The machine itself and how it operated, the timing compared to the Gray recording and the speed that was not a constant and changes the location of the shots compared to Zapruder.
The fact the Dictabelt records over itself without an erase feature, so any 'old data is still layered into the tape.
The placement of the 'open mike', that put the officer in question, H.B. McLain, at 120-140 feet from the President at the first shot, but Zapruder shows him at 250 feet or more.
The Dictabelt recording attributed to McLain's open mike also records a rising and falling siren. McLain was one of the officers escorting the limo to Parkland. His siren was blaring the entire time.
The sounds on the Dictabelt cannot be resolved to the photographic evidence of Zapruder. The timing is off anywhere the 'shots' are placed in reference to where McLain was positioned and where Zapruder shows the officer.
That in itself lends to disputation of the recording.
Erroneous conclusions based on subjective data, and the Dictabelt acoustic evidence is subjective, makes every conclusion after that incorrect.
“Erroneous conclusions based on subjective data....”
Essentially the basis for all of your strenuous objections to any challenge to the Warren Commission Report. You attribute your own arguments to third parties then quote yourself as an authority. Nice work.