Back before the mid 1980s when they settled on an interchange standard. So in my grad research we'd get these mystery tape bit dumps. I had a rough idea of the structure of the data, but not its exact shape, nor even its number format- many more floating point and integer formats in the old days. So with "od -o" I'd coax an image out these mystery bit dumps. I think it would be fairly straight forward to do this with AM, FM signals.