Aren't most audio channels on video recorders, and other things not intended for high quality audio, 3 KHz?
Basically you need a modem of some sort. The data rate is determined by the modulation method. A simple on / off of a tone will give a data rate the same as half the audio bandwidth. By having quadrature modulation and amplitude modulation on top of that you can extend the data rate to be multiples of the audio bandwidth.
do you know of a modulation technique that can get around lossy compression?
Signal components that are perceptually irrelevant are discarded; Redundancies in the coded audio signal are eliminated.
so making sure the signal is chaging a lot might help