Question about Dr. Donald Thomas’s Dictabelt Offset Hypothesis

[Michael T. Griffith]

The gain control (AGC) discussed is not that of the Dicta-belt machine. If you believe it is be specific in you quote.

Okay, let's see if we can clear this up. We need to understand that the dictabelt machine was the medium on which the sounds were recorded; the dictabelt itself did not control how the sounds were processed before they arrived, before they were recorded. The dictabelt received sounds from the DPD dispatch system. The DPD dispatch system included an AGC circuit, among other circuits. The AGC circuit greatly affected how sounds were processed before they arrived at the dictabelt. I quote from the Weiss and Aschkenasy report to the HSCA:

The DPD radio dispatching system contained a circuit, that would have greatly affected the relative strengths of the recorded echoes of a muzzle blast. This circuit, the automatic gain control (AGC), limited the range of variations in the levels of signals by reducing the levels of received signals when they were too strong and increasing their levels when they were too weak. It responded very rapidly to a sudden increase in the level of a signal, but comparatively slowly to a sudden reduction in a signal level. Consequently, the response of the AGC to the sound of a muzzle blast would greatly reduce the recorded levels of echoes and background noise received shortly afterward. Progressively during the next 100 milliseconds, the AGC would allow the recorded levels of received signals to increase until full amplification was finally restored. The effect on the predicted echoes would be to make the recorded levels of late-arriving echoes verv nearly the same as those of the early ones. (8 HSCA 30)

No, we don't know how sound in the case of gunshots were recorded since no baseline recording of gunshots involving a Dicta-belt machine was conducted.

We'll have to agree to disagree. I see this as a baseless and irrelevant argument. The sound impulses were heard by the microphones, processed through the DPD dispatch system's circuits, and recorded on the dictabelt. They were recorded on the dictabelt the same way  all the other sounds were recorded.
 

http://mcadams.posc.mu.edu/odell/

Oh, yes, O'Dell's article. I just re-read it because I had not read it in quite some time. O'Dell's article will probably convince newcomers, but it won't convince anyone who has read the HSCA materials and the defenses of those materials.

O'Dell proposes the same basic explanation that the NAS-NRC-Ramsey panel offered; he simply identifies a different voice transmission as the alleged source of the grassy knoll shot.

If you've read the HSCA materials and their defenses, and if you then read O'Dell's article, one of the first things you notice is that O'Dell never specifically explains the sound-distance-waveform correlations between the dictabelt and the Dealey Plaza test-firing impulses, and he does not even mention the windshield-distortion correlations.

O'Dell even suggests that the HSCA acoustics scientists mistook the waveform of the "hold everything" crosstalk for an N-wave because the waveform of the crosstalk has one feature that looks like that of an N-wave. Leaving aside the problem of the precise timing between the N-wave and the sound impulse that follows it (O'Dell never addresses this point), and leaving aside the problems with the timing and properties of the crosstalk, what about the other N-waves? What crosstalk episodes can O'Dell, or anyone else, nominate to explain the other N-waves? What about the windshield distortions and the fact that they occur and don't occur exactly as they should for a recording made from a patrolman's microphone in Dealey Plaza?

Dr. Thomas deals with O'Dell's arguments at some length in his chapter that responds to attacks on the acoustical evidence in his book Hear No Evil, pp. 632-644. We can say the same thing about O'Dell's article that Dr. Thomas notes about the two NAS-NRC attacks on the acoustical evidence:

Neither this nor the original NRC study attempted to refute the core evidence at the heart of the HSCA conclusion: the fact that the suspect sounds on the police recording matched the test shots fired in Dealey Plaza, and that the matching data was ordered in a way that would not have happened if the matches were spurious. (p. 613)

Incidentally, Dr. Thomas also tackles the assertion that McClain was not in the right location to have recorded the gunfire sounds. Dr. Thomas shows that when you look at the totality of the photographic evidence, that evidence suggests that McClain was in the correct position and that his microphone did record the gunfire impulses (pp. 667-689). Says Dr. Thomas,

Although no films show the specified locations at the requisite times, a motorcycle ridden by a patrolman named H. B. McClain was in a position both before and after the shooting such that with a reasonable trajectory he could have been in the specified locations. (p. 687)

No control for all this stuff was established on a dicta-belt. Deal with it.

Nobody saw a need for such a "control" because the science involved with how a dictabelt records sounds was already well known and undisputed. 

Fine, then show me the specs for the Dicta-belt recording gunshots and inaudible pulses.

What "specs"? What are you talking about? Again, there's never been any dispute or mystery about the process by which sounds of any kind are recorded on a dictabelt. Similarly, the science behind the phenomenon of sub-audible sounds being recorded on sound-recording media was already well known back in the 1970s. This is basic stuff that was explained by the HSCA acoustical scientists. Have you read the BBN and W&A reports?

Straw man arguments doesn't work. Not my claim.

But it does involve your claim. Your claim, as far as I can tell, is that there are no gunshot impulses on the dictabelt but only random bursts of static and crosstalk from other microphones, and that the HSCA acoustical scientists mistook this static and crosstalk for gunshot impulses and their associated N-waves.

Herb Blenner, an electronics engineer, has written some excellent articles on the acoustical evidence. Here are excerpts from some of his articles that address the NAS-NRC-Ramsey claims:

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. . . .

The fundamental problem with this conclusion [that the crosstalk was recorded through a receiver with AGC] is the presented evidence does not show that the cross talk recordings were made through a radio receiver. Although the Committee on Ballistic Acoustics [the formal name of the NAS-NRC-Ramsey panel] 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. . . .

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. . . .

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. (https://jfk.boards.net/thread/201/problems-acoustic-evidence)

[Michael T. Griffith]

Quote from: Joe Elliott on September 09, 2020, 01:44:14 AM
Question about Dr. Donald Thomas’s Dictabelt Offset Hypothesis

The “Hold Everything Secure” phrase, which was said about a minute after the assassination, and the “four impulse patterns” occur at about the same time on the Dictabelt recording. Dr. Donald Thomas explained this away by saying the two channels could drift apart from each other by a minute.

Would you have a source for this "offset" being explained (away)?

He doesn't understand what he's reading, or he's repeating some other person's mischaracterization of this issue.

There is no doubt there are offsets. Nobody denies this. Rush and O'Dell acknowledge there are offsets. The NRC panel acknowledged there are offsets and cited the AGC effect on the heterodynes (high-pitched feedback squeaks) and posited recorder stoppage to explain them. The question is, Was the offset in question imposed on Channel 1 or on Channel 2? NRC defenders claim that the offset was imposed on Channel 2 (or caused by impositions on Channel 2) via recorder stoppage. HSCA defenders assert that the offset was imposed on Channel 1 (or caused by impositions on Channel 1), and they note that this explanation agrees with the dispatcher's time notations. For a full discussion on the offset issue, see Thomas, Hear No Evil, pp. 638-643.

As Dr. Thomas observes, any discussion on the offset issue must consider the multiple intricate correlations between dictabelt gunshot impulses and the Dealey Plaza test-firing impulses.

[Michael T. Griffith]

Mr. Elliott certainly got one thing right: your arguments always result in a copy-paste circus and now it's Herbert Blenner's turn.

So you object that I often include quotes in my replies. Well, sorry about that. Some people like to back up their points with direct quotes instead of always paraphrasing.

I doubt you actually understand what he's saying, he just happens to support your case.

I can tell by your arguments that I understand a whole lot more about this issue than you do.

I know of Blenner and consider him one of the worst technical writers I've encountered. It's a mystery to me what he's driving at and what he's trying to confirm or debunk.

You don't get his point? If so, that's because you don't know enough about the acoustical evidence to grasp his point. Let me simplify his point for you: Blenner was refuting the claim that the dictabelt's grassy knoll shot identified by the HSCA experts is just random noise, and he was explaining some of the reasons that the crosstalk cannot explain away the evidence of gunfire on the dictabelt. I thought that was already plainly obvious from Blenner's first sentence:

"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."

And then he went on to point out some of the errors made by the NAS-NRC-Ramsey panel. But you still did not grasp his point. Well, now, hopefully, you do.

I'm not saying he doesn't know his stuff, I just don't have the patience to deal with him.

If you had done your homework, you would have no problem understanding Blenner's research. Blenner is not the greatest writer, but if you've done the necessary homework, you should be able to readily understand his articles. I might add that his writing is not as bad as that of some WC apologists who frequent online discussion forums.

BTW, being unfamiliar with the term specs tells me you haven't got a clue about audio equipment

Huh? Where do you get the ignorant claim that I don't know the term "specs"? I asked you to explain what specs you were talking about in the context of how the dictabelt would have recorded gunfire, since you seem to have the mistaken idea that it recorded gunfire differently than it recorded all other sounds.

You keep repeating this drivel about the "failure" to establish how the dictabelt recorded gunfire. As I've told you several times now, it recorded gunfire the same way it recorded every other sound.

and I'll bet you have no clue whatsoever how the circuitry of the dictabelt machine would affect the input signal to be recorded.

This is mighty bold talk, not to mention rude talk, from somebody who couldn't understand Blenner's point.

Anyway, first of all, Mr. I Can't Understand Blenner, the dictabelt machine had no "circuitry" that had anything to do with signal processing. The circuitry that affected how sounds were processed and transmitted to the dictabelt was external to the machine. The dictabelt itself had nothing, nothing, nothing to do with this--it was just the recording medium on which the sounds that were sent to it by the DPD dispatch system were recorded. You seem unable to grasp this basic point.

As for how the DPD dispatch system's circuitry affected the sounds that were transmitted to the dictabelt, I discussed this very issue in my last reply to you, and I've addressed this issue at least twice in other replies. In my previous reply, I quoted a detailed explanation from the W&A report about how the AGC circuit affected the processing of the sounds before they were transmitted to the dictabelt. Did you somehow miss all that?

Reading just the first few pages of the HSCA report Vol. III explains a lot. It's unclear in the Foreword what "authorized" means, but if they (BBN) were commissioned I hope they were handsomely paid. It's evident from section 1.2 they were provided three tapes containing Hi-Fi recorded stuff and they seemed to have blind faith in those tapes. Moving on to section 1.7 (p11) it's clear that the quality of the dictabelt recording was so bad that they had to speculate that what they termed "continuous noise" was believed to be the sound of a motorcycle engine. This is repeated on page 12. It immediately raises the question why the noise on the Hi-Fi recording could not be identified as engine noise from a bike and that didn't bother them? Especially in view of this found on a wiki page (I know, it's wiki and the source is Bugliosi) https://en.wikipedia.org/wiki/John_F._Kennedy_assassination_Dictabelt_recording): 

There's nothing to disagree about, I'm stating the facts.

Oh, boy. . . .  These arguments are laughable. They are ignorant jibberish.

As for Bugliosi, he was a total idiot on the acoustical evidence. He knew next to nothing about the acoustical evidence, didn't understand the HSCA research, grossly misrepresented the HSCA research, grossly misrepresented Dr. Scheim's and Dr. Thomas's research, and ignored all responses to his ignorant babbling on the subject after his book was published.

When you are ready to discuss the intricate correlations between the dictabelt gunshot impulses and the impulses from the Dealey Plaza test firing, let me know. But let me save you some time: If your plan is to once again go running to pro-WC sites or to read the NAS-NRC-Ramsey report, be advised that none of these sources ever gets around to dealing with those correlations.

I suspect you are another Joe Elliott in that you won't seriously read anything that you know contradicts what you want to believe. However, on the off chance that you ever decide you really want to study the other side, you might start with chapters 16-19 of Dr. Thomas's book Hear No Evil.

And, Dr. Josiah Thompson will include a detailed defense of the acoustical evidence in his highly anticipated book Last Second in Dallas, which will be published in November. Dr. Thomas and other scholars have been working with Thompson on the acoustics section.

[Joe Elliott]

Okay, let's see if we can clear this up. We need to understand that the dictabelt machine was the medium on which the sounds were recorded; the dictabelt itself did not control how the sounds were processed before they arrived, before they were recorded. The dictabelt received sounds from the DPD dispatch system. The DPD dispatch system included an AGC circuit, among other circuits. The AGC circuit greatly affected how sounds were processed before they arrived at the dictabelt. I quote from the Weiss and Aschkenasy report to the HSCA:
 

The bottom line, despite all the claims you make, despite all the claims the Acoustic experts from the 1978 HSCA study make, despite all the claims Dr. Thomas make, we don’t know what gunshots on a Dictabelt would sound like. We have all sorts of unanswered questions.

•   Would Dictabelt record the sounds of gunshots as N-waves we see on the 1963 Dictabelt recording?
•   Would the Dictabelt record the sounds of gunshots as sounding something like the sound of gunshots, or at least as audible noises, or would it be like the 1963 recording?
•   Can the recording of Channel 1 be offset in time from Channel 2, so that crosstalk could make it appear that events happened a minute apart, even thought they really happened at about the same time?

We don’t know the answer to these questions, and we will never know the answer to these questions because the 1978 Acoustic experts failed to test this out.

So, all we have, is the assurance of these Acoustic experts is that:

•   Yes, the Dictabelt would record the sounds of gunshots, just like the N-waves recorded on the 1963 recording.
•   No, the sound of the gunshots won’t sound like gunshots, or even as loud noises, on a Dictabelt recording.
•   Yes, the sounds recorded can be offset, so the “sound of the gunshots” could appear to happen at the same time as a recorded phrase like “Hold everything secure”, even if they really happened a minute or more apart.

In an ideal world, we would not only have the opinion of these experts, but we would have proof of their claims, in a 1978 Dictabelt recording. Real competent scientists, don’t just give us their expert opinions. They also provide proof when possible. And the test which would have proven, or refuted, some or all of these claims were not run in 1978, even though they could easily have been run. And this failure was caused by these same acoustic experts you ask us to trust.

Question:

How much stronger would the acoustic expert’s claims be if we had:

•   A 1978 Dictabelt recording which recorded gunshots as N-waves quite similar to the 1963 recording.
•   A 1978 Dictabelt recording which recorded gunshots as inaudible sounds, just like the 1963 recording.
•   That demonstrated, the sounds recorded, via crosstalk, could appear to happen at about the same time, but really have occurred about a minute apart.

Answer:

Immensely stronger. Immensely stronger. And disproven If the 1978 Dictabelt recording did not demonstrate this.

Does anyone disagree with my answer?



The bottom line is you and others can claim all day about, what a Dictabelt recording would show, what it would not show, but no one really knows. Because this was not tested out in the real world. And we know how to blame. The acoustic experts who screwed this up back in 1978.

[Joe Elliott]

I doubt you actually understand what he's saying, he just happens to support your case. I know of Blenner and consider him one of the worst technical writers I've encountered. It's a mystery to me what he's driving at and what he's trying to confirm or debunk. I'm not saying he doesn't know his stuff, I just don't have the patience to deal with him.

I am going to get a little off topic here. I can assure you that Mr. Blenner does not know his stuff.

He once objected to the following testimony of Larry Sturdivan

Mr. STURDIVAN.
Now, the next line labeled momentum lost, all I have done is taken the product of the mass-this is 162 grains divided by 7,000 - which gives us the mass of the bullet in pounds. Multiply that mass of bullet in pounds times 800 - feet per second, the velocity lost, and we have a quantity, an unusual quantity, 18.4 pound feet per second of momentum which has been deposited by the bullet.

What was Mr. Blenner’s objection. That 18.4 pound feet per second is not the correct answer, and that it is not even an expression of momentum.

I asked, “What to you mean “pound per second” are not units of momentum. Momentum is expressed as “mass * velocity” or “mass * distance / time”. He responded with a quote from a government report showing momentum being expressed in “pound seconds”, not “pound feet per second”. So “pound feet per second” are not units of momentum. So, Larry Sturdivan did not know basic physics.

Now I confess, I was a little confused about this at first. I only took Physics in high school. And a quarter in college. I had never heard of momentum being expressed in “pound seconds”. But, when I thought about it for a bit, I realized that both made sense. If the “pound” in “pound feet per second” is a unit of mass, then this is a valid unit of momentum. And if “pound” in “pound seconds” is a unit of force, then this is also a valid unit of momentum. But I never presented myself as anything other than a former good high school physics student. Herbert Blenner gives the impression that he is much more than that. But he failed to see how “pound feet per second” is a valid unit for momentum. Like he didn’t understand that momentum is mass times velocity. I don’t think that Herbert Blenner knows as much about physics as I do.

By the way, why was Larry Sturdivan not using the metric system, as any good scientist should do? Because he was giving testimony to laymen and was told to use English units, not Metric units, so they would not be confused.


This conversation was recorded on this forum, but it all disappeared a few years ago when the forum went down due to a hacker attack.

[Michael T. Griffith]

Joe and Otto, if you want to educate yourselves on the basics of the acoustical evidence, I suggest you watch the following video made by Dr. Thomas in 2014. He covers a lot of the evidence that the dictabelt contains gunfire--not all of it, but a lot of it. He also addresses the crosstalk issue and the Sonalysts study. You'll want to watch the Q&A segment as well, which includes questions from Dr. Mantik and from one of the HSCA staffers who worked with the HSCA acoustical experts. The video is only 40 minutes long and includes lots of graphics.

https://aarclibrary.org/dr-donald-b-thomas-jfk-acoustical-evidence-challenge-and-corroboration/

[Joffrey van de Wiel]

Gentlemen,

I have a question about the acoustical evidence that I hope can be answered.

On the one hand, we have video evidence like the Zapruder film but they contain no audio. They are all mute.

On the other hand we have the dictabelt recording of 4 to 6 shots fired at the President at Dealey Plaza.

Can both video and audio files be combined, or overlayed, or compared? If frame 313 of the Zapruder film is taken as a starting point for any one impulse on the dictabelt recording, then presumably we could shift the graph of those impulses to match with the frame. By determining which impulse is linked to frame 313, a shooting scenario could be established, but if any one impulse on the recording can not be matched to any reactions by the President or the Governor then the dictabelt recording interpretation is flawed?

This is very hard for me to explain or even phrase properly in a foreign language. Please forgive any errors. I hope however that you understand the basics of my question. Dr. Thomas's presentation is very compelling, as are the HSCA's, but since I am not an expert on the matter I am perhaps easily impressed.

@ Michael Griffith
Thanks for your extensive responses in this thread. I don't understand it all, but I am learning because of your contributions. Please keep up the good work!