication as the authoritative version for attribution. APPENDIX B frequency ratio is cross talk from Channel II.
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From page 52... ...
A certain amount of subjectivity derives from the fact that the first observer was looking at the sound spectrograms from both channels while he marked points on Channel I The strips in Channel II were one second wide, which is a substantial portion of the entire 3.5 second spectrogram.
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From page 53... ...
The observer was given the experimenter's explanation of the theory that messages were broadcast on Channel II and picked up by the stuck microphone located near a receiver of Channel II. The observer was shown copies of Channel I and II for two other messages that had been well duplicated; Y -- "You want...Stemmons" and S -- "Says they came from...." It was explained that dark portions meant loud signals and sharp changes that were dark would probably be well reproduced under the theory.
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From page 54... ...
If the strip on Channel II is too narrow and that of Channel I is very wide, it will be very easy for the observer to be misled by similar characteristics elsewhere. This would reduce the efficiency and power of the experiment.
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From page 55... ...
c) A more objective experiment on the frequencies The experimenter selected 14 dark horizontal bands on a xerox copy of Channel II.
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From page 56... ...
Please APPENDIX B 56 These data are consistent with a hypotheses that Channel I is a noisy version of Channel II which leads to a wrong pairing about 1/3 of the time and that when the correct pairing is made, the noise distortion and measurement error in the individual central frequency readings corresponds to about kHz or about 15 Hz. By no stretch of the imagination could these readings be consistent with a purely random location of horizontal bands theory.
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From page 57... ...
Please APPENDIX B 57 B-4. DIGITAL CALCULATIONS OF CROSS CORRELATIONS BETWEEN CHANNEL I ANDCHANNEL II If indeed "hold everything..." on Channel II was transmitted to and recorded on Channel I at the time occupied by the assumed "shots", then the digital cross-correlation of the short-time acoustic (energy)
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From page 58... ...
For comparison the cross correlation coefficients of the unambiguous segment "You want...Stemmons" are plotted in Figure 7 with the time scale of Channel II stretched by a factor that varied from 1.013 to 1.015. The shape of the peak is vey similar to that for the "hold eveything..." segment.
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From page 59... ...
The Channel II brief tone is clearly visible in the Channel I spectrogram aligned by the relative timing obtained from Figure 6. A strong Channel I heterodyne is observed to begin at time 32.03 and to end at 32.17 secs.
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