There is an application that uses FSK. But the actual information is
not coded by the frequency shift but rather by the length of time one
of the pulses is turned on. The pulses are about 2 milliseconds long.
The information is coded on one of them. The other is always the
same length. The frequency shift is always a constant.

Now, my question. If you send this signal into a standard FM Rx it
will produce a tone. Is this tone simply the difference between the
two RF frequencys? Is the information coded on the one pulse lost in
such reception? Or is this audio tone something far more complex that
still contains encoded information?

TIA