Josiah Thompson's long-awaited new book Last Second in Dallas (University Press of Kansas, 2021), published last week, presents powerful evidence in support of the HSCA acoustical evidence, which proved there were at least two gunmen and at least four shots. Thompson's chapters on the acoustical evidence account for 98 pages of the book and include separate contributions by BBN scientists James Barger and Richard Mullen. Some highlights:
* Thompson utterly, totally, and completely destroys the NRC panel's report. Among other things, Thompson presents evidence that the panel rigged their PCC test to avoid confirming the acoustical evidence.
* Thompson demolishes the claim that the Fisher "I'll check it" transmission is not crosstalk. He proves, partly via a PCC test done by Mullen, that it most certainly is crosstalk, and that it proves that the dictabelt's gunfire impulses occurred during the assassination. Interestingly, Thompson notes that years ago Jim Bowles himself recognized the Fisher "I'll check it" transmission as a crosstalk transmission, and that the NRC panel attempted to conceal this fact in its report.
* Thompson once and for all resolves the problem of the Decker "hold everything" transmission, proving that it is irrelevant, that it is not time synchronous, and that it must be the result of an overdub that was produced during the copying process. Thompson, summarizing Barger's new research on the subject, presents evidence that Decker's "hold everything" transmission and the two Bellah transmissions were recorded during a separate recording session and not during the session that recorded the three scientifically established crosstalk transmissions, and that, crucially, they were recorded at a different recording speed.
* Thompson establishes that neither the HSCA nor the NRC panel used the original dictabelt recording, and that the extant recording is a second- or third-generation copy.
* Interestingly, Thompson reveals that when the NRC panel sent Dr. Barger a draft of their report, Barger replied with an 8-page critique, and that the panel declined to publish Barger's critique and did not address his objections in their report.
This is a very simplified, general summary of Thompson's chapters on the acoustics evidence. Dozens of the pages in those chapters get rather technical, but Thompson does a good job of putting the information in layman's terms. I have not mentioned some of Thompson's best evidence because doing so would require technical explanations that would take several paragraphs. Barger's and Mullen's chapters are a bit tougher reading, but even a newcomer will be able to grasp their significance.
You wish.
Barger's analysis self-destructs on figure 23-6 on page 344 (it's also reproduced as Figure A-4 in Barger's appendix on page 373). To explain why, remember that the DPD recording system was designed to record only if there was a transmission to record. Normally, the system only recorded intermittently. However, at about 12:28 on November 22, 1963, a microphone on a police motorcycle stuck in the transmit position, broadcasting a steady stream of background noise back to the city hall until about 12:35. This event kept the Dictabelt machine on Channel 1 continuously recording during that interval. At the same time, Channel 2 was operating intermittently, as designed. Because of this, the channel 2 recording consistently loses time against its channel 1 counterpart during this period. If you plot the crosstalk events for channel one along one line, do the same for channel 2, and compare the resulting plots, you'll notice that Channel 2 does indeed lose time to channel one:
from the HOLD crosstalk to the BELLAH1 crosstalk
from the BELLAH1 crosstalk to the BELLAH2 crosstalk
from the BELLAH2 crosstalk to the ATTENTION simulcast
from the ATTENTION simulcast to the I'VE GOT crosstalk
The lone exception is the interval between the putative "I'll check it" crosstalk and the HOLD crosstalk. Between these two points, channel 2 gains about 80 seconds on channel 1. Channel 1 is running continuously at this point, so there is no way that channel two could gain time on channel 1 here. That makes "I'll check it" the outlier. If any external signal was somehow dubbed into the recordings, it's the channel one "I'll check it."
Mullen's critique of the NAS panel's use of PCC is more complex, but it revolves around the use of time scaling various bits of the recordings. Barger and Mullen say that there are multiple overlapping bits of power supply hum in the recording, so choosing which one (or which combination) to use for proper scaling and where to apply it looks to be a significant issue, and probably will be argued about quite a bit in higher circles.
However, PCC is not the only issue that the NAS panel raised with the alleged Fisher crosstalk. They also noted that the supposed "I'll check it" transmission is accompanied by heterodyning, indicating that this particular transmission was native to channel one. The heterodyning occurs when two transmitters attempt to transmit at the same time and interfere with each other. In this case, someone tried to transmit a message while the radio on the open mike bike was transmitting the sweet rumble of Harley Davidson. Crosstalk wouldn't generate a heterodyne like that. No heterodyning accompanies Fisher's channel 2 transmission, nor is there good reason to expect it to, so there is no reason to expect that the heterodyne was carried over from channel 2 to channel one. So far as I've read, I see no mention of this problem by Thompson, Barger, or Mullen. I'm still reading through it, but heterodyning only gets one mention in the index, and it's a trivial reference that doesn't address the NAS panel's point.
BTW, the appearance of the Decker crosstalk on channel 1 has a greater significance than one might expect. Weiss and Aschkenazy's analysis of the "GK shot" is predicated on the assumption that the impulse pattern in question is either a (synthetically-derived) gunshot or a series of random impulses (basically, noise). However, the Decker crosstalk overlies the area where the BRSA/WA "shots" are found. That changes the situation. Proper probabilistic analysis would require the Decker crosstalk be accounted for as a partial or whole source of the "shots" as well as the string-of-random-impulse hypothesis. This is true no matter the origin of "hold everything secure" on channel one.