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Post by Herbert Blenner on Feb 9, 2019 16:29:07 GMT -5
Suggested prerequisite to this reading: Modulation Matters
How Could They Have Been So Wrong?
by Herbert Blenner | Posted August 18, 2004
Proponents of the acoustic evidence staked their reputation that critics would not disprove their restricted and subjective echo-delay matching by a systematic examination of the complete acoustic record. Despite this recognized weakness, the critics ignored an opportunity to impeach their opponents and settled for casting doubt upon the findings of the proponents. These anomalous activities by both sides in the debate indicate they had foreknowledge of the hidden acoustic evidence.
Congress chartered the National Research Council as a private and nonprofit institution to advise the federal government on issues of science, technology and health.
In 1980, the Department of Justice requested the National Research Council to review the methodology of BB&N and W&A. The council formed a Committee on Ballistic Acoustics, commonly known as the Ramsey Panel, who ignored the ballistic and acoustic evidence and reviewed technical aspects of the DPD radio system. This panel concluded:
"(iv) the conclusive acoustic evidence on the Dictabelt itself that the cross talk recordings were made through a radio receiver with automatic gain control (AGC). These different forms of evidence are all 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."
The fundamental problem with this conclusion is the presented evidence does not show that the cross talk recordings were made through a radio receiver. Although the Committee on Ballistic Acoustics should have tested heterodynes for frequency modulation as conclusive evidence of the by-radio nature of the cross talk, they pursued fallacious arguments. In fact, a quantitative detail provided by the committee showed AGC acted on audio. Even worse, they concentrated on attack characteristics that are ambiguous evidence of AGC action and misinterpreted the decay characteristics, which showed AGC acted at two or more places within the system. Not surprising the Committee on Ballistic Acoustics began by confusing the subject that provided a technically correct method of showing by-radio nature of the cross talk.
"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."
In all receivers the presence of two radio signals of nearly equal amplitudes and different frequencies produce a beating of signals at an audio rate. The trigonometric identity for the addition of cosines (1) illustrates this process.
Cos ( bt ) + N Cos ( ct ) = ( N - 1 ) Cos ( ct ) + 2 Cos [( b - c ) t/2 ] Cos [( b + c ) t/2 ]
The N coefficient of the Cos ( ct ) term represents a radio signal whose amplitude is N times the other. Since the two radio frequencies, b and c, are nearly equal, the Cos [ ( b - c ) t/2 ] term describes the only audio frequency. The absence of N as a factor preceding this audio term shows that the weaker of the two signals determines the amplitude of the heterodyne.
In an AM receiver, AGC action would reduce gain if N is much greater than one. Under these circumstances AGC action would decrease the strength of the weaker signal and proportionally reduce the amplitude of the heterodyne. When N is equal or greater than two the heterodyne in an AM receiver would be a pure tone without harmonics.
When two radio signals beat within the earlier IF stages of a FM receiver the high gain of this amplifier levels the peaks of the cosine waveform. This saturation produces sloppy square waves. The limiter stage following the IF amplifier will remove any residual amplitude modulation unless the two radio signals have nearly the same amplitude. Under these circumstances, N is between one and two, the FM receiver produces a heterodyne that is rich in harmonics.
In a FM system as used by the DPD, cross talk modulates the frequency of the transmitter. When another station transmits concurrently and creates a heterodyne, its frequencies shift in accordance with changes in loudness of the cross talk at the transmitter. The Committee on Ballistic Acoustics ignored this simple and conclusive test of the by-radio nature of the cross talk.
Impervious to their oversight, the Committee on Ballistic Acoustics presented indisputable evidence of AGC action on audio.
"However, the channel I receiver was fitted AGC to hold the output level approximately constant; as a result, the cross talk signals decrease in intensity in a few tens of milliseconds (as does any residual transmission from the original open microphone)."
A gain control circuit samples several cycles of the radio signal and requires microseconds to activate AGC in the receiver. However, the limited bandwidth of the audio stages stretches the response time to the order a milliseconds Clearly the explanation for the interval of tens of milliseconds lies elsewhere.
In a communications system, frequencies below one thousand hertz contain most of the audio power. Now a gain control circuit requires many and perhaps tens of milliseconds to sample a few cycles. Without doubt, the sluggish decrease in cross talk intensity conclusively demonstrates the by-audio nature of the change.
The Committee on Ballistic Acoustics mistakenly attributed every decrease in cross talk volumes to AGC actions in response to heterodynes.
In a FM system, received volume depends on the frequency deviation of the radio signal within the receiver. When a second station switches on, it beats with the first signal and halves the frequency deviation of the composite signal. This conclusion follows from the identity for the addition of cosines, where bt + m(t) replaces bt and N is set to one.
Cos [ bt + m(t) ] + Cos ( ct ) = 2 Cos [( bt + m(t) - ct )/2] Cos [( bt + m(t) + ct )/2]
When the second transmitter keys out, the frequency variation doubles and boasts power of the received audio by 6 decibel. In both cases, the limited bandwidth of audio stages stretches response time to hundreds of microseconds.
The multitude of signals on the five-minute Channel-I transmission gave astute investigators many opportunities to test this theoretical predication. Weiss and Aschkenasy reported:
"At 133 seconds after the start of the stuck-microphone transmission, the level of the noise drops by about 6 decibels (that is, to about one-fourth of its previous level). At almost the same moment a voice can be heard, communicating a brief but unintelligible message."
Since keying on of a second transmitter decreases the received audio of the first, this renders attack characteristics of AGC as inconclusive evidence, especially when magnitudes of the decreases are unreported.
The Committee on Ballistic Acoustics observed decay characteristics of AGC and noted:
"At the end of the channel I heterodyne, the AGC gradually increases the receiver gain, and signals on the open-microphone transmission increase in intensity in the recording."
Bolt Beranek and Newman , BB&N, provided details on the decay of AGC action.
"In addition to having had similar effects on the waveforms recorded on Channel 1, the DPD recording shows evidence of a time constant in the 0.1 to 1.0 sec range. This AGC does not occur in any of the Motorola transmitters. It could, therefore, have been caused by the GE transmitter, by the receiver, or by the recorder."
Without doubt, the performance of the Committee on Ballistic Acoustics during their review of the acoustic evidence presented to the HSCA raises issues that transcend the assassination of President Kennedy.
Initially, Columbia University, Harvard University, the Lawrence Berkeley Laboratory, the Massachusetts Institute of Technology and its Lincoln Laboratory, Princeton University, Roll Laboratories, Trisolar Corporation, the Watson Research Center and Xerox Palo Alto Research Center lent their names and prestige to the report of the Committee on Ballistic Acoustics. These endorsements contributed toward corrupting the minds of two generations of assassination researchers.
Unlike the National Research Council whose charter by Congress and nonprofit status bestows a degree of immunity from civil actions, the surviving endorsers of the report are liable for their earlier actions and continued silence.
I call upon these endorsers to renounce their support of the Committee on Ballistic Acoustics.
1. Derivation of the identity for the addition of cosines
Cos ( X + Y ) = Cos ( X ) Cos ( Y ) - Sin ( X ) Sin ( Y )
Cos ( X - Y ) = Cos ( X ) Cos ( Y ) + Sin ( X ) Sin ( Y )
Adding the identities for the cosine of two angles gives
Cos ( X + Y ) + Cos ( X - Y ) = 2 Cos ( X ) Cos ( Y )
Substituting X = ( b + c ) t/2 and Y = ( b - c ) t/2 produces
Cos ( bt ) + Cos ( ct ) = 2 Cos [( b - c ) t/2] Cos [( b + c ) t/2]
Adding ( N - 1 ) Cos (ct) to both sides of the above identity gives the desired result.
Cos ( b t ) + N Cos ( ct ) = ( N - 1 ) Cos ( ct ) + 2 Cos [( b - c ) t/2] Cos [( b +c ) t/2]
Two components, a resistor and a capacitor, determine the time constant of AGC decay. Generally manufacturers specify 10 percent tolerance on these parts. This means a nominal decay constant of 0.2 second may vary between 0.18 and 0.22 second from one piece of equipment to another. Clearly the finding of 1000 percent span of time constants showed AGC action occurred in more than circuit.
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Post by Herbert Blenner on Feb 9, 2019 16:38:23 GMT -5
Interpreting Ear Witness Testimony
by Herbert Blenner | Posted January 14, 2005
An unobvious characteristic of hearing caused many ear witnesses in Dealey Plaza to perceive echoes instead of the direct sounds of gunfire.
Suppose a shooter fired a rifle from TSBD. Two sounds from the muzzle blast would reach an ear witness in Dealey Plaza. The direct sound would arrive tenths of a second before echoes from the County Courts and County Records buildings. Instruments at the location of this witness would measure a higher power for the direct sound and substantially longer duration for the echoes. The geometry of this situation stretches the duration of echoes by a factor of one hundred and reflection of sound diminishes power by a smaller factor, hence the energy of the echoes impinging upon the ears of a witness would exceed the energy from the direct muzzle blast. From these considerations alone we can understand why some ear witnesses heard the sounds of guns shots coming from either Country Courts or Country Records. These witnesses perceived the stretched reflections of far briefer muzzle blasts, which originated elsewhere.
Our ears attenuate brief sounds. Wave files containing sounds with constant and variable durations demonstrate this effect. All sounds have the same power and differ only in their durations. The sounds with selectable durations, being centered around 0.5 and 2.5 second, surround the constant duration sound that begins at 1.0 second and ends at 2.0 second. Users of Sound Recorder can drag their slider to the indicated times and observe the widths and amplitudes of these sounds.
When the duration of sounds are one hundred milliseconds, we begin to notice the decrease in perceived loudness. The attenuation increases slowly until the duration of the sounds becomes tens of milliseconds. Further decrease in the duration, rapidly increases attenuation. As durations approach one millisecond our ears perceive a few percent of the loudness of fixed duration sound.
Hearing relies upon physical mechanisms to convert sound waves to neurological signals. As a result our perception of sound inherits the response characteristics of the mechanisms. In particular our ears ignore the power or amplitude of brief sounds and respond to the contained energy. A wave file containing pulses of equal energies, decreasing amplitudes and increasing durations shows this effect when durations are briefer than tens of milliseconds. |
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Post by Herbert Blenner on Feb 9, 2019 16:47:45 GMT -5
No Evidence of Engine Sounds on the Dictabelt
by Herbert Blenner | Posted May 9, 2005 - Revised March 7, 2015
Many people assume that a motorcycle engine caused the loud interference transmitted by the open microphone. However, a comparison between the sounds of a Harley motorcycle and a repetitious portion of the interference shows quantitative and qualitative differences. These differences are more pronounced when the sounds of the Harley are compared with an early portion of the interference.
Briefly the interference sounds repetitious. A magnitude spectrograph of this signal, from 234.8 to 236.2 second on the Bowles tape, shows a broad concentration of power. 
Figure 1 - Repetitious Signal
This power is concentrated in a broad band extending from 275 to 450 Hz and reflects a lack of periodicity of the signal.
A Harley motorcycle has sound and spectra that differ from the repetitious signal. The concentration of power about the central peak of the spectrum of the Harley is far more pronounced than on the repetitious noise.
Figure 2 - Harley Motorcycle
The prominent line at 196 Hz corresponds to a repetition rate of 11760 rpm per cylinder. For a motorcycle with two cylinders this rate represents a reasonable engine speed of 5880 rpm. Secondary lines at slightly lower frequencies arise from the damping action of the engine block and the muffler.
The full scale frequency range of 2.756 kHz fits the spectrum of the repetitious signal and facilitates comparison.
During an earlier portion of the Bowles tape between 99.6 and 101.0 second the loud interference resembles a buzz saw and its spectrograph shows a strong and nearly narrow-band sinusoid at 900 Hz
Figure 3 - Spectral Characteristics of the Relaxed Interference
However, the sound of this signal resembles a loud noise. Calculating the spectrum over shorter and contiguous intervals show that the sinusoid persisted with slightly varying frequency throughout the duration of the longer spectrum. These results show that simultaneous amplitude and frequency modulation of audio was the primary component of the loud signal during this interval.
The narrow frequency response of the DPD radio system accounts for some features of these spectrographs. A typical low frequency cutoff of 300 Hz explains the attenuation of lower frequencies. Higher frequencies begin a gentle decline at 1 kHz and decrease more acutely above 2 kHz. The dip in magnitudes near 750 Hz is common to the spectrographs and indicates a narrow band siren filter.
The line at one twentieth of full scale is common to all spectrographs of signals from the Dictabelt. This line appeared before the interference began and continued after the noise abated. Its unchanging frequency of 119 Hz identifies the line as representing power supply ripple. The inaudibility of this obvious line shows the ability of Fourier analysis to extract periodic signals from interfering noise.
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Post by Herbert Blenner on Feb 9, 2019 17:05:24 GMT -5
Cardinal Pieces of the Puzzle
by Herbert Blenner | Posted May 20, 2005
Analysis of signals from the Dictabelt resolves a puzzling history of the acoustic evidence.
In the initial phase of their work, Bolt Beranek and Newman Inc. (BB&N) filtered out periodic signals from their tape of the Dictabelt. They demonstrated the effectiveness of autocorrelation and an adaptive filter to recognize and remove periodic signals from a high-fidelity tape recording of a motorcycle. These proven methods failed to filter the loud interfering signal from the recording of the Dictabelt. (1)
After failing to detect periodic engine sounds, BB&N continued to reinforce the unsupported idea that a motorcycle engine was the source of the loud interfering noise. Primarily they promoted this dubious concept by frequent usage of motorcycle, engine and noise in the same sentence. This repetitious practice diminished the impact of their failure to detect and filter out engine sounds. Finally BB&N assumed that loudness of the interfering noise was proportional to the speed of the motorcycle as it carried the open microphone from one acoustically predicated position to another. Clearly, without evidence of engine sounds on the Dictabelt, this assumption did not justify naming H. B. McLain as the probable driver of the motorcycle with the stuck open microphone. These actions are the first piece of the puzzle.
Spectrographs produced by BB&N showed that the interfering noise had temporal persistence, which eliminated intermittent sources. This consideration excluded a chattering relay contact or faulty muffler and allowed a malfunctioning electronic component as the source. Under these conditions, the persistent noise would be stationary.
A stationary noise arises from an astronomically huge number of random events. The hugeness of this number renders the fluctuations of statistical measures of a stationary noise imperceptible. For practical purposes these measures do not change with time. So any probabilistic measurement made now will produce essentially the same result as an earlier or later measurement. This characteristic enables the spectral subtraction technique to anticipate future from present behavior of stationary noise.
In reporting the failure of spectral subtraction to effect a net reduction of the interference, BB&N cleverly disclosed the non stationary nature of the noise. (2) This information excluded most natural sources of persistent noise. The failure of BB&N to explicitly describe their evidence of a synthetic source of the loud interference is the second piece of the puzzle.
The HSCA evaded these problems by reporting that BB&N filtered out repetitive noise such as repeated firings of the pistons of the motorcycle engine. (3)
In 1982, the Committee on Ballistic Acoustics, commonly known as the Ramsey Panel (RP), and the Watson Research Center of IBM (WRC) published their reviews of the work done by BB&N and Weiss and Aschkenasy. (W&A)
BB&N and W&A based their findings of four shots fired during the assassination of President Kennedy upon less than perfect matches between pulse patterns on a tape recording of the Dictabelt and patterns produced by test shots. Although the limiting characteristics of the selected patterns provided evidence of four gunshots, these studies were subjective. They used highly restricted positions for the locations of the shooter and the open microphone.
Neither the RP nor the WRC used their computers to systematically search for better matches between the contents of a noisy Dictabelt and simulated shots either fired from or recorded at absurd positions. Clearly one better match would have discredited the pulse matching technique of BB&N and W&A and nullified their findings.
Alternately these signal processing experts could have mimicked mechanics who analyzed the performance of engines from their sounds. By cross-correlating the periodic sounds of various engines recorded by the Channel-I radio system with the contents of the historic Dictabelt, the experts could have detected periodic signals well below the noise level and have identified the type of engine, which carried the open microphone. Both organizations failed to report cross-correlation between known engine sounds and contents of the Dictabelt.
The decisions of the RP and the WRC to ignore both weaknesses in works of their opponents are the third piece of the puzzle.
Instead of using their talents to explore these weaknesses, the RP and the WRC followed an independent path. They intended to show interactions between the crosstalk and other signals in the receiver prove that the crosstalk was present during reception. This method had merit.
During an instance of crosstalk with a simultaneous reception, an unmodulated carrier from a competing transmitter beats with the existing carrier and decreases the frequency deviation of the composite signal. Since the amplitude of the detected audio is proportional to the frequency deviation, keying in of a competing transmitter abruptly decreases amplitude of the crosstalk. Similarly when the competing station keys out, the amplitude of the detected audio increases with comparable rapidity. In both cases the narrow bandwidth of audio circuits stretches response times to hundreds of microseconds.
Alternately if the crosstalk were louder than the interference then a competing station of nearly equal carrier strength would produce a heterodyne whose frequency varied with instantaneous amplitude of the crosstalk. These considerations form the basis for showing the by-radio nature of the crosstalk.
For example, at 60.9 seconds after the start of the Bowles tape of Channel I, a station broadcasted a brief message, that said seventy-five place. A heterodyne began after the second word. This event marked the start of a simultaneous broadcast. The presence of the unmodulated carrier reduced the frequency deviation of the composite signal and decreased the average magnitude of the third word. An oscillograph clearly shows the interaction between these simultaneously received signals.
 Oscillograph of the Brief Message
The dense black portions of this graph represent average magnitudes and the thin vertical lines show peak magnitudes. Normally the peaks of an uncompressed voice extend three times higher than the average. On this brief message the peaks of the first two words are slightly more than the average. This shows a high degree of audio compression. However the interaction, which produced the heterodyne decreased the average magnitude of the third word and reduced audio compression. These considerations show simultaneous reception of the brief message and the heterodyne by the Channel-I receiver.
A spectral analysis reveals that the third word did not interrupt the heterodyne. This word increased the frequency deviation of the transmitted carrier and imparted rapid and less audible changes to the frequency of the heterodyne. By both standards, this brief message demonstrates the merits of the interaction of received signals as a test of their by-radio nature.
In implementing this meritorious method, the RP and the WRC misapplied principles of AM receiver operation to the FM radio system of the DPD. They showed that AGC action required tens of milliseconds to reduce amplitude of the crosstalk. Both organizations noted recovery times were much longer and did not specify a number to contradict the report of a one second time constant by BB&N. These published figures on the attenuation and recovery times provide clear and convincing evidence that AGC acted on audio.
These fallacious demonstrations of the by-radio nature of the crosstalk by the intelligent and knowledgeable people of the RP and the WRC represent the fourth piece of the puzzle.
The over driving audio and the heterodyne of the brief message show that the audio stages, which connected the receiver to the Dictaphone operated without AGC. However, an oscillograph of signals during the crucial interval of the reported shots shows a heterodyne with indisputable evidence of AGC action. An unmistakable envelope shapes the heterodyne into a decreasing sinusoid. Following termination of this heterodyne a gradual asymptotic increase in the magnitude of the interference shows the slow AGC recovery time. This interval, 233.3 to 234.7 second from the start of the Bowles tape, contains both characteristics of AGC action and is time stamped by crosstalk. Clearly these results show itinerant behavior of the AGC.
 Evidence of AGC Action on Audio
An unwise decision by James Bowles to turn on AGC during the recording of the Dictabelt would account for this itinerant behavior. However, in addition to using the Bowles tape, the RP obtained magnetic recordings of the Dictabelt from James Barger of BB&N and the Department of Justice. So dismissal of the itinerant behavior of the AGC as accidental requires several similar and foolish actions while making as many independent tapes of the Dictabelt. Further BB&N and the RP compared their tapes with the Dictabelt and found no significant differences. For these reasons the itinerant behavior of the AGC challenges the authenticity of the Dictabelt and becomes the first cardinal piece of the puzzle.
The reported time constants of AGC actions are further evidence of an altered Dictabelt. These numbers coincide with specifications for equipment used by studios to emphasize and fade audio. The RCA-BA-25A AGC Program Amplifier (4) typifies this equipment. Since attenuation and recovery times characterize AGC action RCA provided the values of the pertinent components. The 56 K resistor and the 0.22 MF capacitor set the attenuation time constant to [(5.6 X 10 4 Ohm) (2.2 X 10 -7 farad)] or 12.3 millisecond. For the recovery characteristic of the AGC action, the 4.7 MEG resistor and the 0.22 MF capacitor set the time constant to [(4.7 X 10 6 Ohm) (2.2 X 10 -7 farad)] or 1.03 second. These results show excellent agreement with reported attenuation and recovery times.
An analysis of the most prominent and ignored signal from the Dictabelt, rationalizes the denial by BB&N of their own evidence.
Characteristics of the loud interference changed often and with unexpected rapidity. Fortunately between 99.6 and 101.0 second these changes relaxed and enabled a Fourier analysis to provide useful information. A magnitude spectrograph shows a strong and nearly narrow-band sinusoid at 900 Hz.
Spectral Characteristics of the Relaxed Interference
However, the sound of this signal resembles a loud noise. Calculating the spectrum over shorter and contiguous intervals show that the sinusoid persisted with slightly varying frequency throughout the duration of the longer spectrum. These results show that simultaneous amplitude and frequency modulation of audio was the primary component of the loud signal during this interval. This composition describes a frequency modulated heterodyne in the presence of noise and prompted a systematic study of the spectral changes of the loud interference.
On longer time scales, the spectra of the interference show ordered changes. The dominant frequencies fall into two bands. Lower frequencies appear near 375 Hz and the higher frequencies cluster around 1000 Hz. The relative powers in these bands change with time. These characteristics suggest a ratio of relative powers as a measure of these spectral changes. Dividing the relative power in the low frequency band by the sum of relative powers in both bands gives a measure that is independent of the unknown scale factor relating power to spectral magnitude. This ratio provides an absolute measure of power in the low frequency band as a proper fraction of power in both bands. Changes in this ratio measure changes in the spectra of the interference. However, the frequency selectivity of the DPD radio system and widths of the selected bands influence the magnitude of this ratio. Diminishing the ratios by the mean value of the ratios produce measures, called skewness, that are independent of the frequency response of the system and widths of the selected bands. This study used limits of 300 Hz to 450 Hz for the low frequency band and limits of 800 Hz to 1200 Hz for the high frequency band.
More important, the skewness of the relaxed interference coincides with the global minimum of the spectra family. This later consideration is overwhelmingly strong evidence that the loud interference is a simultaneous amplitude and frequency modulation of audio. On this basis the character of the loud interference becomes the second cardinal piece of the puzzle.
During the fifties the standard design for jamming sources of audio used two main oscillators, which operated over different portions of the spectrum. Two secondary oscillators modulated the main oscillators and produced simultaneous amplitude and wide band frequency modulation of audio. This combination yielded a filter resistant and non stationary noise. By the early sixties transistors replaced vacuum tubes in jamming sources and the earlier designs were available on the surplus market.
Without doubt, the signals on the Dictabelt are the cardinal pieces of this puzzle.
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Post by Herbert Blenner on Feb 9, 2019 17:44:46 GMT -5
Studies in Applied Misinformation
by Herbert Blenner | Posted May 31, 2005
The Ramsey Panel and the Watson Research Center used constant amplitude signals called brieftones from Channel-II to measure effect of heterodynes upon the gain of the Channel-I receiver. Spectral analysis shows both organizations misidentified Channel-II heterodynes as brieftones.
The Watson Research Center reported:
"On Channel-II spectra we note that during voice transmissions there are no silence gaps between words. The signal level of Channel II is fairly constant. This could result from the presence of nearby motorcycle radios tuned to Channel II, while someone is transmitting on Channel II. A radio receiver close to a transmitting mike could form a closed loop having greater than unity gain. This will excite a natural frequency of the loop and it will act as an oscillator. The resulting oscillations will be recorded on the Channel-II recorder. We notice this phenomenon on Channel-II recording."
These oscillations overdrive amplifiers and produce distortion. Engineers limit this distortion by ensuring symmetrical clipping of the signal. Although this practice is not perfect, it makes the level of the second harmonic negligible. So manufacturers measure distortion in audio equipment by the level of the third harmonic and call it THD.
"During these periods, the spectra consist of a strong sinusoid (in the frequency range 1300-1800 Hz) and its harmonics. There is virtually no other signal present during these periods. We call these 'Brieftones.' Being high energy and very narrow-band, these are extremely valuable in determining the cross-talk level."
This paragraph provides two significant observations, namely "brieftones" occur when virtually no other signal is present and are narrow-band sinusoids.
"On Channel II spectra second harmonics of brieftones are quite prominent, while on Channel I spectra, all the Channel-II brieftones are present but their harmonics are not visible, indicating the limited frequency range of Channel I (even in the normal recording of Channel-I communications, the Channel-I recording has a similar roll-off at high frequencies.)."
Since brieftones have negligible second harmonics, the reported prominence show misidentification of signals. Further in a FM receiver, heterodynes have prominent second harmonics. (1) When simultaneous transmissions are silent, the heterodynes are narrow-band sinusoids. Of course the absence of audio accompanying these transmissions produce the illusion of no other station being present.
Mislabeling heterodynes as brieftones evaded an important issue. The observed constancy of the Channel-II heterodynes misnamed as brieftones show inactivity of AGC. However, some oscillographs of Channel-I show strong AGC responses to heterodynes.
Coupling this unaddressed issue with the failure to report the itinerant AGC behavior of Channel-I, strongly suggests that recognition of the Barger and Bowles tapes of the Dictabelt as studio editions prompted the actions of the Ramsey Panel and the Watson Research Center.
Notes
1. The Ramsey Panel labeled many Channel-II signals with prominent second harmonics as brieftones. On the same page they show Channel-I heterodynes with prominent second harmonics. |
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Post by Herbert Blenner on Feb 9, 2019 17:47:52 GMT -5
Unheeded Lesson of the Bellah Crosstalkby Herbert Blenner | Posted August 19, 2005The loud brieftone that accompanied the Bellah crosstalk provides an opportunity to measure how Channel-I would have reproduced the brieftone that accompanied the Channel-II Decker broadcast. At about 12:34, Sergeant Bellah asked the dispatcher do you want me to still hold this traffic on Stemmons . . .. The loud squeal, which accompanies this message is a brieftone. Feedback from an operating Channel-II receiver within an earshot of Bellah's microphone created the brieftone. A microphone operating on Channel-I was also within an earshot of an operating Channel-II receiver and broadcasted Bellah's message and the accidental brieftone as crosstalk. Contrary to the declaration of the Watson Research Center, the frequency response of Channel-I was adequate to respond to the Channel-II brieftone. In fact, spectrographs of Bellah's broadcast and its crosstalk show the narrower frequency response of Channel-I attenuated the brieftone by less than four decibels relative to the voice. Similarly a brieftone mars Decker's Channel-II hold everything secure broadcast. In both cases the brieftones are excessively loud signals and only their narrowband characters prevent them from obscuring the broadcasts. Unlike the Bellah crosstalk where the loudness of the brieftone is comparable with the voice, the alleged Decker crosstalk contains no audible nor measurable brieftone. The missing brieftone is the first clue that the alleged Decker crosstalk does not match the corresponding portion of the Decker broadcast while the badly garbled voice of the alleged Decker crosstalk that contrasts sharply with the clarity of the Bellah crosstalk is the second hint.
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Post by Herbert Blenner on Feb 9, 2019 17:49:56 GMT -5
I'll Check Itby Herbert Blenner | Posted January 19, 2007The critics of the acoustic evidence ignored a clear and intelligible candidate for crosstalk occurring a few seconds before the alleged shots on the Dictabelt in favor of a highly garbled and brieftone-deficient candidate known as the Decker crosstalk. About thirty seconds before Chief Curry ordered his officers to go to Parkland Hospital, the Audograph disk contains a broadcast with the words, "I'll check it." This portion of the disk contains no apparent stops so this interval is representative of real time. Approximately eleven seconds before the pulse patterns attributed to the third shot, the Dictabelt contains a highly similar message. The ear has no difficulty in hearing the words, "I'll check it." These circumstances raise the question of why did the Ramsey Panel use highly garbled and practically unintelligible speech to challenge the synchroneity of the pulse patterns attributed to gunfire with the assassination of President Kennedy? In particular the critics of the acoustic evidence focused their attention upon a message concurrent with the patterns attributed to the third and fourth shots. They claimed that the highly distorted speech was crosstalk from a message broadcast by Sheriff Decker about one minute after the assassination. Immediately the ear recognizes that the loud high pitched brieftones, which accompanied the broadcast by Decker are missing from the alleged crosstalk on the Dictabelt. The Watson Research Center attributed the missing brieftones on the Dictabelt to reduced high frequency response of Channel-I. However, the brieftone that accompanied the Bellah crosstalk enables measurement of this reduction. Comparison of the brieftone to voice ratio on the crosstalk with the brieftone to voice ratio of the Bellah broadcast shows that Channel-I reduced this ratio by a mere 3 db. The Bellah crosstalk shows that the Ramsey Panel had no explanation for the absence of a brieftone on the alleged Decker crosstalk. They only pretended they did.
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Post by Herbert Blenner on Feb 9, 2019 17:53:27 GMT -5
Duped by a Dub
by Herbert Blenner | Posted May 26, 2007
For decades students of the acoustic evidence have suspected that the crosstalk and tones became imprinted upon a dictabelt during copying a tape of the historic Dictabelt. Surprisingly, the NAS published clear and irrefutable evidence that they found the alleged Decker crosstalk on a specially prepared tape.
The Ramsey Panel varied the speed of their Channel-II playback of the "hold everything . . . " portion of the Decker broadcast and noted the compression to maximize matching of selected Channel-II frequencies with Channel-I frequencies. They found a compression of 0.911 to 0.913 maximized cross-correlation with the Channel-I segment containing pulse patterns attributed to gunfire.
BB&N studied the frequency compression caused by the Dictaphone and measured an error of 5 percent. Their measurements agree closely with spectral analysis of the segment containing the pulse patterns attributed to the third shot. The Bowels tape of the Dictabelt is the source of this segment.
The spectrographically measured 57.3 Hz for the power line frequency yields a compression ratio of 0.955.
The Ramsey Panel used a phonograph to play the Audograph disk of Channel-II. This method eliminated repeats and skips but introduced a varying frequency scale. A spectral analysis of the concluding words of Decker's "hold everything secure" broadcast and an unmistakeable power line hum show no error in composite playback/recording speeds of the Audograph and phonograph disk. Apparently they targeted the Decker broadcast and adjusted playback rate of the phonograph to produce a 60-Hz hum.
Since tape recorders operate with near clock-like precision, the Dictaphone bears sole responsibility for altering frequencies. So taping a playback of the historic Dictabelt compressed frequencies by a factor of 0.955. Playing the tape had negligible effect. However, if they recorded a new dictabelt from the compressed tape then the net compression during playback would be 0.955 multiplied by 0.955. This product is 0.91205 and falls exactly within the range of reported compressions to maximize matching. |
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Post by Herbert Blenner on Feb 9, 2019 17:56:00 GMT -5
Slowing Twisting in the Windby Herbert Blenner | Posted on June 30, 2007 -Condensed on March 6, 2015Analysis of the signals on the historic Dictabelt suggests that a studio added the acoustic signature of gunfire to distract researchers from the overwhelming strong evidence that a jammer was the source of the loud interference. No matter what the critics say they cannot make the pulse patterns attributed to gunfire vanish from the acoustic records. These patterns contain very special pulses that distinguish themselves from all the other snaps, crackles or pops. I call these special signals limiting pulses. Playing a wave file of these limiting pulses at progressively slower speeds provides audible evidence of the special nature of these pulses. Reducing playing speed dramatically lowers the pitch of the voice and has a similar effect upon a brief heterodyne and the background noise. However, the pitches of the limiting pulses initially resist lowering and change slightly at greatly reduced playing speeds. This demonstration shows that the high frequency contents of the limiting pulses are widely dispersed and extremely rich. These uncommon characteristics are further evidence that these special pulses are the responses of the radio system to impulses generated by the limiting circuit in the audio stage of the transmitter. BBN documented a level of 100 db re 2 X 10-5 Newton per square meter at the microphone as the threshold for activation of the limiting circuit. This means that ears near that microphone would have heard sounds reminiscent of moderately distant gunfire. Two choices arise. One may assert that the Dictaphone recorded gunshots on the Dictabelt or a studio added the limiting pulses and made an untrue acoustic record. Three characteristics of heterodyne tones generated by a FM receiver provide overwhelming strong evidence that a studio altered the contents of the Bowles tape if not the actual Dictabelt. These characteristics are the commonness of heterodyne tones, nonrandom distribution of the heterodyne frequencies and the absence of interaction between the continuous interference with a silent station whose radio signal belonged to a pair that produced the heterodyne tone. In a FM system a narrow-band heterodyne occurs when two unmodulated receptions have nearly the same strength. When a modulated signal is also present, as during the open microphone sequence, the radio strength of the modulated signal must differ from strengths of the unmodulated signal by more than the saturation ratio of the receiver while the simultaneous receptions of the three signals require that their radio signal strengths differ by less than the capture ratio of the radio. These conflicting requirements, if realizable, makes a narrow-band heterodyne in the presence of a modulated signal an extremely unlikely event. The probability that narrow-band heterodynes occur within a given interval is the product of the probabilities of the individual events. So with several narrow-band heterodynes the probability of the events becomes incredibly small. The audio frequency of a heterodyne tone equals half the difference of the frequencies of the radio frequency signals belonging to the two silent stations. In turn the frequency of a quartz crystal determines the radio frequency of each station. The differences in crystal frequencies are randomly distributed over an interval specified by a manufacturing tolerance. These considerations show that the audio frequencies of the true heterodyne tones are randomly distributed over the audio bandwidth of the system. However, the many heterodyne tones that occur briefly before the cessation of the loud interference have a nonrandom distribution of audio frequencies. The lower frequencies are close to the 1 kHz high frequency cutoff and the higher frequencies extend to about 3 kHz, well into the roll off portion of the bandwidth. More important the continuous interference does not show abrupt decreases in amplitude as silent stations keyed in nor abrupt increases in amplitude when the silent stations keyed out. Since each heterodyne tone requires the simultaneous transmission of two silent stations there are at least two and perhaps four keying events associated with each tone. Clearly the failure of the Bowles tape to show this interaction of signals in a FM receiver is further evidence of studio alterations. Further a FM receiver intended for network operation had the option of using a ratio detector that has heterodyne rejection instead of a Foster-Seeley detector. The cost of this improvement was less than one dollar for two resistors and one capacitor. Nevertheless, a six-second interval of the Bowles tape contains the responses of an AM receiver with a beat frequency oscillator to Morse code and an image of music from the FM broadcast band. This obvious alteration tarnishes the indelible evidence of an intentional jamming of the primary police communications channel immediately before, during and after the assassination of President Kennedy.
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Post by Herbert Blenner on Feb 9, 2019 18:00:45 GMT -5
Do You Still Believe the Ramsey Panel?by Herbert Blenner | Posted July 6, 2007 -Expanded August 29, 2007The loud brieftone that accompanied the Channel-II broadcast by Sergeant Bellah and its crosstalk onto Channel-I provides a unique opportunity to test the hypothesis of frequency compression that underlies the crosstalk analysis. The acoustic records contain several events, which enable testing how Channel-I would record a brieftone generated on Channel-II. In particular a loud annoying brieftone accompanied the Channel-II broadcast by Sgt. Bellah. On Channel-I the brieftone, though slightly attenuated nearly three db relative to the voice, is still a conspicuous annoyance. The Bowles tape of the Dictabelt is the source of these wave files. The significance of this event goes beyond showing that a loud brieftone would have accompanied true Decker crosstalk. Spectrographs of the initial portions Bellah's Channel-II broadcast and his message on Channel-I show brieftones with the same 1.68 kHz frequencies. 
Spectrograph of the Bellah Broadcast
Spectrograph of the Bellah Crosstalk
The acoustic research community acknowledges that James Bowles slowed the playback of the Dictabelt and produced a tape with a frequency compression of about 5 percent. As a result the frequency of the 60 Hertz power line hum measures about 57 Hz on his tape. Correspondingly a 1.68 kHz brieftone recorded onto the Dictabelt would have been recorded on the tape as a 1.60 kHz tone. So finding a 1.68 kHz brieftone on our copy of the Bowles tape proves that it is an untrue record of the Channel-I receptions by the DPD at approximately 12:30 p.m. of November 22, 1963.
Now suppose that James Bowles did not slow the Dictaphone during taping. This alternative would allow true Bellah crosstalk and does more than invalidate the matching of pulse patterns from test shots with the Bowles tape of the Dictabelt. Under these conditions the finding of matches that required an unnecessary, and therefore an improper, adjustment for frequency compression would be overwhelmingly strong evidence that a studio amateurishly added the pulse patterns to the acoustic record. So the earlier conclusion that the Bowles tape is an untrue record of the Channel-I receptions would still stand.
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