I mean we could get 1.001khz and 1.002 khz more easily for exemple.
You could put 1.001 and 1.002 frequencies into separate channels.
Putting them into the same channel (or combining them in the air), gives a slow change in the amplitude of the resulting wave eventually cancelling completely, then growing again.
Using 1000, 1000.001, and the combination to illustrate:
It takes about 17 minutes to go through that cycle.