I just extracted the audio from the sample mp4. Each data record seems to be a lead-in tone with a frequency of 3.6kHz, followed by something (data?) followed b

I just extracted the audio from the sample mp4. Each data record seems to be a lead-in tone with a frequency of 3.6kHz, followed by something (data?) followed by a lead-out tone with a frequency of 3.6kHz. The spectrum of the "something" is broadened, suggesting a modulated signal, though it does have a strong peak at approximately 5943Hz.