In this case I think it's mostly about using different sub-carriers (kind of a "channel in the channel"), so that the data information and the audio are separated in frequency and do not disturb each other. That's generally called Frequency Division Multiple Access (FDMA), IIRC.

Another more advanced technique is Code Division Multiple Access (CDMA), e.g. used by GPS and some mobile communication modulation schemes. It allows you to have multiple senders on a single radio carrier frequency, and the receiver "selects" which sender to listen to by knowing its "code".

There's also Time Division Multiple Access (TDMA), i.e. senders take turns sending content in allocated time slots.